Recruiting responses following splitting of the brain-stem in cats

1. 1. In chronic cat preparations the mean threshold for evoking recruiting responses in wakefulness was 280 ± 14 μA, in synchronous sleep 231 ± 14.5 μA, and during desynchronized sleep 350 ± 20 μA. A further increase in threshold was constantly found during rapid eye movement episodes in which recruiting was strongly reduced or abolished, even with stimulation well above threshold. These changes were all significant as revealed by the t test. 2. 2. Both in chronic and acute encéphale isolé preparations a significant increase of threshold (61% ± 6 higher than the control) of recruiting responses was observed after pontine splitting. These changes were seen also in intrathalamic recruiting responses either in intact or in acutely decorticated encéphale isolé cats. 3. 3. The curves expressing the recruiting effect at different intensities of stimulation were modified significantly by pontine splitting. Similar changes were found in intrathalamic recruiting responses both in intact encéphale isolé preparations and in acutely decorticated cats. 4. 4. No variations either in threshold or in amplitude of recruiting responses were found after cerebellar midline section or after splitting the bulb or midbrain in chronic preparations. 5. 5. The results reported after pontine splitting are discussed and attributed to suppression of a tonic stream of impulses coming from the lower brain-stem and facilitating the thalamic synchronizing mechanisms involved in thalamo-cortical control.