Many studies have shown the supplementary motor area (SMA) becomes active during preparation for movement. A recent FMRI study by Albert et al (in preparation) showed that the pre-SMA deactivated as subjects received a signal to move in a choice response task, In this task subjects moved their finger to a signaled location on a touch screen in response to a change in the display. The signals to move were not predictable in time because of jittering in the inter-stimulus interval, and unpredictable occurrence of null trials (trials in which no signal to move occurred).
The deactivation of the pre-SMA is rather puzzling given the well-known activation of the SMA during motor preparation. This project is designed to work out under what conditions this effect occurs, and its time course. Does the deactivation depend on the unpredictability of the stimuli in time, or the fact that it was a relatively complex choice response task?
The project will use FMRI to replicate and extend the previous findings. We plan to repeat the timing of the original task with both choice response and simple reaction time. We will also vary the predictability (in time) of the go signal to investigate whether the ability to prepare influences this effect. We predict that the deactivation of the pre-SMA occurs when different competing responses are possible, so that some or all of the potential responses may need to be suppressed. In contrast, we predict that the SMA will be more interested in the timing of the response rather than the choices involved.
If we succeed in finishing the analysis before the end of the project, there may be an opportunity to look at the time course of the response in more detail in a few MEG and EEG pilot studies.