1985

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Susceptibility to memory interference effects following frontal lobe damage: findings from tests of paired-associate learning.

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Authors:

  • Arthur P. Shimamura

  • Paul J. Jurica

  • Jennifer A. Mangels

  • Felicia B. Gershberg

  • Robert T. Knight

Date: 1995

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Abstract:

Patients with frontal lobe lesions were administered tests of paired-associate learning in which cue and response words are manipulated to increase interference across two study lists. In one test of paired-associate learning (AB-AC test), cue words used in one list are repeated in a second list but are associated with different response words (e.g., LION-HUNTER, LION-CIRCUS). In another test (AB-ABr test), words used in one list are repeated in a second list but are rearranged to form new pairs. Compared to control subjects, patients with frontal lobe lesions exhibited disproportionate impairment of second-list learning as a result of interference effects. In particular, patients exhibited the poorest performance during the initial trial of the second list, a trial in which interference effects from the first list would be most apparent. These findings suggest that the on-line control of irrelevant or competing memory associations is disrupted following frontal lobe lesions. This disruption may be indicative of an impaired gating or filtering mechanism that affects not only memory function but other cognitive function as well.


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Altered Peripheral and Brainstem Auditory Function in Aged Rats

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Authors:

  • Gregory V. Simpson

  • Robert T. Knight

  • Simon Brailowsky

  • Oscar Prospero-Garcia

Date: 1985

PubMed: 4063825

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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.


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Surface auditory evoked potentials in the unrestrained rat: component definition

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Authors:

  • Robert T. Knight

  • Simon Brailowsky

  • Gregory V. Simpson

Date: 1985

PubMed: 2412796

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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.







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Right-sided neglect in a left-hander: Evidence for reversed hemispheric specialization of attention capacity

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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.

Authors

  • Nina F. Dronkers

  • Robert T. Knight

Date: 1985

DOI: 10.1016/0028-3932(89)90118-8

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