Emerging views of corticothalamic function

Abstract

Although it is now generally accepted that the thalamus is more than a simple relay of sensory signals to the cortex, we are just beginning to gain an understanding of how corticothalamic feedback influences sensory processing. Results from an increasing number of studies across sensory systems and different species reveal effects of feedback both on the receptive fields of thalamic neurons and on the transmission of sensory information between the thalamus and cortex. Importantly, these studies demonstrate that the cortico-thalamic projection cannot be viewed in isolation, but must be considered as an integral part of a thalamo-corticothalamic circuit which intimately interconnects the thalamus and cortex for sensory processing.

Figure 1

Schematic diagram of thalamo-cortico-thalamic circuitry. Thalamocortical neurons (blue) receive peripheral inputs and project axons to layer 4 of primary sensory cortex. Corticothalamic neurons (red) receive local input from thalamocortical recipient layer 4 and provide output to layer 4 and to the thalamus. Corticothalamic projections also supply di-synaptic inhibition to thalamic neurons via RTN inhibitory neurons and local thalamic interneurons (black).