Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 1)

Harrisons Internal Medicine Chapter 27. Aphasia, Memory Loss, and Other Focal Cerebral DisordersAphasia, Memory Loss, and Other Focal Cerebral Disorders: IntroductionThe cerebral cortex of the human brain contains ~20 billion neurons spread over an area of 2.5 m2. The primary sensory areas provide an obligatory portal for the entry of sensory information into cortical circuitry, whereas the primary motor areas provide final common pathways for coordinating complex motor acts.The primary sensory and motor areas constitute 10% of the cerebral cortex. The rest is subsumed by unimodal, heteromodal, paralimbic, and limbic areas, collectively known as the association cortex (Fig....
Nội dung trích xuất từ tài liệu:
Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 1) Chapter 027. Aphasia, Memory Loss, and Other Focal Cerebral Disorders (Part 1) Harrisons Internal Medicine > Chapter 27. Aphasia, Memory Loss, andOther Focal Cerebral Disorders Aphasia, Memory Loss, and Other Focal Cerebral Disorders:Introduction The cerebral cortex of the human brain contains ~20 billion neurons spreadover an area of 2.5 m2. The primary sensory areas provide an obligatory portal forthe entry of sensory information into cortical circuitry, whereas the primary motorareas provide final common pathways for coordinating complex motor acts. The primary sensory and motor areas constitute 10% of the cerebral cortex.The rest is subsumed by unimodal, heteromodal, paralimbic, and limbic areas,collectively known as the association cortex (Fig. 27-1). The association cortex mediates the integrative processes that subservecognition, emotion, and behavior. A systematic testing of these mental functions isnecessary for the effective clinical assessment of the association cortex and itsdiseases. Figure 27-1Lateral (top) and medial (bottom) views of the cerebral hemispheres. The numbers refer to the Brodmann cytoarchitectonic designations. Area 17corresponds to the primary visual cortex, 41–42 to the primary auditory cortex, 1–3 to the primary somatosensory cortex, and 4 to the primary motor cortex. The restof the cerebral cortex contains association areas. AG, angular gyrus; B, Brocas area; CC, corpus callosum; CG, cingulategyrus; DLPFC, dorsolateral prefrontal cortex; FEF, frontal eye fields (premotorcortex); FG, fusiform gyrus; IPL, inferior parietal lobule; ITG, inferior temporalgyrus; LG, lingual gyrus; MPFC, medial prefrontal cortex; MTG, middle temporalgyrus; OFC, orbitofrontal cortex; PHG, parahippocampal gyrus; PPC, posteriorparietal cortex; PSC, peristriate cortex; SC, striate cortex; SMG, supramarginalgyrus; SPL, superior parietal lobule; STG, superior temporal gyrus; STS, superiortemporal sulcus; TP, temporopolar cortex; W, Wernickes area.According tocurrent thinking, there are no centers for hearing words, perceiving space, orstoring memories. Cognitive and behavioral functions (domains) are coordinatedby intersecting large-scale neural networks that contain interconnected corticaland subcortical components. The network approach to higher cerebral function has at least fourimplications of clinical relevance: (1) a single domain such as language ormemory can be disrupted by damage to any one of several areas, as long as theseareas belong to the same network; (2) damage confined to a single area can giverise to multiple deficits, involving the functions of all networks that intersect inthat region; (3) damage to a network component may give rise to minimal ortransient deficits if other parts of the network undergo compensatoryreorganization; and (4) individual anatomic sites within a network display arelative (but not absolute) specialization for different behavioral aspects of therelevant function. Five anatomically defined large-scale networks are most relevant to clinicalpractice: a perisylvian network for language; a parietofrontal network for spatialcognition; an occipitotemporal network for face and object recognition; a limbicnetwork for retentive memory; and a prefrontal network for attention andbehavior.