Functional organization of envelope-responsive neurons in early visual cortex: organization of carrier tuning properties.
It is well established that visual cortex neurons having similar selectivity for orientation, direction of motion, ocular dominance, and other properties of first-order (luminance-defined) stimuli are clustered into a columnar organization. However, the cortical architecture of neuronal responses to second-order (contrast/texture-defined) stimuli is poorly understood. A useful second-order stimulus is a contrast envelope, consisting of a finely detailed pattern (carrier) whose contrast varies on a coarse spatial scale (envelope). In this study, we analyzed the cortical organization of carrier tuning properties of neurons, which responded to contrast-modulated stimuli. We examined whether neurons tuned to similar carrier properties are clustered spatially and whether such spatial clusters are arranged in columns. To address these questions, we recorded single-unit activity, multiunit activity, and local field potentials simultaneously from area 18 of anesthetized cats, using single-channel microelectrodes and multielectrode arrays. Our data showed that neurons tuned to similar carrier spatial frequency are distributed in a highly clustered manner; neurons tuned to similar carrier orientation are also significantly clustered. Neurons along linear arrays perpendicular to the brain surface always exhibited similar optimal carrier spatial frequency, indicating a columnar organization. Multi-pronged tetrode recordings indicated that the diameter of these columns is ≥450 μm. Optimal carrier orientation was also significantly clustered but with finer-grain organization and greater scatter. These results indicate a fine anatomical structure of cortical organization of second-order information processing and suggest that there are probably more maps in cat area 18 than previously believed.
McGill Vision Research Unit, Department of Ophthalmology, McGill University, Montreal, Quebec, Canada H3A 1A1. guang.x.li@mail.mcgill.ca
Guangxing
G
Li
Curtis L
CL
Baker
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001931:Brain Mapping; D002415:Cats; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D008297:Male; D009474:Neurons / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D010775:Photic Stimulation; D025341:Principal Component Analysis; D011930:Reaction Time / Q000502:physiology; D014793:Visual Cortex / Q000166:cytology* / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*