duplicated region evolving a new syntactical area. This region was also connected to the IPL, primarily the SMG. From this circuitry, a hierarchichal, multimodal tool assembly process was now possible. The duplicated region now involved with syntactic language ability became linked to the mirror neuron system circuitry, which included the superior temporal lobe semantic abilities, the IPL, and Broca’s area [66].
Social and Emotional Circuitry Revealed by Disruption of the Uncinate Fasciculus
Disruption of the uncinate fasciculus (UF) due to relatively common diseases reveals features of the assembly of the social and emotional circuitry of the human brain. The UF is one of several large scale human cerebral fiber tracts that have expanded dramatically in the course of hominin evolution, with arcuate fasciculus being another. The UF has extensive fiber tracts connecting the anterior temporal lobe and the orbitofrontal cortex (OFC), which has notable inhibitory control. A peculiar feature of this relatively expan
sive fiber tract is its proneness to shearing injury associated with traumatic brain injury (TBI), no matter where the impact of injury occurred on the brain case. Similarly, the inferior frontal lobe as well as the anterior temporal lobe are particularly prone to injury associated with TBI [67,68]. The UF is also impacted in several common neurological disorders such as stroke, frontotemporal lobe syndromes, and multiple sclerosis. Because this fiber tract and associated cortical regions of inferior frontal and anterior temporal lobe reach maturity as late as the third or fourth decades, this makes it uniquely vulner
able to a variety of neuropsychiatric conditions that preferentially affect the young adult population [69].
One of the principal UF functions is the mediation of choice in response to infor
mation acquired from social and emotional stimuli; it also has episodic memory func
tions. The anterior temporal pole hub for memory storage is specific for person related memory, social memories, and theory of mind. Hence, delusional misidentification syn
dromes (DMISs) in which emotions and memory are disconnected is explainable. With Capgras syndrome, for example, a familiar person is viewed by the patient as a stranger despite the emotional reaction remaining intact. In a related but kind of opposite situ
ation, Fregoli’s syndrome involves a disruption of the tracts subserving face processing and the cortical areas for limbic related emotive regions that allow the person to perceive a familiar face but to lack relevant emotional valence. The person so afflicted will therefore conclude that the “familiar” person is a stranger [70]. Other core UF functions include episodic memory processing, social, emotional, and linguistic functions. People with UF dysfunction also report schizophrenic type symptoms, generalized anxiety, uncinate fits, and forme fruste type Klüver–Bücy syndromes [71].
Syndromes
Geschwind-Gastaut Syndrome
“Silent brain lesions” is a term used, albeit less frequently, for inexplicable or absent syn
dromes when known lesions have affected certain brain regions, mostly involving the frontal lobes, temporal and right parietal areas. Geschwind Gastaut Syndrome (GGS) is representative of relatively silent brain syndromes. This constitutes a constellation of signs
and symptoms typified by (1) a viscous personality, (2) metaphysical obsessions, and (3) altered physiological drives. The “viscous personality” is regarded as the principal com
ponent and includes over inclusive verbal discourse, circumstantiality in speech, inordin
ately detailed information that is shared, and a peculiar prolongation of interpersonal discourse or encounters. In addition, hypergraphia (excessive writing), excessive draw
ing, or painting may be additional features. Metaphysical engrossments take the form of moral and intellectual preoccupations in philosophy and religion. Physiological alter
ations include hyposexuality, fear, or aggression [72]. The syndrome was first described in association with epileptic syndromes and subsequently due to temporal lobe brain hemorrhage affecting the uncinate fasiculus (Figure 5.4) [73]. This intriguing syndrome provides a remarkable perspective on the diverse functions of the temporal lobes and their association with the frontal lobes [74]. The cardinal components of this syndrome may be viewed as an unraveling of the recent human brain circuitry associated with the
“cultural explosion” that archeological discoveries have associated with episodic memory enhancement, mental time travel, and ruminations about the afterlife [75].
Other clinical neurological syndromes, such as frontotemporal lobe dementia, yield additional insights into the diversity of human cognitive evolution, such as visual artistry and spiritual processing, by unraveling circuitry in this part of the brain due to vari
ous neurodegenerations. The two way process whereby neuro archeology and clinical neurosciences inform each other about brain evolution is again underscored by these observations.
Frontoparietal Fragmentation, the Visual Dorsal and Ventral Radiations, and Balint’s Syndrome
Frontoparietal sensorimotor skills had evolved to the extent of basic stone knapping, yielding flakes, or lithic mode 1, also termed Oldowan technology, by 3.4 mya (Dikika,
Figure 5.4 Geschwind-Gastaut Syndrome due to isolated right temporal lobe hemorrhage (arrow).
Syndromes 101
Ethiopia). Subsequently more sophisticated stone knapping allowed hand axes or biface tools, termed mode 2 or Archeulean, that required additional cognitive circuitry for pro
cessing visual object shaping and spatial coordinates [76]. Paleoneurological insights allow us to relate these to the two major visual radiations, the ventral radiation and dorsal stream, respectively. From extant primate studies to date, the coordination of these two activities was not within ape competence. The long term procedural memory storage for these capabilities was possible by ~1.8 mya. The skills for constructing hand axes or biface technology requires the recruitment of the anterior intraparietal sulcus (IPS) and inferior frontal sulcus of the left hemisphere, both components of the mirror neuron system. This provides additional support for social learning being a crucial constituent in the acquisi
tion of abilities required for biface technology [77].
Clinical neurological syndromes that may be seen as unraveling of both dorsal and ventral visual radiations come from posterior brain syndromes. Common neurological conditions that cause bilateral parietooccipital lesions include stroke, eclampsia, cerebral infarcts, and posterior reversible encephalopathy syndrome (PRES) (Figure 5.5). These processes cause an unraveling or fragmentation of the ventral and dorsal visual streams.
These present with piecemeal vision (simultanagnosia), optic ataxia (impaired conju
gate gaze direction), and optic apraxia (impaired visual guidance for object pointing).
Although these may occur in isolation or two together, if all three coexist the syndrome is termed Balint’s syndrome.
Alien Hand Syndrome
A relatively infrequent clinical syndrome termed alien hand or anarchic hand syndrome refers to either the hand or arm behaving autonomously. This may take the form of unintended object grabbing, unwittingly hitting a bed partner while asleep, or one hand may obstruct or interfere with the other hand while it is performing a particular action, such as lifting a fork to the mouth while eating. These are involuntary actions, occurring
Figure 5.5 Dorsal and visual field disruption. Piecemeal vision (simultanagnosia), impaired pointing (optic ataxia) and eye gaze (optic apraxia). Balint’s syndrome in a young pregnant woman with eclampsia causing bilateral posterior reversible brain lesions (left image arrows) and vasospasm (vessel narrowing) of intracranial arteries (right image arrows).
non consciously and to some extent may be subsumed under the conditions discussed under “loss of sense of self disorders.” Several different alien hand subtypes have been rec
ognized, including, parietal, frontal, ictal, and corpus callosal. The parietal type presents with a withdrawal reaction from contact (parietal avoidance syndrome), whereas with the frontal type grasping actions occur [60]. In the corpus callosal subtype an inter manual disputation between hands occurs, with the two hands performing opposite actions, also termed diagnostic ideomotor apraxia. In epilepsy associated alien hand or ictal alien hand, these syndromes may present transiently, usually with corpus callosal or mesial frontal damage. From a neurobiological and evolutionary point of view, fMRI studies have yielded insights that the primary motor cortex is relatively isolated from premotor cortical control, where motor programs are finalized. Rehabilitation measures have bene
fited from these insights, with measures for the frontal variant by placing objects in that hand to counter the tendency of grabbing and grasping [61,62,72].
Cerebellar Cognitive Affective Syndromes
With the substantiation of modern human capacities in terms of culture and brain size by
~200 kya, archeological endocast data indicate that the cerebellum achieved modern pro
portions as recently as ~28 kya. These findings may be attributed to the surge in cortico
cerebellar connectivity of the PFC that transpired during the latter part of the Pleistocene period, 2.5 mya to 12 kya). This circuitry has been attributed to improvement in cognitive efficiency, probably co occurring with the development of EWM [78]. Clinical neurologic al evidence of disruption of this neurobiological evolutionary circuitry is represented by cerebellar cognitive dysmetria and cerebellar cognitive affective syndrome. This is further corroborated by neuroimaging findings that demonstrate fractional anisotropic impairment of these tracts in these syndromes as well as the findings of corticocerebellar, crossed diaschisis [79,80].
Remote Brain Effects of Lesions: Hodological Perspectives, Improved Behavior, and Hyperfunction
Frontal network syndromes may at times be due to remote effects of a disease process, termed diaschisis. This may take the form of either hypofunction (decreased function) or hyperfunction (increased function) of the network. In addition, the lesion itself may affect the underlying cortex, rendering it either hypo or hyperfunctioning. Sometimes parts of the brain that have increased function result in dramatic syndromes such as a savant syn
drome. Paradoxical functional facilitation was a hypothesis proposed by Kapur, wherein one brain area reverses an inhibitory influence on another area, with augmentation of function. For example, increased originality is facilitated by relative left hemisphere inhib ition in the setting of an otherwise intact right hemisphere [81]. Specific examples of these syndromes include:
• savant syndromes that may present with various forms, such as superlative talent in mathematics, visual art, music, or visuospatial ability. The acquisition may be acquired prodigiously, suddenly, or be of splinter talented subtypes [82];
• emergent artistic expertise associated with neurodegenerative disease such as frontotemporal dementia, Alzheimer’s disease, or Parkinson’s disease, but also seen with stroke, epilepsy, and migraine [83];
References 103
• literary artist aptitude associated with right temporal lobe impairment [84];
• contentspecific delusion or DMIS, in association with right frontal stroke [85];
• visual imagery loss in the setting of dreaming [86];
• increased sense of humor, reported after right frontal lesions [87].
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