Functional anatomy and interaction of fast and slow visual pathways in macaque monkeys*
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Current dynamic models of visual processing suggest that rapid inputs to higher order ventral stream regions modulate or otherwise "frame" the processing of slower, more information-dense inputs. There is also an indication that the rapid framing inputs may not utilize standard feedforward pathways. To evaluate these propositions, we measured the timing, areal distribution, and laminer profile of fast, wavelength-insensitive and slower, wavelength-sensitive responses in V1 and extrastriate areas, using laminar current-source density analysis in awake macaque monkeys. There were three main findings. (1) We confirmed previously reported significant differences in latency between ventral and dorsal stream responses (V4 mean = 38.7 ms versus MT mean = 26.9 ms) and between responses in IT and STS(dorsal bank) cortical areas (IT mean = 43.4 ms versus STS(dorsal bank) mean = 33.9 ms). (2) We found that wavelength-sensitive inputs in areas V1, V4, and IT cortex lagged the wavelength-insensitive responses by significant margins; this lag increased over successive levels of the system. (3) We found that laminar activation profiles in V4 and IT were inconsistent with feedforward input through the ascending ventral cortical pathway; the likely alternative input routes include both lateral inputs from the dorsal stream and direct inputs from nonspecific thalamic neurons. These findings support a "Framing" Model of ventral stream visual processing in which rapidly conducted inputs, mediated by one or more accessory pathways, modulate the processing of more slowly conducted feedforward inputs.;Key words. Current source density (CSD); wavelength sensitivity; ventral stream; dorsal stream; parvocellular; magnocellular; koniocellular; timing; response latency.;*This is a pre-copy-editing, author-produced material of an article accepted for publication in Cerebral Cortex following peer review. The definitive publisher-authenticated version [Chen, C., Lakatos, P., Shah, A.S., Mehta, A.D., Givre, S.J., Javitt, D.C., & Schroeder, C.E. (2006). Functional anatomy and interaction of fast and slow visual pathways in macaque monkeys. Cerebral Cortex, Advance Access published on 9/1/2006: 10.1093/cercor/bhl067] is available online at: http://cercor.oxfordjournals.org/cgi/content/abstract/bhl067. .
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