Abstract
Visual processing in the brain seems to provide fast but coarse information before information about fine details. Such dynamics occur also in single neurons at several levels of the visual system. In the dorsal lateral geniculate nucleus (LGN), neurons have a receptive field (RF) with antagonistic center-surround organization, and temporal changes in center-surround organization are generally assumed to be due to a time-lag of the surround activity relative to center activity. Spatial resolution may be measured as the inverse of center size, and in LGN neurons RF-center width changes during static stimulation with durations in the range of normal fixation periods (250–500 ms) between saccadic eye-movements. The RF-center is initially large, but rapidly shrinks during the first ∼100 ms to a rather sustained size. We studied such dynamics in anesthetized cats during presentation (250 ms) of static spots centered on the RF with main focus on the transition from the first transient and highly dynamic component to the second more sustained component. The results suggest that the two components depend on different neuronal mechanisms that operate in parallel and with partial temporal overlap rather than on a continuously changing center-surround balance. Results from mathematical modeling further supported this conclusion. We found that existing models for the spatiotemporal RF of LGN neurons failed to account for our experimental results. The modeling demonstrated that a new model, in which the response is given by a sum of an early transient component and a partially overlapping sustained component, adequately accounts for our experimental data.
Highlights
Processing in the visual system seems to proceed through processes where coarse information is analyzed before fine details [1,2]
Rather than reflecting a continuous change of balance between an excitatory center and a delayed inhibitory surround, the dynamics of the receptive field (RF)-center width could reflect two distinctly different sets of spatiotemporal mechanisms. We addressed this question by studying the dynamics of RFcenter width of dLGN neurons with particular focus on the transition from the first to the second component
Experimental analyses We studied neurons from A-laminae of lateral geniculate nucleus (LGN) with RFs within 30 deg from area centralis (N = 51; 32 X, 19 Y-neurons; 14 X-neurons were lagged)
Summary
Processing in the visual system seems to proceed through processes where coarse information is analyzed before fine details [1,2]. Single neurons respond with rapid coarseto-fine changes with respect to several types of stimuli [3,4,5,6,7,8,9] Such changes were observed in various experimental conditions including static stimulus presentations with duration similar to typical fixation periods in natural saccadic inspections [6,10]. The spatial frequency selectivity of the dLGN neurons increased during static presentations of grating stimuli The magnitude of these changes was sufficiently large to account for changes observed in striate cortex during related conditions [6,9]
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