TIME-RESOLVED FMRI OF MENTAL ROTATION

TIME-RESOLVED fMRI seeks to elucidate neuronal activity during a singl e execution of a mental task, which corresponds typically to a timesca le of seconds. However, this is also the timescale of the hemodynamic response, which delays and blurs the signal in time. In order to disti nguish the temporal characteristics of the neuronal activity from that of the hemodynamic response, which is often vaguely known, we recorde d a set of fMRI time courses under conditions of a varying behavioral parameter, and correlated this parameter to the width of the fMRI resp onse. For the task under investigation, the mental rotation of three-d imensional objects, we found that the activation in the parietal lobe is related to an aspect of the task that is described by the reaction time (for example, the very act of mental rotation), and not only to a spects of the task that are constant from trial to trial, such as the visual presentation at the beginning or the decision at the end of the task.