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G R Gates

Publications and source records attributed to G R Gates.

At least 19 recordsLinked to original sources
PubMed1993

Cognitive load as a determinant of the dimensionality of the electroencephalogram: a replication study.

A sequel study to that reported by Gregson, Britton, Campbell and Gates (1990), partially replicating and extending findings which relate estimates of the dimensionality of the EEG to the complexity of task load in a visual scanning task, is described. The correlation dimensionality D2 of the attractor was computed using a variant of the Grassberger-Procaccia algorithm, and was shown to change in the expected direction, increasing as the task became more complicated. The effects are slight but consistent, and may be attenuated by nonstationarity over time, and by idiosyncratic factors. The results are numerically and qualitatively compatible with other recent reported studies, and support an interpretation linking brain dynamics to implied cognitive processes.

Adult↗
PubMed1990

Effects of venom of the olive sea snake, Aipysurus laevis, on the behaviour and ventilation of three species of prey fish.

Venom from the olive sea snake, Aipysurus laevis, was injected into three species of prey fish, Chromis nitida, Dascyllus aruanus and Istiblennius meleagris. Their behaviour and ventilatory patterns were observed for 48 hr. Six progressive stages of envenomation, involving impairment of the locomotory and ventilatory systems, were identified. There were significant interspecific differences in time taken to reach various stages. In nature, the action of the venom not only would facilitate subduing the prey, but recovering it if it escaped.

Animals↗
PubMed1990

Comparisons of the nonlinear dynamics of electroencephalograms under various task loading conditions: a preliminary report.

Comparison of the characteristics of electroencephalogram (EEG) records treated as realizations from a nonlinear process were compared under four different conditions: eyes shut resting, and three silent observation instructions to predict the patterns of randomly generated lights which illuminated every 10 seconds. The correlation dimension of the EEG was calculated by a method involving finding the correlation integral in m-dimensional space, and found to show some variations within time series. The degree and directions of changes in the dimensionality of the process varied between observers and did not clearly confirm some earlier reported findings, but it is demonstrable that the measures of nonlinear brain dynamics can be correlated with psychological variables. Reasons for this are discussed.

Adult↗
PubMed1988

Assessment of a microcomputer-based version of the Austin maze.

The Austin (or Milner) Maze consists of a 10 x 10 array of electrical contacts through which the subject must discover a hidden pathway by touching successive points in the matrix. Trials needed to reach 3 consecutive errorless performances, errors committed, and time taken to reach this criterion are commonly regarded as indicators of frontal lobe function. This study evaluated the equivalence of a computer-based version of this task. Thirty-two male computer science students completed both forms of the maze in counterbalanced order, separated by an interval of 4 weeks. In a 2-year follow-up, 25 remaining subjects completed the tasks in reverse order, again separated by a 4-week interval. Correlational data and analysis of variance supported the proposition that the computer-based version could act as a substitute for the more tediously administered traditional form. Although the sample characteristics may limit the generalizability of this conclusion, the application and development of the software by independent investigators may facilitate its clinical application and allow a more efficient resolution of relevant theoretical issues.

Adolescent↗
PubMed1984

Responses of neurons in inferior colliculus to variations in sound-source azimuth.

This study aimed to classify the responses of single units in the auditory midbrain to acoustic stimuli presented in the free field in order to characterize those units likely to have a role in sound localization in the horizontal plane. The responses of 131 single units in the inferior colliculus of the cat and the brush-tailed possum were studied using tone and noise-burst stimuli presented from a speaker capable of movement at any point along a plane 10 degrees above the horizontal plane. Speaker positions along this plane are referred to as speaker azimuths; those on the same side as the recorded inferior colliculus as ipsilateral, and on the opposite side as contralateral, azimuths. For each unit, spike counts were measured as a function of azimuth either at the best frequency (BF) or using noise bursts. These functions are referred to as azimuth functions and were usually measured for at least two intensities, between 10 and 70 dB above threshold. The recording sites of most units were identified histologically with the aid of microlesions and were related to the major subdivisions of the inferior colliculus: the central nucleus (ICC), the lateral part of the external nucleus (ICX), and the rostroventral process (R-ICX). Two units were located in the pericentral nucleus and two in the dorsal nucleus of the lateral lemniscus. Two major classes of neuron were identified: omnidirectional and directionally sensitive. Omnidirectional units exhibited azimuth functions that were either flat or that declined gradually at progressively ipsilateral azimuths. For the latter units, discharge rates at all points monotonically increased with stimulus intensity. There was no indication, for either type of omnidirectional unit, of significant binaural interaction. A good correlation was found between the summed proportions of excitatory-excitatory (EE) and monaural (EO) units observed in dichotic studies (46-55%) and the proportion of omnidirectional units in the present study (47%). A subgroup of directionally sensitive units (36% of the total) displayed azimuth functions for which the azimuthal position of the discharge border or peak firing azimuth remained essentially unaltered over a range of stimulus intensities. These azimuth-selective units are likely to have a role in the detection of the location of stimuli in the horizontal plane and appear to include units that would be considered excitatory-inhibitory (EI) or delay sensitive in dichotic studies. The azimuths over which directionally sensitive units showed their marked directional effects were influenced by the position of the contralateral pinna.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1983

Connections of the auditory cortex of the brush-tailed possum, Trichosurus vulpecula.

The afferent connections of the auditory cortex of the acallosal marsupial Trichosurus vulpecula have been studied using the retrograde transport of horseradish peroxidase. The enzyme was applied by electrophoresis from a micropipette previously used to define physiologically the organization of the auditory cortex. Three major (lateral, dorsomedial and ventromedial) sectors of the medial geniculate contribute axons to the ipsilateral auditory cortex; the connections from at least the lateral sector are topographically arranged. Axons reach the auditory field from the contralateral cortex by way of the anterior commissure and fasciculus aberrans.

Afferent Pathways↗
PubMed1982

Auditory cortex in the marsupial possum Trichosurus vulpecula.

A microelectrode mapping survey was made of the auditory cortex of the acallosal marsupial possum Trichosurus vulpecula. Single unit and unit cluster responses, as well as evoked potentials, were obtained from 64 tangential, cortical penetrations. Pontamine sky-blue marking of successful tracks aided in later reconstruction of tracks and identification of recording locations. Only one auditory field was identified. The 98 units sampled in this field covered a wide range of best frequencies from 330 Hz to 39 kHz with the most sensitive units (thresholds of best frequency of less than 10 dB SPL) being in the 17-19 kHz range. An orderly representation of cochlear place was found in the cortex with high frequencies located dorsally and low frequencies more ventrally. This orientation of frequencies is unlike that seen in other mammals.

Animals↗
PubMed1982

Representation of the two ears in the auditory cortex: a re-examination.

The current theory of the representation of the two ears in the auditory cortex, namely that both ears are represented in each cerebral cortex and that the contralateral ear receives a stronger representation, is critically reviewed in the light of more recent evidence. On the basis of neurophysiological and behavioral studies in animals and a variety of clinical studies, it is concluded that the notion of contralateral ear dominance in the cortex requires revision, and it is proposed that the contralateral sound field, rather than contralateral ear as such, is represented in each cortex. It is suggested that the contralateral and ipsilateral inputs to the auditory cortex do not so much differ in their relative strengths, but in the qualitative nature of the information they transmit.

Animals↗
PubMed1978

The auditory midbrain of a marsupial: the brush-tailed possum (Trichosurus vulpecula).

A microelectrode survey was made of the midbrain auditory nuclei of the brushtailed possum (Trichosurus vulpecula), a common Australian marsupial. Information was sought on the tuning characteristics of individual neurones, tonotopic organization and mechanisms of sound localization. It was felt that such information would be of use in future studies of the development and evolution of mammalian hearing. Twelve possums were anaesthetized with ketamine and chloralose-urethane, and recordings were made of extracellular unit discharges in the inferior colliculus during monaural and binaural tonal stimulation. The inferior colliculus of the possum consists of a central nucleus - a darkly stained, densely packed group of cells - flanked laterally by an external nucleus with a lower density of paler cells. Tonotopic organization was demonstrated by discretelytuned elements in the central nucleus, but was not observed in the external nucleus. In the latter region broad and irregular tuning was commonly seen. Most units in both divisions were influenced by binaural stimuli, with patterns of binaural interaction similar to those observed in the cat inferior colliculus. Cells influenced by changes in the interaural time and intensity difference were commonly observed, but only a subclass of these were suited in sensitivity for sound localization. In general, the midbrain auditory system of the possum was similar in unit discharge characteristics and organization to those of the eutherian mammals commonly studied.

Acoustic Stimulation↗
PubMed1977

Offset-induced audiogenic seizures.

A relatively stereotyped seizure reaction can be triggered by the "offset" of an intense bell sound in C57BL/6J mice. Susceptibility to this offset-induced audiogenic seizure was found to depend upon the age of the animals tested (higher in older mice) and the duration of the noise exposure (more effective with longer exposure).

Acoustic Stimulation↗
PubMed1976

Effect of morphine and naloxone on priming-induced audiogenic seizures in BALB/c mice.

1 Morphine (1-200 mg/kg s.c.) reduced the incidence and prolonged the latency of priming-induced audiogenic siezures in a dose-dependent manner. 2 This effect was reversed by naloxone (1 and 2 mg/kg) although naloxone was itself inactive. 3 This priming-induces seizure model may be useful in the study of tolerance and physical dependence.

Acoustic Stimulation↗