Single- and multiple-event paradigms for identification of motor cortex activation.

BACKGROUND AND PURPOSE The "single-event" technique has been used as an alternative to the "block-trial" method to detect activation that may be accompanied by head motion. The purpose of this study was to compare the two methods for measuring activation in the sensorimotor cortex secondary to motor tasks. METHODS Functional MR imaging data were acquired from six participants as they performed tasks with their fingers, tongues, and toes in a block-trial and a single-event paradigm. For the block trial, the participant was instructed to perform the task when cued at a rapid self-timed rate for 15 seconds, alternating with 15 seconds of rest. Five periods of task performance and six rest periods were included in one acquisition. For the single-event method, the participant performed the task a single time every 15 seconds when cued by the investigator, for a total of 21 times. Using conventional parcellation methods, activation was detected by a cross-correlation technique and was classified as occurring in the sensorimotor cortex, supplementary motor area (SMA), or as nonspecific. Differences between the two acquisition paradigms were tested using the standard t test at a significance level of P < .05. RESULTS Activation was identified by both the block-trial and the single-event methods for the finger task, for the tongue task, and inconsistently for the toe task. More motion artifact occurred in conjunction with the toe and tongue tasks than with the finger tasks. On average, more activated pixels were identified by the single-event method than by the block-trial method. For these motor tasks, however, a larger percentage of pixels detected by the block-trial method than by the single-event method were specific for the sensorimotor cortex or SMA as sites of activation. CONCLUSION For the tongue and the toe movement tasks, which may produce some head motion artifacts, the single-event paradigm provides a useful alternative to the block-trial method for identifying the sensorimotor cortex or SMA. It does not achieve a greater percentage of activation within primary motor areas. For the finger movement task, which does not usually produce head motion artifacts, the block-trial method generally produced a greater percentage of activated pixels in the sensorimotor cortex or SMA than did the single-event method.