In patients with Gilles de la Tourette syndrome (GTS), both procedural sequence learning and event file binding are enhanced and are potential cognitive mechanisms behind habitual symptoms, such as tics, and contribute to the overall cognitive profile of these patients, according to a review published in European Journal of Neuroscience.

As a complex neuro-psychiatric disorder, in addition to motor and vocal tics, GTS is also associated with cognitive alterations. Previous studies have suggested that internal or external sensory cues can trigger habitual behavior. While several studies have investigated the processing of stimulus-response associations in patients with GTS, these associations were suggested to be facilitated in some studies and impaired in others.

The current review focused on 2 enhanced functions as potential cognitive mechanisms behind habitual behavior in patients with GTS: the procedural memory formation and event file coding.


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Procedural memories are established through repeated exposure to regularities in the environment; this creates persistent, long-term memory traces and relies on the predictability of the events. The formation of habits involves sequences of stimulus-response associations and specific brain structures. Thus, procedural learning and memory have the essential qualities to provide a cognition-driven understanding of habitual behavior.

While procedural learning describes how habits develop as long-term memories, event file binding details habit formation at the level of individual stimulus-response relationships, no matter longevity. Binding of event files can result in changes in episodic memory traces, which provides a link between event file coding and declarative memories.

Data suggest that striatal functions, like event file binding and procedural learning, may shed light on habit and tic formation in patients with GTS.

Learning is intact or even enhanced in children and adolescents with GTS, with evidence to suggest procedural hyperfunctioning in adults with the neuro-psychiatric disorder.

Event files are building blocks of procedural memories; consequently, abnormal binding would lead to abnormal procedural memory. Enhanced event file binding may result in hyperlearning of sequential regularities in GTS. Hyperlearning results in abnormally stable procedural memories that last long after their original significance. Additionally, previous studies have shown a positive correlation between the magnitudes of the binding effect and motor tic frequency.

It is possible that event file binding and procedural learning in GTS “might be [2] sides of the same coin.” On the one hand, hyperbinding explain the creation of strong stimulus-response connections; on the other hand, hyperlearning explains the retention of the event files in a larger time frame.

“Converging evidence of enhanced functions in GTS are probably not coincidental, and they have consequences for cognitive theories in addition to understanding of GTS. Despite their similarities, event file binding and procedural sequence learning have different time scales, different sensitivities to potential impairment in action sequencing, but both contribute to the overall cognitive profile of GTS,” concluded the study researchers.

Reference

Takacs A, Münchau A, Nemeth D, Roessner V, Beste C. Lower-level associations in Gilles de la Tourette syndrome: Convergence between hyperbinding of stimulus and response features and procedural hyperfunctioning theories. Eur J Neurosci. Published online June 21, 2021. doi:10.1111/ejn.15366