A behavioural task to determine the effects of sustained context-related inhibition during motor control

Background: Modulation of learned “motor programs“ is the basis of context-adequate behaviour, consisting of retrieval or non-retrieval (inhibition) of behavioural elements. Evidence was provided that focal activation/deactivation represents contextual modulation [1,2]. It remains open, whether context-related deactivation represents truly behaviourally relevant inhibition. During non-retrieval subjects do not perform a task, thus no behavioural measurement can be acquired. To determine the behavioural effect during non-retrieval we developed a behavioural task and tested it in healthy subjects (HS).

Methods: 32 HS were asked to overlearn a complex finger movement sequence the day before the behavioural experiment as described previously [1,2]. The sequence consisted of 16 key presses; the rhythm of 1Hz was triggered by visual cues without information about which key had to be pressed. The experiment consisted of three conditions, an activation (ACT), inhibition (INH) and control (CO) condition. HS had to retrieve the learned finger movements during ACT, had not to retrieve them during INH but look on the visual cues and had to focus attention on a visual cue presented in the same rhythm of 1Hz during CO. The context of each condition was announced few seconds before it started. During each condition a novel visual cue (red X) appeared randomly, subjects were asked to press a key with their thumb as fast as possible when this target cue appeared, subsequently reaction times (RTs) were acquired. We hypothesized that RTs change depending on the condition, with longer RTs during INH compared to CO as sustained context-related behaviourally relevant inhibition is expected during INH.

Results: RM-ANOVA with the factor CONDITION was highly significant (F=156,5, p<0,001). Post-hoc showed longer RTs for INH (439,6±11,4 msec) compared to CO (412,1±8,9 msec; p<0,001) supporting our hypothesis.

Conclusions: The present data demonstrated behaviourally relevant effects of sustained contextual inhibition during non-retrieval of learned motor programs. These data underline the behavioural relevance of previously described cortical correlates of contextual modulation during motor control [1,2]. Furthermore the present task provides a tool to evaluate contextual inhibition in HS and patients with diseases with deficits in inhibitory control (Tourette) and might be used as a behavioural marker for therapeutic efforts.

[1] Hummel (2002), Brain

[2] Hummel (2004), NIMG