The thalamus and cerebral cortex are linked together to form a vast network of interconnections. Different modes of interactions among the cells in this network underlie different states of consciousness, such as wakefulness and sleep. Interposed between the dorsal thalamus and cortex are the GABAergic neurons of the thalamic reticular nucleus (TRN), which play a pivotal role not only in switching between the awake and sleep states but also in sensory processing during the awake state. The visual, somatosensory, and auditory sectors of TRN share many of the same organizational features. Each of these sectors contains maps, which are related to its inputs and outputs, and organizational components called 'slabs.' It is proposed that, during wakefulness, TRN is crucially involved in resetting the activity levels in sensory nuclei of the dorsal thalamus, which allows the cortex to actively and periodically compare its ongoing sensory processing with the available sensory information.