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Biomedical subjects

G Barrett

Publications and source records attributed to G Barrett.

90 records · Page 5Linked to original sources
PubMed1980

Cortical potentials following voluntary and passive finger movements.

In order to clarify the time relationship and functional significance of post-motion components of the movement-related cortical potential, averaged cortical potentials associated with voluntary and passive movements were compared mainly with respect to their scalp topography. Fourteen channels of scalp EEG, together with EOG and EMG, were simultaneously recorded in 7 healthy adult subjects while the subject was either repeating a self-paced brisk extension of a middle finger or while the experimenter was extending the middle finger by pulling up a string attached to the finger. Potentials associated with the movement were averaged opisthochronically in relation to a trigger actuated by the finger interrupting a beam of light. Seven peaks were identified in the passive movement-evoked potential. A sharp negative peak occurred over the contralateral precentral region 16 msec after the photometer trigger (N15). Another negative component (N70) formed a composite of double-peaked negativity with N15 and was seen over the frontal region with a contralateral predominance. A positive peak (P65) was recorded over the contralateral parietal region with a similar latency to N70. This N70/P65 complex has some marked similarities in terms of wave form and spatial relationship with the N + 50/P + 90 complex recorded with voluntary movement of the same finger. It is postulated that these components may be the projected potential fields from a dipole source within the central sulcus and may represent a kinesthetic feedback from the muscle afferents.

Adult↗
PubMed1980

Components of the movement-related cortical potential and their scalp topography.

In order to clarify the significance of the various components of the movement-related cortical potentials, scalp-recorded potential changes associated with voluntary, self-paced middle finger flexion and extension were studied by an opisthochronic averaging program in 14 normal right-handed subjects. Topographical study, based on 14 simultaneously recorded and averaged EEG channels, enabled us to identify at least 8 components; 4 pre-motion and 4 post-motion. The pre-motion components are the Beretischaftspotential (BP) (a symmetric early negative shift), NS'(-500 to -90) (a negative slope maximal over the contralateral precentral region and culminating in N-90 ipsilaterally), P-50 (corresponding to the pre-motion positivity, PMP), and N-10 (probably corresponding to the motor potential, MP). The post-motion components include N+50 (a sharp negative post-motion activity over the contralateral frontal region), P+90, N+160 (presumably representing sensory functions) and P+300 (a large positivity maximal over the contralateral precentral region but widely distributed).

Adolescent↗
PubMed1980

The incidence and nature of visual pathway involvement in Friedreich's ataxia. A clinical and visual evoked potential study of 22 patients.

Pattern-reversal visual evoked potentials (VEP) were recorded from 22 patients (mean age 33.7 years) with Friedreich's ataxia, 15 of whom also had a detailed neuro-ophthalmological assessment prior to the VEP examination. None had noted symptomatic visual impairment. Eleven of the 15 (73 per cent) examined clinically had one or more neuro-ophthalmic abnormality and 14/22 (64 per cent) had an abnormal VEP study which was always binocular and comprised absent responses, or most commonly, increased P100 component latencies. The maximum P100 latency was 143 ms and the group mean was 118 ms. The P100 amplitude was also generally reduced particularly in those patients with latencies less than 115 ms (upper limit of normal), while in those with latencies above the normal range there was a significant inverse correlation between the P100 amplitude and latency. The waveform, temporal dispersion and interocular differences were normal in almost all patients with identifiable responses, including those with prolonged VEP latencies. Electroretinograms recorded from three selected patients were either normal or minimally abnormal and suggested secondary rather than primary retinal involvement. The only VEP parameter to correlate with either the duration of the generalized disease or the visual acuity was the P100 amplitude. A good correlation was found between the VEP and the clinical neuro-ophthalmic findings. Temporal pallor of the optic disc was most often associated with an abnormal VEP result and impaired visual acuity or colour vision were uncommon in the absence of VEP abnormalities. The VEP changes and those obtained from 24 age- and acuity-matched cases of demyelinating optic neuritis are contrasted and the probable pathophysiology is discussed. Two main conclusions emerge from this study. First, there is a high incidence of asymptomatic visual pathway involvement in Friedreich's ataxia which can be demonstrated by both clinical and VEP examination. Secondly, the VEP changes in Friedreich's ataxia differ from those found in typical demyelinating optic neuropathy and are consistent with progressive nerve fibre loss and associated slowing of conduction, indicating that the visual pathway is affected by the same widespread process of axonal degeneration found throughout the nervous system.

Adult↗
PubMed1980

Differences in proliferation of primary cultures of vascular smooth muscle cells taken from male and female rats.

Vascular smooth muscle cells from thoracic aortas of 10-week-old rats were cultured on different substrates. Cells taken from male animals proliferated more quickly than those taken from females; this was true for all substrates, but the difference was accentuated by growth on collagen membranes. The relationship between these results and the sex-linked incidence of hypertension and atherosclerosis is discussed and a model for future studies proposed.

Animals↗
PubMed1978

The effect of experimental 'scotomata' on the ipsilateral and contralateral responses to pattern-reversal in one half-field.

The averaged cortical responses to a reversing checkerboard pattern presented monocularly in either left or right visual half-fields have been recorded from the occipital scalp using a transverse chain of widely spaced electrodes referred to a common mid-frontal electrode. The half-field responses showed a consistent asymmetry, the dominant feature of which was a positive wave (P100) that was widespread on the ipsilateral scalp and maximally recorded from the midline and ipsilateral electrodes. This formed part of the triphasic negative-positive-negative complex, the other two components being an N75 and an N145. On the contralateral scalp it was generally possible to record a triphasic complex of opposite polarity, but this was usually of smaller amplitude and its components (P75, N105, P135) showed greater variation in latency and morphology than the ipsilateral components. With progressive occlusion of the pattern stimulus from the central regions of the visual half-field, the ipsilateral positive wave (P100) was increasingly attenuated, while components of the contralateral complex were relatively unaffected, or, in some cases, enhanced. By contrast, reducing the radius of the stimulated area had relatively little effect on the ipsilateral P100, while the contralaterally recorded response was attenuated. These differential effects on the half-field response components are discussed in relation to the anatomy of the central and paracentral cortical representation of the visual field. The implications for the interpretation of evoked potential recordings in patients with field defects are considered.

Adolescent↗
PubMed1978

Effects of erotic stimuli on male aggression toward females.

In order to examine the effects of highly erotic films on aggression toward females, male subjects were first either angered or treated in a neutral manner by a male or female confederate. After viewing a highly erotic film or a neutral film, subjects were given an opportunity to both aggress against and reward the confederate. Erotic films were found to increase aggression overall, but there was no indication of differential aggression as a function of sex of target. Results for physiological arousal, however, suggested that aggression was possibly inhibited for subjects exposed to an erotic film and paired with a female. Various suggestions for future lines of research based upon the notion of inhibition are offered, as well as suggestions regarding the sexual arousal and aggression relationship.

Aggression↗
PubMed1978

Trait ambiguity and impression formation sufficiency tests of the meaning change model.

Two experiments tested the meaning change model's prediction for the effect of trait ambiguity on impression formation. Participants were all college students, 43 males and 29 females in Experiment 1 and 20 males and 28 females in Experiment 2. Standard impression formation tasks were used. The results revealed greater context effects for high as compared to low ambiguous traits and greater influence on description ratings for low as compared to high ambigous traits, supporting the meaning change model. When ratings of descriptions and of individual traits were clearly separated, context effects were observed only for low ambiguous traits. The implications of this finding for meaning change and information integration models of impression formation are discussed

Adult↗
PubMed1977

The asymmetrical visual evoked potential to pattern reversal in one half field and its significance for the analysis of visual field defects.

The consistency of the major positive component (P100) of the full-field pattern-reversal response provides a clinically valuable and objective means of detecting visual field defects. Its normally symmetrical distribution about the midline of the occipital scalp results from the summation of two highly asymmetric half-field responses, each of which shows the positive component well lateralised with a widespread distribution on the ipsilateral side. Stimulation of each eye in patients with bitemporal and homonymous hemianopias results in two characteristic patterns of asymmetry, named 'crossed' and 'uncrossed' respectively, in which the major positivity is consistently recorded on the side ipsilateral to the preserved half field. Recordings from a patient after occipital lobectomy confirm the authors' previous suggestion that although the major positive component is recorded from the ipsilateral scalp the typical asymmetric half-field response is generated in the contralateral hemisphere.

Action Potentials↗
PubMed1976

Time line analysis of dental restorative procedures related to dynamic instrument location.

The detailed timing and recording of the sequence of tasks for dental restorative procedures was used to evaluate the effects of the location of the hand-piece and three-way syringe on the dental team performance. Sixty-four audiovisual tapes of ten dental teams, performing complete, actual restorative procedures, were made in two dental operatories that differed only in the location of the dentist's instrument cabinet. Total treatment sessions were divided into four major divisions and expressed as a percentage of the total time: patient preparation, 14%; tooth preparation, 32%; tooth restoration, 50%; and patient release, 4%. Tooth preparation and restoration took longer with the instruments in the 8-o'clock location than with them in the 12-o'clock location. When the teams were reversed, that is, changed to the other operatory, there was an increase in tooth preparation and restoration time. Instrument transfer and use, especially for the three-way syringe, tended to take longer for the 8-o'clock location. In contrast, the dentist's idle time tended to increase working with the 12-o'clock instrument location because of differences in work loads. Time line analysis provided a means of evaluating the impact of instrument location as well as an approach to assessing individual team performance.

Dental Assistants↗
PubMed1975

Comparison of the effects of two handpiece locations on dental team performance.

Using audiovisual tapes of 150 actual dental treatment sessions, five dental teams working with handpieces positioned in the 8-o'clock location were compared with five dental teams working with hand pieces positioned in the 12-o'clock location. Criteria used for analysis were frequency and duration of instrument transfer, critical incidents that interfered with instrument movements, and subjective responses of the dental team members. The data showed that the handpiece transfers were faster and more frequent in the 12-o'clock location where they were done via the assistant. However, the reverse was true for transfers of the three-way syringe. Most critical incidents occurred with equal frequency and were common to both rooms, but some were related to instrument location. The subjective responses indicated that the assistant working with the 12-o'clock instrument location had many more tasks and must be more highly trained.

Dental Assistants↗
PubMedDate not supplied

Event-related potential (ERP) correlates of performance of intelligence tests.

Any relationship between measures of cognitive function and brain electrical activity would be of considerable importance in the objective assessment of patients suspected of intellectual impairment. In healthy subjects, we have found a strong correlation between the event-related potentials evoked by a digit probe identification task and scores on intelligence tests (WAIS). Responses from subjects with higher performance on IQ tests are significantly 'more negative' than those from subjects with lower IQ. The characteristics of these IQ-dependent electrophysiological features suggest that they may be related to the subject's ability to focus on a task.

Adult↗
PubMedDate not supplied

Wave form variations in auditory event-related potentials evoked by a memory-scanning task and their relationship with tests of intellectual function.

The inter-subject wave form variability of auditory event-related potentials (ERPs) evoked by digit probe identification in a memory-scanning task (Sternberg paradigm) and the effects of reaction time (RT) and task difficulty were studied in 26 healthy subjects. The response wave forms were compared with the performance of psychological tests of intelligence and memory. ERPs to 1-digit sets consisted of a sequence of waves identified as P100, N170, P250, N290, P400, P560 and N640. The major inter-subject difference in the response wave form was either the presence or absence of the late parietal positive wave P560. This wave occurred significantly more often in responses associated with larger memory sets and slow RT, suggesting that its presence reflects subjective difficulty in performing a task. With increasing set size, the P400 showed variable effects in different subjects, ranging from relative preservation of amplitude, through attenuation, to replacement or overlap by a broad surface-negative wave. This predominantly 'negative-going' effect of increasing task difficulty on the P400 was significantly correlated with scores of psychological tests; the greater the amplitude difference between the responses to easy and more difficult tasks, the better the scores, suggesting that these wave form changes reflect a more effective cognitive processing mechanism.

Acoustic Stimulation↗