Spindle oscillations during cortical spreading depression in naturally sleeping cats.
Diego Contreras, Alain Destexhe and Mircea Steriade

Neuroscience 77: 933-936, 1997.

Copy of the full paper (PDF)
Spindling activity characterizes the electroencephalogram of animals and humans in the early stages of resting sleep. Spindles are defined as waxing and waning rhythmic waves at 7-14 Hz grouped in sequences that recur periodically every 3 to 10 seconds. Spindling originates in the thalamus 7, but the role of the cerebral cortex in triggering and synchronizing thalamic spindles was shown by stimulation of the contralateral cortex avoiding antidromic activation of thalamocortical axons. Spontaneous spindles under barbiturate anesthesia are waxing and waning, but under ketamine-xylazine anesthesia or when evoked by strong stimuli spindle waves are almost exclusively waning, i.e., they start with maximum amplitude and then decrease progressively. Waxing and waning of spindles has been ascribed to progressive entrainment of units into the oscillation followed by a progressive desynchronization. Therefore, exclusively waning spindles would be produced by an initial high synchrony in the corticothalamic network. Such situation is observable upon strong stimulation or, spontaneously, when spindles are paced by the slow cortical oscillation and preceded by a strong corticothalamic drive. We have conducted experiments in naturally sleeping cats to verify the occurrence of two patterns of spindle oscillations and to test the role of the cortex in synchronizing and shaping spindles. We have found that indeed two types of spindles (waxing and waning or mostly waning) occur in naturally sleeping animals. We also demonstrate that during cortical spreading depression spindles are less synchronous and only of the waxing and waning type. As cortical activity recovers, waning spindles reappear and are preceded by electroencephalogram deflections which are known to be related to corticothalamic depolarizing inputs.