Statistische Eigenschaften der Neuronaktivität im ascendierenden visuellen System

Zusammenfassung/Summary1.The activity of single nerve cells in the visual system of cats (curarized or encéphale isolé preparations) was investigated. Records were sampled from units in the optic tract, the lateral geniculate body, and the striate cortex. The non-sequential interval distribution and the mean discharge rate of spontaneous activity and of that during stimulation of the retina with continuous light was analysed over long periods. An interval analyser was used.2.The mean discharge rate of spontaneous activity is highest in the optic tract and decreases significantly towards the visual cortex. The mean values are: 35.5 per sec in the optic tract (13 units), 14.0 per sec in the lateral geniculate (24 units) and 5.7 per sec in the visual cortex (145 units).3.The variety of possible interval distributions was reduced to 3 characteristic types. As belonging to type I those distributions were classified which showed exponential form. Only the frequency of short intervals was reduced, so that the distribution had a peak at 8–10 msec. The joint interval histogram showed that the successive single discharges were independent from each other. From this it could be assumed that spike generation in these cells occurs according to a Poisson-type process. The initial dead time can be explained by the excitability cycle of the units or by recurrent or collateral synaptic interactions. — Bi- or trimodal interval distributions were labelled as type II. The different peaks were attributed to different activity determining factors. A third group (type III) is found by those distributions which show transitional characteristics between the other two. Only one peak of short intervals is distinguishable and flanked by a wide and unsystematic distribution of longer intervals.4.In the optic tract mainly type I, in the lateral geniculate mainly type II and in the visual cortex almost always type III distributions were found.5.The interval distribution from each unit in darkness remained essentially the same under continuous illumination, even though the average discharge rate of optic nerve fibers was considerably changed by stimulation. In cortical cells only little changes of discharge rate were induced by continuous illumination of the retina.