Responses evoked in the cerebellar cortex by pontine stimulation.

Abstract

1. Responses in the cat cerebellar cortex evoked by the pontine stimulation were recorded and analysed with microelectrode trackings in the cortex. Silver ball electrodes freely attachable to the cortical surface were also used to complement the microelectrode analysis.2. The analysis of laminar field potentials in the cerebellar cortex elicited by the pontine nucleus stimulation revealed that responses appeared at a short latency of about 1msec are due to pure mossy fibre volleys and, consequently, the nucleus sends direct mossy fibres to the cerebellar cortex.3. The conduction velocity of ponto-cerebellar mossy fibres could be estimated to be of about 30m/sec at maximum and possibly about 10m/sec on the average, distributing rather widely when compared with that of, for instance, lateral reticular nucleus mossy fibres.4. The mossy fibre responses to the pontine nucleus stimulation appeared most markedly in the lateral part of the cerebellar cortex on the contralateral side though sharp discriminative localization of the ponto -cerebellar projection could not be found by stimulating various foci of the nucleus and by recording from different parts of the cortex.5. The pontine nucleus stimulation often produced the climbing fibre responses in the cerebellar cortex at a latency of 5-10msec. Much more powerful responses through climbing fibres were provoked at a latency of 5-8msec by the stimulation of the pontine tegmentum. By the experimental procedure cutting along the midline between the inferior olives on both sides, it was concluded that the climbing fibre responses set up from both the pontine nucleus and the tegmentum were mediated by the inferior olive.6. The presumed climbing fibre responses of a short latency of 3-4msec were encountered, although seldom, by stimulating the border region between the pontine nucleus and the tegmentum, suggesting existence of some direct climbing fibres from the pontine region to the cerebellar cortex.7. The stimulation of the cerebral motor cortex and the analyses of laminar field potentials in the cerebellar cortex ascertained that the stimulation produced the early mossy fibre responses at a latency of about 3msec and the late climbing fibre ones at a latency of about 10msec. They could be mediated by the pontine nucleus and the inferior olive respectively.