The postsubiculum as a head-direction cortex.

The organisation of thalamocortical networks follows a conserved structure. Traditionally, these are divided into primary sensory systems that receive subcortical sensory signals, and higher-order systems that are driven predominantly by cortical activity. The rodent head-direction system - the neural 'compass' and a key input to the hippocampal formation - encodes orientation in the horizontal plane through a thalamocortical loop that links the anterodorsal thalamic nucleus and the postsubiculum. We argue that this circuit shares several hallmark features with canonical primary sensory systems, including a driver thalamic input, specific laminar targeting, and receptive field transformations. Drawing on recent anatomical and physiological studies in rodents, we propose that the postsubiculum functions as a primary cortex for the head-direction signal.