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Xiaofeng Tao, Bin Zhang, Guofu Shen, Earl Smith, Yuzo Chino; Oblique effects in V2 neurons of infant macaque monkeys. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1517.
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The neural basis of oblique effects is elusive. We previously reported that the spatial matrix of facilitatory subfields (subunits) in the receptive fields of individual V2 neurons in adult monkeys exhibits an orientation anisotropy; the homogeneity of the subfields is greater if a neuron preferred the cardinal orientations compared to oblique orientations (Tao et al, 2012). In this study, we asked whether a similar orientation anisotropy (an oblique effect) exists in V2 of infant monkeys shortly after birth. In addition we asked whether or not we find an oblique effect if we analyze the responses of a large number of adult V2 neurons (> 600 units) using sine-wave grating stimuli.
Extracellular recording was made in individual V2 neurons of anesthetized and paralyzed 4-, 8-, and 16-week-old macaque monkeys. The results from infants were compared to those obtained in adults. Standard sine-wave grating stimuli were initially used to determine the preferred orientation, spatial frequency and size of neuron’s receptive fields. Neurons were classified into vertically, horizontally, or obliquely oriented units after we determined the preferred orientation of each neuron. This was followed by the use of dynamic two dimensional noise stimuli and a reverse correlation (LSRC) method to obtain the spatial matrix of subfields with facilitatory profiles.
1) Using grating stimuli, we found that V2 neurons in adult monkeys show an oblique effect. 2) The oblique effect in the spatial matrix of subfields was absent in V2 at 4 and 8 weeks of age but emerged sometime between 8 and 16 weeks; the average maximal orientation differences between adjacent subfields were smaller for those neurons preferring the cardinal orientations.
1) Our results with grating stimuli represent the first demonstration of oblique effects in monkey extrastriate cortex. 2) The oblique effect in the spatial matrix of facilitatory subfields may not be present at birth, but appears to result from experience-dependent maturation of the connections between V1 and V2. However, the effects of optical factors including higher-order aberrations have not been ruled out.
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