A new cell type identified in the external globus pallidus casts a 'Hunter's Net' of inhibition in striatum

A recent study from Dr. Magill's group published in Neuron [Mallet et al. (2012). Dichotomous Organization of the External Globus Pallidus. Neuron 74 (6): 1075-86] breaks new ground in our understanding of the anatomical and functional understanding of the external globus pallidus (GPe). The classical understanding of GPe as a monolithic population of neurons serving the indirect pathway to subthalamic nucleus and basal ganglia output neurons is given its final parting shot. We learn that up to half of GPe neurons in the rat project solely back to striatum with massive axonal termination areas. This newly identified cell type termed 'arkypallidal' (from Greek 'arkys' for 'Hunters Net') further shows distinct phase relationships with oscillatory activity patterns in unilaterally 6-OHDA lesioned rats. While pallido-striatal connections have been identified before, the new-found dominance of this pathway and its distinct activity pattern call for a fundamental re-evaluation of the functional integration of GPe into basal ganglia networks. Significantly, the potential for a maintained separation of direct and indirect pathways in the GPe is raised, and an important role for arkypallidal neurons in the generation of beta oscillations is suggested. This work is sure to spawn a multitude of future experimental studies and calls for important modifications of existing basal ganglia network models.