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Biomedical subjects

J T Marsh

Publications and source records attributed to J T Marsh.

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

Electrophysiological indices of CNS function in hemodialysis and CAPD.

Fourteen Center hemodialysis (CHD) patients, 13 continuous ambulatory peritoneal dialysis (CAPD) patients, and 10 normals matched by group for age and sex were compared using a battery of evoked (EP) and event-related (ERP) brain potential measures to determine the effects on central nervous system (CNS) functioning of these two dialysis modes. While some differences were observed in early brainstem EP waves, the majority of differences occurred in the later waves associated with higher levels of cognitive processing. With tasks involving easy discriminations, CHD patients had longer latencies, indicative of less efficient cognitive processing, than CAPD patients who resembled controls. With difficult tasks, both CHD and CAPD groups showed abnormally-delayed later components. Similar results were obtained for the amplitude of the middle latency N1-P2 component, that is, reduced amplitudes for the CHD group with respect to both CAPD and control groups under low task demand, while both dialysis groups had reduced amplitudes under high task demand. These results suggest that CAPD patients are more similar to normals than CHD patients in ERP indices of attention and the efficiency of cognitive processing.

Adult↗
PubMed1984

Event-related potential concomitants of information processing dysfunction in schizophrenic children.

ERPs were recorded from 10 schizophrenic and 13 normal children during the performance of the Span of Apprehension task (Span). This task involves the discrimination of a randomly placed target letter among distractors, and it has been shown to discriminate between normal and schizophrenic individuals. The EEG was recorded at 7 scalp loci, and ERPs were averaged over a 1500 msec interval initiated by a warning tone which preceded the visual Span stimuli by 500 msec. Stimulus arrays were grouped into 4 levels of difficulty. The data from both subject groups were combined in a single principal components analysis (separate PCAs exhibited few differences between groups) generating 8 rotated factors which were readily interpreted in terms of conventional ERP components. Factor scores for the two groups were examined using Analysis of Variance. The schizophrenic children produced a small CNV which was slow to develop and resolve as well as diminished amplitudes for the N1, P3 and slow wave components. This suggests that these children are impaired in their ability to regulate processes involved in the mobilization and direction of attention and the discrimination of target stimuli. Significantly, the schizophrenic children did not show progressive increases in N1 and SW amplitudes in response to increases in information processing demand (array difficulty) as was the case in the normal children. ERP components of the schizophrenic children were most aberrant at frontal leads, but midline and lateralized deficits were also seen at vertex and posterior recording sites.

Adolescent↗
PubMed1983

Exponential electrophysiological aging: P3 latency.

Forty-nine normal volunteer subjects ranging in age from 15 to 80 years were studied in an 'auditory oddball' event-related potential paradigm. In certain respects our results replicate other studies, finding significant correlations between age and both N2 and P3 latency. Slopes of the linear age/ERP latency regression function increased with component number (i.e., N1 less than P2 less than N2 less than P3). Further analysis disclosed that the age/ERP component latency relationship is non-linear. Separate age/ERP component latency linear regression functions were computed for subjects 15-45 and 46-80. None of these functions were significant for subjects under 45. Age/latency slopes were significant in the older group for P2, N2 and P3. The age/P3 latency slope for the subjects under 45 was 0.53 msec/year, versus 3.14 msec/year for the subjects over 45. The data for P3 latency and age are best fitted with a curvilinear first and second degree orthogonal polynomial, which describes a positively accelerating latency increase with age. Clinical implications of the form of the age/P3 latency regression function (curvilinear vs. linear) are discussed.

Adolescent↗
PubMed1982

Event-related potentials in psychiatry: differentiating depression and dementia in the elderly.

Event-related potentials (ERPs) were recorded from 25 elderly patients and 26 normal controls to determine whether ERPs can aid in the differential diagnosis of depression and dementia. Two ERP measures were used: (1) P300 latency, and (2) N1 amplitude increase for a 14db tone intensity increase (i.e. intensity augmenting-reducing). While augmenting-reducing proved of little benefit, P300 latency was highly correlated with Mini-Mental State (MMS) scores and correctly identified 10 of 18 demented patients. None of the seven patients with psychiatric disorders (primarily depression) or 26 normals were misclassified. Better differentiation of depression and dementia resulted from combined use of P300 latency and MMS scores.

Aged↗
PubMed1979

Principal component analysis of ERP differences related to the meaning of an ambiguous word.

Event-related potentials (ERPs) to the noun and verb meanings of/'led/in the single ambiguous phrase 'it was/'led/' were re-analyzed using principal component analysis (PCA). These data had previously been analyzed by SWDA and reported in this journal. PCA defined 3 meaning-related components, comprising 40.3% of the entire data variance. The N150 component was shown to be larger for the noun meaning than for the verb meaning; the P230 epoch differed in its anterior-posterior distribution according to meaning; and N370 for noun responses was relatively more negative at the right posterior lead and positive at the left anterior. All components taken together, the left anterior lead showed the greatest meaning-related difference. Previous analysis by SWDA had resulted in significant discriminant functions for left hemisphere ERPs, but this analysis did not yield a clear definition of the effects of meaning on specific ERP components or of the scalp distributions of meaning-related components. Thus, while the results of both analyses support the interpretation that the perceived meaning of words has a substantial effect on ERP wave forms, PCA appears to provide the clearest definition of the ERP component effects.

Adult↗
PubMed1978

Human auditory frequency-following responses to a missing fundamental.

Both a complex tone perceived as a 365-hertz "missing fundamental" and a 365-hertz pure tone evoked 365-hertz far-field frequency-following responses. Narrow-band masking noise centered at 365 hertz attenuated the responses to the pure tone but not to the complex tone. Results support the concept that perception of the missing fundamental is based on periodic neural activity.

Auditory Pathways↗
PubMed1976

Evoked potential waveform differences produced by the perception of different meanings of an ambiguous phrase.

To test the effects of perceived linguistic meaning on evoked potential (EP) waveform, an experiment was performed using the stimulus homophone "led" or "lead" in the single ambiguous phrase "it was /'led/". The phrase was presented aurally in sets of 60 repetitions, instructing the subject before each set as to the specific meaning of the stimulus word to be perceived. Averages of one hundred responses were obtained for each of the two meanings of the stimulus. Responses were recorded from scalp locations over Broca's and Wernicke's areas and homologous right hemisphere loci. Average waveforms evoked by the two meanings of the stimulus word were dissimilar for the left anterior locus and similar for the other three loci as indicated by correlations. The application of the Discrimination Index to these data disclosed that the EP waveform differences observed at the left anterior locus would not be attributed to random variability. Stepwise Discriminant Function Analysis on the same data revealed that responses from individual subjects could be classified according to experimental conditions at a greater-than-chance level. Discrimination was best for responses from left hemisphere loci. There was some commonality of discriminative EP components across subjects, specifically components late in the EP epoch. These data are interpreted as demonstrating an EP correlate of the processing of the contextual meaning of words.

Adult↗
PubMed1975

Far-field recorded frequency-following responses: evidence for the locus of brainstem sources.

Two experiments were performed to determine the brainstem origins of the scalp recorded auditory frequency-following response (FFR). The first was a study of FFR onset latency in which responses observed by direct recording from depth electrodes in brainstem auditory nuclei were compared with those obtained from the scalp. The mean onset latency of scalp recorded FFR (5.8 msec) closely approximated the 5.4 msec mean latency of response recorded from within the inferior colliculus (IC). In a second experiment, cooling of the IC greatly reduced or eliminated FFR both within this nucleus and at the scalp. FFR at the medial superior olive was unaffected during cooling. It was concluded that at moderate intensities of stimulation the primary source of scalp recorded FFR is the IC.

Animals↗
PubMed1975

Far-field recorded frequency-following responses: correlates of low pitch auditory perception in humans.

The recent demonstration that auditory frequency-following responses (FFR) can be recorded by signal averaging from the human scalp, opened the way for studies correlating FFR with auditory experience. This report describes FFR amplitude changes as a function of stimulus intensity and the addition of masking noise. The first experiment revealed a high degree of consistency both within and across subjects in the latency, phase and waveform of averaged FFR. This experiment also demonstrated a monotonic relationship between average FFR amplitude and stimulus intensity between 40 and 65 dB SL. Results of the second experiment showed a close correlation between the detectability of a tone in a noise masker and FFR amplitude. FFR amplitude diminishes precipitously as noise intensity approaches or exceeds the threshold for masking of the tone. These results are interpreted as emphasizing the role of neural periodicity mechanisms in the preception of low frequencies.

Acoustic Stimulation↗
PubMed1970

Auditory frequency-following response: neural or artifact?

An electrical response which reproduces the waveform and frequency of the sound stimulus can be recorded from the central neural pathway for audition. Controversy has existed for some years over whether this frequency-following response (FFR) is neural or an artifact such as remote pickup of the cochlear microphonic or cross talk in the recording system. Two experiments resolve this issue by demonstrating that the frequency-following response depends upon functionally intact neural pathways. The frequency-following response, as well as auditory evoked potentials, is abolished by section of the eighth nerve; it is reversibly abolished by cooling of the cochlear nucleus.

Cochlear Nerve↗