[Neuronal and synaptic mechanisms of cortical inhibition].

Data are presented concerning the latencies, amplitude and durations of IPSPs evoked in neurons of different cortical regions by peripheral and thalamocortical fibre stimulations and intracortical microstimulation in cat. The duration of IPSPs developing due to single afferent stimulus ranged between 20 and 250 ms (60-80 ms as a rule). In response to intracortical microstimulation monosynaptic IPSPs of 5-10 ms duration arose parallel with IPSPs of 20-100 ms duration. Barbiturates and chloralose increased the duration of IPSP up to 300-500 ms. The latencies of 73% of IPSPs evoked in the auditory cortex neurons by thalamocortical fibres stimulation exceed the latencies of monosynaptic EPSPs evoked by the same kind of stimuli not more than by 1.2 ms. Conclusion is made that inhibition developing in neurons of the cortical projection areas in response to afferent volley is a direct one and is produced by cortical inhibitory interneurons. Some cortical neurons were inhibited by a recurrent mechanism. Only 2% of IPSPs developed monosynaptically. The synaptic delay of IPSP evoked by intracortical microstimulation ranged between 0.3-0.4 ms. The length of the inhibitory neuron axons in layer IV of the auditory cortex reached 1.5 mm. The excitation conduction velocity in these axons was calculated to be 1.6-2.8 m/s (2.2 m/s on the average).