FAST (MAINLY 30-100 HZ) OSCILLATIONS IN THE CAT CEREBELLOTHALAMIC PATHWAY AND THEIR SYNCHRONIZATION WITH CORTICAL POTENTIALS

1. Intracellular recordings from 216 thalamocortical (TC) neurones in the ventrolateral (VL) nucleus of intact-cortex and decorticated cats under ketamine-xylazine anaesthesia revealed spontaneously occurring f ast oscillations (mainly 30-100 Hz) in 86% of investigated cells. The fast depolarizing events consisted of excitatory postsynaptic potentia ls (EPSPs), giving rise to fast prepotentials (FPPs) in 22% of neurone s, which eventually lead to full-blown action potentials. The frequenc y of fast events changed by factors of 2-5 in periods as short as 0.3- 1.0 s. 2. The spontaneous oscillations were similar to responses evoke d in VL relay neurones by stimuli to the afferent cerebellofugal axons in brachium conjunctivum (BC) and mere strikingly reduced or abolishe d after electrolytic lesion of BC axons, 3. The amplitude and duration of fast depolarizing events were significantly reduced during the des cending phase of the inhibitory postsynaptic potentials (IPSPs) in TC cells, related to spontaneous spindles or evoked by local thalamic sti mulation. 4. Averaged field potentials recorded from motor cortex and triggered by EPSPs and/or action potentials of intracellularly recorde d VL cells demonstrated that both spontaneous and BC-evoked fast depol arizations in VL relay neurones were coherent with fast rhythms in cor tical area 4. 5. These results show that, in addition to the thalamic and cortical generation sites of the fast (so-called gamma) oscillatio ns, prethalamic relay stations, such as deep cerebellar nuclei, are ma jor contributors to the induction of fast rhythms which depend on the depolarization of thalamic and cortical neurones and which represent a hallmark of brain activation patterns.