Slow intrinsic rhythm in the koniocellular visual pathway.

Slow rhythmic changes in nerve-cell activity are characteristic of unconscious brain states and also may contribute to waking brain function by coordinating activity between cortical and subcortical structures. Here we show that slow rhythms are exhibited by the koniocellular (K) pathway, one of three visual pathways beginning in the eye and projecting through the lateral geniculate visual relay nucleus to the cerebral cortex. We recorded activity in pairs and ensembles of neurons in the lateral geniculate nucleus of anesthetized marmoset monkeys. We found slow rhythms are common in K cells but are rare in parvocellular and magnocellular cell pairs. The time course of slow K rhythms corresponds to subbeta (<10 Hz) EEG frequencies, and high spike rates in K cells are associated with low power in the theta and delta EEG bands. By contrast, spontaneous activity in the parvocellular and magnocellular pathways is neither synchronized nor strongly linked to EEG state. These observations suggest that parallel visual pathways not only carry different kinds of visual signals but also contribute differentially to brain circuits at the first synapse in the thalamus. Differential contribution of sensory streams to rhythmic brain circuits also raises the possibility that sensory stimuli can be tailored to modify brain rhythms.