September 2005
Volume 5, Issue 8
Vision Sciences Society Annual Meeting Abstract  |   September 2005
Mapping cone specific activity in primary visual cortex
Author Affiliations
  • Elizabeth N. Johnson
    Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
  • Thomas R. Tucker
    Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
  • David Fitzpatrick
    Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
Journal of Vision September 2005, Vol.5, 1018. doi:10.1167/5.8.1018
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      Elizabeth N. Johnson, Thomas R. Tucker, David Fitzpatrick; Mapping cone specific activity in primary visual cortex. Journal of Vision 2005;5(8):1018. doi: 10.1167/5.8.1018.

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      © ARVO (1962-2015); The Authors (2016-present)

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We are investigating how cone inputs are mapped across the cortical surface using intrinsic signal optical imaging in the dichromatic tree shrew. We determined an empirical short wavelength (S-) cone isolating stimulus using color-exchange during extracellular recordings of multiunit sites. In these experiments, the blue CRT gun contrast was held constant at 0.8 (80%), while the green gun contrast varied from 0 to −0.8, with the green and blue modulation 180° out of phase. This produced heterochromatic blue/green gratings with a spatial frequency of 0.4 cycles/deg drifting at 8 Hz. A prediction of color-exchange is that a particular value of blue:green modulation will produce no net change (a null) in response from the dominant middle-long wavelength (ML-) cones. At this modulation ratio, only S-cones produce a differential response, so this stimulus isolates the contribution from the S-cones. The color-exchange experiments yielded a mean response minimum at a green gain of −0.19±0.03 (s.d.), with most sites giving a response null at or below the spontaneous firing rate. An ML-cone-isolating stimulus of approximately the same cone contrast as the S-cone-isolating stimulus was calculated from the known tree shrew S-cone spectral sensitivity. We then performed optical imaging experiments while presenting full-screen drifting sinusoidal S- and ML-cone isolating gratings of varying orientation and spatial frequency. The spatial tuning for S-cone activation peaks at lower spatial frequency with more high frequency attenuation than the ML-cone response. In addition, S-cone isolating stimuli produce activity that is roughly half the magnitude of ML-cone isolating stimuli of equivalent cone contrast. The map of orientation tuning is comparable in orientation preference, but has broader tuning with S-cone isolating stimuli. These results suggest that although the S-cone mediated signals are lower in spatial frequency resolution, they are able to drive orientation specific responses in V1.

Johnson, E. N. Tucker, T. R. Fitzpatrick, D. (2005). Mapping cone specific activity in primary visual cortex [Abstract]. Journal of Vision, 5(8):1018, 1018a,, doi:10.1167/5.8.1018. [CrossRef]
 This research was supported by NIH-EY06821 and EY015357.

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