Field potentials produced by the parallel fibre stimulation in the cerebellar cortex.

Abstract

1. Field potentials in the cerebellar cortex generated by parallel fibre stimulation were recorded and analysed with microelectrode trackings. To comprehend the sink-source relation of PSP currents in the cortical neurones, special attention was paid to compare the potentials in the cortex with different surface resistance covering over it. The surface resistance change was achieved by stopping the flow of Ringer solution over the cortex and drying the cortical surface for a few minutes.2. Parallel fibre spike potentials and slow negative potentials in the beam of excited parallel fibres, strangely small in the cortex under Ringer solution oragar (wet state), became much larger by drying the cortex (dry state). Furthermore slow positive potentials recorded under and beside the beam in the wet state were reduced in size, markedly, and of ten reversed to slow negative potentials in the dry state. These changes were reversible and repeatable.3. The changes had been expected from the assumption that the slow positive potential under and beside the beam of excited parallel fibres should be largelydue to EPSP currents generated directly by the excited parallel fibres in superficial dendrites of Purkinje cells and probably of interneurones (basket, stellate and Golgi cells). Relations of sink and source due to the PSP currents in the neuronal elements in the cortex and interpretations of the field potentials thereby were discussed with the aid of a simplified circuit diagram.4. In the cerebellar cortex of the dry state, the excited parallel fibres could be detected much more precisely and extensively in depth of the molecular layer than in the wet cortex. Thus it was possible to compare the conduction velocities of deep and superficial parallel fibres. The results were discussed in connection with anatomical findings about parallel fibres in the cerebellar cortex.