Authors:
V. Pai
Ingrid L. Kwee
Robert T. Knight
Tsutomu Nakada
Date: 1989
Epstein-Barr virus causing encephalitis in an elderly woman
Abstract:
Although infectious mononucleosis commonly afflicts young persons, it is now being described more frequently in the elderly. Neurologic manifestations are uncommon, and encephalitis is rare, especially in elderly patients. We have reported a case of acute Epstein-Barr virus infection causing acute encephalitis in a 64-year-old woman. Despite the severity of encephalitis, the patient recovered fully after several weeks.
Visual search performance in the neglect syndrome
Authors:
Mirjam Eglin
Lynn C. Robertson
Robert T. Knight
Date: 1989
DOI: 10.1162/jocn.1989.1.4.372
Abstract:
Patients with hemispatial neglect fail to respond to stimuli on one side of space. We assessed to what extent the complexity and number of visual stimuli on both sides determine the severity of neglect. Patients with neglect were required to find specified targets in a cluttered visual field. Two sets of stimuli were used. One set produced effortless and parallel search performance in normal controls; the other set was more complex and produced serial search performance in normal controls. Both sets of stimuli resulted in a serial performance pattern in the patients. Their baseline search performance on both sides was similar when all stimulus items were restricted to one side. A pronounced difference between the two sides was evident when stimuli appeared on both sides. Search for targets on the intact side of space was unaffected by distractors on the neglected side, whereas search for targets on the neglected side was slowed disproportionately by distractors on the intact side. The slowing on the neglected side was more severe during the more demanding search task and when more items were present on the intact side. The results indicate that neglect is associated with an inability to move attention from objects on the intact side to items on the neglected side.
Effects of Lesions of Temporal-Parietal Junction on Perceptual and Attentional Processing in Humans
Abstract:
When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.
Effects of lesions of temporal-parietal junction on perceptual and attentional processing in humans
ABSTRACT
When stimuli with larger forms (global) containing smaller forms (local) are presented to subjects with large lesions in the right hemisphere, they are more likely to miss the global form than the local form, whereas subjects with large lesions in the left are more likely to miss the local than the global form. The present study tested whether the global/local impairment in subjects with posterior lesions was due to deficits in controlled attentional processes, passive perceptual processes, or both. Attentional control was examined by measuring reaction time changes when the probability of a target appearing at either the global or local level was varied. Patients with unilateral right or left lesions centered in temporal-parietal regions and age-matched controls served as subjects. Because neurophysiological and neuropsychological evidence have implicated temporal regions in visual discrimination and inferior parietal regions in the allocation of attention to locations in the visual field, patients with left hemisphere lesions were further subdivided into those with lesions centered in the superior temporal gyrus (LSTG) or rostral inferior parietal lobule (LIPL). Patients with right hemisphere injury could not be analogously subdivided. The results revealed that the LSTG group was able to control the allocation of attention to global and local levels normally, while the LIPL group was not. In contrast, the LSTG group showed a strong baseline reaction time advantage toward global targets, while normals and the LIPL group showed no advantage toward one level or the other. Finally, the perceptual component was affected differentially by lesions in the right hemisphere and LSTG, with lesions in the left favoring global targets and lesions in the right favoring local targets. These findings indicate that the hemispheric global/local asymmetry is due to a perceptual mechanism with a critical anatomical locus centered in the STG.
AUTHORS
Lynn C. Robertson
Marvin R. Lamb
Robert T. Knight
Date: 1988
DOI: 10.1523/JNEUROSCI.08-10-03757.1988
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.
The effects of lesions of superior temporal gyrus and inferior parietal lobe on temporal and vertex components of the human AEP.
Abstract:
We recorded auditory evoked potentials (AEPs) to 1 kHz tone bursts in controls and patients with unilateral lesions centered in posterior superior temporal gyrus and adjacent caudal inferior parietal lobule (STG) or in rostral inferior parietal lobule (IPL). Controls generated a vertex maximal N94 (N1b) and P200 (P2) and additional P45, N78 and N127 temporal AEP components (P45, N1a, N1c). Similar to prior reports, in controls the N1a was most prominent over the left temporal lobe and the P45 was largest over the right temporal lobe consistent with behavioral and anatomical data indicating differential organization of left and right human temporal lobe. The N1c was recorded equally from both T3 and T4 electrodes and was enhanced in the temporal site contralateral to the ear of stimulation. The patient groups had differential effects on AEPs. Unilateral STG lesions resulted in bilateral reductions of the N1b and P45 and marked unilateral reductions of the N1a and N1c over lesioned hemisphere. IPL lesions resulted in bilateral but non-significant reductions of the N1b and N1c. The scalp topography results in normal subjects combined with the effects of unilateral STG lesions provide supportive evidence that the temporal maximal components of the human AEP (P45, N1a, N1c) are generated by radially oriented neuronal dipole sources located in STG. The bilateral reduction of the N1b vertex response by unilateral STG lesions is compatible with a unilateral disruption of a vertically oriented dipole situated in the posterior superior temporal plane. The results emphasize the critical role of the superior temporal plane and lateral superior temporal gyrus in generation of human long latency AEPs.
Attention and interference in the processing of global and local information: effects of unilateral temporal-parietal junction lesions
Abstract:
The processing of hierarchical stimuli was examined in patients with lesions in the temporal-parietal junction. In separate blocks of trials, subjects were instructed to identify the letter at the local or the global level of a hierarchical stimulus. Consistent with previous findings, reaction times for controls were faster in the globally than in the locally directed condition and reaction times to the local level were longer when the letters at the two levels were different (e.g. local "S"s forming a global "H") than when they were the same (e.g. local "S"s forming a global "S"). In other words, controls exhibited interference when locally directed. Patients with lesions centered in the rostral inferior parietal lobe (IPL) showed interference effects similar to controls. In contrast, patients with lesions centered in the posterior superior temporal gyrus and adjacent caudal inferior parietal lobe (STG) showed no interference. The data suggest that the posterior superior temporal plane and adjacent caudal inferior parietal lobe plays an important role in the integration of and/or attention to local and global level information.
Differential effects of parietal or temporal-parietal lesions on the human N200 and P300
Authors:
Robert T. Knight
David L. Woods
Clay Clayworth
Date: 1987
PubMed: 3587487
Recovery From GABA-Mediated Hemiplegia in Young and Aged Rats: Effects of Catecholaminergic Manipulations
Abstract:
We investigated the participation of catecholaminergic mechanisms in the functional recovery from motor cortex lesions in young (9 months) and aged (26 months) rats. The animals were studied during the recovery period from an hemiplegic syndrome secondary to small motor cortex lesions potentiated by the localized, chronic (7 days) infusion of GABA into the lesion site. Acute administration of haloperidol (0.1 mg/kg IP) to these recovered animals induced a re-emergence of the contralateral motor syndrome in both groups. In the young group, the haloperidol-induced hemiplegia lasted one day whereas in the aged animals the deficit was significantly prolonged lasting three days. Apomorphine administration (0.5 mg/kg IP) prior to or immediately after haloperidol injection failed to prevent or reverse the reappearance of the motor deficit. Adult animals recovered from motor cortex aspirations performed 7 to 12 months prior were refractory to haloperidol effects. Amphetamine administration to young rats treated chronically with saline or GABA infusion into the somatomotor region also failed to alter the clinical evolution of the motor deficit. The evidence suggests that dopaminergic mechanisms are involved in the functional recovery from brain lesions and that these mechanisms are most susceptible to neuroleptic blockade during the early post-lesional period. The deleterious effects of dopaminergic blockade are heightened in aged populations. The use of dopaminergic antagonists in brain-lesioned subjects, and particularly in geriatric populations, is considered potentially harmful, particularly in the early stages of the recovery process.
Appraisal and diagnosis of neurogenic communicative disorders in remote settings
Authors:
Robert T. Wertz
Nina F. Dronkers
Ellen Bernstein-Ellis
Yvonne Shubitowski
Roberta Elman
Gregory K Shenaut
Robert T. Knight
Jon L. Deal
Date: 1987
Abstract:
Patients who suffer neurogenic communication disorders and reside in remote settings either do not receive services or they must travel long distances or become inpatients for extended periods. No services is unacceptable, because all patients merit appraisal and a diagnosis, and many respond to treatment with improvement in their communication. Traveling long distances for services is unacceptable, because it is expensive, inconvenient, may be contraindicated by the patient's medical condition, requires a means of transportation which often does not exist, and must be frequent and protracted. Hospitalization is also unacceptable, because the communication disorder does not necessitate hospitalization, it usurps a bed, carries a patient beyond DRG length-of-stay criteria, removes him or her from the home environment, and is expensive. There is a need to develop means for managing patients who live in remote settings.
Appraisal and diagnosis of neurogenic communicative disorders in remote settings
Authors:
Robert T. Wertz
Nina F. Dronkers
Ellen Bernstein-Ellis
Yvonne Shubitowski
Roberta Elman
Gregory K Shenaut
Robert T. Knight
Jon L. Deal
Date: 1987
Generators of middle- and long-latency auditory evoked potentials: implications from studies of patients with bitemporal lesions
Authors:
David L. Woods
Clay Clayworth
Robert T. Knight
Gregory V. Simpson
Margaret A. Naeser
Date: 1987
PubMed: 2435529
Abstract:
We recorded middle- and long-latency auditory evoked potentials (AEPs) in 5 patients (ages 39-72 years) with bilateral lesions of the superior temporal plane. Reconstructions of CT sections revealed that primary auditory cortex had been damaged bilaterally in four of the patients, while in the fifth an extensive left hemisphere lesion included primary auditory cortex while a right hemisphere lesion had damaged anterior auditory association areas but spared primary auditory cortex. Normal middle-latency AEPs (MAEPs) were recorded at the vertex electrode in all of the patients. In 3 of the 5 patients, MAEPs also showed normal coronal scalp distributions and were comparable in amplitude following stimulation of either ear. Two patients showed abnormalities. In one case, Na (latency 17 msec)-Pa (latency 30 msec) amplitudes were reduced over both hemispheres following stimulation of the ear contralateral to the more extensive lesion. In another, with both subcortical and cortical involvement, the Pa was abolished over the hemisphere with the more extensive lesion. Long-latency AEPs were normal in 2 patients whose lesions were largely confined to the superior temporal plane. In 2 patients with lesions extending into the inferior parietal lobe, N1s were abolished bilaterally. In the fifth patient, the N1 showed a slight reduction over the hemisphere with the more extensive lesion. Middle- and long-latency AEPs were differentially affected by some lesions. For example, patients with absent N1s could produce normal Pas. A review of these results and those of previous studies of bitemporal patients suggests that abnormalities in middle- and long-latency AEPs do not necessarily reflect damage to primary auditory cortex per se, but rather the degree of damage to adjacent areas. Abnormalities in MAEPs are associated with subcortical lesions, or cortical lesions extensive enough to denervate thalamic projection nuclei. Abnormalities in the long-latency N1 reflect lesion extension into the multi-modal areas of the inferior parietal lobule. This area appears to exert a critical modulatory influence over N1 generators outside of the superior temporal plane.
Aging decreases auditory event-related potentials to unexpected stimuli in humans
Abstract:
A P300 event-related potential (P3a) was recorded to unexpected, deviant auditory stimuli requiring no behavioral response. This brain potential underwent systematic latency prolongation and amplitude decrease with advancing age. The age-related changes paralleled those of the P300 (P3b) recorded in target detection tasks. These results provide physiological evidence of a decremented CNS response to unexpected stimuli with aging.
Phenytoin Increases the Severity of Cortical Hemiplegia in Rats
Abstract:
The effects of systemic phenytoin administration on the motor deficit resulting from a cortical lesion were studied in rats trained to walk coordinately on a narrow beam. The somatomotor cortex lesion was produced by an indwelling cannula through which saline or GABA were infused chronically via an osmotic minipump. Phenytoin (50 mg/kg i.p.) administered between days 3 and 5 after the intracortical catheter implantation produced a significant increase in the severity of the resulting hemiplegic syndrome. This DPH effect was more noticeable in those animals also receiving intracortical GABA infusions. The anticonvulsant at the dose used had no effect on motor performance when administered preoperatively or when given to the animals 14 days after surgical intervention when their hemiplegic syndrome had cleared. These findings suggest that phenytoin administration to brain-damaged individuals in the initial postlesion stage may be deleterious.
Status Epilepticus Manifesting as Reversible Wernicke's Aphasia
ABSTRACT
Ictal aphasia in adults is a rare phenomenon, with the majority of reported cases showing a nonfluent Broca's or mixed aphasic speech pattern associated with disturbances of level of consciousness. There is usually only one prolonged episode of aphasia with evidence of lateralized neurological findings and structural pathology on CAT scan. We describe a patient with intermittent episodes over a 10‐year period of a fluent Wernicke's aphasia associated with paroxysmal posterior temporoparietal spike‐wave activity on the EEG. Interictally, the patient was clear of neurologic signs and symptoms. These episodes were repeatedly misdiagnosed as psychotic breaks and treated with antipsychotic medication and psychiatric hospitalization. Unless language performance is assessed, these cases of focal epilepsy may be diagnosed as schizophrenic “word‐salad,” leading to delay of appropriate treatment.
Electrophysiologic evidence of increased distractibility after dorsolateral prefrontal lesions
Abstract:
Patients with left prefrontal lesions and control subjects showed enhanced event-related potentials (ERPs) to attended tone sequences presented in a dichotic attention task. ERP enhancements were comparable at short and long interstimulus intervals (ISIs), and did not depend upon whether attended stimuli were preceded by other attended stimuli or by distracting stimuli in the opposite ear. In contrast, patients with right prefrontal lesions showed absent ERP attention effects to contralateral (left ear) tones at all ISIs, and reduced attention effects to ipsilateral tones at long ISIs and when these were preceded by distracting sounds. The results are consistent with an asymmetric organization of dorsolateral prefrontal cortex, and indicate that increased distractibility may contribute to the attention disorders that follow prefrontal lesions.
Gamma-Aminobutyric Acid-Induced Potentiation of Cortical Hemiplegia
Authors:
Simon Brailowsky
Robert T. Knight
Katherine Blood
Donatella Scabini
Date: 1986
PubMed: 3942881
Abstract:
A novel model of hemiplegia in young and aged rats is described. Osmotic minipumps were used to deliver a chronic (7 days), localized application of gamma-aminobutyric acid (GABA) (100 micrograms/microliter/h), to the somatomotor cortex of unrestrained rats. This resulted in an easily quantifiable, contralateral and reversible motor syndrome in both young and aged animals. In the young group, the motor deficit cleared over 5-day period, while in the aged animals it persisted for at least a 2-week period. Control animals treated with saline-filled minipumps did not develop a long-lasting motor deficit. The GABA-induced facilitation of hemiplegia due to small motor cortex lesions and the age effects on behavioral recovery of function are discussed. Cortical inhibitory mechanisms may play a role in debilitating syndromes such as stroke or post-epileptic paralysis.
Altered Peripheral and Brainstem Auditory Function in Aged Rats
Authors:
Gregory V. Simpson
Robert T. Knight
Simon Brailowsky
Oscar Prospero-Garcia
Date: 1985
PubMed: 4063825
Abstract:
A technique for conducting free-field brainstem auditory evoked potential (BAEP) audiometry in unanesthetized, unrestrained rats revealed a non-recruiting 18 dB elevation of click threshold in aged rats. BAEPs were first recorded in young and aged rats to clicks of equal intensity (80 dB SPL). Compared to the young group, aged animals exhibited longer wave I and wave IV latencies with no difference seen in the I-IV central conduction time. The prominent negative wave (No) following wave IV was also delayed and the I-No and IV-No conduction times increased in the aged group. When BAEPs were recorded to clicks with intensities adjusted to 35 dB above individual threshold, no differences in wave I or wave IV latencies or in the I-IV central conduction time were found between groups. However, the No component was delayed and the I-No and IV-No conduction times remained prolonged in the aged group. The results suggest that in addition to changes in peripheral auditory structures, changes in the rostral auditory brainstem accompany age-related hearing loss in rats.
Surface auditory evoked potentials in the unrestrained rat: component definition
Abstract:
Auditory evoked potentials (AEPs) to click and pure tone stimuli were recorded in unrestrained, unanesthetized rats. The middle latency rat AEPs (N17, P23, N38) had midline scalp distributions similar to human MAEPs and were recorded to within 15 dB above BAEP threshold. In contrast to human MAEPs, rat MAEPs were decreased in amplitude at high stimulation rates and only the N17 component was unaltered by slow wave sleep. The longer latency N50, N80 and P130 components had several response properties comparable to human N100-P200 vertex potentials. These included restricted midline fronto-central scalp distributions, progressive increases in amplitude at ISIs up to 4-8 sec and marked attenuation during slow wave sleep. The frequency sensitivity of the rat AEP revealed a decreased response to pure tones below 4 kHz but robust responses for stimuli up to at least 45 kHz. There was a notch in the rat audiogram with decremented component amplitudes to pure tone stimuli centered at 35 kHz. When equated for intensity, click and pure tone stimuli in the range of the rats maximal audiometric sensitivity (8-20 kHz) generated comparable AEP components. These results provide normative data on rat surface recorded AEPs. It is suggested that these surface recorded rat AEPs are generated by subcortical neural systems involved in the detection of auditory transients.