Global motion integration in the postero-medial part of the lateral suprasylvian cortex in the cat.

In cats, the postero-medial part of lateral suprasylvian cortex (PMLS) is generally considered a key area for motion processing. While behavioral studies have indeed supported the role of PMLS cortex in higher order motion integration (Cereb Cortex 6:814-822, 1996), there is no evidence that individual PMLS cells can perform such analysis (Vis Neurosci 5:463-468, 1990; J Neurophysiol 63:1529-1543, 1990). Given the fundamental importance of understanding the neural substrate subtending higher order motion processing, we investigated whether PMLS neurons can signal the direction of motion of complex random dot kinematograms (RDKs) wherein comprising elements do not provide any local coherent motion cues. Results indicated that most PMLS cells (82%) can integrate the displacement of individual elements into a global motion percept. Their large receptive fields allowed the integration of motion for elements separated by large spatial intervals (up to 4 degrees ). In most cases, the analysis of complex RDK motion necessitated the contribution of the area of the visual field beyond the classical receptive field. None of the complex RDK-sensitive cells were found to be pattern-motion selective when tested with plaid patterns. Our results provide the first evidence that receptive fields of PMLS neurons can perform global motion analysis and support the behavioral evidence that this area is implicated in complex motion processing (Cereb Cortex 6:814-822, 1996). It also further corroborates the findings that PMLS neurons cannot signal the true direction of a plaid pattern (Vis Neurosci 5:463-468, 1990; J Neurophysiol 63:1529-1543, 1990). Providing that these same neurons can signal the direction of complex RDKs, there may be distinct cortical mechanisms for processing different types of complex motion.