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Yeon Jin Kim, Orin S. Packer, Peter B Detwiler, Dennis M Dacey; Achromatic contrast adpatation in parasol and midget ganglion cells of the macaque monkey retina. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5276. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Adaptation to temporal variation in light intensity, or contrast, is a fundamental property of the visual system that first appears at the retinal level. In the primate lateral geniculate nucleus (LGN) it has been shown that magnocellular (LGNmagno) but not parvocelluar (LGNparvo) relay cells (Solomon et al., Neuron, 42:155, 2004) show “profound” contrast adaptation. This result seems counterintuitive since the parvocellular pathway mediates achromatic spatial resolution and is critical for form perception (Lennie & Movshon, JOSA, 22:2013, 2005). Our purpose was to record from the LGNparvo- and magno-projecting midget and parasol ganglion cells respectively and directly measure contrast adaptation in these cell types at the retinal level.
Midget and parasol ganglion cells were selectively targeted for extracellular recording in the in- vitro macaque monkey retina. Spike responses to low contrast (10-50%) stimuli were recorded before and after exposure to high-contrast (75-100%) stimuli. All stimuli were achromatic spots sinusoidally modulated in intensity around a fixed mean luminance at 6 or 10 Hz temporal frequency with a diameter approximately equal to that of the receptive field center.
We found strong contrast adaptation for both midget and parasol ganglion cells during and after high contrast temporal modulation for 20-30 sec. During exposure to the high-contrast stimulus response amplitude for most cells exponentially decayed from a transient peak to a sustained plateau (time constant, midget = 8.60 sec; parasol = 6.74 sec). Following adaptation, the low contrast response was markedly reduced relative to the preadapted state (midget = 33% and parasol = 36% reduction), recovering slowly over about 30 sec.
Unlike the previous report for LGN relay cells, we observed achromatic contrast adaptation in both parvo- and magno-projecting midget and parasol ganglion cells respectively. We suggest that the discrepancy may be due to the use of large stimulus fields in the LGN study whereas in our experiments midget cells were very sensitive to achromatic stimuli restricted to the receptive field center. We conclude that contrast adaptation in midget ganglion cells is consistent with a fundamental role for the parvocellular pathway in achromatic spatial vision (Wool et al., J. Neurosci., 38:1520, 2018).
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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