Thalamic rhythms in cat during quiet wakefulness and immobility.

In this study we tried to get some more information on the cortical 'mu' rhythms in normal cat and their thalamic pacemaker. Mu (14 c/sec) activity develops when the animal is motionless, in a state of 'quiet waking.' It is distinct from other sensorimotor rhythms, with distinct cortical distributions, distinct frequencies and appearing under different behavioural and environmental conditions. The cortical mu focus was shown to be centred within a restricted part of area SI, in the forepaw and wrist projection field. The related thalamic focus was localized in a small zone of the VP nucleus that also corresponded to the hand and wrist projection area. A coherence study confirmed the close relationship between the two foci, thalamic and cortical. After unilateral electrolytic destruction of the thalamic area, a small mu activity persisted, on the ipsilateral cortex, originating from the opposite side. After bilateral lesion of the VP foci, no mu activity could ever be recorded on either side, while the other sensorimotor rhythms were left intact.