Spindle oscillations during cortical spreading depression in naturally
sleeping cats
Diego Contreras, Alain Destexhe and Mircea Steriade
Neuroscience 77: 933-936, 1997.
Abstract
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
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