THE TIME-COURSE OF CHANGES DURING MOTOR SEQUENCE LEARNING - A WHOLE-BRAIN FMRI STUDY

There is a discrepancy between the results of imaging studies in which subjects learn motor sequences. Some experiments have shown decreases in the activation of some areas as learning increased, whereas others have reported learning-related increases as learning progressed. We h ave exploited fMRI to measure changes in blood oxygen level-dependent (BOLD) signal throughout the course of learning. T2-weighted echo-pla nar images were acquired over the whole brain for 40 min while the sub jects learned a sequence eight moves long by trial and error. The move ments were visually paced every 3.2 s and visual feedback was provided to the subjects. A baseline period followed each activation period. T he effect due to the experimental conditions was modeled using a squar e-wave function, time locked to their occurrence. Changes over time in the difference between activation and baseline signal were modeled us ing a set of polynomial basis functions. This allowed us to take into account linear as well as nonlinear changes over time. Low-frequency c hanges over time common to both activation and baseline conditions lan d thus not learning related) were modeled and removed. Linear and nonl inear changes of BOLD signal over time were found in prefrontal, premo tor, and parietal cortex and in neostriatal and cerebellar areas. Sing le-unit recordings in nonhuman primates during the learning of motor t asks have clearly shown increased activity early in learning, followed by a decrease as learning progressed. Both phenomena can be observed at the population level in the present study. (C) 1998 Academic Press.