CHAPTER 7

Functions of the Cerebral Cortex and Regional Cerebral Diagnosis

It has not always been accepted that parts of the brain have specific functions. Flourens (1823) thought that all cerebral tissue was equipotential, and his influential views held sway for the better part of a century. Broca’s seminal aphasic patient (1861) demonstrated that speech functions were localized to the left inferior frontal gyrus. Based on his studies of epilepsy, Hughlings Jackson was the first to point out that there is a motor cortex. Many subsequent experiments have amply demonstrated that certain areas of the cerebral cortex have specific functions. Brodmann created maps based on regional histologic differences (Figure 6.3). The correlation between histology and function is imprecise. Many areas with identical histology have differing functions. Disease involving specific areas can cause widely differing clinical manifestations. Destruction of an inhibitory area can cause the same clinical manifestations as overactivity of the area inhibited. Because of the plasticity of the nervous system, other structures or areas may assume the function of a diseased or injured part.

In addition to being localized in a specific brain region, a function can also be lateralized to one or the other hemisphere. The hemisphere to which a function is lateralized is said to be dominant for that function. In lower animals, both hemispheres seem to have equal influence. A particular attribute of the human brain, however, is the dominance of one hemisphere over the other for certain functions. This is especially true for language, gnosis (the interpretation of sensory stimuli), and praxis (the performance of complex motor acts).

Modern functional imaging techniques such as positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and other methods of studying the metabolic activity of the brain have provided another dimension to the traditional notions of cerebral localization. For even simple tasks, such studies have shown a pattern of involvement of multiple brain regions overlapping the anatomical divisions into discrete lobes. The fact that a lesion produces defects in a particular function does not necessarily imply that under normal circumstances, that function is strictly localized to a particular region. Despite these limitations, it remains clinically useful to retain the traditional concepts of localization of functions in the various lobes of the dominant and nondominant hemispheres.

The Frontal Lobes

Chapter 6 discusses the gross anatomy of the frontal lobe. Clinically, important areas include the motor strip, the premotor and supplementary motor areas (SMAs), the prefrontal region, the frontal eye fields, and the motor speech areas. The frontal lobe anterior to the premotor area is referred to as the prefrontal cortex. The anterior portion of the cingulate gyrus is sometimes considered part of the frontal lobe, although its connections are primarily with limbic lobe structures. Frontal lobe areas related to motor function are discussed in Chapter 25. The frontal eye fields are discussed in Chapter 14, and the motor speech area is covered in Chapter 9. Figure 7.1 shows some of these areas.

FIGURE 7.1 Motor areas of the frontal lobe in monkeys (A) and homologous areas in the human (B). In humans, the border between areas 6 and 4 on the lateral surface is located in the anterior bank of the central sulcus. FEF, frontal eye field; M1, primary motor cortex; PMd, dorsal premotor cortex; PMv, ventral premotor cortex; RCZa, anterior rostral cingulate zone; RCZp, posterior rostral cingulate zone; SMA, supplementary motor area. (Reprinted from Picard N, Strick PL. Imaging the premotor areas. Curr Opin Neurobiol 2001;11[6]:663–672. Copyright © 2001 Elsevier. With permission.)

The Prefrontal Area

The portions of the frontal lobe anterior to area 6, area 8, and the motor speech centers are areas referred to as the prefrontal cortex. It includes areas 9 to 12, 32, and others. These areas are connected with the somesthetic, visual, auditory, and other cortical areas by long association bundles and with the thalamus and the hypothalamus by projection fibers. The prefrontal cortex is the main projection site for the dorsomedial nucleus of the thalamus. The prefrontal cortex projects to the basal ganglia and substantia nigra; it receives dopaminergic fibers that are part of the mesocortical projection from the midbrain. The dopaminergic neurons are associated with reward, attention, short-term memory tasks, planning, and drive.

Clinically, the prefrontal region can be divided into the dorsolateral prefrontal cortex (DLPFC), the medial prefrontal cortex (MPC), and the orbitofrontal cortex (OFC). The cellular structure of the prefrontal region is strikingly different from areas 4 and 6 (the motor and premotor areas). The cortex is thin and granular; the pyramidal cells in layer 5 are reduced in both size and number. These brain areas are highly developed in humans, and they have long been considered the seat of higher intellectual functions. Much of the information about the functions of the frontal association areas has come from clinical observation of patients with degeneration, injuries, or tumors of the frontal lobes and from examination of patients who have had these regions surgically destroyed. Beginning with Phineas Gage, many examples of patients with dramatic changes in personality or behavior after frontal lobe damage have been reported (Figure 7.2; Box 7.1). Mataro et al. reported a modern case similar to Phineas Gage with a 60-year follow-up.

FIGURE 7.2 erior communicating and posterior cerebral arteries; the anterior choroiPhineas Gage, a three-dimensional computer reconstruction of the original skull from a thin-slice computed tomographic image and of the tamping iron. (Reprinted from Ratiu P, Talos IF. Images in clinical medicine. The tale of Phineas Gage, digitally remastered. N Engl J Med 2004;351:e21. Copyright © 2004 Massachusetts Medical Society. Reprinted with permission from Massachusetts Medical Society.)

BOX 7.1

Frontal Lobotomy

In a famous incident in 1848, Mr. Phineas Gage, a 25-year-old railroad worker, sustained severe damage to his frontal lobes when a metal tamping rod was blasted through his head after a freak accident (the “case of the crowbar skull”). The rod entered through the left cheek and exited in the midline near the intersection of the sagittal and coronal sutures. Surprisingly, he survived and has become a celebrated patient in the annals of medicine. Following the accident, there was a dramatic change in his character and personality. He died 13 years later after having traveled extensively and having been, for a period of time, exhibited in a circus. He reportedly became irreverent, profane, impatient, and unable to hold a job. He was “a child in his intellectual capacities, with the general passions of a strong man.” Reports of the case strengthened prevailing ideas about cerebral localization, particularly about the importance of the frontal lobes in personality. Gage’s accidental frontal lobotomy laid some of the groundwork for the surgical procedure of frontal (prefrontal) lobotomy or leukotomy, which was thought to decrease emotional and affective responses and relieve anxiety, apprehension, and “nervous tension.” The operation consisted of cutting the white matter coronally in each frontal lobe, dividing the association fibers that connect the prefrontal areas with other brain regions. This operation became popular in the mid-20th century; it was done extensively over a period of years as a treatment not only for psychosis but also for neurosis and depression. It was even used to control the behavior of criminals and recommended for “difficult” children. A popular procedure was the “ice-pick” lobotomy in which an ice pick was inserted above the eye and pounded through the orbital roof with a mallet, then swept to and fro to sever the connections of the prefrontal region from the rest of the brain. The primary proponent of this technique used a gold-plated ice pick and kept speed records for the procedure. A lobotomy was once done on an eccentric actress who had no mental illness. The abuse of frontal lobotomy was dramatized in the motion picture One Flew Over the Cuckoo’s Nest. The procedure has been abandoned. See Ginat for an illustration of the neuroradiologic sequelae.

There is a paucity of information regarding the functions of the different regions of the prefrontal cortex. The DLPFC is important in the organization of self-ordered tasks. It plays a critical role in the neural network subserving working memory (Chapter 8). The responsibility for executive function largely resides with the DLPFC and its connections. Frontal lobe executive function is the ability to plan, carry out, and monitor a series of actions intended to accomplish a goal. It is concerned with planning and organizational skills, the ability to benefit from experience, abstraction, motivation, cognitive flexibility, and problem solving. Disturbed executive function is common with frontal lobe lesions. Defects in executive function occur with frontal lobe lesions, but may occur with lesions elsewhere because of the extensive connections of the frontal lobes with all other parts of the brain. The DLPFC is also important in oculomotor control, which is responsible for decision-making regarding voluntary eye movements and inhibiting unwanted reflex saccades. It may also play a role in pain perception. There is evidence of DLPFC dysfunction in schizophrenia. The prefrontal region likely plays a role as well in the ability to predict the consequences of actions, emotional expression (affect), “go/no-go” decision-making, personality, and the sense of time. Widespread changes in prefrontal activation are associated with calculating and thinking.

The MPC has connections with the several thalamic nuclei, particularly the dorsomedian, and with the superior temporal cortex. There are connections with other portions of the frontal lobe, including the OFC, the DLPFC, and the medial motor areas. The MPC is important in auditory and visual associations. The ventrolateral prefrontal cortex is concerned with mnemonic processing of objects. The OFC has important connections with the limbic system, including the amygdala. Disinhibition syndromes, ranging from mildly inappropriate social behavior to full-blown mania, may occur with dysfunction of the OFC, particularly of the right hemisphere. Patients with OFC dysfunction are also prone to display emotional lability, poor judgment and insight, and distractibility.

Frontal association areas may be involved in various degenerative processes, especially those such as frontotemporal dementia, which are likely to affect frontal lobe function. The earliest change is often a loss of memory, especially of recent memory or of retention and immediate recall. This may be followed by impaired judgment, especially in social and ethical situations. Absence of the inhibitions acquired through socialization may lead to inappropriate behavior and carelessness in dress and personal hygiene. Sexual promiscuity may develop. Loss of ability to carry out business affairs and attend to personal finance is common. The ability to perceive abstract relationships is impaired early. The patient may carry out simple well-organized actions, but he may be incapable of dealing with new problems within the scope and range expected for a person of similar age and education. Tasks requiring a deviation from established routine and adaptation to unfamiliar situations are the most difficult. There is loss of attentiveness, and distractibility may be marked. There are problems with comprehension and loss of ability to make associations. Acquisition and synthesis of new material is difficult. The time needed for solving intellectual problems is prolonged, and the patient fatigues rapidly.

Emotional lability may be prominent, with vacillating moods and outbursts of crying, rage, or laughter, despite a previously even temperament. There may be marked irritability. The mood is often euphoric, with an increased sense of well-being. Facetiousness, levity, and senseless joking and punning (witzelsucht) or moria (Gr. “silliness”), or apathy, indifference, emotional blunting, and lack of initiative and spontaneity may be present. Abulia refers to difficulty in initiating and sustaining spontaneous movements and reduction in emotional responsiveness, spontaneous speech, and social interaction. It is characteristic of frontal lobe and basal ganglia lesions. The patient may fail to link immediate impressions with past experience, leading to confusion and disorientation. There is usually progressive deterioration and increasing difficulty with intellectual functions. Extensive bilateral prefrontal lesions may culminate in akinetic mutism or a state of persistent unresponsiveness (see Chapter 51).

Similar symptoms may occur with frontal lobe neoplasms. Either witzelsucht and euphoria or indifference and apathy are early manifestations, and they may be evident before memory loss and difficulties with judgment become apparent. There are often other signs of intracranial disease, such as weakness, focal or generalized seizures, frontal ataxia, forced grasping, anosmia, or visual field defects. Evidence of increased intracranial pressure usually occurs late. Although severe impairment of function may occur with lesions of the anterior frontal lobes, further localization may not be possible from the examination alone. There is no definite focus for which removal leads to dementia, and massive lesions of the frontal lobe, especially if unilateral, may cause few symptoms, particularly if the lesion is in the nondominant hemisphere.

The severe disability that may result from a frontal lobe lesion is strikingly illustrated by Eslinger and Damasio’s patient “EVR” (Box 7.2). Following frontal lobotomy, patients often developed indifference, lack of insight, euphoria, emotional outbursts, tactlessness, and social ineptitude, but without demonstrable memory or cognitive deficits.

BOX 7.2

Frontal Lobe Dysfunction

At the age of 35, a previously healthy patient, “EVR,” underwent removal of a large orbitofrontal meningioma. Surgical recovery was uneventful, and there was never any evidence of tumor recurrence. Although he seemed superficially normal, with a verbal IQ of 120 and normal neuropsychological testing, the patient’s behavior, judgment, and social interactions were forever impaired. He invested and lost his life’s savings in an ill-advised business venture. He was fired from a succession of jobs because of tardiness and disorganization. His wife divorced him, and, unemployed, he moved back in with his parents. He required 2 hours to prepare for work each morning. He took job 100 miles from his home but was fired for lack of punctuality. He spent entire days shaving and washing his hair. Minor decisions were scrutinized ad infinitum, including simple purchases and deciding where to eat. He collected outdated and useless items (see also Volle et al.), including dead houseplants, old phone books broken fans broken television sets bags of empty orange juice cans cigarette lighters, and countless stacks of old newspapers. The New York Times provided a poignant and very personalized description of the personality changes and other effects of frontal lobe dysfunction in When Illness Makes a Spouse a Stranger (D. Grady, May 5), an article on frontotemporal dementia.

Frontal Motor Areas

The motor areas of the frontal lobe include the primary motor cortex (area 4) as well as the premotor and SMAs. The motor cortex contains the large motor neurons (Betz cells) that give rise to the corticospinal and corticobulbar tracts. The premotor cortex lies just anterior to the primary cortex, squeezed between the precentral gyrus and the posterior border of the prefrontal area (area 6); it is involved in the planning and execution of movements, particularly sequences of movements (the basis for Luria’s hand sequence or fist-edge-palm test, Chapter 8). It receives afferents from other areas of the cortex, including the sensory cortex and elsewhere in the frontal cortex, and projects to the motor cortex and the motor thalamus. Some fibers descend and make up part of the extrapyramidal system.

The SMA consists of areas of cortex lying on the medial aspect of the hemisphere just anterior to the primary motor cortex at the posterior medial aspect of the frontal lobe (area 6). The SMA functions in planning motor movements, such as a sequence of actions provided from memory. The SMA areas are crucial for the temporal organization of multiple movements. In animals, lesions of the SMA impair memory-based sequencing of movements. The SMA also coordinates movements between the hands, and lesions in this area may cause the alien hand syndrome (see Chapter 10). Lesions of the more anterior and medial parts of the motor cortex cause less paralysis and more spasticity and may allow the emergence of primitive reflexes, such as grasping and groping responses.

The syndrome of the SMA is not well recognized and can easily be confused with corticospinal weakness. Patients have reduced spontaneous movements and difficulty in performing volitional motor acts to command in the contralateral limbs, although the limbs function normally in automatic motor activities, for example, dressing. Hemineglect and apraxia may also be present, but the deficit results from a frontal lobe rather than a parietal lobe lesion. Unilateral prefrontal lesions may cause imitation and utilization behavior (Chapter 8).

Seizures may arise from the frontal lobe and may either be simple partial or complex partial. Seizures arising from the motor cortex typically produce focal Jacksonian epilepsy of the contralateral limbs. Partial complex seizures arising from the frontal lobe resemble those arising from the temporal lobe but are more bizarre and likely to be confused with pseudoseizures. Seizures arising from the SMA often involve tonic posturing that is either unilateral or asymmetric and often accompanied by facial grimacing and automatisms, as well as vocal symptoms such as laughing or speech arrest. Seizures arising from the orbitofrontal or frontopolar area often involve pedaling, thrashing movements easily confused with pseudoseizures. Seizures arising from the DLPFC are often adversive, with turning of the head and eyes to the contralateral, less commonly ipsilateral, side.

The frontal eye fields lie in the middle frontal gyrus and control movement of the eyes to the contralateral side. Destructive lesions in this area cause gaze deviation ipsilaterally, whereas epileptiform activity causes gaze deviation contralaterally. Gaze palsies and gaze deviations are discussed more fully in Chapter 14. The motor speech areas (Broca’s area) lie in the inferior frontal gyrus anterior to the motor strip. Lesions in this area cause aphasia (Chapter 9). Lesions of the frontal lobe may also cause incontinence, particularly with involvement of the paracentral lobule, or a gait disorder (Chapter 44).

The Parietal Lobes

Chapter 6 discusses the gross anatomy of the parietal lobe. The primary sensory (somesthetic) cortex (S1; areas 3, and 2) occupies all but the lowest part of the postcentral gyrus, continuing onto the medial surface into the adjoining part of the paracentral lobule. Recent work suggests that the designation primary sensory cortex should be restricted to area 3. The secondary somatosensory cortex (S2) lies in the parietal operculum adjacent to the lower portion of S1 near the sylvian fissure. In the depth of the central sulcus, area 3 abuts area 4. The postcentral cortex is homotypical (granular) cortex with six well-developed layers. The interparietal sulcus extends posteriorly from the midpoint of the postcentral gyrus and divides the remainder of the parietal lobe into the superior parietal lobule above and the inferior parietal lobule below. Area 5a—the preparietal area, in the upper part of the parietal lobe just posterior to area 2—contains large, deep pyramidal cells, some as large as the smaller Betz cells in area 4. Area 5b, the superior parietal area, occupies a large part of the superior parietal lobule, extending over the medial surface of the hemisphere to include the precuneus. Area 7, the inferior parietal area, constitutes the major portion of the parietal lobule; it includes the supramarginal and angular gyri and receives many afferents from the occipital lobe. S1 receives enormous projections from the ventral posterolateral and ventral posteromedial nuclei of the thalamus. These relay impulses from the spinothalamic tracts, medial lemnisci, and trigeminothalamic tracts, which send fibers through the posterior limb of the internal capsule to the postcentral gyrus. Body regions are represented in specific parts of the postcentral gyrus; the pattern roughly parallels the motor homunculus localization of the precentral gyrus but is not as well defined (Figure 6.7). Cortical sensory functions are discussed further in Chapter 35. The superior and inferior parietal lobules are sensory association areas. They connect with the postcentral gyrus by means of the association pathways, and they receive fibers from the nuclei lateralis dorsalis and posterior.

The functions of the parietal lobe are essentially those of reception, correlation, analysis, synthesis, integration, interpretation, and elaboration of the primary sensory impulses received from the thalamus. S1 is the initial reception center for afferent impulses, especially for tactile, pressure, and position sensations. It is necessary for discriminating finer, more critical grades of sensation and for recognizing intensity. Stimulation produces paresthesias on the opposite side of the body, with tactile and pressure sensations, numbness, tingling, sensations of constriction and movement, and occasional thermal sensations, but rarely pain. Such sensations may precede or accompany Jacksonian convulsions as part of a seizure; the spread of the sensory disturbance follows the same general pattern as in the motor area.

The sensory association areas are essential for the synthesis and interpretation of impulses, appreciation of similarities and differences, interpretation of spatial relationships and two-dimensional qualities, evaluations of variations in form and weight, and localization of sensation. Overactivity of these areas causes minimal symptoms, for example, vague paresthesias or hyperesthesias on the opposite side of the body. Destructive lesions affect mainly the gnostic (knowing, recognition) aspects of sensation. Simple appreciation of primary sensations remains, but associative functions are impaired. These deficits are discussed further in Chapters 10 and 35. Parietal lobe lesions produce abnormalities of higher-level sensory functions, which require association cortex: stereognosis, graphesthesia, two-point discrimination, and tactile localization. Patients with nondominant parietal lobe lesions may display various forms of apraxia, hemi-inattention, hemineglect, and denial of disability, culminating in the striking syndrome of anosognosia, in which patients may deny owning their contralateral limbs (see Chapter 10). The parietal lobes, through connections with the temporal and occipital lobes, integrate somatosensory with visual and auditory information.

The inferior parietal lobule—especially the angular and supramarginal gyri and the areas in close proximity to the occipital and temporal lobes—is functionally associated with the visual and auditory systems. The angular and supramarginal gyri of the dominant hemisphere are important in relation to language and related functions. Lesions in these areas may cause aphasia, agnosia, and apraxia; these are discussed in Chapter 10. The optic radiations course through the deep parietal lobe to reach the visual cortex. A deeply placed parietal lesion may cause either an inferior quadrantic or hemianopic visual field defect. Parietal lesions have been reported to cause contralateral muscular atrophy and trophic skin changes. Deafferentation may produce hypotonia, slowness of movement—especially of the proximal muscles—ataxia, updrift (Figure 27.59), and pseudoathetoid movements (sensory wandering) of the opposite side of the body (Figure 30.6). Incoordination of movement because of sensory loss from a parietal lobe lesion may mimic cerebellar ataxia (pseudocerebellar syndrome). Dystonia has also been described. Focal motor seizures and partial paralysis involving the contralateral parts of the body can occur with parietal lesions. These may be due to impaired communication with areas 6 and 4, or they may indicate that the parietal lobes also possess some motor function.

The Occipital Lobes

Chapter 6 discusses the gross anatomy of the occipital lobe, which is more nearly a structural and functional entity than the other cerebral lobes; all of its functions are concerned either directly or indirectly with vision. It is composed of Brodmann’s areas 17, and 19. The primary visual cortex (area 17) is located on the lips of the calcarine fissure and adjacent portions of the cuneus above and the lingual gyrus below. The cortex is granular in type and extremely thin. Layer 4 is relatively thick with a prominent outer band of Baillarger (line or band of Gennari), which is visible grossly and gives the area its designation of striate cortex. Area 17 receives the geniculocalcarine projection, which is retinotopically organized (see Chapter 13). The striate area receives primary visual impressions: color, size, form, motion, and illumination. Ictal activity or electrical stimulation of the calcarine cortex produces unformed visual hallucinations, such as scotomas and flashes of light. Destructive lesions cause defects in the visual field supplied by the affected areas. The most familiar and classical deficit is a congruous, contralateral, macular-sparing hemianopia with a preserved optokinetic nystagmus response.

The parastriate region (area 18) and the peristriate region (area 19) receive and interpret impulses from area 17. Areas 18 and 19 are visual association cortex, essential for the recognition and identification of objects. The visual association cortex projects to the angular gyrus, lateral and medial temporal gyri, the frontal lobe, the limbic system, and to corresponding areas in the opposite hemisphere through the splenium of the corpus callosum. Interruption of these pathways leads to disconnection syndromes (see Chapter 10). There are other extrastriate visual areas beyond areas 18 and 19. Some cortical areas mediate special visual functions. The posterior parts of the lingual and fusiform gyri are important for color vision, the posterior portion of the middle temporal gyrus is involved in recognition of movement (motor vision), and the fusiform gyrus is important in facial recognition.

Visual memories are stored in the association cortex. It functions in more complex visual recognition and perception, revisualization, visual association, and spatial orientation. The association cortex is thicker than the striate cortex, with an increase in the size and number of cells in layer 3, but almost complete absence of large cells in layer 5; no line of Gennari is present. Stimulation of these regions causes formed visual hallucinations. Destruction causes difficulty with ocular fixation and with maintaining visual attention, loss of stereoscopic vision, impairment of visual memory, difficulty with accurate localization and discernment of objects, and disturbances in the spatial orientation of the visual image, especially for distance. There is loss of ability to discriminate size, shape, and color. The patient may lose the ability to localize either himself or objects in space, and he may have impaired perception of visual spatial relationships. There may be distortion of objects (metamorphopsia).

Lesions involving the occipital lobes bilaterally result in various degrees of visual loss, often accompanied by other deficits (cortical blindness, biposterior syndrome). Adjacent parietal and temporal cortical areas are often involved as well. There may be bilateral hemianopia with or without macular sparing, bilateral superior or bilateral inferior altitudinal hemianopia, or bilateral homonymous scotomas. Pupillary light reflexes are preserved. Patients with bilateral occipital or occipitoparietal lesions may have other defects of higher cortical function, such as color agnosia, prosopagnosia, and simultanagnosia (see Chapter 10). In addition, patients may lack awareness of their deficit, or they may have awareness but deny that the deficit exists (Anton’s or denial visual hallucination syndrome; cortical blindness; anosognosia for blindness). The patient may behave as if he can see—try to walk, bump into objects, and fall over things. There is the belief that the patient confabulates or “hallucinates his environment.” Cortical blindness may occur after stroke, cardiorespiratory arrest, head trauma, bacterial meningitis, progressive multifocal encephalopathy, and even as a postictal phenomenon. The occipital lobe is also important in ocular motility. The central control of eye movements is discussed in the chapter on the ocular motor nerves (see Chapter 14). Balint’s (Balint-Holmes) syndrome consists of “psychic” impairment of visual fixation and alterations in visual attention. The patient has an inability to reach for objects using visual guidance despite normal visual acuity and intact visual fields (optic ataxia) and an inability to voluntarily direct gaze (optic apraxia). The patient can see only one object and cannot move his eyes from it, but he cannot reach out and take it. Balint’s syndrome is typically seen in patients with bilateral parietooccipital lesions. Recovery from cortical blindness typically evolves through a stage of visual agnosia (see Chapter 10).

The Temporal Lobes

The temporal lobe includes the superior, middle and inferior temporal, lateral occipitotemporal, fusiform, lingual, parahippocampal, and hippocampal gyri. Heschl’s gyri and the planum temporale lie on the superior surface. The superior temporal gyrus subserves auditory and language functions. The middle and inferior gyri receive abundant projections from the occipital lobe and serve to integrate vision with temporal lobe auditory and language functions. The hippocampal formation is a center for learning and memory. There are abundant connections between the temporal lobe and the limbic system.

The auditory radiations run from the medial geniculate body to the auditory cortex (areas 41 and 42) in the superior temporal gyrus. Area 41 is composed of granular cortex similar to that in the parietal and occipital regions; area 42 has large pyramidal cells in layer 3. Hearing is bilaterally represented in the temporal lobes, although there is a contralateral predominance. Nearby areas in the superior temporal gyrus allow for the differentiation and the interpretation of sounds. The superior temporal gyrus may also receive vestibular impulses. Electrical stimulation of the auditory area causes vague auditory hallucinations (tinnitus, sensations of roaring and buzzing), and stimulation of adjacent areas causes vertigo and a sensation of unsteadiness. Because hearing is bilaterally represented, unilateral destruction of the auditory cortex does not cause deafness, although there may be difficulty with sound localization and a bilateral dulling of auditory acuity. Sophisticated audiometric testing may reveal mild hearing defects in the contralateral ear in a patient with a unilateral temporal lobe lesion. Bilateral temporal lobe destruction may cause deafness. Patients with cortical deafness may seem unaware of their deficit similar to the way in which patients with Anton’s syndrome are unaware of their blindness. Temporal lobe lesions that do not disturb hearing may cause auditory distortions and illusions. Auditory hallucinations may also occur, especially in temporal lobe epilepsy, sometimes with accompanying visual, olfactory, and gustatory hallucinations. Involvement of the temporal lobe vestibular areas may cause difficulty with equilibrium and balance. A destructive lesion in the posterior superior temporal area of the dominant hemisphere causes Wernicke’s aphasia (see Chapter 9).

Lesions involving the temporal lobe geniculocalcarine pathways (Meyer’s loop) may have contralateral upper visual field defects. Bilateral ablation of the temporal lobes, particularly the anterior regions, in experimental animals causes a characteristic constellation of abnormalities referred to as the Kluver-Bucy syndrome. Affected animals have psychic blindness or visual agnosia. They can see objects but do not recognize them until they are explored and identified nonvisually, particularly orally. There is loss of fear and rage reactions, hypersexuality, bulimia, and severe memory loss. There is an excessive tendency to attend and react to every visual stimulus. Partial forms of Kluver-Bucy syndrome occur in patients with temporal lobe lesions, but the complete syndrome occurs only rarely.

Patients with temporal lobe lesions may have visual hallucinations and perversions. These occur most often during complex partial (partial complex, temporal lobe, psychomotor) seizures (CPS). The visual hallucinations in temporal lobe CPS are complex and often include the patient (autoscopy). Autoscopy has been invoked as an explanation for some of the phenomenology of near death experiences. Visual perceptions may be distorted with objects appearing too large (macropsia) or too small (micropsia), or too near or too far away. The complex hallucinations may have an auditory component; the hallucinated figure may speak. Electrical stimulation of the temporal lobe may cause hallucinations, illusions, automatisms, and emotional responses, and call forth memories. Hughlings Jackson described seizures characterized by olfactory and visual hallucinations, dreamy states and reminiscences, automatisms, and gastric and autonomic symptoms. He observed that these occurred with lesions involving the medial temporal lobe in the region of the uncus and referred to them as uncinate fits. Currently, the term uncinate fits is generally used only for those CPS that include olfactory hallucinations. CPS may include some or all of the following: automatisms; illusions and hallucinations (visual, auditory, olfactory, or gustatory); and pilomotor erection (gooseflesh). Automatisms are common and consist of brief or prolonged inappropriate but seemingly purposeful automatic movements such as chewing, swallowing, and lip smacking. There is alteration of consciousness, usually with amnesia for the period of the event. Disorders of recognition and recall are common. Déjà vu (Fr. “already seen”) refers to the delusion or misperception that something new and novel has been seen or experienced before. There are many variations on the theme of déjà, of something new seeming strangely familiar (déjà pensée, déjà vacu, and others), but déjà vu is typically used to include all of them. The converse, jamais vu, is the misperception or illusion that something familiar is strange or new. Tornado epilepsy refers to vertigo due to involvement of the vestibular cortex in a seizure discharge.

CPS may include psychic manifestations, such as anxiety, fear, rage, obsessive thoughts, compulsive speech or actions, or feelings of unreality. These phenomena are associated with abnormal electrical discharges or lesions involving the anterior and medial portions of the temporal lobes, including the hippocampal gyrus, uncus, amygdaloid complex, parahippocampal gyrus, or the connections of these structures. Impulses from these structures may be relayed to the thalamus, hypothalamus, or mesencephalic reticular formation. Some instances of CPS may also involve the insula, posterior orbital surface of the frontal lobe, basal ganglia, frontal association areas, or contiguous structures. Surgical extirpation of abnormal foci may be curative. A syndrome similar to that described by Kluver and Bucy in animals has been seen in humans when temporal lobe surgery was attempted bilaterally. A variety of tools are currently used to localize and characterize abnormal seizure foci, including imaging—MRI, PET, and single photon emission computed tomography—and electroencephalographic recordings, both from the scalp and intracranially.

Neoplasms of the temporal lobe are second only to those of the frontal lobes in the frequency with which they cause mental symptoms. These may include the following: psychic manifestations varying from vague personality changes to frank behavioral disturbances; emotional abnormalities such as anxiety, depression, fear, and anger; paranoia; memory defects; learning and cognitive disabilities; and apathy.

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