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J. Zheng, H. Bi, I. Watanabe, B. Zhang, I. Maruko, E.L. Smith, III, Y.M. Chino; Contrast–dependent Receptive–field Center–surround Interactions in V1 and V2 Neurons of Infant Macaque Monkeys . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5669.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:Stimulation outside the classic receptive–field (CRF) of cortical neurons in adult monkeys is known to exert subthreshold influences over CRF responses and the nature of this surround effect, i.e., excitatory or inhibitory, is known to depend on stimulus contrast. In this study we determined at what age this contrast–dependent surround effect emerges in V1 and V2 of infant monkeys. Methods:Nine macaque infant monkeys (Maca mulatta) served as subjects; 2 weeks of age (n=3); 4 weeks (n=2); and 8 weeks (n=2). Two normal monkeys served as adult controls. Microelectrode recording experiments were conducted under anesthesia and paralysis. Following optimizing stimulus orientation /direction and spatial frequency for each unit, area summation functions were obtained (contrast = 80%, TF = 3.1Hz). After determining of the center and surround size, contrast–response functions were obtained under three conditions, center stimulus alone, center plus iso–oriented surround and center plus cross–oriented surround. Results:We found that with stimulation of the CRF alone, the contrast response functions of both V1 and V2 units in all infant groups were qualitatively adult like. In V1 of infant monkeys, adult–like contrast–dependent surround effects were found as early as at two weeks of age. However, at 2 and 4 weeks of age, iso–oriented surround gratings had relatively small suppressive effects on center responses for higher contrasts, and facilitatory effects for lower contrasts were greater than surround facilitation in adults. With orthogonally oriented surround gratings, surround effects were minimal at any infant age as in adults. In V2, surround suppression initiated by iso–oriented gratings was virtually absent during the first 8 weeks of life except for small suppression at higher contrasts. Instead robust surround facilitation was found and this surround facilitation was largest for 2 week–old infants and became progressively smaller with age. However, unlike in V1, even at 8 weeks of age, the overall surround suppression was relatively small. Conclusions:These results suggest that the functional maturation of inhibitory long–range connections both V1 and V2 is relatively delayed compared to excitatory connections, and that the receptive–field center surround organization of V2 neurons matures later than that in V1.
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