Brbiturate spindle activity in the association cortex of the cat and its relation to spindle activity in the...

(1) Spontaneous barbiturate spindle activity was recorded simultaneously from nucleus ventralis poster-lateralis (VPL) of the thalamus, from the corresponding projection site in the primary somatosensory cortex (SI) and from the lateral (LAT) and middle suprasylvian (SSM) gyri. (2) Barbiturate spindles occurred more frequently in LAT and SSM than in the somatosensory cortex. Spindles in LAT and SSM were of longer duration than SI spindles while the intraspindle frequency was higher in spindles from the latter areas. The amplitude of the spindle waves was significantly higher in LAT and SSM than in SI. The largest spindle waves were recorded from the anterior part of LAT and SSM. (3) Barbiturate spindles recorded at various interelectrode distances were cross-correlated. In LAT and SSM the cross-correlation coefficients remained high up to an interelectrode distance of 4-5 mm while spindles recorded at this distance in SI gave low coefficients when cross-correlated. (4) Extensive removal of the somatosensory cortex had no effect on spindle formation in LAT or SSM. Furthermore, cutting of the cortico-cortical connections between two recording sites in either of these gyri produced no reduction in spindle wave synchrony between the recording sites. (5) Spindles in the VPL-SI only rarely started simultaneously with spindles in LAT and SSM. Those few coincident spindles which occurred were cross-correlated. The cross-correlation coefficients were invariably low suggesting that no wave synchrony existed between spindles in the VPL-SI system and those in the LAT and SSM.