Determination of the transfer ratio of cat's geniculate neurons through quasi-intracellular recordings and the relation with the level of alertness
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Quasi-intracellular recordings from neurons in the lateral geniculate nucleus of the cat have been made. From these recordings the excitatory input of these neurons could be determined.
The experiments suggest, that the excitatory input of a geniculate neuron is originating from one single optic tract fibre.
The experiments were performed on non-anaesthetized paralyzed cats which showed different levels of alertness such as sleep, drowsiness and wakefulness. During these different levels the input of the geniculate neurons remains constant but the output varies considerable. Thetransfer ratio, defined as the ratio between the spike frequency (output) and the EPSP frequency (input) of a neuron is high (0.9–1.0) during wakefulness and low (0.4–0.5) during sleep with intermediate values at intermediate states.
The control of the transfer ratio is caused bychanging the amplitude of the EPSPs. During wakefulness nearly all EPSPs are large enough to reach the threshold; duringsleep the EPSPs are smaller than the threshold potential. A mechanism working like presynaptic inhibition might be responsible for the change of the EPSP amplitude.
The control of the flow of information to the visual cortex according to the level of alertness is probably one of the functions of the lateral geniculate nucleus.
Key wordsLateral geniculate nucleus Quasi-intracellular recording Transfer ratio Level of alertness EPSP amplitude
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