Human area MT(+) shows load-dependent activation during working memory maintenance with continuously morphing stimulation

BACKGROUND: Initially, human area MT(+) was considered a visual area solely processing motion information but further research has shown that it is also involved in various different cognitive operations, such as working memory tasks requiring motion-related information to be maintained or cognitive tasks with implied or expected motion. In the present fMRI study in humans, we focused on MT(+) modulation during working memory maintenance using a dynamic shape-tracking working memory task with no motion-related working memory content. Working memory load was systematically varied using complex and simple stimulus material and parametrically increasing retention periods. Activation patterns for the difference between retention of complex and simple memorized stimuli were examined in order to preclude that the reported effects are caused by differences in retrieval. RESULTS: Conjunction analysis over all delay durations for the maintenance of complex versus simple stimuli demonstrated a wide-spread activation pattern. Percent signal change (PSC) in area MT(+) revealed a pattern with higher values for the maintenance of complex shapes compared to the retention of a simple circle and with higher values for increasing delay durations. CONCLUSIONS: The present data extend previous knowledge by demonstrating that visual area MT(+) presents a brain activity pattern usually found in brain regions that are actively involved in working memory maintenance.