Sequential activation of the motor network in single subjects

The spatially and temporally separated contribution of primary motor, premotor and prefrontal areas in delayed movements can be illustrated with fMRI in group (n=10) analysis (Hülsmann et al., NeuroImage 2003, 20: 1485–1492). In order to study the impact of heterogeneous lesions on the timing of cortical motor control (e.g. in recovery after stroke), reliable consistent results on a single subject basis are essential. The aim of this study was to prove that detection of sequential activation in single subjects is feasible.

Methods: We studied a right-handed woman of 30 years with event-related fMRI during a visually cued choice reaction time paradigm. The cue consisted of an arrow, pseudorandomly either pointing to the right or to the left. Subjects were told to respond with the corresponding hand after a temporal delay, which they had to deliberately choose between 2 to 15 seconds. The state of neuronal activity as indexed by BOLD-signal changes was calculated separately for each time point prior (-6, -5, -4, -3, -2, -1 seconds) to motor response.

Results: First activation appeared in the rostral supplementary motor area (SMA) and left ventral premotor cortex 6 seconds prior to the motor response and migrated, within 4 seconds, ventrally to the anterior cingulate cortex and caudally to SMA proper. Activity in the primary sensory-motor cortex grew to full extent within 1–2 seconds prior to the movement. (see Figure).

Discussion: The present study shows for the first time that sequential contribution of prefrontal, premotor and primary motor areas in delayed movements can be illustrated with fMRI on a single subject basis. This will allow for study of patients with heterogeneous lesions such as stroke.