Gain control in the visual thalamus during perception and cognition.

The thalamus has traditionally been thought to passively relay sensory information to the cortex. By showing that responses in visual thalamus are modulated by perceptual and cognitive tasks, recent fMRI and physiology studies have helped revise this view. The modulatory input to the visual thalamus derives from functionally distinct cortical and subcortical feedback pathways. These pathways enable the lateral geniculate nucleus and pulvinar to regulate the information transmitted to cortical areas according to cognitive requirements. Emerging evidence suggests that such regulation involves changing the degree of synchrony between neurons as well as changing the magnitude of thalamic activity. These findings support a role for the thalamus that extends as far as contributing to the control of visual attention and awareness.