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Christine Bredfeldt, Dario Ringach; Dynamics of spatial frequency tuning of macaque LGN. Journal of Vision 2002;2(7):219. doi: 10.1167/2.7.219.
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© ARVO (1962-2015); The Authors (2016-present)
The dynamics of spatial frequency tuning in macaque primary visual cortex (V1) reveal changes in both selectivity and preferred spatial frequency over the timecourse of the response (Bredfeldt and Ringach, J. Neurocience, in press). We are interested in determining whether these phenomena can be accounted for by the convergence of feed-forward signals from the lateral geniculate nucleus (LGN) onto V1 cells. Here, we measure the dynamic spatial frequency tuning of macaque LGN using the same reverse correlation technique used to measure dynamic tuning in V1. We recorded the responses of individual cells to a rapid sequence of sinusoidal gratings with random spatial frequencies and spatial phases, at a fixed orientation. Blanks were interleaved to provide an estimate of baseline response. We find that when the response to a given spatial frequency is averaged across spatial phases we observe a flat response that is near baseline. This implies that under the conditions of our experiments the input from the LGN to V1 is approximately linear. When we measure the amplitude of the modulation of the response with respect to spatial phase at each spatial frequency, we find that most cells show a fairly stereotyped dynamic pattern. For short time delays, the response modulation is low pass. This initial response decays back to baseline and is followed by a second response that is also low-pass in spatial frequency. A few neurons in our population, however, also showed a transition to a band-pass tuning curve after the initial low-pass response. We are presently using these data to investigate the extent to which the dynamics of spatial frequency in V1 might be accounted for by a model that sums LGN inputs followed by rectification with threshold.
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