[Discharge mechanism of pigeon optic tectum neurons in an in vitro preparation].

The pattern of discharge of neurones of the pigeon's optic tectum to directly injected depolarizing current was investigated in in vitro slice preparation. Three patterns of discharge were found: some neurones (types I and II) give a tonic response: type I-neurones exhibited a repetitive firing whereas type II-neurones showed grouped discharges (doublets or triplets). Type III-neurones displayed a phasic response formed by a few action potentials of decreasing amplitude, triggered at the onset of the current pulse. Each pattern of response was associated with a specific shape of action potential.