SUPPLEMENTAL DIGITAL CONTENT 10
Senior residents demonstrated greater technical performance stability across workload conditions along with sustained activation in lateral prefrontal regions during all but the highest workload condition, and only then was prefrontal deactivation observed. In contrast, less experienced residents demonstrated performance degradation in line with increasing workload, prefrontal deactivation during low workload levels, and increased activation only during the most cognitively demanding condition.
Subjective Workload
Among PGY1-2 residents, subjective workload increased with mental demands, suggesting that the two-minute time-limit and decision-making tasks were valid methods of increasing workload. In contrast, there were no significant between- condition differences in subjective workload in the PGY5+ cohort; furthermore, in all conditions, subjective workload was significantly lower among PGY5+ subjects compared with less experienced participants. These trends in subjective workload, coupled with changes in technical performance across conditions, reveal some interesting differences between junior and senior residents. It is apparent that as task demands increased, PGY1-2 residents experience greater mental workload which is associated with a deterioration in technical performance. However, PGY5+ residents do not seem to perceive the task demands to be as challenging and technical performance remains relatively stable. Whilst this may reflect skill automaticity characteristic of surgical expertise,1 there may also be neurocognitive differences between junior and senior residents in the way in which competing mental demands are handled.
Junior Residents
The PGY1-2 and PGY3-4 groups demonstrated deactivation responses in the bilateral VLPFC and DLPFC during the lowest workload conditions, and activation responses during the highest workload condition in which both temporal and cognitive demands were imposed, indicating an improvement in prefrontal engagement. Reinvestment theory suggests that high workload conditions result in disruption of automaticity and a subsequent ‘reinvestment’ of attentional resources in the primary motor task.2 However, if reinvestment strategies are successful during dual-task performance and then stable motor task performance would be expected as opposed to the degradation in progression score and leak volume we observed. Thus, an alternative explanation for the increase in PFC activity during the highest workload condition is required.
In order to cognitively attend to multiple tasks demands simultaneously, allocation of processing resources to different brain systems is required in order to make decisions, plan responses and implement actions in relation to each demand.3 However, the processing capacity of the human brain is limited and, if exceeded, has to be rationed to competing brain systems.4 It is conceivable that, during episodes of combined suturing and decision-making under temporal demand, junior residents were unable to cognitively attend to multiple demands and therefore choose to engage in a single task.
In this case, the motor task (laparoscopic suturing) is unlikely to be ingrained and automated among less experienced residents and would demand greater prefrontal engagement.5 However, technical performance declined the most when dual-tasking under time pressure which suggests that the PFC activation observed may not be due to additional engagement with the motor task. Our previous work highlighted that
laparoscopic suturing under time pressure elicits prefrontal response attenuation rather than the increase in activation observed in the combined suturing and cognitive condition here.6 Therefore, it is unlikely that these subjects are processing the temporal demand in the highest workload condition as they are in the other experimental conditions. It follows, that the increase prefrontal activation observed is likely to be due to subjects consciously or unconsciously allocating processing resources to the decision- making scenarios. Indeed, others have demonstrated that cognitive tasks elicit greater prefrontal responses compared to motor tasks among surgeons.7
Senior Residents
In contrast to the PGY1-2 and PGY3-4 groups, more experienced residents exhibited typical activation responses predominantly in the bilateral VLPFC and DLPFC during the lowest three workload conditions but deactivation responses at the highest workload, suggesting a loss of focus and concentration. Unlike less experienced residents who employ selective attention to focus on one of multiple competing demands, PGY5+
surgeons may be unconsciously attempting to process all mental demands simultaneously (i.e. suturing, time pressure and decision-making). Since such ‘divided attention’4 strategies depend on lateral prefrontal engagement,8 the deactivation patterns observed may represent a breakdown in the ability to attend to multiple competing stimuli simultaneously.
As attending surgeons were not recruited in this study, our data does not enable us to determine how the prefrontal response to multitasking changes after several years of
independent practice. However, our previous has shown that when placed under a temporal demand, attendings are better able to maintain prefrontal engagement and stabilize motor performance under stress compared with less experienced residents.6 Whilst this previous study did not impose a multitasking stress on the participants, it could be hypothesised that attending surgeons would exhibit sustained prefrontal activation when attending to motor and cognitive tasks simultaneously.
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