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This Article Full Text Full Text (PDF) All Versions of this Article: 98/3/1253    most recent 00416.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Laycock, R. Articles by Crewther, S. G. Search for Related Content PubMed PubMed Citation Articles by Laycock, R. Articles by Crewther, S. G.

Evidence for Fast Signals and Later Processing in Human V1/V2 and V5/MT+: A TMS Study of Motion Perception

¹ Department of Psychological Science, La Trobe University, Melbourne, Victoria; ² Brain Sciences Institute, Swinburne University, Melbourne, Victoria; ³ Alfred Psychiatry Research Centre, School of Psychology, Psychiatry and Psychological Medicine, The Alfred and Monash University, Melbourne, Victoria, Australia

Submitted 13 April 2007; accepted in final form 11 July 2007

Evidence from human and primate studies suggests that fast visual processing may utilize signals projecting from primary visual cortex (V1) through the dorsal stream, to area V5/MT+ or beyond and subsequently back into V1. This coincides with the arrival of parvocellular signals en route to the ventral pathway and infero-temporal cortex. Such evidence suggests that the dorsal stream region V5/MT+ is activated rapidly through the traditional hierarchical pathway and also via a less-well-established direct signal to V5/MT+ bypassing V1. To test this, 16 healthy humans underwent transcranial magnetic stimulation (TMS) of V1/V2 and V5/MT+ while performing a motion-direction detection task. A three-alternate forced-choice design (left/right motion, stationary) allowed analysis of the quality of errors made, in addition to the more usual performance measures. Transient disruption of V1/V2 and V5/MT+ significantly reduced accuracy when TMS was applied at or near motion onset. Most participants also showed disrupted performance with TMS application over V1/V2 125 ms post motion onset, and significantly reduced accuracy at 158 ms with V5/MT+ stimulation. The two periods of disruption with V1/V2 TMS are suggestive of feedforward/feedback models, although the earlier period of disruption has not been reported in previous TMS studies. Very early activation of V5/MT+, evidenced by diminished accuracy and reduced perception of motion after TMS may be indicative of a thalamic-extrastriate pathway in addition to the traditionally expected later period of processing. A profound disruption of performance prestimulus onset is more likely to reflect disruption of top-down expectancy than disruption of visual processing.