Cortical Areas

Complex brain functions such as cognition, language, sexuality, sleep/wakeful-ness, emotions, and memory require constant information processing. Of the human cortex, 75% is association cortex (Fig. 4). The ability to attend, identify, and plan a

Fig. 4. Role of brain cortical areas: after identification of a stimulus by temporal regions, parietal areas attend to the stimulus, and frontal areas plan the appropriate behavioral responses. CB1 receptors are dense in all cortical areas.

meaningful response to external or internal stimuli depends to a large extent on that association cortex, and one could define cognition as the processes by which we come to know and understand the world. Most inputs to the association cortex come from other cortical areas (hence the name "association"), either on the same hemisphere or the opposite one. Classically, three big areas are described. Imagine a driver and the sound of a horn—the temporal association cortex identifies the stimulus. The information is then relayed to the parietal association cortex, which decides whether to attend to the stimulus or not. In turn, the processed information is sent to the frontal association cortex for planning of appropriate behavioral response. The remainder (25%) of the cortical areas is subdivided into the primary sensory cortex, which receives inputs from the periphery by the intermediate of the thalamus, and the motor cortex, which receives inputs from the basal ganglia and the cerebellum, also through the thalamus. Two structures, the corpus callosum and the anterior commissure, allow communication from one side of the brain to the other.

Much of our understanding of brain regional neurophysiology comes from pathological lesions and their observation. Often, a drug, by altering physiological systems, can mimic in part what the pathology describes. For example, lesions of the temporal lobes result in recognition deficits. The patient has difficulty recognizing, identifying, or naming familiar objects. Syndromes of temporal lobe lesions are called agnosias, such as prosopagnosia, in which the patient cannot name things. Lesions of the parietal lobes lead to attention and perception deficits, often referred to as contralateral neglects—the patient fails to report, respond, or orient to a stimulus presented to the

Fig. 5. Role of basal ganglia and cerebellum in the programmation of movements: whereas the basal ganglia allows the initiation of movement, the cerebellum controls the ongoing aspects of it. CB1 receptors are highly expressed in the basal ganglia and cerebellum.

side of the body or visual space opposite the brain lesion. Finally, lesions of the frontal lobes alter the individual's personality, the ability to plan a behavior in relationship to the environment, and to use memories as a guide to appropriateness of behavior in various situations.

CB1 receptors are particularly dense in all cortical areas (31), particularly the cingulate cortex (see Section 3), and inhibition of evoked release of a number of neu-rotransmitters would result in cognitive impairment such as perception, attention, and behavioral deficits. It is difficult to ascribe specific deficits because of the complexity of the neural wiring in cortical regions.

Continue reading here: Basal Ganglia and Cerebellum

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