The time distribution of linked spike activity of rabbit sensorimotor cortex neurons in the presence of a rhythmic motor dominant.

The existence of a cryptic stationary focus of excitation induced in the cortex by rhythmic electrical stimulation of the paw was detected using sound test stimuli which were previously indifferent to the experimental animals. Neuron activity was recorded in the sensorimotor cortex of rabbits. Neuron pairs were identified which operated in a correlated fashion in the dominant focus. Analysis of linked spike activity in such neuron pairs demonstrated the predominant appearance of linked spikes with intervals of about 2 sec when the focus was created by stimulation with a 2-sec rhythm; intervals were at or about 3 sec when the focus was created by stimulation with a 3-sec rhythm. The studies demonstrated that long-term persistence of the rhythmic nature of the dominant focus occurred at the level of interneuron interactions, i.e., it was a system process. The assimilated rhythm in linked cell activity was observed not only at the point of summation, when output was sent to an effector-i.e., when the dominant was realized as a movement response-but also in the intervals between test stimuli.