Trans-thalamic Pathways: Strong Candidates for Supporting Communication between Functionally Distinct Cortical Areas

The thalamus was long considered a passive relay of sensory information with little or no active role in higher cognitive functions. However, mounting evidence suggests that thalamic nuclei form complex loops with the cortex and are involved in a myriad of cognitive processes, including attention and working memory (Ward, 2013). Although first-order thalamic nuclei (e.g., lateral geniculate nucleus) play a key role in the transmission of ascending sensory input to the cortex, higher-order nuclei (e.g., pulvinar or mediodorsal nucleus) are believed to be involved in sustaining and modulating communication within and between cortical regions (Guillery, 1995). Understanding the functional role of such nuclei in a mechanistic manner requires, in addition to behavioral experiments, a detailed anatomical and physiological mapping of the thalamocortical circuitry