UNIT ACTIVITY IN SPINDLE BURSTS

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Abstract
Microelectrode recordings from the diffusely projecting nuclei of the cat''s thalamus show that, when the electrical activity in this area is "synchronized" and spindle bursts are present, there are definite relations between unit activity and slow waves. The units discharge in groups of 5-30 spikes whose peaks are separated by intervals of 2-6 ms. and whose amplitude and polarity varies from the beginning to the end of the group. The spikes are negative and of low amplitudes initially, frequently biphasic and of high amplitudes in the middle of the group and come back to low amplitudes at the end. Each group is consistently followed by a positive wave of 30-200 ms duration. The variation in amplitude and polarity of the spikes suggests that each group represents discharges of several neurones firing at different distances from the recording point and in a regular pattern: consecutive discharges approaching, reaching and going beyond the tip of the microelectrode. The consistent association of groups of spikes with slow waves suggests that the development of the latter is closely related to the activity of the units which generate the spikes. Furthermore, the time, phase and amplitude relations between unit spikes and slow waves suggestb that the summation of positive after-potentials resulting from the consecutive firing of the units in a group may be responsible for the development of the positive phase of the slow wave that follows the group.

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