[Changes in the postsynaptic and spike potentials of a cortical neuron during habituation]

Changes in the spikes, EPSPs and IPSPs of neurons in the general cortex of the turtle forebrain were studied intracellularly during irregular repetition of light flasches. The amplitudes of these intracellular potentials decreased during habituation without any change in the resting potential. Their dependence on the membrane potential level changed. The short-latent evoked spikes decreased more considerably as compared with the spontaneous spikes and the spikes after IPSP. Probably, the decrease of the spontaneous spike and the spike after the IPSP reflects a nonspecific decrease in the excitability of a neuron because of the long intracellular recording so far as during extracellularly recording only the short-latent evoked spike decreased with habituation. The decrease of the short-latent evoked spike reflects neuronal habituation. A disinhibition of spikes and PSPs was observed. A suggestion is advanced that the pattern of synapses activated by a definite repetitive stimulus evokes a transitory change of the electrogenic properties of the neuronal membrane.