Objective: The aim of the study was to investigate in healthy subjects whether somatosensory temporal discrimination threshold (STDT) is influenced by movement execution and preparation.

Background: STDT is abnormally increased in patients with movement disorders. Knowing more about how STDT is influenced by movement execution in healthy subjects might clarify the pathophysiological role of altered STDT values in movement disorders.

Methods: Seventeen healthy subjects underwent a main experimental protocol designed to disclose how and when movement execution modulates STDT values. Paired stimuli applied to the right index finger for STDT were triggered by the movement (index finger abductions) at 0ms, 100ms, 200ms, 500ms and 5 seconds after the movement onset. STDT was also tested during the motor preparation phase (250ms and 150ms prior to movement onset). Control experiments were designed to investigate whether STDT changes induced by the movement were specific for the body segment moved, depended on the intensity of electrical stimuli used for STDT, or depended on the kinematic properties of movement execution (fast, slow and passive movements). We also sought whether movement-induced STDT changes were due to cortical mechanisms by testing STDT during motor imagery and after continuous theta burst stimulation (cTBS) over S1.

Results: STDT values significantly increased in comparison to baseline values when tested on the right moving hand concomitantly to movement onset and up to 200ms after the movement onset. STDT significantly changed during fast as well as slow index finger movements, when we increased the intensity of electrical stimuli used for STDT and also mildly increased with passive index finger abductions. Conversely, STDT remained unchanged when tested in body parts other than those involved in movement execution and during movement preparation. STDT remained unmodified during imagined movement and cTBS over S1 failed to influence the degree of movement-induced STDT changes.

Conclusions: Movement execution interferes with temporal sensory processing possibly at subcortical level, through basal ganglia-thalamus connectivity, thus affecting ascending thalamus-S1 signaling.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/movement-execution-but-not-preparation-modulates-somatosensory-temporal-discrimination-thresholds-in-healthy-subjects/