College of Life Sciences, Anhui Normal University, Wuhu, Anhui, 241000, China.
College of Life Sciences, Anhui Normal University, Wuhu, Anhui, 241000, China.
Brain Res Bull. 2021 Feb;167:89-98. doi: 10.1016/j.brainresbull.2020.12.007. Epub 2020 Dec 14.
The visual system lowers its perceptual sensitivity to a prolonged presentation of the same visual signal. This brain plasticity, called visual adaptation, is generally attributed to the response adaptation of neurons in the visual cortex. Although well-studied in the neurons of the primary visual cortex (V1), the contribution of high-level visual cortical regions to the response adaptation of V1 neurons is unclear. In the present study, we measured the response adaptation strength of V1 neurons before and after the top-down influence of the area 21a (A21a), a higher-order visual cortex homologous to the primate V4 area, was modulated with a noninvasive tool of transcranial direct current stimulation (tDCS). Our results showed that the response adaptation of V1 neurons enhanced significantly after applying anode (a-) tDCS in A21a when compared with that before a-tDCS, whereas the response adaptation of V1 neurons weakened after cathode (c-) tDCS relative to before c-tDCS in A21a. By contrast, sham (s-) tDCS in A21a had no significant impact on the response adaptation of V1 neurons. Further analysis indicated that a-tDCS in A21a significantly increased both the initial response (IR) of V1 neurons to the first several (five) trails of visual stimulation and the plateau response (PR) to the prolonged visual stimulation; the increase in PR was lower than in IR, which caused an enhancement in response adaptation. Conversely, c-tDCS significantly decreased both IR and PR of V1 neurons; the reduction in PR was smaller than in IR, which resulted in a weakness in response adaptation. Furthermore, the tDCS-induced changes of V1 neurons in response and response adaptation could recover after tDCS effect vanished, but did not occur after the neuronal activity in A21a was silenced by electrolytic lesions. These results suggest that the top-down influence of A21a may alter the response adaptation of V1 neurons through activation of local inhibitory circuitry, which enhances network inhibition in the V1 area upon an increased top-down input, weakens inhibition upon a decreased top-down input, and thus maintains homeostasis of V1 neurons in response to the long-presenting visual signals.
视觉系统会降低对长时间呈现相同视觉信号的感知灵敏度。这种大脑可塑性被称为视觉适应，通常归因于视觉皮层神经元的反应适应。虽然在初级视觉皮层 (V1) 的神经元中得到了很好的研究，但高级视觉皮层区域对 V1 神经元反应适应的贡献尚不清楚。在本研究中，我们使用经颅直流电刺激 (tDCS) 这一非侵入性工具，在调节 21a 区 (A21a) （与灵长类动物 V4 区同源的高级视觉皮层）的自上而下影响之前和之后，测量了 V1 神经元的反应适应强度。结果显示，与 tDCS 之前相比，A21a 施加阳极 (a-) tDCS 后，V1 神经元的反应适应显著增强，而 A21a 施加阴极 (c-) tDCS 后，V1 神经元的反应适应相对于 c-tDCS 之前减弱。相比之下，A21a 的假 (s-) tDCS 对 V1 神经元的反应适应没有显著影响。进一步分析表明，A21a 中的 a-tDCS 显著增加了 V1 神经元对前几个（五个）视觉刺激试验的初始反应 (IR) 和对长时间视觉刺激的平台反应 (PR)；PR 的增加低于 IR，导致反应适应增强。相反，c-tDCS 显著降低了 V1 神经元的 IR 和 PR；PR 的减少低于 IR，导致反应适应减弱。此外，tDCS 诱导的 V1 神经元反应和反应适应的变化在 tDCS 效应消失后可以恢复，但在 A21a 神经元活动被电解损伤沉默后不会发生。这些结果表明，A21a 的自上而下影响可能通过激活局部抑制回路来改变 V1 神经元的反应适应，从而在增加的自上而下输入下增强 V1 区域的网络抑制，在减少的自上而下输入下减弱抑制，从而维持 V1 神经元对长时间呈现的视觉信号的反应平衡。
