Spindle wave synchrony in the somatosensory cortex of the cat.

(1) Spontaneous barbiturate spindles were recorded from the primary and secondary somatosensory cortex. The recordings were concentrated to areas surrounding several reference loci. The recording sites producing the maximal response evoked by stimulation of an exposed nerve in a contralateral limb were used as reference loci. (2) Spindles recorded at various distances from the respective reference loci were cross-correlated to spindles developing simultaneously in the latter. High correlation coefficients, indicating a considerable degree of wave synchrony, were obtained between spindles in the reference locus and spindles recorded a few millimeters from this site. The correlation coefficients decreased with increasing interelectrode distance. A relatively sharp fall in the correlation coefficients was generally found 2-3 mm from the reference locus. Small amounts of sodium pentobarbital, given intravenously at intervals of 5 min, had no effect upon this pattern. (3) The change in the correlation coefficients was followed by a parallel change in the amplitude of the evoked potentials. The iso-correlation lines of spindle wave synchrony and the iso-amplitude lines of the evoked potentials had a similar distribution and extension for each particular reference locus. (4) Lateral spread of spindle waves in the cortex seems to be of minor importance, since a vertical lesion cutting the cortico-cortical fibres did not reduce the wave synchrony of the spindles recorded from either side of the lesion. (5) The majority of the spindles recorded in the close vicinity of a reference locus started simultaneously within +/- 0.1 sec. This pattern changed with increasing distance from the reference locus and 5.6 mm away only a fraction of the spindles started simultaneously. However, within the entire primary somatosensory cortex a small but significant coupling existed between onset of the spindles.