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S R Butler

Publications and source records attributed to S R Butler.

At least 37 records · Page 2Linked to original sources
PubMed1992

The effects of lesions of area V4 on the visual abilities of macaques: colour categorization.

Monkeys with V4 lesions and unoperated controls were tested behaviourally for their perception of the colour categories red, green, blue and yellow. As expected, the monkeys with V4 lesions took longer to acquire the colour discriminations. However, the pattern of learning was the same in the two groups of animals. Both the lesioned and the control animals made more errors when the stimuli to be discriminated belonged to the same colour category than when they belonged to different categories and thus showed normal colour categorization. The results suggest that monkeys with V4 lesions perceive the colour spectrum according to the same fundamental perceptual categories as normal monkeys and humans, and thus support the view that, in the colour domain, the four basic perceptual categories are constructed by chromatic mechanisms operating earlier than visual area V4.

Animals↗
PubMed1992

The effects of V4 lesions on the visual abilities of macaques: shape discrimination.

Monkeys with bilateral ablation of cortical visual area V4 were compared with unoperated controls for their ability to relearn postoperatively a series of preoperatively acquired two-choice visual discrimination problems. The animals with V4 lesions were impaired on relearning to discriminate between different shapes, and discrimination between identical shapes presented at different orientations was also impaired. Some of the deficits were consistent with disrupting the input to inferotemporal cortex, but discrimination of a subset of the stimuli is known to be unaffected by inferotemporal cortex lesions and could not be explained in the same way. To clarify the nature of the deficit, and to test the hypothesis that shapes differing in orientation are analyzed in the occipitoparietal processing pathway, animals with V4 lesions were also compared to normals on their ability to acquire a version of the landmark task. The V4 animals performed as well as the control animals on this task. The results suggest that V4 is important for the shape discrimination abilities that survive inferotemporal cortex lesions. The role of V4 in shape analysis is discussed in the light of recent evidence that V4 neurones are modulated by visual attention.

Animals↗
PubMed1987

Cortical generators of the CI component of the pattern-onset visual evoked potential.

Thirteen-channel visual evoked potentials (VEPs) to pattern-onset were recorded with stimuli restricted to individual octants of the peripheral field, to halves and to quadrants of the fovea. The voltage of the CI component was measured in each channel to define its topography for each stimulated sector. The potential fields so obtained were then analysed to find the orientation and location of a dipole that would produce a corresponding pattern of voltages at the scalp. The locations of the computed dipoles are consistent with the hypothesis that CI is generated in striate cortex. The computed locations and orientations are not compatible with alternative arrangements of sources in extrastriate cortex. A significant problem remains. If CI is indeed generated by the striate cortex then the orientation of the dipoles excited by stimulation of the peripheral field indicates that the cortex is surface negative. This leads to the prediction that foveal stimuli will elicit a CI which is negative at posterior electrodes. The experiments reported here confirm that CI is positive with such stimuli, and its source is calculated as a horizontal dipole with its positive pole oriented posterolaterally. Two possible explanations are considered for the reversed polarity of foveal CI: (a) that macropotentials associated with stimulation of the fovea are opposite in polarity from those associated with stimulation of the peripheral field; (b) that the foveal area of the retinotopic map extends into the lateral calcarine fissure with the effect that much of it faces in the reverse direction from the cortex at the pole.

Adolescent↗
PubMed1984

Does amnesia after transection of the fornix in monkeys reflect abnormal sensitivity to proactive interference?

Monkeys in whom the fornix had been transected and controls were tested in two versions of delayed non-matching to sample (DNMS). On DNMS-LSS both of the stimuli for each trial were selected from a large set of junk objects that were already familiar to the subjects. On DNMS-CSN the new stimulus at the retention test of each trial was one which the animals had never encountered before. Memory for the sample was assessed with retention intervals of 10, 70 and 130 s. In DNMS-LSS the lesioned animals were impaired, being more susceptible than controls to increases in the retention interval. However, no impairment in DNMS-CSN was observed. The abnormally fast forgetting by lesioned animals in DNMS-LSS seems therefore to reflect abnormal sensitivity to proactive interference. The results are compared with similar findings from amnesic humans and their implications for theoretical accounts of the effects of hippocampal disruption are discussed.

Amnesia↗
PubMed1984

Hemispheric asymmetry of EEG alpha activation: effects of gender and familial handedness.

Twenty-four male and twenty-four female undergraduates took part in an experiment to investigate the effects of gender and familial handedness on hemispheric activation during numeric and visuospatial thinking. Each gender group was divided into twelve subjects with close left handed relatives and twelve subjects without. All subjects were overtly right handed. EEG alpha activity was recorded from left and right occipital and parietal regions with respect to mastoid references while the subjects performed numeric tasks with eyes open and with eyes closed, a face-recognition and a tactile-discrimination (figural-unification) task. EEG alpha power was quantified during these conditions and during relaxed wakefulness with eyes open and eyes closed. Relative activation, (suppression of alpha activity from rest) of left and right parietal regions during numeric and spatial tasks was found to depend upon gender and familial handedness. Males, not females, tended to switch from left hemisphere activation during face recognition. Irrespective of gender and to some extent of task, a tendency towards greater activation of the right hemisphere was associated with the possession of left handers among close relatives.

Adolescent↗
PubMed1984

Iodination of thyroliberin by use of Iodogen.

In this method of labeling thyroliberin for radioimmunoassay, 1,3,4,6-tetrachloro-3 alpha,6 alpha-diphenylglycoluril (Iodogen) is used as oxidant. By cation-exchange chromatography and in response to antibody, thyroliberin so labeled behaved similarly to that produced by the conventional Chloramine-T method. Major advantages of the Iodogen method are its reliability, simplicity, and higher yield of stable RIA label in its most convenient (diiodinated) form.

Chromatography, Ion Exchange↗
PubMed1981

Amnesia after transection of the fornix in monkeys: long-term memory impaired, short-term memory intact.

Monkeys in whom the fornix had been transected and controls were trained on two versions of delayed non-matching to sample (DNMS). On DNMS-LSS the stimulus pair for each trial was selected from a large set of junk objects so that the animals saw particular stimuli infrequently. On DNMS-RS the same two stimuli were presented repeatedly. Memory for the sample was assessed with retention intervals of 10, 70 and 130 sec spent either in the dark or with levels of illumination designed to promote interference effects. On DNMS-LSS the lesioned animals were impaired, being more susceptible than controls to increases in the retention interval. However, neither group was particularly sensitive to interference. In contrast, on DNMS-RS the lesioned monkeys were unimpaired, both groups showing a marked decrement in performance with increasing retention interval and a high sensitivity to the effects of interference. These data suggest that monkeys possess a short-term memory which is intact after transection of the fornix and a long-term memory which is not.

Animals↗
PubMed1981

Asymmetries of the contingent negative variation (CNV) and its after positive wave (APW) related to differential hemispheric involvement in verbal and non-verbal tasks.

The CNV and the subsequent positive wave (including both the P300 wave and the slow positivity following it) were recorded at left and right frontal and central electrodes during the performance of tasks in which nine right-handed subjects (male and female) had to determine whether S1 and S2 were the same or different. In one task, works had to be matched for meaning while in a second, faces had to be matched for identity. Words elicited CNVs which were more negative over left than right frontal regions. This effect was reversed when the stimuli were faces. Since the CNV is presumed to reflect processes of anticipation rather than stimulus processing, the asymmetry cannot be explained in terms of the lateralisation of neural mechanisms specialised for the analysis of verbal or visuospatial stimuli. Instead the observation is regarded as evidence for mechanisms of lateral activation of a more general nature than would be necessary for the facultative selection of cognitive mode. The amplitude of the CNV relative to baseline was affected by the amplitude of P300 response to S1. This was larger to faces than words in both hemispheres. A small asymmetry in the positive wave following S2 was observed, the amplitude being greater over the right hemisphere for words and over the left for faces. This is interpreted in terms of the subjective probability of the two types of stimulus for a hemisphere ill-equipped to receive them.

Adult↗
PubMed1978

Selective depression of serum growth hormone during maternal deprivation in rat pups.

Maternal deprivation was associated with a decline in immunoreactive growth hormone in the serum of rat pups. Pups that were returned to the mother showed a rapid reversal in this deprivation-induced decrease. The change in growth hormone concentration was not accompanied by changes in the concentrations of prolactin, thyrotropin, or corticosterone in the serum, but were correlated with alteration in the activity of ornithine decarboxylase in the brain. Treatment of neonatal rat pups with cyprohepatadine, a serotonin antagonist that suppresses growth hormone secretion, resulted in a significant decline in both serum growth hormone concentration and brain ornithine decarboxylase activity. These findings suggest that maternal deprivation elicits a specific suppression of growth hormone release which mediates the decrease in ornithine decarboxylase activity. The study is consistent with clinical findings of impaired growth hormone "responsitivity" in human maternal deprivation syndrome.

Animals↗
PubMed1978

Maternal behavior as a regulator of polyamine biosynthesis in brain and heart of the developing rat pup.

Rat pups removed from the mother and placed in a warm incubator for 1 hour or more show a 50 percent reduction in ornithine decarboxylase activity in the brain and heart. The decline is not caused by lack of nutrition. Instead, these studies suggest that active maternal behavior is necessary to maintain normal polyamine metabolism in brain and heart of the pup during development.

Adrenalectomy↗
PubMed1975

The localization of equivalent dipoles of EEG sources by the application of electrical field theory.

A technique is described for finding the position, magnitude and orientation of the equivalent electrical dipole of EEG activity given the pattern of potential differences recorded at the scalp. The technique is based on an iterative computer program implementing equations describing the electrical field of a dipole in a spherical conductor. The computer program was tested in vitro against data obtained from an inert spherical conductor (a bowl containing physiological saline, fitted with recording electrodes and a movable dipole) and an anisotropic conductor (a similarly equipped human skill including a simulated scalp). In both practical models, the computer program accurately located the dipole, the mean differences between observed and computed loci being of the order of 1 cm at widely different locations. This accuracy was maintained in the anisotropic model even though potentials transmitted through the skill were attenuated by 80%. In vivo, the program successfully located the equivalent generator of blink artefacts within the remaining eye of a one-eyed subject and, in a normal subject, localized the dipole of corresponding potentials to a midline inter-ocular position. In further investigation of normal subjects, the distribution of amplitudes at latencies within Wave V of the visual evoked response confirmed the loci of equivalent generators within posterior cerebral regions. The technique was also applied to the alpha rhythm indicating a posterior locus compatible with the view that alpha rhythm is generated chiefly by posterior cerebral cortex. Factors affecting the accuracy of the technique and the limitations of one-dipole models are discussed.

Action Potentials↗