Spatial frequency columns in the primary visual cortex of adult cats and macaques

Purpose: Several parameters, (e.g., ocular dominance and orientation) are spatially organized in columns tangential to the cortical surface. Previous investigators including Tootell et al., '81, '88, and Hubener, et al., '95 reported that spatial frequency is also organized in this fashion. We have attempted to image spatial frequency columns tangential to the cortical surface in adult mammals to determine if spatial frequency columns exist and, if so, how they relate to the known functional architecture. Method: We imaged intrinsic optical signals in the visual cortex of anaesthetized and paralyzed cats and macaques with a CCD camera at approximately 3 degrees retinal eccentricity. The animals viewed drifting sinusoidal gratings of various spatial frequencies at a fixed temporal frequency and several contrasts, and with monocular and binocular stimulation. We generated indicator functions (activity maps) of areas which responded preferentially to low or high spatial frequencies with extensions of Karhunen-Loève principal component analysis developed in our laboratory. Results: Spatial frequency was mapped in columns tangential to the cortex in cat area 17 and macaque VI. We compared the arrangement of the columns with that of known cortical structures, including ocular dominance columns and orientation domains. Spatial frequency columns may represent the earliest step in a sequence of neuronal interactions which could lead to scale invariance in perception at higher cortical levels.