Within-session and between-session reproducibility of cerebral sensorimotor activation: A test-retest effect evidenced with functional magnetic resonance imaging

The aim of the current study was to assess the reproducibility of functiona l magnetic resonance imaging (fMRI) brain activation signals in a sensorimo tor task in healthy subjects. Because random or systematic changes are like ly to happen when movements are repeated over time, the authors searched fo r time-dependent changes in the fMRI signal intensity and the extent of act ivation within and between sessions. Reproducibility was studied on a senso rimotor task called "the active task" that includes a motor output and a se nsory feedback, and also on a sensory stimulation called "the passive task" that assessed the sensory input alone. The active task consisted of flexio n and extension of the right hand. The subjects had performed it several ti mes before fMRI scanning so that it was well learned. The passive task cons isted of a calibrated passive flexion and extension of the right wrist. Tas ks were 1 Hz-paced. The control state was rest. Subjects naive to the MRI e nvironment and non-MRI-naive subjects were studied. Twelve MRI-naive subjec ts underwent 3 fMRI sessions separated by 5 hours and 49 days, respectively . During MRI scanning, they performed the active task. Six MRI-naive subjec ts underwent 2 fMRI sessions with the passive task 1 month apart. Three non -MRI-naive subjects performed twice an active 2-Hz self-paced task. The dat a were analyzed with SPM96 software. For within-session comparison, for act ive or passive tasks, good reproducibility of fMRI signal activation was fo und within a session (intra- and interrun reproducibility) whether it was t he first, second, or third session. Therefore, no within-session habituatio n was found with a passive or a well-learned active task. For between-sessi on comparison, for MRI-naive or non-MRI-naive subjects, and with the active or the passive task, activation was increased in the contralateral premoto r cortex and in ispsilateral anterior cerebellar cortex but was decreased i n the primary sensorimotor cortex, parietal cortex, and posterior supplemen tary motor area at the second session. The lower conical signal was charact erized by reduced activated areas with no change in maximum peak intensity in most cases. Changes were partially reversed at the third session. Part o f the test-retest effect may come from habituation of the MRI experiment co ntext. Less attention and stress at the second and third sessions may be co mponents of the inhibition of cortical activity. Because the changes became reversed, the authors suggest that, beyond the habituation process, a lear ning process occurred that had nothing to do with procedural learning, beca use the tasks were well learned or passive. A longterm memory representatio n of the sensorimotor task, not only with its characteristics (for example, amplitude, frequency) but also with its context (fMRI), can become integra ted into the motor system along the sessions. Furthermore, the pattern ob s erved in the fMRI signal changes might evoke a consolidation process.