Search PubMed⌕ Search

Biomedical subjects

H G Vaughan

Publications and source records attributed to H G Vaughan.

At least 37 records · Page 2Linked to original sources
PubMed1995

The mismatch negativity of event-related potentials as a probe of transient auditory memory: a review.

The use of the mismatch negativity as a probe to study the memory upon which it depends is reviewed. Topics about the memory include its duration, its capacity, the kind of information that can be stored in the memory, how the information is stored, whether the memory is accessed in parallel or in series, whether it is hard-wired or can be modified by experience, and its relationship to sensory memory.

Evoked Potentials, Auditory↗
PubMed1995

Developmental studies and clinical application of mismatch negativity: problems and prospects.

There is wide interest in the clinical application of mismatch negativity (MMN) to assess discriminative capabilities in individuals whose auditory capacities are difficult to determine, including infants, young children and those with severe cognitive impairment. Before MMN can be used as a clinical electrophysiologic measure, it is necessary to establish that it can be reliably elicited in normal individuals. This chapter describes a detailed analysis of MMN recorded in a group of healthy 8-yr-old children to assess intrasubject and intersubject reliability of the response. We conclude that although statistically reliable results can be obtained with group data, and perhaps even in individuals when large numbers of stimuli can be delivered, the unfavorable signal to noise ratio of individual MMN data currently limits its clinical applicability. Suggestions for approaches to surmount these difficulties are presented for its eventual clinical usefulness.

Auditory Perception↗
PubMed1995

Dynamic neuroimaging of brain function.

To fully characterize the brain processes underlying sensorimotor and cognitive function, the spatial distribution of active regions, their interconnected regions must be measured. We describe methods for imaging brain sources from surface-recorded EEG and magnetoencephalographic data, called electromagnetic source imaging (EMSI). EMSI provides brain source locations within the common framework of magnetic resonance (MR) images of brain anatomy. This allows integration of data from other functional brain imaging methods, like positron emission tomography and functional MR imaging, which can improve the accuracy of EMSI localization. EMSI also provides submillisecond temporal resolution of the dynamic processes within brain systems. Examples are given of applications to visual perceptual and attentional studies.

Arousal↗
PubMed1995

Event-related potential correlates of early processing in normal aging.

Auditory event-related potentials were recorded from normal elderly and young adult subjects during simple reaction time and discrimination conditions. In both response conditions, the stimuli were randomly presented, as in an auditory "oddball" paradigm. It was found that NA, an index of early information processing, was significantly delayed in the elderly. Although the latency of N1 was not significantly different between the groups, the latencies of N2 and P3 were significantly longer for the aged subjects. The amplitudes of N1, NA1, NA2 and N2 showed no group differences. The raw amplitude of P3 showed a group difference in topography: Pz was greater than Fz for the young group, but not for the aged. When the amplitudes of NA1, NA2, and P3 were scaled, however, the topography of these components showed no significant group differences. These findings suggest that the age-related slowing of later ERP components and behavior may be partially accounted for by delays in early attention dependent perceptual processes, as indexed by NA.

Adult↗
PubMed1995

Relations between infant neurobehavioral performance and cognitive outcome in very low birth weight preterm infants.

The predictive utility of three aspects of neonatal neurobehavioral performance was examined in 144 very low birth weight (< 1500 g) preterms who were followed until 6 years of age. Visual-following and auditory-orienting composites derived from the Einstein Neonatal Neurobehavioral Assessment Scale were modestly related to the Mental Developmental Index (MDI) and IQ scores at several ages, whereas the active motility composite was only related to MDI scores at 1 year of age (corrected). Infants who showed deviant performance on both visual following and auditory orienting composites had significantly lower cognitive test scores at 1 and 6 years of age and were more likely to be classified as subaverage at 6 years of age (IQ < 85). Group differences were independent of both neonatal health status and motor scores and were not due to the performance of children with severe sensory impairments. These findings suggest that visual following and auditory orienting measured in the neonatal period can offer a useful way of indexing initial capacities.

Birth Weight↗
PubMed1994

Detection of stimulus deviance within primate primary auditory cortex: intracortical mechanisms of mismatch negativity (MMN) generation.

Mismatch negativity (MMN) is a cognitive, auditory event-related potential (AEP) that reflects preattentive detection of stimulus deviance and indexes the operation of the auditory sensory ('echoic') memory system. MMN is elicited most commonly in an auditory oddball paradigm in which a sequence of repetitive standard stimuli is interrupted infrequently and unexpectedly by a physically deviant 'oddball' stimulus. Electro- and magnetoencephalographic dipole mapping studies have localized the generators of MMN to supratemporal auditory cortex in the vicinity of Heschl's gyrus, but have not determined the degree to which MMN reflects activation within primary auditory cortex (AI) itself. The present study, using moveable multichannel electrodes inserted acutely into superior temporal plane, demonstrates a significant contribution of AI to scalp-recorded MMN in the monkey, as reflected by greater response of AI to loud or soft clicks presented as deviants than to the same stimuli presented as repetitive standards. The MMN-like activity was localized primarily to supragranular laminae within AI. Thus, standard and deviant stimuli elicited similar degrees of initial, thalamocortical excitation. In contrast, responses within supragranular cortex were significantly larger to deviant stimuli than to standards. No MMN-like activity was detected in a limited number to passes that penetrated anterior and medial to AI. AI plays a well established role in the decoding of the acoustic properties of individual stimuli. The present study demonstrates that primary auditory cortex also plays an important role in processing the relationships between stimuli, and thus participates in cognitive, as well as purely sensory, processing of auditory information.

Acoustic Stimulation↗
PubMed1994

Speech-evoked activity in primary auditory cortex: effects of voice onset time.

Neural encoding of temporal speech features is a key component of acoustic and phonetic analyses. We examined the temporal encoding of the syllables /da/ and /ta/, which differ along the temporally based, phonetic parameter of voice onset time (VOT), in primary auditory cortex (A1) of awake monkeys using concurrent multilaminar recordings of auditory evoked potentials (AEP), the derived current source density, and multiunit activity. A general sequence of A1 activation consisting of a lamina-specific profile of parallel and sequential excitatory and inhibitory processes is described. VOT is encoded in the temporal response patterns of phase-locked activity to the periodic speech segments and by "on" responses to stimulus and voicing onset. A transformation occurs between responses in the thalamocortical (TC) fiber input and A1 cells. TC fibers are more likely to encode VOT with "on" responses to stimulus onset followed by phase-locked responses during the voiced segment, whereas A1 responses are more likely to exhibit transient responses both to stimulus and voicing onset. Relevance to subcortical speech processing, the human AEP and speech psychoacoustics are discussed. A mechanism for categorical differentiation of voiced and unvoiced consonants is proposed.

Animals↗
PubMed1993

Impairment of early cortical processing in schizophrenia: an event-related potential confirmation study.

Abnormalities of auditory information processing represent a core feature of schizophrenic psychopathology. Event-related potentials (ERP) provide an objective index of the information processing deficits associated with schizophrenia and a tool for investigation of the underlying pathophysiology. The best established abnormality is a decrease in the amplitude of auditory P300. In an "oddball" paradigm, P300 is preceded by a series of earlier, negative-polarity ERP components that index discrete, prior information-processing events. The earliest such component, mismatch negativity (MMN), is elicited whenever a deviant, "oddball" stimulus interrupts a sequence of repetitive standard stimuli. MMN is generated principally within primary auditory cortex or adjacent structures on the superior temporal plane, suggesting that it indexes the earliest cortical event in the cognitive processing of auditory information. In the present study, MMN was studied in a group of 14 chronic schizophrenic subjects relative to 12 age- and IQ-matched normal controls in a passive auditory oddball paradigm in order to test the hypothesis that auditory information processing is impaired in schizophrenia, even at the level of primary sensory cortex. Schizophrenic subjects showed a significant reduction in MMN amplitude relative to controls, with a trend toward a greater deficit on the left than the right side. The finding of impaired MMN generation in schizophrenia suggests that information processing is impaired even at the level of auditory cortex and that the pathophysiological processes underlying information processing dysfunction in schizophrenia are widespread throughout the cortex, rather than limited to high-order association cortex such as prefrontal or mesial temporal cortex.

Adult↗
PubMed1993

Interpretation of high-resolution current source density profiles: a simulation of sublaminar contributions to the visual evoked potential.

Current source density (CSD) analysis provides an index of the location, direction, and density of transmembrane currents that arise with synchronous activation of neural tissue and that generate an evoked potential profile in the extracellular medium. In neocortex and other laminated structures, a simplified, one-dimensional CSD analysis can be computed by differentiation of voltages sampled at discrete points in a linear array. One-dimensional CSD analysis is a practical and accurate method for defining both regional activity patterns and neural generators of surface-recorded evoked and event-related potentials. In computing the CSD, common practices of differentiating across spatial grids of 200 microns or more and use of spatial smoothing routines help to reduce noise, but severely limit the spatial resolution available to the analysis. High-resolution CSD procedures (i.e., 3 point differentiation using a spatial grid of 100 microns or less) are more suited to identification of processes within individual cortical laminae or sublaminae, but can magnify the contributions of computational artifacts. Despite the inclusion of independent indices of cellular activity (e.g., multiunit activity), both high- and low-resolution analyses may indicate current source and sink configurations for which there is more than one plausible physiological interpretation. In the present study we examined the resolving capacity and pitfalls of common CSD procedures using simulated ensembles of current dipoles. These were positioned and oriented to model the depolarization of lamina 4C stellate cells and thalamocortical afferents in macaque striate cortex. Empirically, the surface N40 appears in association with a CSD configuration which includes current sinks within the thalamorecipient (stellate) subdivisions of lamina 4C and a large current source extending considerably below 4C. Dipole ensemble contributions to the CSD profile were computed and compared to physiological data from this region. Small asymmetries in activation of model stellate laminae were sufficient to produce substantial open field contributions. However, the best fit with empirical CSD profile was found when the simulation included contributions from thalamocortical axons, along with both open and closed field contributions from dual stellate cell sublaminae. High-resolution CSD profiles were shown to be interpretable when computational artifacts characteristic of closed and open fields were identified using a series of differentiation grids.

Afferent Pathways↗
PubMed1992

Endogenous event-related potentials as indices of dementia in multiple sclerosis patients.

Auditory event-related potentials (ERPs) were recorded in a "double oddball" paradigm requiring an easy and a hard pitch discrimination from multiple sclerosis (MS) patients with and without dementia, and a group of age and sex matched normal subjects. Cognitive function was assessed by a short battery of neuropsychologic (NP) tests, and the two groups of MS patients were selected on the basis of substantial non-overlapping degrees of cognitive deficit in the demented as compared to the non-demented group. The N100, P200 and P300 ERP components were longer in latency in the demented patients, and the N100-P300 interval was prolonged as well, compared to the non-demented patients, whose ERP latencies did not differ from those of the normal subjects. Increased P300 latency was associated with poorer performance on the NP tests, especially those sensitive to impairment of learning and retrieval from memory. The reaction times of both patient groups were prolonged as compared to the controls, whereas the accuracy of the demented patients was significantly poorer than that of the non-demented patients.

Adult↗
PubMed1992

Demonstration of mismatch negativity in the monkey.

In humans, deviant auditory stimuli elicit an event-related potential (ERP) component, termed "mismatch negativity" (MMN), that reflects the operation of a cortical detector of infrequent stimulus change. Epidural auditory ERPs were recorded from 3 cynomolgous monkeys in response to soft and loud clicks. "Oddball" loud or soft stimuli elicited a long-duration frontocentral negativity, peaking at approximately 85 msec, that was superimposed upon cortically generated obligatory ERP components. These data suggest that monkeys might serve as a heuristically valuable system in which to study the neurochemical and neuroanatomical substrates of early context-dependent ERP generation.

Acoustic Stimulation↗
PubMed1992

Flash and pattern-reversal visual evoked potential abnormalities in infants and children with cerebral blindness.

Visual evoked potentials (VEPs) were recorded of 60 infants and children with cerebral blindness, aged between six weeks and 10 years, and compared with age-matched normative data. Every patient had abnormal VEPs. 18 had absent flash and pattern VEPs and 13 had atypical or atypical and asymmetrical flash and pattern VEPs. Of the remaining 29, most had greater abnormality of pattern than of flash VEPs and greater abnormalities over parietal and temporal than occipital areas. Eight patients had normal occipital responses to flash and five others had delayed responses with normal morphology. One had normal occipital responses to pattern stimuli. All of these had abnormal late occipital responses or abnormal responses over the parietal and temporal areas. It is recommended that visual assessments using VEPs employ both flash and pattern stimuli, that pre-occipital as well as occipital recordings be made and that tracings be compared with age-specific normative data.

Blindness↗
PubMed1992

Mismatch detection and the latency of temporal judgements.

Event-related potentials were recorded in two auditory tasks involving the discrimination of pitch or duration of binaurally presented tones. Frequently-presented nontarget tones, when compared to the same tones in a simple reaction time task, elicited two negative peaks, NA1 and NA2, followed by a positive peak, nontarget positivity. Infrequently-presented target tones, when compared to the nontargets, elicited mismatch negativity (MMN), followed by N2 and P3b. The peak latencies of NA1 and NA2 did not differ between the pitch and duration tasks, but the duration of NA1 and the peak latencies of mismatch negativity, N2, and P3b, as well as reaction time, increased in parallel for the duration task. It is proposed that the NA1-nontarget positivity sequence reflects the initiation, maintenance, and termination of an attention-modulated process, which is required for the performance of an auditory discrimination task, and that the MMN-N2-P3b sequence reflects a process elicited by infrequently-presented targets, which is the main determinant of reaction time under these testing conditions.

Adult↗
PubMed1992

The chronometry of attention-modulated processing and automatic mismatch detection.

Event-related potentials were recorded from normal subjects in an auditory selective attention task. Targets were rare longer (170-ms) tones of a designated pitch, embedded in a sequence of 100-ms standard tones. The effects of attention-modulated processing were evident in the event-related potentials elicited by the standards. Those to relevant standards were similar for easy (1000 Hz vs. 2000 Hz) and hard (1000 Hz vs. 1030 Hz) pitch separations, and were more negative frontocentrally than those to irrelevant standards. Difference waveforms (attended minus unattended standards) revealed Nd, a negative deflection that was earlier in latency for the easy task (onset, 120 ms; peak, 250 ms) than for the hard task (onset, 250 ms; peak, 350 ms). The speed of detection of the deviant longer tones was insensitive to the attention-modulated processes indexed by Nd. Median reaction time did not differ between tasks, although there were more misses and false alarms in the hard task (and nearly all of the latter were to the irrelevant longer tones). Neither direction of attention nor task difficulty affected the latency of mismatch negativity, N2, or P3 (as identified in difference waveforms: attended or unattended longer tones minus their respective standards). The data suggest that performance was guided by two independent but converging processes, automatic mismatch detection of the longer tone and attention-modulated processing of pitch, followed by selection of response.

Adult↗