Functional architecture for speed tuning in primary visual cortex of carnivores

Abstract

Perception of motion critically depends on detecting the speed and direction of moving stimuli. The primary visual cortex (V1) of some mammals, including primates and carnivores, exhibits functional organization for key receptive field properties such as orientation, direction, and spatial frequency; however, less is known about the organization of speed-tuned cells. While individual V1 neurons have been shown to exhibit speed selectivity, functional architecture for speed preference has been primarily reported in higher cortical areas such as primate area MT. Using multi-channel electrophysiology in anesthetized female ferrets, we investigated the joint tuning of V1 neurons for spatial frequency, temporal frequency, orientation/direction, and speed. We found significant clustering of cells tuned for speed and for speed preference within single electrode penetrations. We found that both simple and complex cells can exhibit speed tuning, and no strong variation across cortical layers. In reanalysis of intrinsic signal imaging data from cat V1, we observed repeating "hot spots" of high speed selectivity separated by "cold spots" with low tuning for speed. These findings indicate that a functional architecture for speed tuning is present within V1 itself and transmitted to downstream cortical regions. Significance StatementTo perceive moving objects, the visual system must detect both their direction and speed. The primary visual cortex, the first cerebral visual area to receive visual information from the retina via the lateral geniculate nucleus, plays a key role in this process. Here, we demonstrate that the primary visual cortex in carnivores contains speed-tuned neurons. Moreover, these neurons are organized into clustered "hot spots" that repeat across the cortical surface, suggesting a functional architecture for speed. While speed-tuned functional maps were previously thought to exist only in higher visual areas, such as area MT in primates, our findings reveal their presence at the level of primary visual cortex.