Disfunction of Specific Areas of the Brain	77

patients include tachycardia, excessive sweating, and rapid breathing.

Akinetic mutism is often due to extensive, bilateral frontal lobe damage or to a lesion affecting the projections of the ascending reticular activating system to the frontal lobes, e. g., a bilateral thalamic or midbrain lesion. Swallowing and extrinsic muscle reflexes are intact and the patient’s eye movements are usually normal, yet spontaneous verbal or motor expressions are lacking. The patient still appears to be awake and can sometimes be induced to speak or move with intensive prompting.

Locked-in syndrome is not a disturbance of consciousness, though it can be mistaken for one. The patient is awake and alert, but can express himor herself only through vertical eye movements and eyelid movements, because all four limbs are paralyzed, as well as all of the muscles innervated by the lower cranial nerves. The unwary clinician may have the false impression of a comatose patient who does not respond to external stimuli. A detailed description of the locked-in syndrome and its causes is found in the next section.

Dysfunction of Specific Areas of the Brain

Up to this point, we have described the characteristic neurological deficits produced by lesions of individual functional components of the nervous system. “Normally,” however, more than one functional component is affected. There is often simultaneous impairment of motor function, cooordination, sensation, and possibly consciousness. The individual clinical signs and symptoms described above often appear together in particular constellations (= syndromes) that are characteristically associated with the region of the nervous system in which the lesion is located and largely independent of the nature of the lesion itself.

We will now describe the major syndromes of individual regions of the brain.

Syndromes of the Individual Lobes of the

Cerebral Hemispheres

Frontal lobe syndrome is characterized by the following manifestations, in variable severity, depending on the extent and precise location of the causative lesion:

abnormalities of personality and behavior (loss of drive and initiative, apathy, indifference; if only the orbitofrontal cortex is affected, there may be disinhibition, absent-mindedness, and socially inappropriate behavior);

primitive reflexes, e. g., grasp reflex and brisk palmomental reflex;

motor phenomena, e. g., spontaneous, compulsive grasping of objects, copying of other people’s gestures (echopraxia), motor perseveration, and sometimes contralateral gaze paresis;

lateralized deficits: motor aphasia in lesions of the language-dominant hemisphere, anosognosia (nonrecognition of one’s own illness, e. g., hemiparesis) and contralateral apraxia (p. 42) in lesions of the nondominant hemisphere;

akinetic mutism, usually caused by extensive, bilateral lesions (the patient is awake, but does not re-

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spond to environmental stimuli and does not speak; see above):

in lesions affecting the frontal eye fields: déviation conjuguée to the side of the lesion, because voluntary gaze to the opposite side is impossible;

irritative signs: adversive seizures (epileptic seizures in which the head and trunk are involuntarily turned to the side opposite the lesion; the contralateral arm is sometimes raised as well).

Syndrome of lesions of the precentral and postcentral gyri. Each of these gyri contains a somatotopic cortical representation of the entire body, as described in detail 50 years ago by the neurosurgeon Wilder Penfield (Fig. 5.4 shows the classic “Penfield homunculus”). Lesions involving these paracentral gyri thus impair the function of specific parts of the body, with the specific site and extent of bodily dysfunction depending on the site and extent of the brain lesion. This can be most impressively observed in lesions of the precentral gyrus:

There are focal motor deficits, e. g., monoplegia of a limb; if the lesion is restricted to the precentral gyrus itself, the weakness may be flaccid, but this is rarely the case. Simultaneous dysfunction of the premotor cortex usually causes spastic weakness.

Sensory deficits are less frequently observed in such patients and cannot be clinically distinguished from those caused by thalamic lesions.

The intrinsic muscle reflexes are generally increased on the contralateral side of the body and there are accompanying pyramidal tract signs.

Irritative phenomena may appear in the form of Jacksonian epilepsy of focal onset (motor and/or somatosensory) or Kozhevnikov’s epilepsia partialis continua (p. 166).

Temporal lobe syndrome takes different forms depending on the precise location of the lesion:

impairment of memory (e. g., in lesions affecting the hippocampus on both sides);

sensory aphasia (Wernicke aphasia, p. 41) in lesions involving the language-dominant (usually left) hemisphere;

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78 5 Topical Diagnosis and Differential Diagnosis of Neurologic Syndromes

			Neck	Trunk	Hip	Leg
		Scalp
	Arm
	ForearmElbow
	Hand
	Finger
	Thumb
Nose	Eye
Face
Lips
Teeth					Genitals
Palate
Jaw
Tongue
Throat
Viscera

Knee

Toes

Hip

Trunk

Shoulder

Arm

Elbow	Wrist	Hand
			Fingers
			Thumb
			Neck
			Eyebrows
			Eye
			Face
			Lips
			Jaw
			Tongue
			Swallowing

Somatosensory cortex

Motor cortex

Fig. 5.4 The cortical representation of different parts of the body in the primary somatosensory cortex of the postcentral gyrus (left) and the primary motor cortex of the precentral gyrus (right) in

possible disturbance of spatial orientation in lesions involving the non-language-dominant (usually right) hemisphere;

in deep-seated lesions, a visual disturbance taking the form of contralateral homonymous upper quadrantanopsia;

irritative phenomena: complex partial seizures (temporal lobe seizures, p. 166), sometimes with ictal olfactory or gustatory hallucinations (uncinate fits)— these are usually reported as unpleasant;

mental abnormalities: irritability, depression.

Parietal lobe syndrome manifests itself in somatosensory deficits and a variety of neuropsychological abnormalities:

The most prominent sign is usually a hemisensory deficit.

Lesions of the language-dominant hemisphere (usually left) can cause left/right confusion, finger agnosia, acalculia, and agraphia (Gerstmann syndrome), and/or astereognosia.

Lesions of the nondominant hemisphere (usually right) can cause anosognosia (see above).

With regard to motor function, there are often poorly coordinated, ataxic hand and foot movements on the side opposite the lesion.

With regard to somatic sensation, there may be neglect for the contralateral half of the body (so-called extinction phenomenon: raw sensation is intact bilaterally, but if the examiner touches the patient simultaneously and equally intensely at mirror-

the human being. (After Penfield, W., H. Jasper: Epilepsy and the Functional Anatomy of the Human Brain. Little, Brown, Boston 1954.)

image sites on the two sides, the patient will report having felt something on one side only).

Deep-seated lesions may produce contralateral homonymous lower quadrantanopsia or hemianopsia, or else only visual neglect for the contralateral hemifield.

Occipital lobe syndrome is mainly characterized by:

a contralateral visual field defect (homonymous hemianopsia; cf. Fig. 3.6, p. 19);

possible cortical blindness (in the case of bilateral occipital lobe lesions), in which elementary or formed visual hallucinations, or seeing gray, may be present; patients often deny being blind (anosognosia);

visual agnosia, i. e., the inability to recognize colors or shapes, despite normal visual acuity;

irritative phenomena: visual hallucinations, perhaps as the initial symptom of an epileptic seizure.

Syndromes of the Extrapyramidal Motor

System

Function. The extrapyramidal motor system plays an important role in the smooth and purposeful execution of all motor processes, both voluntary and involuntary. One of its functions is to efficiently combine individual motor components into complex patterns of movement and to enable their largely automatic execution. Further

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Disfunction of Specific Areas of the Brain

ones are to give the signals for the initiation and termination of a movement and to regulate muscle tone.

Anatomical substrate. The main nuclei of the extrapyramidal motor system are the basal ganglia (caudate nucleus, putamen, and globus pallidus). Further components are the subthalamic nucleus (in the diencephalon) as well as the substantia nigra and the red nucleus (both in the midbrain). Extensive fiber connections link these nuclei to each other and to higher motor cortical areas (by way of the thalamus). They influence the activity of spinal motor neurons through a number of afferent and efferent spinal pathways.

Deficits. Lesions of individual components of the extrapyramidal motor system produce various types of disturbance, corresponding to the precise location of the lesion. Because the functions of the extrapyramidal system are essentially as described above, functional impairments can manifest themselves as an excess or deficiency of movement-initiating impulses, automatic movement, and/or muscle tone:

There may be diminished spontaneity of movement, i. e., hypokinesia (e. g., in Parkinson disease) usually combined with elevated muscle tone, i. e., rigidity hypertonic−hyperkinetic syndrome, p. 127.

On the other hand, there may be hyperkinesia of a wide variety of types, which may be thought of as the uncontrolled expression of complex motor programs resulting from a removal of their normal inhibition by the extrapyramidal motor system. These involuntary, repetitive movements include chorea, athetosis, ballism, and dystonia, all of which are described in detail on p. 131. Choreatic syndromes are often associated with diminished muscle tone hypotonic− hyperkinetic syndrome.

Acute basal ganglionic lesions can also cause transient hemiparesis.

Thalamic Syndromes

Function. The thalamus is the synaptic relay station for many somatosensory and special sensory pathways; it transmits afferent impulses from peripheral exteroand proprioceptors, as well as from the higher sensory organs (eye, ear), to higher centers. In the thalamus, impulses pertaining to the body’s various senses are integrated, affectively colored, and then passed on to the cortex (conscious perception appears to be possible only if the impulses reach the cortex). The thalamus also receives neural input from the extrapyramidal motor system and participates in the regulation of attention and drive as a component of the ascending reticular activating system (see below). Finally, certain components of the thalamus play a role in memory.

Deficits. Because the functions of the thalamus are as we have just described, lesions affecting it can produce the following deficits:

Somatosensory deficits: these mainly consist of impaired proprioception on the side opposite the lesion. There may also be painful, burning sensations that either arise spontaneously (dysesthesia) or are

induced by, and outlast, a tactile stimulus delivered to the skin (hyperpathia).

Deficits of movement and coordination: there may be contralateral hemiparesis (which is usually transient) or hemiataxia.

Contralateral hemianopsia may be present.

Abnormal posture, particularly of the hands, may be present. In the “thalamic hand,” the metacarpophalangeal joints are flexed, while the interphalangeal joints are hyperextended.

Brainstem Syndromes

Function. The brainstem is a “throughway” for many fiber pathways of the nervous system, which lie adjacent to one another here in a very tightly confined space. All of the motor and somatosensory projections to and from the periphery pass through the brainstem; some of them cross here (decussate) to the other side and some undergo a synaptic relay. In addition, the brainstem contains many nuclei: all of the somatic and visceral motor and sensory nuclei of cranial nerves III through XII are located within it. Two brainstem nuclei, the red nucleus and substantia nigra, belong to the extrapyramidal motor system. Finally, among the nuclei of the reticular formation are found the vital autonomic regulatory centers controlling cardiovascular and respiratory function, as well as nuclei of the ascending reticular activating system that send activating impulses to the cerebral cortex and are essential for the maintenance of consciousness.

Deficits. As one would expect from the very large number of important neural structures located within the brainstem and fiber tracts passing through it, a correspondingly wide variety of deficits can be produced by lesions of different sizes and at different locations in the brainstem. The pattern of clinical manifestations usually enables the clinician to localize the level of the lesion to one of the three brainstem segments (midbrain, pons, or medulla). One can also clinically distinguish focal lesions from partial or complete cross-sectional lesions of the brainstem:

Unilateral focal lesions are usually of vascular origin (lacunar infarct). The typical clinical picture is the socalled alternating hemiplegia syndrome, in which a cranial nerve deficit on the side of the lesion appears together with a motor and/or sensory deficit on the contralateral half of the body. There are different alternating hemiplegia syndromes depending on the level of the lesion; some of these are described further in Table 6.4,

p.86.

Focal diencephalic lesions can produce diabetes in-

sipidus as well as disturbances of thermoregulation, the sleep−wake cycle, eating behavior, and other instinctual behaviors.

Bilateral partial cross-sectional lesions of the brainstem. The classic example of a disturbance produced by this type of lesion is the locked-in syndrome, which is due to an extensive lesion of the ventral portion of the pons (e. g., an infarct secondary to thrombosis of the basilar a.). The corticobulbar and corticospinal pathways

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Topical Diagnosis and Differential Diagnosis

80	5 Topical Diagnosis and Differential Diagnosis of Neurologic Syndromes
		Table 5.7 Findings in deep brainstem lesions
		Site of lesion or	Pupils: appearance and	Corneal reflexes	Vertical VOR	Horizontal VOR	Respiration
		functional	reactivity to light		(see p. 186)	(see p. 186)
		disturbance
		Cerebral hemi-	equal, reactive	bilaterally present	present	present (elicitable	Cheyne−Stokes
		spheres (bilateral)				in both directions)	respiration,
							continual hyperven-
							tilation
		Midbrain	unilaterally or bilaterally	present	absent	present	may be irregular,
			fixed and dilated				with pauses
		Pons	small, equal, fixed	unilaterally or	may be absent	absent	may be irregular,
				bilaterally absent			with pauses
		Medulla	equal, reactive	present	may be absent	may be absent	irregular, apneustic
		Extensive brainstem	unilaterally or bilaterally	unilaterally or	absent	absent	irregular, apneustic
		lesion	fixed and dilated	bilaterally absent

of the basis pontis are totally interrupted and part of the pontine reticular formation may be as well. All four limbs are paralyzed (quadriplegia), and the caudal cranial nerves are dysfunctional: the patient cannot swallow, speak, or, usually, produce facial expressions. Vertical eye movements and lid closure, both of which are midbrain functions, are preserved, but horizontal eye movements, which are a function of the pons, are abolished. Consciousness remains intact because the reticular formation is largely spared. The patient can communicate through vertical eye movements and lid closure.

Bulbar palsy and pseudobulbar palsy are two further syndromes caused by bilateral partial cross-sectional lesions of the brainstem. (True) bulbar palsy is produced by system atrophy of the motor cranial nerve nuclei of the medulla and therefore manifests itself as bulbar dysarthria, dysphagia, and tongue atrophy, with fasciculations. In pseudobulbar palsy, the causative lesion does not involve the cranial nerve nuclei themselves, but rather their innervating corticonuclear pathways bilaterally, or else the cortical areas from which these pathways arise. The clinical picture resembles that of bulbar palsy, but tongue atrophy and fasciculations are absent because the peripheral motor neuron is intact.

Complete cross-sectional lesions of the brainstem

(brainstem transection) are due either to a pathological process in the posterior fossa or the brainstem itself (infratentorial lesion), or to acute intracranial hypertension in the supratentorial compartment, with secondary herniation and brainstem compression. Systemic processes (prolonged hypoxia or cardiorespiratory arrest; see above) can also cause extensive damage to the brainstem, as well as to the cerebral hemispheres. Midbrain lesions cause severe impairment of consciousness, ranging to deep coma, and characteristic motor and oculomotor signs. The same is true of pontine lesions. The most prominent sign of medullary transection is loss of all autonomic function. The level of brainstem injury can almost always be correctly deduced from the pattern of clinical deficits and the findings of a few special tests (particularly of the brain stem reflexes), as described in Table 5.7. A patient who survives acute, extensive damage to the midbrain will probably be quadri-

plegic and suffer from akinetic mutism (see above).

Cerebellar Syndromes

Function. The tasks of the cerebellum are to optimize the amplitude, speed, and precision of voluntary movement and simultaneously to regulate the motor control of balance and adapt muscle tone to the demands placed on the body’s movement apparatus. The cerebellum also plays a role in the regulation of gaze-related movements of the eyes and in ensuring the smooth complementary functioning of agonist and antagonist muscle groups.

In order to perform these coordinating tasks, the cerebellum requires information from various different parts of the nervous system. These different types of information are processed separately in three parts of the cerebellum that are distinct from one another both functionally and phylogenetically:

Impulses from the cerebral cortex for the initiation and planning of voluntary movement travel in the corticopontocerebellar pathway, by way of the brachium pontis (middle cerebellar peduncle), to the neocerebellum (located in the cerebellar hemispheres). This phylogenetically youngest part of the cerebellum is mainly responsible for the fine control of very precise movements, particularly of the limbs (especially the hands and fingers) and of the motor apparatus of speech.

Information regarding joint position and muscle tone from peripheral proprioceptors (muscle spindles and Golgi tendon organs) travels, by way of the anterior and posterior spinocerebellar tracts, through the restiform body and brachium conjunctivum (inferior and superior cerebellar peduncles) to the paleocerebellum (located in part of the vermis and the paraflocculus). This part of the cerebellum is mainly responsible for the smooth, synergistic functioning of the muscles when the individual stands or walks (see above).

Impulses from the vestibular system travel by way of the restiform body (inferior cerebellar peduncle) to the archicerebellum (nodulus and flocculus). This phylogenetically oldest part of the cerebellum

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Disfunction of Specific Areas of the Brain	81

mainly serves to keep the upright body in balance during standing and walking.

The cerebellum integrates the various types of afferent impulses it receives and then influences the motor regulatory functions of the brain and spinal cord in the manner of a feedback system. Efferent impulses travel:

from the cerebellar cortex to the dentate nucleus, where further processing takes place, and then through the superior cerebellar peduncle to the lateral nucleus of the thalamus, and onward to the cerebral cortex (Fig. 5.5),

while other efferent impulses travel from the dentate nucleus via the red nucleus to the thalamus, or via the red nucleus to the olive, and then back to the cerebellum. These two neuronal loops give off descending fibers to the rubrospinal and reticulospinal tracts, which terminate in the motor nuclei of the spinal cord (Fig. 5.5).

The integration of the cerebellum in the complex

functional system controlling voluntary movement is shown in Fig. 5.6.

Deficits. In accordance with the functions of the cerebellum described above, cerebellar lesions produce disturbances of muscle tone and movement:

basal lesions near the midline (mainly affecting the archicerebellum) produce disturbances of truncal posture and the maintenance of balance, which are particularly evident when the patient tries to sit;

vermian lesions (mainly affecting the paleocerebellum) produce impaired coordination of stance and gait;

lesions of the cerebellar hemispheres (mainly affecting the neocerebellum) produce impaired coordination of (fine) movements of the limbs on the side of the lesion.

A detailed list of clinical manifestations of cerebellar disease is provided in Table 5.8.

Fig. 5.5 Anatomical connections of the cerebellum. The connec-	Thalamus
tions to the cerebral cortex, brainstem, vestibular system, and spi-
nal cord are illustrated. For details, see text.
	Red nucleus
	Corticospinal
	tract
Fastigial
nucleus
Dentate nucleus

Pontine nuclei

Reticular formation

Olivary nucleus

Vestibular nucleus

Vestibulospinal nucleus

	Rubrospinal tract				Olivospinal tract
	Reticulospinal tract
	Regulatorycircuit1:				Regulatorycircuit2:
	Cortex—pontine nuclei—				red nucleus—olivary nucleus—
	cerebellar cortex—dentate				cerebellar cortex—dentate
	nucleus—thalamus—cortex				nucleus—red nucleus
	Efferent pathways to spinal cord

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			Basal
			ganglia
	Idea	Association	Motor	Movement
		cortex	cortex
		Cerebellum		Cerebellum
				Somato-
				sensory
				influences

Fig. 5.6 Functional relations of the cerebellum to other motor centers. To keep the diagram simple, the sensory feedback to the cerebellum and basal ganglia is not shown (modified from Ellen and Tsukahara 1974).

Table 5.8 Clinical manifestations of cerebellar disease

Clinical manifestation	Definition/description	Remarks
Diminished muscle tone	can be felt by the examiner during repeated passive
	movement, e. g., pronation and supination of the
	forearm

Dyssynergia	lack of coordination of the various muscle groups
	participating in a single movement

e. g., when walking on all fours, lack of precise alternation of limbs (each arm with opposite leg)

Dysmetria	poor control of the force, speed, and amplitude of
	voluntary movement
Intention tremor	alternating, progressively severe deviation from the
	ideal course of a directed movement as the limb
	approaches the target

e. g., opening fingers too wide when trying to grasp a small object

cf. Fig. 3.20

Pathological rebound phenomenon	when a muscle is actively contracted against re-	cf. Fig. 3.21
	sistance and the resistance is suddenly released, the
	antagonist muscles fail to contract within a nor-
	mally brief interval after the release
Dysdiadochokinesia	the alternating contraction of agonists and antago-	cf. Fig. 3.17
	nists cannot be performed as rapidly and smoothly
	as normal

Sinking of a limb in postural testing the tonic muscle contraction needed to keep the limb in a particular antigravity posture cannot be sustained as long as normal on the affected side

the sinking limb is ipsilateral to the cerebellar lesion

Truncal ataxia	the patient is unable to stay sitting up	indicates a vermian lesion
Unsteady stance	observable in the Romberg test	cf. Fig. 3.1e
Cerebellar gait	wide-based, unsteady, ataxic gait	indicates involvement of the vermis
Past-pointing in the Bárány pointing	slowly lowering the extended arm onto a previously	also positive in ipsilateral vestibular le-
test	demonstrated target, with eyes closed; deviation to	sions, cf. p. 26
	the side of the affected cerebellar hemisphere
Nystagmus	coarse nystagmus toward the side of the lesion, in-	cf. Fig. 11.1
	creasing with gaze toward the side of the lesion,
	decreasing on closure of the eyes

Pathological nystagmus suppression the patient stands up, stretches out his or her arms test forwards, stares at his or her own extended thumbs,

and keeps on doing so while the examiner rapidly rotates the patient around the bodily axis; staring at the thumbs completely suppresses the induced vestibular nystagmus in normal persons, but not in persons with cerebellar disease

Cerebellar dysarthria

choppy, explosive speech (“scanning dysarthria”)

cf. Fig. 11.5

patients with degenerative cerebellar diseases are said to develop a “lion’s voice”

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