The Basal Ganglia Talk Back: Striato-Cortical and Pallido-Cortical Return Pathways in Basal Ganglia-Cortical Communication.

A central framework in basal ganglia neuroscience is that the cerebral cortex sends excitatory information to the striatum, where it is integrated with thalamic and neuromodulatory signals to shape action selection, learning, and behavioral flexibility [1-10]. In this classical view, the striatum acts as the major input structure of the basal ganglia, whereas processed output returns to the cortex indirectly through pallidal, nigral, and thalamocortical pathways [1-4, 10, 11]. However, recent evidence indicates that striatal and pallidal circuits can influence cortical processing through more direct, specialized, and neurochemically diverse routes than previously appreciated [12-16], revealing an unexpected diversity of basal ganglia return pathways. In particular, the identification of a previously uncharacterized cholinergic projection from the dorsal tail of the striatum to the auditory cortex suggests that specialized striatal circuits can directly modulate cortical sensory processing [15]. These findings provide a new entry point for reconsidering basal ganglia-cortical communication beyond the classical indirect loop model. In this review, we use this striato-cortical cholinergic pathway as a recent example, considered alongside the more established pallidocortical literature, to discuss the emerging concept of striato-pallidal-cortical return signaling. We first revisit the historical organization of corticostriatal and basal ganglia-thalamocortical loops, discuss the dorsal tail of the striatum as a sensory-associated basal ganglia node, and finally integrate recent evidence for direct and reciprocal pallidocortical pathways. Together, we propose an expanded model in which basal ganglia circuits may influence cortical gain, timing, sensory salience, and behavioral relevance through multiple return channels. Rather than replacing the classical model, this emerging view expands it: the striatum is not only a recipient of cortical input, but also a participant in return pathways that can contribute to shaping cortical computation.