Basic circuits linking TRN with the cortex and the thalamus. Driving input reaching the thalamus from the sensory periphery, subcortical regions or the cortex, activates thalamocortical projection neurons, which then transmit that information to the cortex. Thalamocortical axons, on their way to the cortex, give off collateral branches that terminate in TRN. In the feedback loop of this circuit, corticothalamic axons give off collateral branches that innervate the same TRN regions. The TRN sends inhibitory projections only to the thalamus.