Right-sided neglect in a left-hander: Evidence for reversed hemispheric specialization of attention capacity
Abstract
Severe hemi-spatial neglect, anosognosia, contralateral hypokinesia, aprosodia, and visual-spatial constructive difficulties—typically seen in right-handers with right hemisphere lesions—were observed in a left-handed patient with an acute left frontal cortical and subcortical infarct. There was no evidence of accompanying aphasia and the neglect syndrome gradually resolved over a 2-week period. The assumption by the left hemisphere of a classic right hemisphere attention, visuo-spatial and prosodic superiority may represent a case of reversed hemispheric specialization.
Electrophysiology in Behavioral Neurology.
AUTHORS
Robert T. Knight
Date: 1985
Inhibitory modulation of cat somatosensory cortex: a pharmacological study
Abstract:
In anesthetized preparations, GABA and taurine produced rapid, reversible inhibition of the negative component (N20) of the primary somatosensory evoked potential (SEP) without effect on the earlier positivity (P11). This effect was also produced by low doses of 4-aminopyridine. Neither bicuculline or picrotoxin antagonized these drug effects. A predominance of type B GABA receptors in the superficial layers of the somatosensory cortex is proposed.
Bitemporal lesions dissociate auditory evoked potentials and perception.
Abstract:
We studied auditory evoked potentials (AEPs) in an 82-year-old female patient who became suddenly deaf following the second of two strokes. The patient showed markedly elevated pure tone thresholds, was unable to discriminate sounds and could not understand speech. Brain-stem auditory evoked potentials (BAEPs) were normal. CT scans revealed bilateral lesions of the superior temporal plane which included auditory cortex. Two experiments were performed. In the first, tones, complex sounds and speech stimuli were presented at intensities above and below the patient's perceptual threshold. P1, N1 and P2 components were elicited by each of the stimuli--whether or not they were perceived. In particular, stimuli presented below threshold evoked large amplitude, short latency responses comparable to those produced in a control subject. In a second experiment, the refractory properties of the N1-P2 were examined using trains of tones. They were also found to be similar to those of normal subjects. Shifts in the pitch of the tones near the end of the train (when refractory effects were maximal) evoked N1-P2s with enhanced amplitudes, although the change in pitch was not perceived by the patient. In both experiments AEP scalp topographies were normal. The results suggest that bitemporal lesions of auditory cortex can dissociate auditory perception and long-latency auditory evoked potentials. A review of evoked potential studies of cortical deafness suggests that the neural circuits responsible for N1-P2 generation lie in close proximity to those necessary for auditory perception.
Decreased Response to Novel Stimuli After Prefrontal Lesions in Man
Abstract:
Experiments were conducted to study the contribution of prefrontal cortex to the generation and modulation of two varieties of P300 activity. Control subjects generated typical parietal maximal P300 responses to detected target stimuli. Unexpected, novel auditory stimuli presented to controls generated an earlier latency, fronto-centrally distributed P300 response. A similar earlier latency, fronto-central P300 is generated to unexpected, novel visual stimuli. The occurrence of this phenomenon in both the auditory and visual modalities suggests that it may reflect neural activity of a common CNS system involved in the orienting response. Subjects with unilateral prefrontal damage generated P300 complexes to target stimuli that did not differ from the control responses. Prefrontal damage, however, resulted in a specific defect in the P300 response to the unexpected novel stimulus. Prefrontal patients showed neither N200 enhancement nor the fronto-central P300 response to the novel stimulus that was found in control subjects. These findings indicate that prefrontal regions are critical for the organism's response to unexpected novel stimuli. Abnormalities in prefrontal control of sensory-limbic integration may be a critical element in the decreased P300 to novel stimuli found in these unilateral prefrontal lesioned patients. It is suggested that major features of the human frontal lobe syndrome may be explained by a physiological inability to control attention and orientation systems after prefrontal damage.
Alcohol and the central nervous system
Abstract:
Acute Wernicke-Korsakoff syndrome is an underdiagnosed cause of reversible coma in the alcoholic patient. Chronic toxic effects of ethanol include nutritional polyneuropathy, cerebellar degeneration, and diffuse cortical damage with resultant alcoholic dementia. The rapid correction of hyponatremia can result in the iatrogenic syndrome of central pontine myelinolysis.
Chewing Oscillopsia: A Case of Voluntary Visual Illusions of Movement
Abstract:
A 60-year-old man had a history of frontal headaches and chewing-related oscillopsia. Examination disclosed a retro-orbital epidermoid cyst that had eroded through the lateral orbital wall and under the temporalis muscle. The illusion of movement was due to mechanical displacement of the tumor mass and eye by contraction of the temporalis muscle. Removal of the cyst produced complete remission of the oscillopsia.
Pa component of cat auditory evoked potential originates in primary auditory cortex
Authors:
Robert T. Knight
Simon Brailowsky
Date: 1983
Non-Portuguese motor system degeneration in a black family
ABSTRACT
Autosomal dominant motor system degeneration has been described primarily in Portuguese families from the Azorean Islands. The symptoms include various combinations of ataxia, pyramidal and extrapyramidal signs, appendicular dystonias, tics, ophthalmoplegias, and peripheral neuropathies with amyotrophy. One non Portuguese, non‐Azorean black family has been described previously; this report describes a second such family affected by autosomal dominant motor system degeneration.
AUTHORS
Joanna A. Cooper
Tsutomu Nakada
Robert T. Knight
Robert P. Friedland
Date: 1983
Kinetics of attention following prefrontal lesions
Authors:
David L. Woods
Robert T. Knight
Steven A Hillyard
Helen J. Neville
Date: 1983
Methodological problems in the study of information processing using ERPs in neurological populations
Authors:
Robert T. Knight
Date: 1983
Solitary metastasis of systemic malignant lymphoma to the cerebellopontine angle
ABSTRACT
Systemic malignant lymphoma rarely produces solitary metastasis to the brain. We report such a case in the cerebellopontine (CP) angle mimicking an acoustic neurinoma. CT scan showed a large, round mass in the CP angle which enhanced homogeneously following contrast infusion. The internal auditory meatus appeared to be eroded. The clinical, radiological, and pathological findings are presented.
Reversed hemispheric organization in a left-hander
Abstract:
For left-handers, cognitive functions are organized in the brain similarly to right-handers or they are more diffusely represented. In this study, we report a left-handed patient with a focal right temporal-parietal lesion who evidenced a lasting Wernicke's aphasia and visual-spatial functioning typical of a right-hander with left-hemisphere in involvement. The patient's performance on other tasks (e.g. praxis, singing) as well as observed behavioral changes also resembled those of a right-hander with left-hemisphere compromise. This case suggests that it is possible for cognitive functions to be inversely represented in the two hemispheres.
Intermittent venous claudication of the upper extremity: the pectoralis minor syndrome
Aphasia in a prelingually deaf woman
Abstract:
A left parietal infarct in a prelingually deaf person resulted in an aphasia for both American Sign Language (ASL) and written and finger-spelled English. Originally the patient had a nearly global aphasia affecting all language systems. By five to seven weeks post-onset her symptoms resembled those of hearing aphasics with posterior lesions: fluent but paraphasic signing, anomia, impaired comprehension and repetition, alexia, and agraphia with elements of neologistic jargon. In addition, there was a pronounced sequential movement copying disorder, reduced short-term verbal memory and acalculia. In general, the patient's sign errors showed a consistent disruption in the structure of ASL signs which parallels the speech errors of oral aphasic patients. We conclude that most aphasic symptoms are not modality-dependent, but rather reflect a disruption of linguistic processes common to all human languages. This case confirms the importance of the left hemisphere in the processing of sign language. Furthermore, the results indicate that the left supramarginal and angular gyri are necessary substrates for the comprehension of visual/gestural languages.
The effects of frontal cortex lesions on event-related potentials during auditory selective attention.
Authors:
Robert T. Knight
Steven A Hillyard
David L. Woods
Helen J. Neville
Date: 1981
PubMed: 6172256
Abstract:
We compared electrophysiological indices of auditory selective attention in control subjects and in patients with unilateral lesions of the dorsolateral frontal lobes. In control subjects, ERPs following attended tones showed an enhanced negativity from 80 to 500 msec post-stimulus which had a different topographic distribution than the N120. Lesions of the frontal lobes reduced the attention-related negativity and impaired behavioral performance. The ERP reductions were equivalent in recordings obtained from electrodes placed over the damaged and intact cortex. A difference was noted between left and right frontal groups as a function of ear of delivery of the stimuli. Patients with left frontal lesions showed reduced attention effects following tones presented to either ear. Patients with right frontal lesions showed intact attention effects to right ear tones, but no attention-related negativity to left ear tones. When the left and right frontal groups were considered together, tones in ignored channels produced larger responses when presented to the ear contralateral to damaged cortex. These results underline the important role of the frontal lobes in processes of selective attention. Although the endogenous negativity produced in selective attention tasks does not appear to originate in dorsolateral frontal cortex, the frontal lobes exhibit a modulating influence upon it. In addition, the endogenous attention related negativity and exogenous N120 components apparently arise from different neural generators.
The effects of frontal and temporal-parietal lesions on the auditory evoked potential in man.
Authors:
Robert T. Knight
Steven A Hillyard
David L. Woods
Helen J. Neville
Date: 1980
PubMed: 6159179
Abstract:
We compared the properties of long-latency auditory evoked potentials (AEPs) in patients with unilateral lesions of the dorsolateral frontal cortex (N = 10) or temporal-parietal cortex (N = 10) to those of a group of age-matched normal subjects. Extensive lesions of the frontal cortex had no effect on AEP amplitudes, scalp distributions or refractory properties. However, following frontal lesions AEPs were larger to tones presented in the ear contralateral to the lesion than they were for tones presented ipsilaterally. Following unilateral temporal-parietal lesions, the N1 component (98 msec latency) was markedly reduced in amplitude at all scalp sites, and no increase in N1 amplitude occurred with lengthening ISIs. The P2 component (200 msec), however, showed the same amplitude and refractory properties as in the normal subjects. The results underline the critical role played by the cortex of the posterior-superior temporal plane and the adjacent cortex of the parietal lobe in the production of the N1 component.