Gravity responses of Purkinje cells in the nodulus.

In cats, either decerebrated or under chloralose anaesthesia, Purkinje cells (P-cells) of the cerebellar nodulus have been examined with the animal under static lateral tilt (roll +/- 20 degrees). The cell activity was extracellularly recorded and both "simple" and "complex" spike discharge patterns were studied. In 20 cells out of a population of 198, "simple" spike firing was found to be affected by static roll. Ten cells had an alpha-type response, 8 a beta-type, while only single examples of gamma and delta activations were found. Out of 67 Purkinje cells tested for "complex" spike activation, 5 were found to be sensitive to static roll, 4 with an alpha or beta response and one with a gamma response. The results are to be attributed to pure otolith activation and show that this input is able to modulate P-cell activity in the nodulus through both the mossy fibre and the climbing fibre systems.