Stopping an action at the right moment is a fundamental form of cognitive control. Whether avoiding an obstacle, cancelling a planned movement, or adapting to a sudden change in the environment, the brain must sometimes rapidly suppress an action that is already being prepared. This process, known as reactive inhibitory control, has classically been attributed mainly to the hyperdirect pathway, in which cortical stop signals recruit the subthalamic nucleus to suppress motor output through the basal ganglia.
In this study, in collaboration with Timothy Verstinen and Catalina WIch, we revisit this classical view by focusing on a less conventional player: arkypallidal neurons in the external globus pallidus. These neurons send inhibitory projections back to the striatum, forming pallidostriatal pathways that are well positioned to influence the competition between action-promoting and action-suppressing striatal populations.
Using a biologically constrained spiking model of cortico-basal ganglia-thalamic circuits, the authors examined how arkypallidal neurons interact with key inhibitory-control nodes, including the subthalamic nucleus and indirect-pathway spiny projection neurons. Their simulations show that arkypallidal pathways can facilitate action cancellation not simply by adding another “brake”, but by reshaping the internal competition within the striatum. In particular, arkypallidal input weakens the dominance of the direct pathway during evidence accumulation, allowing the suppressive influence of the indirect pathway to more effectively control basal ganglia output.
The main conceptual advance is therefore a shift from a one-way view of inhibitory control to a bidirectional circuit logic. The external globus pallidus is not merely a relay in the indirect pathway; it can act as an active mediator of both descending and ascending control signals. Through its arkypallidal projections to the striatum, it helps determine whether an emerging action plan will continue toward execution or be successfully cancelled.
A useful way to summarize the result is: stopping an action is not only about pressing a global brake. It is also about changing the balance of competition inside the decision circuit itself. Arkypallidal neurons appear to do precisely this, by modifying how direct and indirect striatal pathways compete during action selection.
This work contributes to a broader rethinking of basal ganglia function. Rather than treating the external globus pallidus as a passive intermediate structure, it highlights its role as a dynamic hub for regulating information flow in cortico-basal ganglia-thalamic loops. This has implications not only for models of decision-making and inhibitory control, but also for neurological and psychiatric disorders in which action suppression, impulsivity, or basal ganglia dynamics are altered.
To know more:
- Giossi, C., Bahuguna, J., Rubin, J. E., Verstynen, T., & Vich, C. (2024). Arkypallidal neurons in the external globus pallidus can mediate inhibitory control by altering competition in the striatum. Proceedings of the National Academy of Sciences, 121, e2408505121. https://doi.org/10.1073/pnas.2408505121.