Cell-type diversity in the brain enables the assembly of complex neural circuits, whose organization and patterns of activity give rise to brain function. However, the identification of distinct neuronal populations within a given brain region is often complicated by a lack of objective criteria to distinguish one neuronal population from another. In the external segment of the globus pallidus (GPe), neuronal populations have been defined using molecular, anatomical, and electrophysiological criteria, but these classification schemes are often not generalizable across preparations and lack consistency even within the same preparation. Here, we present a novel use of existing transgenic mouse lines, Lim homeobox 6 (Lhx6)-Cre and parvalbumin (PV)-Cre, to define genetically distinct cell populations in the GPe that differ molecularly, anatomically, and electrophysiologically. Lhx6 -GPe neurons, which do not express PV, are concentrated in the medial portion of the GPe. They have lower spontaneous firing rates, narrower dynamic ranges, and make stronger projections to the striatum and substantia nigra pars compacta compared with PV-GPe neurons. In contrast, PV-GPe neurons are more concentrated in the lateral portions of the GPe. They have narrower action potentials, deeper afterhyperpolarizations, and make stronger projections to the subthalamic nucleus and parafascicular nucleus of the thalamus. These electrophysiological and anatomical differences suggest that Lhx6 -GPe and PV-GPe neurons participate in different circuits with the potential to contribute to different aspects of motor function and dysfunction in disease.

Background: Secondary self-injurious behavior (SSIB) is underreported and predominantly not associated with suicide. In both adults and children, SSIB can cause intractable self-harm and is associated with a variety of clinical disorders, particularly those involving dysfunctional motor control. Methods: We performed a literature review evaluating the clinical efficacy of deep-brain stimulation (DBS) as modulating SSIB observations and review current progress in preclinical SSIB animal studies. Results: Neuromodulation is an effective therapeutic option for several movement disorders. Interestingly, this approach is emerging as a potentially effective treatment for movement disorder-associated SSIB (secondary); however, it is important to understand the neuroanatomy, clinical appraisal, and outcome data when considering surgical therapy for SSIB. Conclusion: The current review examines the literature encompassing animal models and human case studies while identifying existing hypotheses from cytoarchitectonic-based targeting to neurotransmitter-based pathways. This review also highlights the need for awareness of an underrecognized pathology that may be amenable to DBS.