Abstract
Devaluation protocols reveal that Tourette patients show an increased propensity to habitual behaviors as they continue to respond to devalued outcomes in a cognitive stimulus-response-outcome association task. We use a neuro-computational model of hierarchically organized cortico-basal ganglia-thalamo-cortical loops to shed more light on habit formation and its alteration in Tourette patients. In our model, habitual behavior emerges from cortico-thalamic shortcut connections, where enhanced habit formation can be linked to faster plasticity in the shortcut or to a stronger feedback from the shortcut to the basal ganglia. We explore two major hypotheses of Tourette pathophysiology—local striatal disinhibition and increased dopaminergic modulation of striatal medium spiny neurons—as causes for altered shortcut activation. Both model changes altered shortcut functioning and resulted in higher rates of responses towards devalued outcomes, similar to what is observed in Tourette patients. We recommend future experimental neuroscientific studies to locate shortcuts between cortico-basal ganglia-thalamo-cortical loops in the human brain and study their potential role in health and disease.
Highlights
Neurological disorders, such as the Gilles de la Tourette Syndrome, can reveal fundamental properties of neural circuits involved in learning habitual responses
Based on the suggested commonalities of tics and habits, we propose a neurocognitive model of enhanced habit formation in Tourette syndrome
We here propose that enhanced habit formation in Tourette patients, as observed by Delorme et al (2016), may be grounded in aberrant activation within cortico-thalamic shortcut connections
Summary
Neurological disorders, such as the Gilles de la Tourette Syndrome, can reveal fundamental properties of neural circuits involved in learning habitual responses. Tourette patients are typically known for repeatedly making movements and sounds that are not entirely voluntary. Such tics are sometimes described as responses towards involuntary premonitory sensations or urges that stop upon tic execution (Brandt et al 2016; Kwak et al 2003; Leckman et al 1993). This view inspired the comparison of tics and habits, which are automatic and fast, yet inflexible responses towards stimuli. It relies on the idea that tics share key features with habits and may have a common neural underpinning (Leckman and Riddle 2000)
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