Rosa M G, Krubitzer L A, Molnár Z, Nelson J E
Vision, Touch and Hearing Research Centre, Department of Physiology and Pharmacology, University of Queensland, QLD 4072, Australia.
Eur J Neurosci. 1999 Mar;11(3):907-15. doi: 10.1046/j.1460-9568.1999.00497.x.
Two visual areas, V1 and V2 (first and second visual areas), appear to be present in the posterior neocortex of all eutherian mammals investigated so far. However, previous studies have not established whether an area homologous to V2 also exists in metatherian mammals (marsupials). Using electrophysiological techniques, we mapped the visual receptive fields of neurons in the striate and peristriate cortices of the northern quoll, an Australian marsupial. We found that neurons in a 2-mm-wide strip of cortex rostrolateral to V1 form a single, relatively simple representation of the complete contralateral hemifield. This area resembles V2 of eutherians in several respects: (i) neurons in the medial half of the peristriate area represent the lower visual quadrant, whereas those in the lateral half represent the upper visual quadrant; (ii) the vertical meridian of the visual field is represented adjacent to V1, while the visual field periphery is represented along the lateral and rostrolateral borders of the peristriate area; (iii) there is a marked anisotropy in the representation, with a larger magnification factor parallel to the V1 border than perpendicular to this border; and (iv) receptive fields of multiunit clusters in the peristriate cortex are much larger than those of cells in V1 at comparable eccentricities. The cortex immediately rostral and lateral to V2 did not respond to visual stimulation under our recording conditions. These results suggest that V1 and V2 together form a 'core' of homologous visual areas, likely to exist in all therian mammals.
到目前为止，在所有已研究的真兽类哺乳动物的后新皮质中似乎都存在两个视觉区域，即V1和V2（第一和第二视觉区域）。然而，之前的研究尚未确定在有袋类哺乳动物中是否也存在与V2同源的区域。我们运用电生理技术，绘制了澳大利亚有袋动物北袋鼬纹状皮质和纹周皮质中神经元的视觉感受野。我们发现，在V1前方外侧2毫米宽的皮质条带中的神经元形成了对整个对侧半视野的单一、相对简单的表征。该区域在几个方面类似于真兽类动物的V2：（i）纹周区域内侧一半的神经元代表下视觉象限，而外侧一半的神经元代表上视觉象限；（ii）视野的垂直子午线在V1附近表征，而视野周边沿着纹周区域的外侧和前外侧边界表征；（iii）表征存在明显的各向异性，与V1边界平行方向的放大倍数大于垂直于该边界方向的放大倍数；（iv）在可比的偏心率下，纹周皮质中多单位簇的感受野比V1中的细胞的感受野大得多。在我们的记录条件下，紧邻V2前方和外侧的皮质对视觉刺激没有反应。这些结果表明，V1和V2共同构成了同源视觉区域的“核心”，可能存在于所有兽亚纲哺乳动物中。
