Cell Types in the Thalamus and Cortex

Abstract The dorsal thalamus and cerebral cortex contain a variety of cell types that form functional circuits. The two major cell types in the thalamus are glutamatergic relay cells with axons that project to the cortex and local GABAergic interneurons. A third group of cells that embryologically are part of the ventral thalamus but play a major role in thalamic circuits of the dorsal thalamus are the GABAergic cells of the thalamic reticular nucleus that integrate feedforward and feedback inputs and provide inhibition to relay cells. The cortex is also comprised of glutamatergic and GABAergic neurons. While some glutamatergic cells are strictly interneurons and others are projection neurons that also provide local input, GABAergic neurons are all interneurons. These cell types form circuits within the cortex that have stereotypical patterns of connectivity between the six cortical layers as well as with other cortical and subcortical structures, including, importantly, the thalamus. This chapter explores the cell types and connections of neurons in the thalamus and cortex.