Chasing tics in the human brain: Development of open, scheduled and closed loop responsive approaches to deep brain stimulation for tourette syndrome

Tourette syndrome is a childhood-onset disorder characterized by a combination of motor and vocal tics, often associated with psychiatric comorbidities including attention deficit and hy­peractivity disorder and obsessive-compulsive disorder. Despite an onset early in life, half of pa­tients may present symptoms in adulthood, with variable degrees of severity. In select cases, the syndrome may lead to significant physical and social impairment, and a worrisome risk for self injury. Evolving research has provided evidence supporting the idea that the patho­physiology of Tourette syndrome is directly related to a disrupted circuit involving the cortex and subcortical structures, including the basal ganglia, nucleus accumbens, and the amygdala. There has also been a notion that a dysfunctional group of neurons in the putamen contrib­utes to an abnormal facilitation of competing motor responses in basal ganglia structures ulti­mately underpinning the generation of tics. Surgical therapies for Tourette syndrome have been reserved for a small group of patients not responding to behavioral and pharmacological thera­pies, and these therapies have been directed at modulating the underlying pathophysiology. Lesion therapy as well as deep brain stimulation has been observed to suppress tics in at least some of these cases. In this article, we will review the clinical aspects of Tourette syndrome, as well as the evolution of surgical approaches and we will discuss the evidence and clinical re­sponses to deep brain stimulation in various brain targets. We will also discuss ongoing re­search and future directions as well as approaches for open, scheduled and closed loop feed­back-driven electrical stimulation for the treatment of Tourette syndrome.