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Biomedical subjects

E Valenstein

Publications and source records attributed to E Valenstein.

At least 37 records · Page 2Linked to original sources
PubMed1986

Normal tactile threshold in monkeys with neglect.

To learn whether animals with parietotemporal lesions have sensory inattention or defective intention, we trained monkeys to respond with the contralateral limb to a threshold tactile stimulus. After parietotemporal lesions that induced neglect, the monkeys continued to respond normally to threshold stimuli on the side opposite the lesion (the neglected side), but made errors when stimulated on the normal side (ipsilateral to the lesion), often failing to use the contralateral extremity. On this learned task, there was no abnormality of sensory input or sensory attention. The problem was attributed to an impaired preparation to respond (intention).

Animals↗
PubMed1986

The right hemisphere: neuropsychological functions.

In the past two to three decades, clinicians and neuroscientists have been studying the functions of the right hemisphere. Neither hemisphere seems to be dominant in the absolute sense. Each appears to be specialized and is dominant for different functions. However, most functions require the cooperation of both hemispheres. When one is damaged, the other can often compensate for the damaged one. Lesions of the left hemisphere are associated with language (speech, reading, and writing) and praxic disorders, and lesions of the right hemisphere can result in visuospatial, attentional, and emotional disorders. The authors review some of the major behavior disorders associated with right hemisphere dysfunction and concentrate on three major types of disorders--visuospatial, attentional, and emotional. Although not all the behavioral defects associated with right hemisphere damage can be subgrouped under these three types, they are the ones most often associated with right hemisphere lesions.

Agnosia↗
PubMed1984

The effect of corpus callosum lesions on unilateral neglect in monkeys.

The cerebral hemispheres may be mutually inhibitory. An injured hemisphere may continue to be inhibited while the uninjured hemisphere is released from inhibition, inducing attentional bias. Patients with neglect might therefore benefit from transection of the corpus callosum. To test this hypothesis, we ablated the frontal arcuate gyrus alone or several months after corpus callosum transection in monkeys. Neglect was significantly worse in animals with a corpus callosum transection. Therefore, the hemispheres may be mutually excitatory or compensatory, and a callosal transection would not be therapeutic. Because the rate of recovery in the two groups was not different, recovery seemed to be an intrahemispheric phenomenon.

Animals↗
PubMed1982

Nonsensory neglect from parietotemporal lesions in monkeys.

Monkeys trained to perform with the extremity contralateral to a stimulus had unilateral neglect induced by a parietotemporal lesion. Their performance was normal postoperatively when stimulated on the side contralateral to the lesion, but they made errors when stimulated on the normal side (the side ipsilateral to the lesion), often failing to use the extremity on the neglected side (the side contralateral to the lesion). Although we expected parietotemporal lesions to induce sensory neglect (failure to respond to contralateral stimuli), we could show only that these animals had a defect of intention (contralateral hypokinesia). In this respect, neglect induced by parietotemporal lesions is similar to that induced by frontal or medial thalamic lesions.

Animals↗
PubMed1982

Two forms of ideomotor apraxia.

Destruction of parietal areas containing visuokinesthetic motor engrams, where motor acts may be programmed, should be distinguishable from apraxia induced by disconnection of these parietal areas from frontal motor areas. Destruction should result in inability to distinguish well-performed from poorly performed movements, whereas disconnection should not. We gave movement and act-discrimination tasks to apraxic and nonapraxic patients with anterior lesions or nonfluent aphasia, and to patients with posterior lesions or fluent aphasia. On both tasks, the performance of posterior/fluent patients was worse than that of all other patients. Our results suggest that there are two types of patients with ideomotor apraxia.

Aphasia, Broca↗
PubMed1981

Thalamic neglect. Possible role of the medial thalamus and nucleus reticularis in behavior.

A patient had an ischemic infarction of the right medial thalamus, with a resultant contralateral neglect syndrome. We propose that the medial thalamic nuclei, particularly centromedian and parafascicularis (CMPF), are normally involved in the arousal-activation process by which an organism can be aroused by and respond to novel or important stimuli. Specifically, we propose that (1) the mesencephalic reticular formation subserves tonic arousal to novel or painful stimuli by inhibiting the nucleus reticularis thalami (NR) and (2) that selective attention is mediated by cortical input to NR. The CMPF is closely associated with motor systems (basal ganglia, ventrolateral nucleus of the thalamus [VL], and frontal lobes). A pathway involving CMPF, the frontal cortex, and the portion of NR associated with VL may be important in preparing the tonically aroused organism for action. Unilateral lesions of CMPF therefore induce an asymmetric hypokinesia, and bilateral lesions may induce akinetic mutism.

Arousal↗
PubMed1981

Unilateral hypokinesia and motor extinction.

A patient with a right caudate hemorrhage demonstrated left limb hypokinesia but did not have sensory inattention or sensory extinction. The left-sided hypokinesia was increased by bilateral simultaneous movements (motor extinction).

Attention↗
PubMed1980

Mirror-reading and writing in association with right-left spatial disorientation.

A left-handed patient suddenly developed a right hemiparesis, mirror-reading, and mirror-writing. Although he could discriminate between right and left on himself, he demonstrated right/left spatial disorientation. We propose that his right/left spatial disorientation was induced by a scanning defect. It has been demonstrated that mirror-image engrams are normally available. We believe that a reversal of the learned left-to-right scanning process with the availability of mirror engrams induced mirror-reading. Similarly, reversal of the normal left-to-right writing pattern, with the availability of mirror engrams, induced mirror-writing.

Dominance, Cerebral↗
PubMed1979

Apraxic agraphia with neglect-induced paragraphia.

Agraphia may result from the loss or unavailability of the memory of movements necessary to form written letters. For this mechanism to be invoked, it must first be demonstrated that there is no language deficit and that there is no disconnection between language and motor areas. A left-handed patient demonstrated bilateral agraphia and apraxia, but not aphasia, following a right parietal infarction. Preservation of the ability to type with the left hand demonstrated that the right hemisphere was not disconnected from language input. In addition, paragraphic errors while typing were shown to be secondary to left hemispatial neglect.

Aged↗
PubMed1979

Mechanisms underlying hemispatial neglect.

If patients with left-sided hemispatial neglect bisect lines incorrectly because hemianopia or sensory hemiinattention prevents them from seeing how far the line extends to the left, a strategy that ensures their seeing the left side of the line in their normal field should improve performance. If patients have hemispatial hypokinesia, moving the line toward the normal half of body space should improve performance. Six patients with left-sided neglect from right hemisphere infarctions were required to identify a letter at either the right or the left end of a line before bisecting that line. The task was given with the lines placed at either the right, the center, or the left of the body midline. Performance in trials when subjects were required to look to the left before bisecting a line did not differ from when they were required to look right. Performance was significantly better when the line was placed to the right side of the body than to the left. These observations support the hypothesis that patients with hemispatial neglect have hemispatial hypokinesia. An alternative hypothesis is that these subjects had a hemispatial memory defect. Although they saw the left side of the line in their normal field, they were incapable of forming a stable trace and performed as if they did not see the left side of the line.

Dominance, Cerebral↗
PubMed1979

When to suspect spinal cord lesions in the elderly.

Motor or sensory disturbance in the lower extremities--sometimes with gait disturbance--is the most common symptom of spinal cord disease. History and examination may localize the lesion, but spine x-rays and myelography usually are necessary to determine its cause. The most common causes of cord compression in the elderly are spondylosis and neoplasm. Compressive lesions are usually treated by surgery. Once compression has been excluded and diagnosis established, treatment should be directed toward the underlying disorder.

Aged↗
PubMed1978

Myokymia, muscle hypertrophy and percussion "myotonia" in chronic recurrent polyneuropathy.

Three unusual features were observed in a patient with chronic relapsing polyneuropathy: myokymia, muscle hypertrophy, and prolonged contraction in response to muscle percussion. Low nerve conduction velocity and conduction block were demonstrated in all motor nerves tested, indicating a demyelinating peripheral neuropathy. Myokymia was caused by spontaneous motor unit activity which was shown to originate in peripheral nerves, since it persisted after nerve block and was abolished by regional curarization. Muscle hypertrophy was attributed to increased peripheral nerve activity, and the prolonged contraction of muscle in response to direct percussion was attributed to irritability of intramuscular nerve terminals.

Adult↗
PubMed1976

A case of mixed transcortical aphasia with intact naming.

Altholgh Lichtheim recognized that Wernicke's 'reflex arch' (primary auditory area, to Wernicke's area, to Broca's area, to primary motor area) was important for repetition, he recognized that other areas of the brain (for example, area of concepts or semantic area) must be important in comprehension and voluntary speech. He suggested that Wernicke's area (phonemic area) not only projected to Broca's area (as Wernicke suggested) but that it also projected to the area of concepts. A lesion of this latter pathway or in the area of concepts would produce a syndrome where repetition was intact but comprehension was impaired (e.g. transcortical sensory aphasia). Lichtheim also thought that the area of concepts projected directly to Broca's area and that voluntary speech was mediated by this pathway. Although Lichtheim's model could explain the mechanism underlying transcortical aphasia, his schema could not explain anomic aphasia. Unlike Lichtheim's schema, Kussmaul's schema suggested that the area of concepts projects back to Wernicke's area before projecting to Broca's area. With this schema, a patient with a hypothetical lesion which interrupted the pathway from the area of concepts to Wernicke's area (but did not interrupt the pathway from Wernicke's area to the area of concepts) should be anomic, with normal comprehension and repetition. In order for this latter schema to be plausible there should also be a lesion which interrupts the pathway from Wernicke's area to the area of concepts but does not interrupt the pathway which goes from the area of concepts to Wernicke's area. A patient with this hypothetical lesion should comprehend poorly; however, in spite of poor comprehension, naming and repetition should be intact. We report a patient who demonstrates poor comprehension with intact naming and repetition. This patient could also read aloud but could not comprehend written language. Not only could this patient name objects but he could demonstrate their use. These observations suggest that comprehension of written language is mediated by a different pathway than the recognition of visually presented objects.

Aphasia↗
PubMed1976

Making sense of cerebral dominance and syndromes of the nondominant hemisphere.

Knowing the special function of each half of the brain is important to the clinician. If he doesn't understand what damage to the nondominant hemisphere can do, he may mistake the resulting syndrome for a psychiatric illness or generalized dementia, and the patient won't get proper treatment and counseling. The tendency is to think of dominance in terms of language, but other functions are asymmetrically located even though their input and output are bilateral. Generally, lesions in the left hemisphere cause problems with language and those in the right disrupt visual and spatial skills, attention, and emotional behavior. By far the most common syndrome in right hemisphere lesions is neglect of the left side. A patient may show lack of concern about his illness or he may deny that he is sick or even that the left side of his body belongs to him. Patients with left hemisphere lesions may neglect the right side but rarely to this extreme.

Aged↗