Receptive fields in cat visual cortex during natural locomotion

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Understanding how visual information is processed during natural behavior is a fundamental problem of neuroscience. Despite recent insights from research in alert head-fixed subjects, it remains largely unknown how visual processing is affected by active behavior: self-motion and active selection of visual targets for serving on-going behavior. Proposed research aims to establish a unique experimental paradigm of active vision in freely moving cats during natural locomotion, while testing a specific hypothesis that visual processing is shaped by the needs of on-going behavior. This new paradigm builds on complementary strength of visual and motor physiology, and allows to study vision under conditions in which it is naturally used: during coordinated and coherent motor activity, sensory feedback, allocation of attention and dynamically changing visual input. Cats readily walk in environments that impose different demands on accuracy of stepping and vision: from simple flat surfaces (low demand) to stepping on elevated objects (high demand). Using this robust and repetitive natural behavior we will measure (i) visual input, (ii) neuronal activity, and (iii) behavioral output. We will take footage from a head-fixed camera and record the eye position, gaze trajectory, and biomechanics of head and body. Using these measurements, we will calculate visual input in retinotopic and body-centric coordinates. While cat is walking, we will record activity of neurons in primary visual (a.17 and a.18) and multisensory parietal (a.5b) cortical areas. We will use reverse-correlation to reconstruct receptive fields of neurons in retinotopic and body-centric coordinates. To measure behavioral output, we will use state-of-the-art 3-dimensional analysis of biomechanics of head, body and limbs, and the accuracy of steps. To determine how the needs of locomotion shape visual processing we will use environments with different demands on accuracy of stepping and visual information: from low demand (walking on flat surface) to high demand (stepping on elevated platforms). Our overarching hypothesis maintains that processing in visual cortex is task-dependent: higher demands on accuracy of stepping lead to an increasing precision of space representation in visual system. Our Specific Aim is to understand how demands of locomotion task shape visual input and processing of visual information. We hypothesize that higher demands on precision of visual information for locomotion will be met by increasing both precision of visual input by more frequent fixations on locations for future foot placement, and precision of visual processing by increasing the strength of visual responses and decreasing the size of visual receptive fields. We will ask: (1a) How the visual input, determined by the pattern of gaze behavior, changes during locomotion in diverse environments; and (1b) How visual responses and receptive fields change during locomotion in environments with different demands on vision. Obtained results will provide (i) rigorous testing and validation of the new experimental paradigm for research into active vision; and (ii) tests for our hypothesis, that during locomotion in environments with higher requirements on accuracy of stepping and higher demand on visual information, visual responses will be stronger and receptive fields smaller than during locomotion in low-demand environments. This new knowledge will aid the development of new rehabilitation strategies for patients with deficits in using vision during locomotion.