Imagination and Will

1. Evoked potentials generated by cerebral self-stimulation were studied in white rats. Stimulus trains of 30 biphasic rectangular waves of various repetition rates (30, 50, 100, 150, 200 pps) were employed. The pulses were always 4 msec in width and of fixed intensity at all repetition rates for a given animal. Potential changes during a 2-second interval after the termination of a stimulus train were recorded from various points in the cerebral mass and averaged electronically.

2. The early portion of the 2-second interval was characterized by rhythmic oscillations in the alpha range whose number and amplitude were related to repetition rate of the rectangular waves within the stimulus train. The periodicity of the oscillations when they occurred was not so affected and remained practically constant over subjects, intensity of stimulus, and repetition rate.

3. The number of oscillations was greatest at 200 and 150 pps and diminished with diminishing stimulus repetition rates, the drop being greatest below 100 pps.

4. There was a positive covariation between the rate of lever pressing for self-stimulation and the phenomenon of rhythmic after oscillations in the evoked potential. Animals who refused to press the lever for cerebral self-stimulation showed no rhythmic potentials when the stimulus was delivered by E; animals who had become pressers gave good after-discharges when so stimulated.