School of Medical Sciences and Bosch Institute, Sydney Node of ARC Centre of Excellence in Vision Science, The University of Sydney, NSW, Australia.
Brain Res. 2010 Apr 30;1328:34-48. doi: 10.1016/j.brainres.2010.02.069. Epub 2010 Mar 3.
'Feedback' signals from mammalian extrastriate visual cortices are reported to exert primarily an excitatory influence on the classical receptive field (CRF) of neurons in the primary visual cortex (V1). However, given the much larger CRFs of neurons in extrastriate visual cortices it is not yet understood how feedback signals influence the spatial integration of visual signals by V1 neurons. To investigate this, we reversibly inactivated one of the 'form-processing' extrastriate visual cortices, the postero-temporal visual (PTV) cortex, and examined changes in responses of V1 neurons to drifting grating patches up to 28 degrees in diameter. We found that during inactivation of PTV cortex the magnitude of the responses to CRF-confined stimuli and that to large stimuli inducing maximum suppression (i.e. minimum responses) was significantly reduced, while the spatial extent of the CRF remained largely unaffected. As a result, the relative strength of the surround suppression increased marginally. This effect was apparent in both simple and complex cells. It was also strong and consistent in cells located in supragranular and infragranular layers. For those cells exhibiting some relief from surround suppression or 'counter-suppression' when large stimuli patches were applied, the effect on counter-suppression was heterogeneous. Overall, the relative integrated responses to the 28 degrees grating patches were also decreased when PTV cortex was inactivated. Thus, a substantial reduction in the CRF response and the largely unaffected spatial extent of the CRF as well as a weak surround effect observed in the present study are consistent with a multiplicative scaling effect.
从哺乳动物的外纹状视觉皮质中传出的“反馈”信号被报道主要对初级视觉皮质（V1）中的神经元的经典感受野（CRF）施加兴奋性影响。然而，鉴于外纹状视觉皮质中的神经元的 CRF 要大得多，因此尚不清楚反馈信号如何影响 V1 神经元对视觉信号的空间整合。为了研究这一点，我们可逆地使一个“形态处理”的外纹状视觉皮质，即后颞叶视觉（PTV）皮质失活，并检查了 V1 神经元对直径达 28 度的漂移光栅贴片的反应的变化。我们发现，在 PTV 皮质失活期间，对 CRF 受限刺激的反应幅度以及对诱导最大抑制（即最小反应）的大刺激的反应幅度显著降低，而 CRF 的空间范围基本不受影响。因此，周围抑制的相对强度略有增加。这种效应在简单和复杂细胞中都很明显。在位于颗粒层上和颗粒层下的细胞中，这种效应也很强且一致。对于那些在施加大刺激贴片时表现出周围抑制或“反抑制”减轻的细胞，对反抑制的影响是不均匀的。总体而言，当 PTV 皮质失活时，对 28 度光栅贴片的相对积分反应也降低了。因此，本研究中观察到的 CRF 反应的大幅降低、CRF 的空间范围基本不受影响以及较弱的周围效应与乘法缩放效应一致。
