EFFECT OF MONDAY-THURSDAY FASTING
ON COGNITIVE FUNCTION
By:
DIAN ERLANGGA
G34102049
DEPARTMENT OF BIOLOGY
FACULTY OF MATHEMATIC AND NATURAL SCIENCE
BOGOR AGRICULTURAL UNIVERSITY
ABSTRACT
DIAN ERLANGGA. Effect of Monday-Thursday Fasting on Cognitive Function. Supervised by BAMBANG SURYOBROTO and AKICHIKA MIKAMI.
Human memory is a complex cognitive function. Based on its storage capacity, memory can be distinguished into two kinds. They are term and long-term memories. A kind of short-term memory is called working memory. Working memory is a limited capacity system that holds items of information transiently in mind in the service of comprehension, thinking, and planning. To perform cognitive task, brain requires large energy. Fasting declines blood glucose concentration similar to skipping breakfast. Many people in Indonesia habitually perform fasting every Monday and Thursday irrespective of the month. The Monday-Thursday fasting therefore provides a model of how habitual fasting influences performances on working memory task. Present research used Delayed Matching to Sample paradigm is a widely used method to study visuospatial working memory in human and animal. Test was analyzed by linear mixed effect statistical model using statistical language S which is implemented in lme4 package of program R. Result shows that performance of visuospatial working memory task did not affected by Monday-Thursday fasting and its duration. It also did not affected by sleep length, and did not differ between male and female. It increased session by session which reflect the ability of subjects to learn the pictorial stimuli.
ABSTRAK
DIAN ERLANGGA. Efek dari Puasa Senin-Kamis terhadap Fungsi Kognisi. Dibimbing oleh BAMBANG SURYOBROTO dan AKICHIKA MIKAMI
EFFECT OF MONDAY-THURSDAY FASTING
ON COGNITIVE FUNCTION
Minithesis
To obtain Bachelor’s of Science
In Faculty of Mathematic and Natural Science
Bogor Agricultural University
By:
DIAN ERLANGGA
G34102049
DEPARTMENT OF BIOLOGY
FACULTY OF MATHEMATIC AND NATURAL SCIENCE
BOGOR AGRICULTURAL UNIVERSITY
Title : Effect of Monday-Thursday Fasting on Cognitive Function
Name : Dian Erlangga
NRP : G34102049
Approved:
Advisor 1
Advisor 2
Dr. Bambang Suryobroto
Prof. Dr. Akichika Mikami
NIP 131779503
Endorsed by:
Decant Faculty of Mathematic and Natural Science
Bogor Agricultural University
Prof. Dr. Ir. Yonny Koesmaryono, M.S.
NIP 131473999
FOREWORD
The title of this minithesis is Effect of Monday-Thursday Fasting on Cognitive Function. It is made after doing experiment since March 2006. The experimental took place in the Laboratory of Zoology, Department of Biology Faculty of Mathematic and Natural Science Bogor Agricultural University, Bogor.
Writer acknowledgments are sending to Dr. Bambang Suryobroto and Prof. Dr. Akichika Mikami M.D. as writer’s advisors. Also deepest gratitude to Dra. Taruni Sri Prawasti, Dr.Ir. Achmad Farajallah, M.Si, Dr. Ir. Diah Perwitasari , Dr. Ir. Rika Raffiudin, M.Si, Ir. Tri Heru, M.Sc, Ir. Tri Atmowidi, M.Si and all staff in Zoology laboratory for their support and kindness. To Kak Ati, Kak Kanthi, Adit, Riza, Bacool, Ammay for their motivation friendship. All Writer friend in Laboratory of Zoology such as Andros, Anifa, Singa, Qbal, Bian, Apri, Rifah, Isma, Ani, Kak KC, Kak Nina, Kak Andre, Omen, WT for our good time and kindness. To Akhmaisyah, Ninda, Ade Bowie, Laruku, and All of My Probandus for their support and motivation. Writer’s acknowledgment especially send to GOD, Parent and Whole Family for their all they love, support, kindness, motivation, and their pray so writer could finished this minithesis.
Bogor, March 2007
CURRICULUM VITAE
Writer was born in Makassar on 27th October 1984 as the first child of two brothers from parent, Juwono Prabawadi and Susini.
On 2002, writer graduated from SMUN 5 Bogor and entered the Department of Biology, Faculty of Mathematic and Natural Science, Bogor Agricultural University via ‘Undangan Saringan Masuk IPB’ (USMI).
CONTENTS
Page
LIST OF FIGURES... vii
LIST OF APPENDIX... vii
INTRODUCTION... 1
MATERIAL AND METHODS DMTS ... 1
Procedures ... 2
Statistical analytic ... 2
RESULT ... 3
DISCUSSION Fasting ... 3
Learning from past sessions... 5
CONCLUSION ... 5
REFERENCE ... 5
LIST OF FIGURES
Page
1 Structures of simple DMTS ... 2
2 Model of experiment ... 2
3 Level Attained ... 4
4 Performance Attained... 4
5 Weight Error Attained... 4
6 Response Time Attained ... 4
7 Normalized Reaction Attained... 4
8 Level per Number Attained ... 4
LIST OF APPENDIX
Page 1 Measures of Working Memory ... 72A Confidence interval for estimate of fasting parameter to measures of working memory... 8
2B Confidence interval for estimate of fasting-duration parameter to measures of working memory... 8
2C Confidence interval for estimate of session parameter to measures of working memory... 8
2D Confidence interval for estimate of sex parameter to measures of working memory... 8
INTRODUCTION
Human memory is a complex cognitive function. It shapes our thought and behavior because information processing at one point in time influences processing at later points in time. Construction of memory consists of three separate stages: encoding, storage, and retrieval (Baddeley 1996). Encoding refers to initial processing of information that will potentially be stored as memory episodes. Storage maintains and consolidates information over extended period of time. Retrieval refers to process that results in remembering the encoded episodes. Both encoding and retrieval process occur in hippocampus and modulated by acetylcholine (Hasselmo 1999).
Based on its storage capacity, memory can be distinguished into two kinds. They are short-term and long-term memories. Short-term system has a limited capacity and memory traces can spontaneously fade within seconds. Long-term memory has a massive capacity and durability so the memories can be held for a long time. There are three kinds of long-term memory: episodic, semantic, and procedural memories. Episodic memory is a kind of memory that results from our past personal experiences. Semantic memory relates to general knowledge, such as geography and history. Procedural memory involves skill and habit.
A kind of short-term memory is called working memory. Working memory is a limited capacity system that holds items of information transiently in mind in the service of comprehension, thinking, and planning. It is assumed to be an integral part of human memory system. Working memory encompasses both storage and processing functions simultaneously, such as: imaging a sequence of chess moves, constructing a sentence, mental arithmetic, creation of music or poetry (Goldman 1996).
To perform cognitive task, brain requires large energy. Although brain weighs only 2% of total body weight, the brain uses about 20% of the total body’s energy. Commonly brain energy comes from aerobic glucose degradation. The brain’s energy storage is extremely small, so without glucose replacement, the brain would be depleted of glucose in less than 10 minutes. When someone sleeps, blood glucose concentration tends to decrease due to no food intake. By taking breakfast in the next morning, the glucose concentration will increase again.
Breakfast consumption influences performance in memory tasks, especially one that requires the retention of new information (Benton 1998). Skipping breakfast leads to slower value of stimulus discrimination, increased error, and slower memory recall (Pollit 1998).
Moslem religious fasting is a situation where subject does not consume any food and water from dawn (±4 AM in Indonesia) until sunset (± 6 PM) in the lunar calendar month of Ramadhan. Ramadhan fasting is compulsory for moslem people; however, for variety of reasons, many people in Indonesia habitually perform fasting every Monday and Thursday (MTFast) irrespective of the month. Fasting declines blood glucose concentration similar to skipping breakfast (Sunram-Lea 2001). It may influences performance in memory task due to metabolic changes in plasma glucose regulation in the brain. The MTFast therefore provides a model of how habitual fasting influences performance on memory task
Objective
To investigate whether MTFast influences performance of working memory task or not.
Place and Time
Research was done from February until July 2006 at Laboratory of Zoology, Department of Biology, Faculty of Mathematics and Natural Sciences IPB.
MATERIAL AND METHODS
DMTS
2
Figure 1 Structures of simple DMTS.
The scheme of Simple DMTS used in present experiment can be seen in figure 1. In the experiments, the stimuli were presented on a computer screen. Subject matched the stimuli by using computer mouse. Firstly subject pressed the mouse for 1500 milliseconds (ms) in a blank screen. After that visual stimulus appeared in center of the screen for 1500ms while subject must still pressing the mouse. The delay time was presented for 1500ms in the form of a blank screen. Then a screen consisted of eight objects was displayed and subject must release mouse and pursue a matched stimulus within 5000ms time frame. A feedback screen would be shown indicating correct (green) or error (red) choice for about 1050ms. If the subject did not response within 5000ms time frame, he/she was considered as fail. Task was repeated for 30 times.
The Sequential DMTS test consisted of up to eight visual stimuli contained in consecutive levels. Each level (for instance, level 2) corresponded to the number of stimuli that had to be kept in memory (for instance, two stimuli); also, subject should remember the order of appearance of each stimulus. The highest level 8 corresponded to the number of stimuli to be matched. To go to the next level, subject must perform three successively correct trials. If he/she failed in one trial, he/she was downgraded one level.
Figure 2 Model of experiment.
Figure 2 is a model of the experiment. If subject reach the highest level 8 for three consecutive trials, the session was ended. If not, session would be stopped after 60 trials, whether subject reached level 8 or not.
Procedures.
Many moslem university students observe MTFast habitually. Ten participants (5 females, ages 21-23 years; 5 males, ages 20-22 years) volunteered to participate in the study. Participants had study experience for at least 14 years. The recruitment was done in university campus via mouth to mouth to subjects that perform habitual MTFast.
The sessions of memory test were done at 12.30-15.00 PM so the actual length of fasting is about 8-11 hours. The reason why the assessments were done at around 1 PM was based on subjects' perception that 13.00 PM is the hardest time of the day because they were hungry, tired, and difficult to concentrate. It may be the best moment to see the effects of fasting on working memory task. The experiments were done at isolated places free from distortion/noise. Each participant did 6 sessions of assessment with at least 2 sessions in fasting. In doing later sessions, subject might learn from their experience in former sessions. To counterbalance this learning effect, half of subjects were in fasting condition in their first session of assessment, which was at Monday or Thursday, and other half were not.
Statistical analysis
3
Table 1 Estimates of statistical parameters
Measures of Working Memory Level Relative Performance Weight Error Response time Normalized reaction times Level per number
Fasting -0.59 -1.72 0.05 -71.15 56.169 0.99
Fasting- duration
0.03 0.04 0.01 13.86 -3.34 -0.23
Sessions 0.21* 3.76* -0.22* -95.19* -71.775* 1.01*
Sex 0.36 3.04 0.029 341.68 29.582 0.61
Sleep length
-0.06 -0.78 0.059 -21.11 -0.325 -0.19
* Statistically significant (see appendix 2). sample of students who habitually observe the fasting. However, beside fasting and its duration, working memory is also affected by subject's ability to learn from past sessions, his/her sleepiness condition and probably also their sex.
In statistical analysis, each measure of working memory is a response which can be modeled by fixed and random effects contained in the experiment. By considering the experimental conditions above, the fixed effects for this model were: fasting and its duration, session, sex, and sleep length. In this model, subjects were considered as were recruited in a random fashion so they were taken as the random effect. Analysis which combine fixed and random effects is known as mixed-effect model (Pinheiro & Bates 2004). In this research, linear mixed-effect analyses were conducted using statistical language S which is implemented in lme4 package (Bates 2005) of program R (R Development Core Team 2005). The parameters which were of interest were those which associate with fixed effects. Diagnostic of fixed-effect parameters were done by Markov Chain Monte Carlo (MCMC) simulations using CODA package of program R.
RESULT
Performances of working memory are shown in Figures 3-8. Subjects were getting better from session to session. Most of them got higher level and relative performance and decreased response times and errors in later sessions.
Estimates of statistical parameters for fixed effects are tabulated in Table 1. Fasting and its duration did not significantly influence performance of working memory. Except sessions, all other covariates also did not give
significant influence. Length of sleep varied between each subject. At first, I think that sleep would had an effect on performances of working memory due to acetylcholine as neuromodulator related to sleep factors. When someone sleeps, acetylcholine helps people in facilitating the process of consolidation of separate memory traces (Hasselmo 1999). In fact, subjects could get better or bad results both in short-term (less than 5 hours) and long-term sleep (more than 6 hours). But maybe there was also individual difference in sleep quality thus obscuring the results. Also, difference between sexes is relatively small and had no significant effect on performance of working memory.
The improvement in the performance of working memory from session to session shows learning effect. After getting experience with the DMTS task, subjects became familiar with the stimuli therefore their performances got relatively better than previous sessions.
DISCUSSION
Fasting
Present research investigates whether MTFast influences working memory task or not. Subject could get better result although they were in fasting condition. At first, I think that fasting duration might affect to performance task. It was due to the relationship between fasting duration and the concentrations of glucose in body and brain. Subject with shorter duration of fasting may had a bigger chance to get better result compared with the longer one because he/she had higher glucose concentrations.
4
Figure 3 Level Attained
Figure 4 Performance Attained
Figure 5 Weighted Error Attained
Figure 6 Response Time Attained
Figure 7 Normalized Reaction Times Attained
5
First, duration of the fasting in our case might be too short to reduce the glucose level (actual fasting durations were about 9 hours). This caused the ineffectiveness of fasting to reduce performance because both the body's and brain's glucose levels were sufficient to maintain body's and brain's metabolisms. Secondly, we didn’t control the time and amount of the dinner in the preceding day of test. Subjects differed at the time and amount of the last dinner. This may reduce the fasting effect to average. Third, there were individual differences in the way they fasted. For instance, subjects who practiced MTFast for prolonged time may resist the effects of fasting and may be able to maintain their glucose level relatively high. If that happened, that may cause the relatively higher performance in fasting condition in those subjects.
Learning from past sessions
When someone completed a session, he/she learned the visual stimuli of the DMTS task. Some of the pictorial stimuli which were hold in working memory may got consolidated into long term memory and session by session these would be accumulated. Learning effect lead the subjects to increasing chances to get better result, decreasing error count and faster timing when they chose stimuli. In this case, response time got faster and also affected weighted error to become lower compared than previous sessions. Beside that, by doing more sessions, chances of level downgradations became lower and chances to attain highest level became increased with only smaller number of trials. It leads to better result of level, relative performance and level-per-number attained. Such learning effects may mask the effect of fasting. That way session had more influence to performance of working memory rather than fasting.
CONCLUSION
Performance of visuospatial working memory task did not affected by Monday-Thursday fasting and its duration. It also did not affected by sleep length, and did not differ between male and female. It increased session by session which reflect the ability of subjects to learn the pictorial stimuli.
REFERENCE
Baddeley A. 1996. The fractionation of working memory. Proc Natl Acad Sci 9:13468-13472.
Benton D, Parker PY. 1998. Breakfasts, blood glucose, and cognition. Am J Clin Nutr 67:772-781.
Bates D. 2005. Fitting linear mixed models in R. R News 5:27-30.
Elliot R. 1999. Differential neural responses during performance of matching and nonmatching to sample tasks at two delay intervals. J Neuroscience 19(12):5066– 5073.
Goldman PS. 1996. Regional and cellular fractionation of working memory. Proc Natl Acad Sci. 93:13473-13480.
Hasselmo ME. 1999. Neuromodulation acetylcholine and memory consolidation. J Neuroscience 3:351-358.
Pinheiro JC, Bates DM. 2000. Mixed-effects models in S and S-Plus. Springer, New York.
Pollit E, Jacoby E. 1998. Fasting and cognition in well and undernourished school children. Am J Clin Nutr 67:779-812.
Sunram-Lea S, Foster JK, Durlach P, Perez C. 2001. Glucose facilitation of cognitive performances in healthy young adults. J Phsychopharmacology 157:46-54. R Development Core Team. 2005. R: A
7
7
Appendix 1 Measures of Working Memory
There six variables that were used in this research (such as: level; relative performance; weighted error; response time; normalized reaction times; and level-per-number attained)
1. Level attained is the first sustained highest level (without downgradation) that was achieved by subject in the current session.
Sometimes we called level attained as highest level reached in that session/day
2. Relative performance is a ratio between accumulated scores divided by maximum cumulative scores that can be obtained without downgradations. Scores were assigned to every trial according to the particular levels of the trials. For instances, a trial at level 2 would get two scores, level 3 three scores, and so on
3. Weighted error is a number of errors for each level that was performed by subject. Weighted error was gained by calculating error count for each level divided by actual number of object.
The difficulty may increase if the number of item to remember increased. In other word, more chance to make error in higher level.
If the subject reached level 4 and he/she made 1 error for level 1, 2 errors for level 2, 4 errors for level 3 and 6 errors for level 4. In total normalized total error (weight error): 1/1 + 2/2 + 4/3 + 6/4
4. Response time is a duration that was gained by calculating reaching time plus r.time. Reaching time is duration between time to touch the targets and button release time. r.time is duration between time to touch next targets minus time to touch previous targets.
5. Normalized reaction time is total time from the eight stimuli presentation to the final touch divided by number of objects
For example if level 3 and took 3000 ms from the all possible objects appeared to the selection of the 3rd object, 3000/3 is normalized reaction time. We called normalized reaction time as “ an averaged reaction time for a trial”
6. Level-per-number attained was acquired by calculating sustained highest levels times 60 divided by number of trials to attain that level.
For example; if the subject reached level 8 as his/her sustained highest level and requires 24 numbers of trials to attained that level, level per number:
Weighted Error = Error count for each level Actual number of object
Normalized Reaction Time = Total time from eight stimuli presentation to final touch Number of objects
8 * 60 24 Relative Performance = Cumulative Scores
8
Appendix 2A Confidence intervals for estimates of fasting parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate -0.59 -1.72 0.05 -71.15 56.169 0.99
Lower -1.27 -9.89 -0.57 -576.687 -38.901 -1.68
Upper 0.09 6.73 0.66 471.046 149.26 4.14
Appendix 2B Confidence intervals for estimates of fasting-duration parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate 0.03 0.04 0.01 13.86 -3.34 -0.23
Lower -0.04 -0.78 -0.05 -39.62 -57.69 -0.525
Upper 0.097 0.85 0.07 63.50 6.03 0.026
Appendix 2C Confidence intervals for estimates of session parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate 0.21* 3.76* -0.22* -95.19* -71.775* 1.01*
Lower 0.109 2.49 -0.31 -174.47 -85.99 0.525
Upper 0.31 5.007 -0.12 -14.27 -57.69 1.48
* Statistically significant.
Appendix 2D Confidence intervals for estimates of sex parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate 0.36 3.04 0.029 341.68 29.582 0.61
Lower -1.48 -17.09 -1.19 -410.71 -254.002 -1.18
Upper 2.14 22.72 1.26 1103.89 304.14 2.37
Appendix 2E Confidence intervals for estimates of sleep length parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate -0.06 -0.78 0.059 -21.11 -0.325 -0.19
Lower -0.16 -2.04 -0.035 -101.20 -14.78 -0.58
EFFECT OF MONDAY-THURSDAY FASTING
ON COGNITIVE FUNCTION
By:
DIAN ERLANGGA
G34102049
DEPARTMENT OF BIOLOGY
FACULTY OF MATHEMATIC AND NATURAL SCIENCE
BOGOR AGRICULTURAL UNIVERSITY
ABSTRACT
DIAN ERLANGGA. Effect of Monday-Thursday Fasting on Cognitive Function. Supervised by BAMBANG SURYOBROTO and AKICHIKA MIKAMI.
Human memory is a complex cognitive function. Based on its storage capacity, memory can be distinguished into two kinds. They are term and long-term memories. A kind of short-term memory is called working memory. Working memory is a limited capacity system that holds items of information transiently in mind in the service of comprehension, thinking, and planning. To perform cognitive task, brain requires large energy. Fasting declines blood glucose concentration similar to skipping breakfast. Many people in Indonesia habitually perform fasting every Monday and Thursday irrespective of the month. The Monday-Thursday fasting therefore provides a model of how habitual fasting influences performances on working memory task. Present research used Delayed Matching to Sample paradigm is a widely used method to study visuospatial working memory in human and animal. Test was analyzed by linear mixed effect statistical model using statistical language S which is implemented in lme4 package of program R. Result shows that performance of visuospatial working memory task did not affected by Monday-Thursday fasting and its duration. It also did not affected by sleep length, and did not differ between male and female. It increased session by session which reflect the ability of subjects to learn the pictorial stimuli.
ABSTRAK
DIAN ERLANGGA. Efek dari Puasa Senin-Kamis terhadap Fungsi Kognisi. Dibimbing oleh BAMBANG SURYOBROTO dan AKICHIKA MIKAMI
INTRODUCTION
Human memory is a complex cognitive function. It shapes our thought and behavior because information processing at one point in time influences processing at later points in time. Construction of memory consists of three separate stages: encoding, storage, and retrieval (Baddeley 1996). Encoding refers to initial processing of information that will potentially be stored as memory episodes. Storage maintains and consolidates information over extended period of time. Retrieval refers to process that results in remembering the encoded episodes. Both encoding and retrieval process occur in hippocampus and modulated by acetylcholine (Hasselmo 1999).
Based on its storage capacity, memory can be distinguished into two kinds. They are short-term and long-term memories. Short-term system has a limited capacity and memory traces can spontaneously fade within seconds. Long-term memory has a massive capacity and durability so the memories can be held for a long time. There are three kinds of long-term memory: episodic, semantic, and procedural memories. Episodic memory is a kind of memory that results from our past personal experiences. Semantic memory relates to general knowledge, such as geography and history. Procedural memory involves skill and habit.
A kind of short-term memory is called working memory. Working memory is a limited capacity system that holds items of information transiently in mind in the service of comprehension, thinking, and planning. It is assumed to be an integral part of human memory system. Working memory encompasses both storage and processing functions simultaneously, such as: imaging a sequence of chess moves, constructing a sentence, mental arithmetic, creation of music or poetry (Goldman 1996).
To perform cognitive task, brain requires large energy. Although brain weighs only 2% of total body weight, the brain uses about 20% of the total body’s energy. Commonly brain energy comes from aerobic glucose degradation. The brain’s energy storage is extremely small, so without glucose replacement, the brain would be depleted of glucose in less than 10 minutes. When someone sleeps, blood glucose concentration tends to decrease due to no food intake. By taking breakfast in the next morning, the glucose concentration will increase again.
Breakfast consumption influences performance in memory tasks, especially one that requires the retention of new information (Benton 1998). Skipping breakfast leads to slower value of stimulus discrimination, increased error, and slower memory recall (Pollit 1998).
Moslem religious fasting is a situation where subject does not consume any food and water from dawn (±4 AM in Indonesia) until sunset (± 6 PM) in the lunar calendar month of Ramadhan. Ramadhan fasting is compulsory for moslem people; however, for variety of reasons, many people in Indonesia habitually perform fasting every Monday and Thursday (MTFast) irrespective of the month. Fasting declines blood glucose concentration similar to skipping breakfast (Sunram-Lea 2001). It may influences performance in memory task due to metabolic changes in plasma glucose regulation in the brain. The MTFast therefore provides a model of how habitual fasting influences performance on memory task
Objective
To investigate whether MTFast influences performance of working memory task or not.
Place and Time
Research was done from February until July 2006 at Laboratory of Zoology, Department of Biology, Faculty of Mathematics and Natural Sciences IPB.
MATERIAL AND METHODS
DMTS
INTRODUCTION
Human memory is a complex cognitive function. It shapes our thought and behavior because information processing at one point in time influences processing at later points in time. Construction of memory consists of three separate stages: encoding, storage, and retrieval (Baddeley 1996). Encoding refers to initial processing of information that will potentially be stored as memory episodes. Storage maintains and consolidates information over extended period of time. Retrieval refers to process that results in remembering the encoded episodes. Both encoding and retrieval process occur in hippocampus and modulated by acetylcholine (Hasselmo 1999).
Based on its storage capacity, memory can be distinguished into two kinds. They are short-term and long-term memories. Short-term system has a limited capacity and memory traces can spontaneously fade within seconds. Long-term memory has a massive capacity and durability so the memories can be held for a long time. There are three kinds of long-term memory: episodic, semantic, and procedural memories. Episodic memory is a kind of memory that results from our past personal experiences. Semantic memory relates to general knowledge, such as geography and history. Procedural memory involves skill and habit.
A kind of short-term memory is called working memory. Working memory is a limited capacity system that holds items of information transiently in mind in the service of comprehension, thinking, and planning. It is assumed to be an integral part of human memory system. Working memory encompasses both storage and processing functions simultaneously, such as: imaging a sequence of chess moves, constructing a sentence, mental arithmetic, creation of music or poetry (Goldman 1996).
To perform cognitive task, brain requires large energy. Although brain weighs only 2% of total body weight, the brain uses about 20% of the total body’s energy. Commonly brain energy comes from aerobic glucose degradation. The brain’s energy storage is extremely small, so without glucose replacement, the brain would be depleted of glucose in less than 10 minutes. When someone sleeps, blood glucose concentration tends to decrease due to no food intake. By taking breakfast in the next morning, the glucose concentration will increase again.
Breakfast consumption influences performance in memory tasks, especially one that requires the retention of new information (Benton 1998). Skipping breakfast leads to slower value of stimulus discrimination, increased error, and slower memory recall (Pollit 1998).
Moslem religious fasting is a situation where subject does not consume any food and water from dawn (±4 AM in Indonesia) until sunset (± 6 PM) in the lunar calendar month of Ramadhan. Ramadhan fasting is compulsory for moslem people; however, for variety of reasons, many people in Indonesia habitually perform fasting every Monday and Thursday (MTFast) irrespective of the month. Fasting declines blood glucose concentration similar to skipping breakfast (Sunram-Lea 2001). It may influences performance in memory task due to metabolic changes in plasma glucose regulation in the brain. The MTFast therefore provides a model of how habitual fasting influences performance on memory task
Objective
To investigate whether MTFast influences performance of working memory task or not.
Place and Time
Research was done from February until July 2006 at Laboratory of Zoology, Department of Biology, Faculty of Mathematics and Natural Sciences IPB.
MATERIAL AND METHODS
DMTS
2
Figure 1 Structures of simple DMTS.
The scheme of Simple DMTS used in present experiment can be seen in figure 1. In the experiments, the stimuli were presented on a computer screen. Subject matched the stimuli by using computer mouse. Firstly subject pressed the mouse for 1500 milliseconds (ms) in a blank screen. After that visual stimulus appeared in center of the screen for 1500ms while subject must still pressing the mouse. The delay time was presented for 1500ms in the form of a blank screen. Then a screen consisted of eight objects was displayed and subject must release mouse and pursue a matched stimulus within 5000ms time frame. A feedback screen would be shown indicating correct (green) or error (red) choice for about 1050ms. If the subject did not response within 5000ms time frame, he/she was considered as fail. Task was repeated for 30 times.
The Sequential DMTS test consisted of up to eight visual stimuli contained in consecutive levels. Each level (for instance, level 2) corresponded to the number of stimuli that had to be kept in memory (for instance, two stimuli); also, subject should remember the order of appearance of each stimulus. The highest level 8 corresponded to the number of stimuli to be matched. To go to the next level, subject must perform three successively correct trials. If he/she failed in one trial, he/she was downgraded one level.
Figure 2 Model of experiment.
Figure 2 is a model of the experiment. If subject reach the highest level 8 for three consecutive trials, the session was ended. If not, session would be stopped after 60 trials, whether subject reached level 8 or not.
Procedures.
Many moslem university students observe MTFast habitually. Ten participants (5 females, ages 21-23 years; 5 males, ages 20-22 years) volunteered to participate in the study. Participants had study experience for at least 14 years. The recruitment was done in university campus via mouth to mouth to subjects that perform habitual MTFast.
The sessions of memory test were done at 12.30-15.00 PM so the actual length of fasting is about 8-11 hours. The reason why the assessments were done at around 1 PM was based on subjects' perception that 13.00 PM is the hardest time of the day because they were hungry, tired, and difficult to concentrate. It may be the best moment to see the effects of fasting on working memory task. The experiments were done at isolated places free from distortion/noise. Each participant did 6 sessions of assessment with at least 2 sessions in fasting. In doing later sessions, subject might learn from their experience in former sessions. To counterbalance this learning effect, half of subjects were in fasting condition in their first session of assessment, which was at Monday or Thursday, and other half were not.
Statistical analysis
3
Table 1 Estimates of statistical parameters
Measures of Working Memory Level Relative Performance Weight Error Response time Normalized reaction times Level per number
Fasting -0.59 -1.72 0.05 -71.15 56.169 0.99
Fasting- duration
0.03 0.04 0.01 13.86 -3.34 -0.23
Sessions 0.21* 3.76* -0.22* -95.19* -71.775* 1.01*
Sex 0.36 3.04 0.029 341.68 29.582 0.61
Sleep length
-0.06 -0.78 0.059 -21.11 -0.325 -0.19
* Statistically significant (see appendix 2). sample of students who habitually observe the fasting. However, beside fasting and its duration, working memory is also affected by subject's ability to learn from past sessions, his/her sleepiness condition and probably also their sex.
In statistical analysis, each measure of working memory is a response which can be modeled by fixed and random effects contained in the experiment. By considering the experimental conditions above, the fixed effects for this model were: fasting and its duration, session, sex, and sleep length. In this model, subjects were considered as were recruited in a random fashion so they were taken as the random effect. Analysis which combine fixed and random effects is known as mixed-effect model (Pinheiro & Bates 2004). In this research, linear mixed-effect analyses were conducted using statistical language S which is implemented in lme4 package (Bates 2005) of program R (R Development Core Team 2005). The parameters which were of interest were those which associate with fixed effects. Diagnostic of fixed-effect parameters were done by Markov Chain Monte Carlo (MCMC) simulations using CODA package of program R.
RESULT
Performances of working memory are shown in Figures 3-8. Subjects were getting better from session to session. Most of them got higher level and relative performance and decreased response times and errors in later sessions.
Estimates of statistical parameters for fixed effects are tabulated in Table 1. Fasting and its duration did not significantly influence performance of working memory. Except sessions, all other covariates also did not give
significant influence. Length of sleep varied between each subject. At first, I think that sleep would had an effect on performances of working memory due to acetylcholine as neuromodulator related to sleep factors. When someone sleeps, acetylcholine helps people in facilitating the process of consolidation of separate memory traces (Hasselmo 1999). In fact, subjects could get better or bad results both in short-term (less than 5 hours) and long-term sleep (more than 6 hours). But maybe there was also individual difference in sleep quality thus obscuring the results. Also, difference between sexes is relatively small and had no significant effect on performance of working memory.
The improvement in the performance of working memory from session to session shows learning effect. After getting experience with the DMTS task, subjects became familiar with the stimuli therefore their performances got relatively better than previous sessions.
DISCUSSION
Fasting
Present research investigates whether MTFast influences working memory task or not. Subject could get better result although they were in fasting condition. At first, I think that fasting duration might affect to performance task. It was due to the relationship between fasting duration and the concentrations of glucose in body and brain. Subject with shorter duration of fasting may had a bigger chance to get better result compared with the longer one because he/she had higher glucose concentrations.
3
Table 1 Estimates of statistical parameters
Measures of Working Memory Level Relative Performance Weight Error Response time Normalized reaction times Level per number
Fasting -0.59 -1.72 0.05 -71.15 56.169 0.99
Fasting- duration
0.03 0.04 0.01 13.86 -3.34 -0.23
Sessions 0.21* 3.76* -0.22* -95.19* -71.775* 1.01*
Sex 0.36 3.04 0.029 341.68 29.582 0.61
Sleep length
-0.06 -0.78 0.059 -21.11 -0.325 -0.19
* Statistically significant (see appendix 2). sample of students who habitually observe the fasting. However, beside fasting and its duration, working memory is also affected by subject's ability to learn from past sessions, his/her sleepiness condition and probably also their sex.
In statistical analysis, each measure of working memory is a response which can be modeled by fixed and random effects contained in the experiment. By considering the experimental conditions above, the fixed effects for this model were: fasting and its duration, session, sex, and sleep length. In this model, subjects were considered as were recruited in a random fashion so they were taken as the random effect. Analysis which combine fixed and random effects is known as mixed-effect model (Pinheiro & Bates 2004). In this research, linear mixed-effect analyses were conducted using statistical language S which is implemented in lme4 package (Bates 2005) of program R (R Development Core Team 2005). The parameters which were of interest were those which associate with fixed effects. Diagnostic of fixed-effect parameters were done by Markov Chain Monte Carlo (MCMC) simulations using CODA package of program R.
RESULT
Performances of working memory are shown in Figures 3-8. Subjects were getting better from session to session. Most of them got higher level and relative performance and decreased response times and errors in later sessions.
Estimates of statistical parameters for fixed effects are tabulated in Table 1. Fasting and its duration did not significantly influence performance of working memory. Except sessions, all other covariates also did not give
significant influence. Length of sleep varied between each subject. At first, I think that sleep would had an effect on performances of working memory due to acetylcholine as neuromodulator related to sleep factors. When someone sleeps, acetylcholine helps people in facilitating the process of consolidation of separate memory traces (Hasselmo 1999). In fact, subjects could get better or bad results both in short-term (less than 5 hours) and long-term sleep (more than 6 hours). But maybe there was also individual difference in sleep quality thus obscuring the results. Also, difference between sexes is relatively small and had no significant effect on performance of working memory.
The improvement in the performance of working memory from session to session shows learning effect. After getting experience with the DMTS task, subjects became familiar with the stimuli therefore their performances got relatively better than previous sessions.
DISCUSSION
Fasting
Present research investigates whether MTFast influences working memory task or not. Subject could get better result although they were in fasting condition. At first, I think that fasting duration might affect to performance task. It was due to the relationship between fasting duration and the concentrations of glucose in body and brain. Subject with shorter duration of fasting may had a bigger chance to get better result compared with the longer one because he/she had higher glucose concentrations.
3
Table 1 Estimates of statistical parameters
Measures of Working Memory Level Relative Performance Weight Error Response time Normalized reaction times Level per number
Fasting -0.59 -1.72 0.05 -71.15 56.169 0.99
Fasting- duration
0.03 0.04 0.01 13.86 -3.34 -0.23
Sessions 0.21* 3.76* -0.22* -95.19* -71.775* 1.01*
Sex 0.36 3.04 0.029 341.68 29.582 0.61
Sleep length
-0.06 -0.78 0.059 -21.11 -0.325 -0.19
* Statistically significant (see appendix 2). sample of students who habitually observe the fasting. However, beside fasting and its duration, working memory is also affected by subject's ability to learn from past sessions, his/her sleepiness condition and probably also their sex.
In statistical analysis, each measure of working memory is a response which can be modeled by fixed and random effects contained in the experiment. By considering the experimental conditions above, the fixed effects for this model were: fasting and its duration, session, sex, and sleep length. In this model, subjects were considered as were recruited in a random fashion so they were taken as the random effect. Analysis which combine fixed and random effects is known as mixed-effect model (Pinheiro & Bates 2004). In this research, linear mixed-effect analyses were conducted using statistical language S which is implemented in lme4 package (Bates 2005) of program R (R Development Core Team 2005). The parameters which were of interest were those which associate with fixed effects. Diagnostic of fixed-effect parameters were done by Markov Chain Monte Carlo (MCMC) simulations using CODA package of program R.
RESULT
Performances of working memory are shown in Figures 3-8. Subjects were getting better from session to session. Most of them got higher level and relative performance and decreased response times and errors in later sessions.
Estimates of statistical parameters for fixed effects are tabulated in Table 1. Fasting and its duration did not significantly influence performance of working memory. Except sessions, all other covariates also did not give
significant influence. Length of sleep varied between each subject. At first, I think that sleep would had an effect on performances of working memory due to acetylcholine as neuromodulator related to sleep factors. When someone sleeps, acetylcholine helps people in facilitating the process of consolidation of separate memory traces (Hasselmo 1999). In fact, subjects could get better or bad results both in short-term (less than 5 hours) and long-term sleep (more than 6 hours). But maybe there was also individual difference in sleep quality thus obscuring the results. Also, difference between sexes is relatively small and had no significant effect on performance of working memory.
The improvement in the performance of working memory from session to session shows learning effect. After getting experience with the DMTS task, subjects became familiar with the stimuli therefore their performances got relatively better than previous sessions.
DISCUSSION
Fasting
Present research investigates whether MTFast influences working memory task or not. Subject could get better result although they were in fasting condition. At first, I think that fasting duration might affect to performance task. It was due to the relationship between fasting duration and the concentrations of glucose in body and brain. Subject with shorter duration of fasting may had a bigger chance to get better result compared with the longer one because he/she had higher glucose concentrations.
4
Figure 3 Level Attained
Figure 4 Performance Attained
Figure 5 Weighted Error Attained
Figure 6 Response Time Attained
Figure 7 Normalized Reaction Times Attained
5
First, duration of the fasting in our case might be too short to reduce the glucose level (actual fasting durations were about 9 hours). This caused the ineffectiveness of fasting to reduce performance because both the body's and brain's glucose levels were sufficient to maintain body's and brain's metabolisms. Secondly, we didn’t control the time and amount of the dinner in the preceding day of test. Subjects differed at the time and amount of the last dinner. This may reduce the fasting effect to average. Third, there were individual differences in the way they fasted. For instance, subjects who practiced MTFast for prolonged time may resist the effects of fasting and may be able to maintain their glucose level relatively high. If that happened, that may cause the relatively higher performance in fasting condition in those subjects.
Learning from past sessions
When someone completed a session, he/she learned the visual stimuli of the DMTS task. Some of the pictorial stimuli which were hold in working memory may got consolidated into long term memory and session by session these would be accumulated. Learning effect lead the subjects to increasing chances to get better result, decreasing error count and faster timing when they chose stimuli. In this case, response time got faster and also affected weighted error to become lower compared than previous sessions. Beside that, by doing more sessions, chances of level downgradations became lower and chances to attain highest level became increased with only smaller number of trials. It leads to better result of level, relative performance and level-per-number attained. Such learning effects may mask the effect of fasting. That way session had more influence to performance of working memory rather than fasting.
CONCLUSION
Performance of visuospatial working memory task did not affected by Monday-Thursday fasting and its duration. It also did not affected by sleep length, and did not differ between male and female. It increased session by session which reflect the ability of subjects to learn the pictorial stimuli.
REFERENCE
Baddeley A. 1996. The fractionation of working memory. Proc Natl Acad Sci 9:13468-13472.
Benton D, Parker PY. 1998. Breakfasts, blood glucose, and cognition. Am J Clin Nutr 67:772-781.
Bates D. 2005. Fitting linear mixed models in R. R News 5:27-30.
Elliot R. 1999. Differential neural responses during performance of matching and nonmatching to sample tasks at two delay intervals. J Neuroscience 19(12):5066– 5073.
Goldman PS. 1996. Regional and cellular fractionation of working memory. Proc Natl Acad Sci. 93:13473-13480.
Hasselmo ME. 1999. Neuromodulation acetylcholine and memory consolidation. J Neuroscience 3:351-358.
Pinheiro JC, Bates DM. 2000. Mixed-effects models in S and S-Plus. Springer, New York.
Pollit E, Jacoby E. 1998. Fasting and cognition in well and undernourished school children. Am J Clin Nutr 67:779-812.
Sunram-Lea S, Foster JK, Durlach P, Perez C. 2001. Glucose facilitation of cognitive performances in healthy young adults. J Phsychopharmacology 157:46-54. R Development Core Team. 2005. R: A
5
First, duration of the fasting in our case might be too short to reduce the glucose level (actual fasting durations were about 9 hours). This caused the ineffectiveness of fasting to reduce performance because both the body's and brain's glucose levels were sufficient to maintain body's and brain's metabolisms. Secondly, we didn’t control the time and amount of the dinner in the preceding day of test. Subjects differed at the time and amount of the last dinner. This may reduce the fasting effect to average. Third, there were individual differences in the way they fasted. For instance, subjects who practiced MTFast for prolonged time may resist the effects of fasting and may be able to maintain their glucose level relatively high. If that happened, that may cause the relatively higher performance in fasting condition in those subjects.
Learning from past sessions
When someone completed a session, he/she learned the visual stimuli of the DMTS task. Some of the pictorial stimuli which were hold in working memory may got consolidated into long term memory and session by session these would be accumulated. Learning effect lead the subjects to increasing chances to get better result, decreasing error count and faster timing when they chose stimuli. In this case, response time got faster and also affected weighted error to become lower compared than previous sessions. Beside that, by doing more sessions, chances of level downgradations became lower and chances to attain highest level became increased with only smaller number of trials. It leads to better result of level, relative performance and level-per-number attained. Such learning effects may mask the effect of fasting. That way session had more influence to performance of working memory rather than fasting.
CONCLUSION
Performance of visuospatial working memory task did not affected by Monday-Thursday fasting and its duration. It also did not affected by sleep length, and did not differ between male and female. It increased session by session which reflect the ability of subjects to learn the pictorial stimuli.
REFERENCE
Baddeley A. 1996. The fractionation of working memory. Proc Natl Acad Sci 9:13468-13472.
Benton D, Parker PY. 1998. Breakfasts, blood glucose, and cognition. Am J Clin Nutr 67:772-781.
Bates D. 2005. Fitting linear mixed models in R. R News 5:27-30.
Elliot R. 1999. Differential neural responses during performance of matching and nonmatching to sample tasks at two delay intervals. J Neuroscience 19(12):5066– 5073.
Goldman PS. 1996. Regional and cellular fractionation of working memory. Proc Natl Acad Sci. 93:13473-13480.
Hasselmo ME. 1999. Neuromodulation acetylcholine and memory consolidation. J Neuroscience 3:351-358.
Pinheiro JC, Bates DM. 2000. Mixed-effects models in S and S-Plus. Springer, New York.
Pollit E, Jacoby E. 1998. Fasting and cognition in well and undernourished school children. Am J Clin Nutr 67:779-812.
Sunram-Lea S, Foster JK, Durlach P, Perez C. 2001. Glucose facilitation of cognitive performances in healthy young adults. J Phsychopharmacology 157:46-54. R Development Core Team. 2005. R: A
5
First, duration of the fasting in our case might be too short to reduce the glucose level (actual fasting durations were about 9 hours). This caused the ineffectiveness of fasting to reduce performance because both the body's and brain's glucose levels were sufficient to maintain body's and brain's metabolisms. Secondly, we didn’t control the time and amount of the dinner in the preceding day of test. Subjects differed at the time and amount of the last dinner. This may reduce the fasting effect to average. Third, there were individual differences in the way they fasted. For instance, subjects who practiced MTFast for prolonged time may resist the effects of fasting and may be able to maintain their glucose level relatively high. If that happened, that may cause the relatively higher performance in fasting condition in those subjects.
Learning from past sessions
When someone completed a session, he/she learned the visual stimuli of the DMTS task. Some of the pictorial stimuli which were hold in working memory may got consolidated into long term memory and session by session these would be accumulated. Learning effect lead the subjects to increasing chances to get better result, decreasing error count and faster timing when they chose stimuli. In this case, response time got faster and also affected weighted error to become lower compared than previous sessions. Beside that, by doing more sessions, chances of level downgradations became lower and chances to attain highest level became increased with only smaller number of trials. It leads to better result of level, relative performance and level-per-number attained. Such learning effects may mask the effect of fasting. That way session had more influence to performance of working memory rather than fasting.
CONCLUSION
Performance of visuospatial working memory task did not affected by Monday-Thursday fasting and its duration. It also did not affected by sleep length, and did not differ between male and female. It increased session by session which reflect the ability of subjects to learn the pictorial stimuli.
REFERENCE
Baddeley A. 1996. The fractionation of working memory. Proc Natl Acad Sci 9:13468-13472.
Benton D, Parker PY. 1998. Breakfasts, blood glucose, and cognition. Am J Clin Nutr 67:772-781.
Bates D. 2005. Fitting linear mixed models in R. R News 5:27-30.
Elliot R. 1999. Differential neural responses during performance of matching and nonmatching to sample tasks at two delay intervals. J Neuroscience 19(12):5066– 5073.
Goldman PS. 1996. Regional and cellular fractionation of working memory. Proc Natl Acad Sci. 93:13473-13480.
Hasselmo ME. 1999. Neuromodulation acetylcholine and memory consolidation. J Neuroscience 3:351-358.
Pinheiro JC, Bates DM. 2000. Mixed-effects models in S and S-Plus. Springer, New York.
Pollit E, Jacoby E. 1998. Fasting and cognition in well and undernourished school children. Am J Clin Nutr 67:779-812.
Sunram-Lea S, Foster JK, Durlach P, Perez C. 2001. Glucose facilitation of cognitive performances in healthy young adults. J Phsychopharmacology 157:46-54. R Development Core Team. 2005. R: A
7
7
Appendix 1 Measures of Working Memory
There six variables that were used in this research (such as: level; relative performance; weighted error; response time; normalized reaction times; and level-per-number attained)
1. Level attained is the first sustained highest level (without downgradation) that was achieved by subject in the current session.
Sometimes we called level attained as highest level reached in that session/day
2. Relative performance is a ratio between accumulated scores divided by maximum cumulative scores that can be obtained without downgradations. Scores were assigned to every trial according to the particular levels of the trials. For instances, a trial at level 2 would get two scores, level 3 three scores, and so on
3. Weighted error is a number of errors for each level that was performed by subject. Weighted error was gained by calculating error count for each level divided by actual number of object.
The difficulty may increase if the number of item to remember increased. In other word, more chance to make error in higher level.
If the subject reached level 4 and he/she made 1 error for level 1, 2 errors for level 2, 4 errors for level 3 and 6 errors for level 4. In total normalized total error (weight error): 1/1 + 2/2 + 4/3 + 6/4
4. Response time is a duration that was gained by calculating reaching time plus r.time. Reaching time is duration between time to touch the targets and button release time. r.time is duration between time to touch next targets minus time to touch previous targets.
5. Normalized reaction time is total time from the eight stimuli presentation to the final touch divided by number of objects
For example if level 3 and took 3000 ms from the all possible objects appeared to the selection of the 3rd object, 3000/3 is normalized reaction time. We called normalized reaction time as “ an averaged reaction time for a trial”
6. Level-per-number attained was acquired by calculating sustained highest levels times 60 divided by number of trials to attain that level.
For example; if the subject reached level 8 as his/her sustained highest level and requires 24 numbers of trials to attained that level, level per number:
Weighted Error = Error count for each level Actual number of object
Normalized Reaction Time = Total time from eight stimuli presentation to final touch Number of objects
8 * 60 24 Relative Performance = Cumulative Scores
8
Appendix 2A Confidence intervals for estimates of fasting parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate -0.59 -1.72 0.05 -71.15 56.169 0.99
Lower -1.27 -9.89 -0.57 -576.687 -38.901 -1.68
Upper 0.09 6.73 0.66 471.046 149.26 4.14
Appendix 2B Confidence intervals for estimates of fasting-duration parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate 0.03 0.04 0.01 13.86 -3.34 -0.23
Lower -0.04 -0.78 -0.05 -39.62 -57.69 -0.525
Upper 0.097 0.85 0.07 63.50 6.03 0.026
Appendix 2C Confidence intervals for estimates of session parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate 0.21* 3.76* -0.22* -95.19* -71.775* 1.01*
Lower 0.109 2.49 -0.31 -174.47 -85.99 0.525
Upper 0.31 5.007 -0.12 -14.27 -57.69 1.48
* Statistically significant.
Appendix 2D Confidence intervals for estimates of sex parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate 0.36 3.04 0.029 341.68 29.582 0.61
Lower -1.48 -17.09 -1.19 -410.71 -254.002 -1.18
Upper 2.14 22.72 1.26 1103.89 304.14 2.37
Appendix 2E Confidence intervals for estimates of sleep length parameter to measures of working memory (50000 MCMC simulations).
Level Relative
Performance
Weight Error
Response Time
Normalized Reaction Time
Level per Number
Estimate -0.06 -0.78 0.059 -21.11 -0.325 -0.19
Lower -0.16 -2.04 -0.035 -101.20 -14.78 -0.58
