Die Informationsübertragung im afferenten visuellen system

SummaryThe activity of single units of the optic tract, lateral geniculate body, optic radiations and striate cortex was recorded in cats (encephale isolé preparations) by means of microelectrodes. The optic nerves or radiations were stimulated with electrical shocks (0.3–1400 per sec). In other experiments binocular light stimuli were used.1.When 50–200 msec trains of stimuli were applied, the maximal impulse rate transmitted by optic nerve or radiation fibers was found to be between 350 and 1100 per sec. Above these values fiber discharges followed successive stimuli in 1∶2 or 1∶3 ratios. The transmission through a geniculate or cortical synapse reduced this maximal impulse rate to 30–50 percent of that of the fibers.2.Presynaptic stimulation frequencies above 100–400 per sec were observed to block impulse transmission through the synaptic stations about 10–120 msec after onset of electrical stimulation. Within a small range of stimulation frequency, just below that eliciting blocking, 1∶2, 1∶3 or 1∶4 transmission occured through cortical or geniculate synapses.3.The maximal impulse frequency transmitted through a neuronal chain decreased as the number of neurons in the chain increased.4.The information capacity of one afferent channel can be estimated to be 20–120 bit/sec. The information given by a neuronal impulse is not comparable to that of a binary digital unit pulse. Neuronal information can be understood as result of the operation of a system having a pulse frequency modulation code with considerable statistical fluctuation. These considerations do not take in account the added margin of information which is made possible by the spatial and temporal relationships of activity between different channels.5.The information capacity af the afferent visual system is limited by the frequency properties of synaptic transmission and not by those of afferent fibers.6.In single cortical units that could be activated by electrical stimulation of either optic nerve, the statistical conditions for “both” — or “either-or” — responses could be demonstrated using bilateral optic nerve stimuli separated by different intervals.7.With binocular light stimuli summation of excitatory and inhibitory processes were found at the level of cortical neurons.8.Some neurons in the visual cortex had the capacity of “measuring” the time difference between two light stimuli, one applied to the ipsilateral eye and the other to the contralateral one.9.The results are compared with the findings of Kuepfmuellee and Jenik regarding transmission and processing of information by an electronic model neuron.