Action Control Deficits in Patients With Essential Tremor

Hughes, Shelby; Claassen, Daniel O.; Wery P. M. van den Wildenberg; Phibbs, Fenna T.; Bradley, Elise B.; Wylie, Scott A.; van Wouwe, Nelleke C. · 2018 · OpenAlex-citations

DOI: 10.1017/s1355617718001054

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Summary

This study investigated whether Essential Tremor (ET), a movement disorder characterized by disrupted cerebellar-thalamo-cortical networks, impairs action control mechanisms beyond motor execution deficits. While ET is known to affect motor performance, the authors hypothesized that it might also interfere with the cognitive control required to inhibit or stop actions, a capability critical for daily functioning. The research specifically examined two forms of action control: response stopping (inhibitory control) and proactive slowing (strategic slowing of responses in anticipation of potential stop signals). The study included 33 ET patients and 25 age-matched healthy controls (HCs). Participants completed a choice reaction task to measure baseline action initiation speed and a stop-signal task to assess inhibitory control. In the stop-signal task, participants responded to directional arrows but had to inhibit their response when a visual cue appeared on 30% of trials. The stop-signal delay was adjusted dynamically to maintain a 50% inhibition success rate. Motor severity in ET patients was assessed using the Fahn-Tolosa-Marin (FTM) or Washington Heights-Inwood Genetic Study of ET (WHIGET) scales. Statistical analyses compared reaction times, stop-signal reaction times (SSRT), and proactive slowing between groups, while also correlating clinical motor severity with behavioral measures. Results indicated that ET patients exhibited significantly slower action initiation (Go reaction time) compared to HCs (649 ms vs. 526 ms). Crucially, ET patients showed impaired inhibitory control, evidenced by significantly longer SSRTs (320 ms) than HCs (258 ms). However, proactive slowing did not differ between groups; both ET patients and HCs slowed their go responses by approximately 140 ms in the stop-signal context, suggesting that strategic compensation mechanisms remained intact in ET. Furthermore, in a subset of patients, more severe motor symptoms (higher FTM scores) were positively correlated with longer stopping latencies, indicating that greater tremor severity is associated with poorer inhibitory control. The findings demonstrate that ET involves specific deficits in inhibitory action control, distinct from general slowing of motor execution. The impairment in stopping speed, coupled with intact proactive slowing, suggests that while ET patients can strategically adjust their behavior to accommodate the need for inhibition, the actual neural mechanism for halting an initiated action is compromised. The correlation between motor severity and stopping latency implies that progressive changes in cerebellar-thalamo-cortical networks may underlie these cognitive-motor deficits. These results highlight the need for future imaging studies to identify the specific structural and functional changes in ET that explain impaired inhibitory control, potentially informing better clinical management of the disorder.

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• cognitive impairment