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Science 20 April 2001:
Vol. 292. no. 5516, p. 393
DOI: 10.1126/science.292.5516.393m
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The processing of visual signals from the retina of the eye all the way to the highest brain centers has been studied in great detail for many years. What is still unknown, however, are where the cortical signals are that underlie awareness, and when they travel. Pascual-Leone and Walsh (p. 510) used dual transcranial magnetic stimulation, in both area V1 and area MT, in human subjects to investigate the role of feedback projections in visual awareness. Stimulation strength in V1 was adjusted to disrupt the feedback from MT to V1. With MT stimulation alone, the subjects perceived moving flashes of light. However, when V1 was stimulated shortly (5 to 45 milliseconds) after MT, the perception of moving dots was weak or diminished. This finding indicates that recurrent fast feedback connections into area V1 are necessary for visual awareness.




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Science. ISSN 0036-8075 (print), 1095-9203 (online)