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SG Solomon, EC Clark, PR Martin; Contrast Sensitivity In The Primate Lateral Geniculate Nucleus Is Modulated By The Extraclassical Receptive Field . Invest. Ophthalmol. Vis. Sci. 2002;43(13):3928.
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Purpose: The presence of an extraclassical receptive field (ECRF), termed the 'suppressive surround', has been demonstrated in lateral geniculate nucleus (LGN) cells of primates and cats. Here we quantified the effects of ECRF stimulation on contrast-response properties in the magnocellular (MC), koniocellular (KC) and parvocellular (PC) layers of the LGN in a New World monkey, the marmoset Callithrix jacchus. Methods: extracellular recordings of single-unit activity were made in anaesthetised and paralyzed marmosets. The classical receptive field (CRF) was stimulated with a grating patch of optimal spatial frequency and radius 3-4 times that of the classical centre. The ECRF was stimulated with a contiguous annulus grating of variable contrast or orientation. Results: stimulation of the ECRF suppressed visually evoked activity. The contrast-response relationship of this inhibition parallels that of the CRF: for MC cells, threshold contrast for inhibition is close to 10% and saturates at 50% contrast. For PC cells, the contrast-relationship of inhibition was more linear. Contrast detection thresholds were determined by receiver-operating characteristic analysis. Detection thresholds were raised by ECRF stimulation for most units (30/34). Increasing ECRF contrast from 0% to 50% increased CRF threshold contrast for PC cells (from 29.2% to 36.7%, p < 0.02, paired Wilcoxin) and to a larger extent in MC cells (from 20.3%% to 63.7%, p < 0.02). Thresholds also increased for KC cells (from 15.0% to 38.1%, p=0.06). These effects were independent of annulus orientation. Conclusion: the ECRF of all primate LGN cells acts to reduce contrast sensitivity and the reliability of signal transmission. We suggest that the non-orientation tuned inhibition seen in the ECRF of cortical receptive fields is inherited from their subcortical inputs.
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