Spatial frequency maps in the mammalian straite cortex: Optical imaging and electrophysiology

Neurons of similar orientation and neu ar preference cluster together m the cortex. Since cortical neurons are also tuned to spatial frequency, il is ol interest to investigate the tangential cortical organisation of spatial frequency selectivity. Recently, spatial frequency columns hav : been reported in kitten cortex (Huhner et al. '95) and in the adult cat and monkey cortex (O'Brien el al. '96). We sought to validate the optical imaging results with electrophysiologieal recordings. We used a CCD camera to image inlriisic optical signals from the striate cortex ol anaestheti/ed and paraly/ed eats and m< nkeys while the animals viewed drifting sinusoidal gratings of various spatial frequencies at four orientations and lixed temporal frequency. We generated acth ity maps of regions which respond to different spatial frequencies using exten: ions of the Karhunen-Loève principal component analysis. Subsequent e lee t n-physio logical recordings of the spatial frequency tuning of single cells at several regions in the optically imaged area were compared with the optical activity maps The clustering of cells observed with ihe two methods was similar. Based on these data, we propose a model for the organ zation of spatial frequency tuning in cat and monkey striate cortex.