RAPID COMMUNICATION Recovery of fMRI Activation in Motion Area MT Following Storage of the Motion Aftereffect

Culham, Jody C., Sean P. Dukelow, Tutis Vilis, Frank A. Hasmotion appears for an additional period only slightly shorter sard, Joseph S. Gati, Ravi S. Menon, and Melvyn A. Goodale. than the original duration, suggesting that the decay of the Recovery of fMRI activation in motion area MT following storage MAE does not necessarily proceed automatically with the of the motion aftereffect. J. Neurophysiol. 81: 388–393, 1999. passage of time. We used functional magnetic resonance imaging ( fMRI) during Here we use functional magnetic resonance imaging storage of the motion aftereffect (MAE) to examine the relation( fMRI) to examine activity in the human extrastriate motion ship between motion perception and neural activity in the human complex MT/ during and after storage of the MAE. Neuroicortical motion complex MT/ ( including area MT and adjacent maging has shown that MT/ is activated by both physical motion-selective cortex) . MT/ responds not only to physical momotion (Tootell et al. 1995b; Watson et al. 1993; Zeki et tion but also to illusory motion, as in the MAE when subjects who have adapted to continuous motion report that a subsequent al. 1991) and illusory motion (Zeki et al. 1993), including stationary test stimulus appears to move in the opposite direction. the MAE as shown by Tootell et al. (1995a). Furthermore, In the phenomenon of storage, the total decay time of the MAE is the decay of MT/ activity during the MAE correlates well extended by inserting a dark period between adaptation and test with the decay of the perceptual illusion (Tootell et al. phases. That is, when the static test pattern is presented after a 1995a). We reasoned that if MT/ activation following adapstorage period equal in duration to the normal MAE, the illusory tation is related only to observers’ perception of motion, motion reappears for almost as long as the original effect despite MT/ activity should be absent during a completely dark the delay. We examined fMRI activation in MT/ during and after storage interval following adaptation when no motion is perstorage. Seven subjects viewed continuous motion, followed either ceived, but should return when the static test is presented. by an undelayed stationary test ( immediate MAE) or by a comHowever, if processing in MT/ is also related to nonperceppletely dark storage interval preceding the test (stored MAE). Like the perceptual effect, activity in MT/ dropped during the storage tual factors, enhanced activation may also be observed durinterval then rebounded to reach a level much higher than after the ing the storage interval following adaptation even though no same delay without storage. Although MT/ activity was slightly motion is perceived. enhanced during the storage period following adaptation to continuous motion (compared with a control sequence in which the adaptation grating oscillated and no MAE was perceived), this enhanceM E T H O D S ment was much less than that observed during the perceptual phenomenon. These results indicate that following adaptation, activity Procedure in MT/ is pronounced only with the presentation of an appropriate visual stimulus, during which the MAE is perceived. fMRI was used to measure the blood oxygenation level dependent (BOLD) signal in seven normal, healthy subjects. First, we examined the ‘‘immediate MAE’’ by presenting a moving pattern I N T R O D U C T I O N followed by a stationary test with no delay. Subjects viewed a continuously contracting and rotating stimulus (36 s) , leading to After viewing continuous motion in one direction, observa perceptual MAE during a subsequent stationary test (30 s; Fig. ers report that a stationary stimulus appears to move in the 1, A and B) . Subjects pressed a button when the MAE ended. opposite direction, a phenomenon known as motion afterefActivation during this ‘‘MAE sequence’’ was compared with a fect (MAE) (Mather et al. 1998; Wohlgemuth 1911). Typi‘‘control sequence’’ in which the grating oscillated and no subsecally, this aftereffect lasts tens of seconds, but remarkably, it quent MAE was observed. Two scans were collected, each with two MAE sequences and two control sequences, providing four can be ‘‘stored’’ when the test pattern does not immediately measures of immediate MAE. follow the adaptation pattern (Spigel 1960; Wohlgemuth Next, we examined the ‘‘stored MAE.’’ Between motion adapta1911). That is, if the observer closes his eyes for the normal tion and the stationary test, a storage interval was inserted in which duration of the MAE and then reopens them, the illusory subjects kept their eyes open in complete darkness while light from the video projector was occluded by a computer-triggered shutter The costs of publication of this article were defrayed in part by the such that the room became pitch black. The storage duration was payment of page charges. The article must therefore be hereby marked determined for each subject based on the perceptual duration of ‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. the immediate MAE. Four scans were acquired, each with two