Top-Down Versus Bottom-Up Control of Attention in the Prefrontal and Posterior Parietal Cortices
Tóm tắt
Attention can be focused volitionally by “top-down” signals derived from task demands and automatically by “bottom-up” signals from salient stimuli. The frontal and parietal cortices are involved, but their neural activity has not been directly compared. Therefore, we recorded from them simultaneously in monkeys. Prefrontal neurons reflected the target location first during top-down attention, whereas parietal neurons signaled it earlier during bottom-up attention. Synchrony between frontal and parietal areas was stronger in lower frequencies during top-down attention and in higher frequencies during bottom-up attention. This result indicates that top-down and bottom-up signals arise from the frontal and sensory cortex, respectively, and different modes of attention may emphasize synchrony at different frequencies.
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Tài liệu tham khảo
See supporting material on Science Online.
A sliding window of 25 ms was stepped every 25 ms. Significance was determined by constructing a null distribution through randomization tests ( 12 ). A neuron was said to first indicate the target location when significant at P = 0.05 for two bins in a row.
The cumulative distribution is the cumulative sum of the histogram of when each cell first carried significant information about the target location (Fig. 2 top row). The cumulative sum was then normalized for the number of significant cells expected at each point in time by chance. This procedure corrected for multiple comparisons and determined when an area carried information about the target location allowing us to infer the order of selectivity. See ( 12 ) for details.
N. Kopell, G. B. Ermentrout, M. A. Whittington, R. D. Traub, Proc. Natl. Acad. Sci. U.S.A.97, 1867 (2000).
Supported by NSF grant SBE0354378 and National Institute of Neurological Disorders and Stroke grant R01NS035145. We thank S. Henrickson J. Roy and M. Wicherski for comments on the manuscript; W. Asaad and K. Maccully for technical and other support; and E. N. Brown for help with the statistical analyses.