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B D Burns

Publications and source records attributed to B D Burns.

44 records · Page 3Linked to original sources
PubMed1968

Factors affecting the conductivity of pathways in the cerebral cortex.

1. We have investigated the conductivity of neural pathways in slabs of unanaesthetized, isolated, cerebral cortex, cut from the isolated forebrains of twenty-five cats.2. Neurones within the isolated area were indirectly excited, either by a small electrode thrust into the subcortical white matter, or by remote stimulation of the pial surface. Sometimes a small electrode was employed for intracortical stimulation.3. The response of single neurones to these stimuli was recorded with extracellular micropipettes. Submaximal stimuli produced a stochastic response which was measured from the post-stimulus histogram (PSH) and provided an estimate of the probability of discharge at various times after the stimulus.4. The PSH often displayed several discrete humps of different latencies, indicating several pathways between stimulated and recording point. Conductivity measurements were usually restricted to the pathway of shortest latency.5. The conductivity of a pathway was defined as C = xy/x, averaged over 1 or 2 min, wherex = frequency of afferent test volleys,xy = frequency of response: i.e. of those action potentials contained within a well-defined hump of the PSH,(y = frequency of all discharges of the recorded neurone).6. The progress of conductivity was tested with some constant form of cortical stimulation, repeated at regular intervals of 1-5 sec. Reliable results were obtained for twenty-six pathways subjected to thirty-eight experiments.7. Temporary alteration of x, y or xy (conditioning with Deltax, Deltay or Deltaxy), for a period of 6-25 min, often caused a subsequent change in the conductivity (DeltaC) of a pathway which sometimes attenuated with a time constant of about 10 min, but which could persist without detectable attenuation for 20-30 min.8. Conditioning periods less than 6 min rarely produced changes in conductivity; alterations of conductivity were more likely to be caused by conditioning periods longer than 17 min, than by periods of 6-16 min.9. Changes in conductivity were usually correlatednegatively with temporary changes in xy,negatively with temporary changes in x,positively with temporary changes in y.10. Nineteen of twenty-six pathways tested showed properties consistent with the formula [Formula: see text], whereG(1) lies between -1.0 and -0.16, with mean value -0.50,G(2) lies between 0 and 0.42, with mean value +0.12,G(3) lies between -0.61 and 0 with mean value -0.38,K is a coefficient which is usually different for each experiment. Four out of twenty-six pathways so tested provided results which did not fit this formula; three out of twenty-six pathways did not give adequate information.

Animals↗
PubMed1968

Cortical conditions for fused binocular vision.

1. The behaviour of twenty-six single neurones has been studied in the visual cerebral cortex of the cat's neurologically isolated and unanaesthetized forebrain. In a separate series of experiments binocular vision was investigated in five human subjects.2. Units in the cat's brain were excited by two straight, light-dark edges, projected independently, one upon each retina; these edges were given identical, artificial saccadic movements. The average response of neurones was measured from the post-stimulus-histogram (P.S.H.), which provided the probability of unit-discharge at various times after the pattern movement.3. A district within either eye-field could usually be found, such that the saccadic movements of edges passing through this part of the field, caused maximal responses; this part of each field is termed the ;representative district'. The most exciting orientations of the stimulating patterns were similar for both eyes. A cell excited by similarly oriented patterns, ;aligned' through the representative districts for each eye, exhibited dramatic spatial summation. Mutual inhibition between retinal inputs was never seen.4. The response of cortical neurones to such aligned patterns was always greater than that when one pattern was misaligned by displacement in either direction from its representative district.5. When the pattern in one eye was inverted, the cell gave less response to aligned than to misaligned patterns.6. Human subjects, viewing similar inverted patterns through a mirror stereoscope, could only obtain stable fusion with a 5 min arc misalignment of the optic axes.7. In other experiments, one eye of each subject was presented with a white rectangular bar upon a black background, while the other eye was excited by a similar black bar upon a white background. Stable fusion was reported, providing percepts of either one single low contrast bar or two neighbouring bars of high contrast. There was a range of relative pattern positions over which alignment of the eyes sought the former percept in preference to the high contrast pattern.8. These results are consistent with the hypothesis that the mammalian visual system maintains binocular fusion by continuously hunting those eye directions that provide the greatest local cortical responses to saccadic movements, restricted to the smallest possible areas of the visual cortex.

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