Program Nr: 265

Temporal frequency tuning of cross orientation inhibition in the striate cortex of cats. J.D. Allison 1, K.R. Smith 2, M.E. Atherton 2, J.M. Samonds 2, A.B. Bonds 1,2. Electrical Engineering & Computer Science, Vanderbilt University, Nashville, TN1, Biomedical Engineering, Vanderbilt University, Nashville, TN2.

Purpose: A sinusoidal mask grating oriented orthogonal to and superimposed on an optimally oriented base grating reduces a striate cortical neuron's response amplitude. The spatial parameters of this cross-orientation inhibition have been previously measured. In this study we examine the temporal properties of the inhibitory mechanism. Methods: We recorded from single neurons (n = 61) in the striate cortex of cats anesthetized with Propofol and paralyzed with Pavulon following established guidelines. After quantifying the structure of each cell's classical receptive field, we measured the temporal frequency tuning of the cross orientation inhibition by systematically varying the temporal frequency of a mask grating at one, then a second, "null" orientation outside the cell's excitatory response domain. Results: The average peak temporal frequency of the neurons in our sample was 2.7(± 1.2) Hz. The average cutoff frequency for the sample was 12.4 (± 5.6) Hz. In contrast, the average peak temporal frequency (6.7 ± 3.4 Hz) and cutoff frequency (18.1 ± 6.2 Hz) were higher for the cross-orientation inhibitory mechanism. The temporal frequency bandwidth (full-width at half-height) of our sample averaged 1.5 (± 0.1) octaves while the temporal frequency bandwidth of the inhibitory mechanism averaged 2.4 (± 0.7) octaves. For 55% of our sample, the temporal frequency response profile of the inhibitory mechanism differed as a function of the orientation of the mask grating. On average, the absolute differences between the values obtained at the two mask orientations were 1.1 (± 0.7) octaves for the peak frequencies, 0.4 (± 0.3) octaves for the cutoffs, and 0.75 (±0.6) octaves for the bandwidths. Conclusions: The neural substrate of cross-orientation inhibition is composed of a network of cells with temporal frequency bandwidths similar to most striate cortical neurons, but which prefer higher frequencies. The exact organization of this inhibitory network is unknown.
CR: None      Support: EY03778