The thalamus is an obligatory station through which nearly all sensory information must pass before reaching the cerebral cortex. One of the major functions of the thalamus is the selective control of the flow of sensory-motor information to the cerebral cortex during different states of the sleep-wake cycle and arousal, and is controlled through the actions of various neurotransmitter systems in the brainstem, hypothalamus, and cerebral cortex. Recent investigations have detailed the cellular mechanisms, including the role of GABAA and GABAB receptors, involved in the generation of both normal (e.g. spindle waves) and abnormal (e.g. generalized seizures) patterns of activity in thalamocortical circuits. In addition, in vivo investigations have also revealed that the dense projection from the cerebral cortex to the thalamus may synchronize thalamocortical activity in a manner useful for sensory analysis. Together, these data suggest that oscillations and synchronization are important for both normal and abnormal function in thalamocortical circuits.