Funciones Corticales Superiores

Editors: Waxman, Stephen G.
Title: Clinical Neuroanatomy, 25th Edition
Copyright ©2003 McGraw-Hill
> Table of Contents > Section V - Functional Systems > 21 - Higher Cortical Functions
Higher Cortical Functions
In addition to containing networks of neurons related to the initiation of movement and to sensation from the body and the special sensory organs, the cortex is the substrate forfunctions that convey comprehension, cognition, and communication.
FRONTAL LOBE FUNCTIONS
The frontal lobes serve as an “executive” part of the cortex. They participate in higher-order functions that include reasoning and abstraction; planning and initiating of activity; monitoring and shaping of behavior to ensure adaptive actions; inhibiting maladaptive behavior; prioritizing and sequencingactions; problem solving; and coordinating elementary motor and sensory functions into a coherent and goal-directed stream of behavior.
Damage to the frontal lobes (as can occur, eg, with brain tumors or head trauma) can produce profound behavioral changes. Several syndromes are especially common: Following damage to the dorsolateral part of the frontal lobes (the convexity), patients tend to becomeindifferent, abulic, or apathetic (mute and motionless in some cases). Following damage to the orbitofrontal area of the cortex, there is a syndrome of disinhibition, in which the patient appears labile and irritable. These patients are inattentive and distractible, with impaired judgment and loss of the usual inhibitions and social graces. Damage to the medial part of the frontal lobes can producea syndrome of akinesia (lack of spontaneous movements) and apathy. Injury to the basal part of the frontal lobes can also result in impairment of memory. These frontal lobe syndromes are more frequently seen in patients with bilateral lesions.
LANGUAGE & SPEECH
Language is the comprehension and communication of abstract ideas. This cortical function is separate from the neural mechanisms relatedto primary visual, auditory, and motor function.
The ability to think of the right words, to program and coordinate the sequence of muscle contractions necessary to produce intelligible sounds, and to assemble words into meaningful sentences depends on Broca's area (areas 44 and 45) within the inferior frontal gyrus, located just anterior to the motor cortex controlling the lips and tongue.
Theability to comprehend language, including speech, is dependent on Wernicke's area. This area is located in the posterior part of the superior temporal gyrus within the auditory association cortex (area 22).
The arcuate fasciculus provides a crucial association pathway within the hemisphere white matter, connecting Wernicke's and Broca's areas (Fig 21-1). Because the arcuate fasciculus connectsthe speech comprehension area (Wernicke's area) with the area responsible for production of speech (Broca's area), damage to this white matter tract produces impairment of repetition.
Dysarthria
Dysarthria is a speech disorder in which the mechanism for speech is damaged by lesions in the corticobulbar pathways; in one or more cranial nerve nuclei or nerves V, VII, IX, X, and XII; in thecerebellum; or in the muscles that produce speech sounds. Dysarthria is characterized by dysfunction of the phonation, articulation, resonance, or respiration aspects of speech.
Aphasia
Aphasia, as the term is generally used, refers to loss or impairment of language function as a result of brain damage. There are a number of distinct types of aphasia and most of these result from lesions in specificregions of the cerebral hemispheres (Table 21-1). In testing for aphasia, the clinician first listens to the patient's spontaneous speech output and then explores the patient's speech during conversation. Speech may be categorized as fluent (more than 50 words per minute, effortless, absence of dysarthria, normal phrase length, and normal intonation). In contrast, nonfluent aphasia is effortful,...