Prefrontal Network Mechanisms of Psychiatric Deep Brain Stimulation

Deep brain stimulation (DBS) is an emerging treatment for otherwise treatment-refractory psychiatric disorders. It can produce remarkable clinical results in expert hands, but has not fared as well in controlled, multisite trials. That difficulty with scaling up arises in part because DBS' mechanisms are poorly understood, meaning that it is difficult to objectively identify patients likely to respond and/or to customize stimulation to match individual patients' needs. In the first part of this review, we overview converging anatomic and physiological evidence that psychiatric DBS acts by modulating distributed networks centered on the prefrontal cortex (PFC). We discuss potential physiological mechanisms of that modulation, including mixed excitatory/inhibitory effects, changes in local field potential oscillations, and neuroplastic changes. A major challenge is that mechanistic data from humans are limited and sometimes contradictory, in part because these studies can only be conducted at low N with limited technical replication. Animal models may overcome that challenge, but are challenging themselves because psychiatric disorders are not fully recapitulated in animal models and are defined primarily by self-reports that are unavailable in nonverbal model species. Thus, in the second part, we review paths to more reliable animal models of psychiatric DBS, including putative disease models and models based on cognitive and decision-making impairments. The latter class includes traditional cognitive assays and newer approaches based on computational modeling, both of which also implicate PFC-centric networks. Taken together, these approaches may yield new insights into DBS' mechanisms that can in turn improve its scalability and clinical reliability.