College of Life Sciences, Anhui Normal University, Wuhu, 241000, Anhui, China.
Sci Rep. 2021 Aug 6;11(1):16034. doi: 10.1038/s41598-021-95407-7.
How top-down influence affects neuronal activity and information encoding in the primary visual cortex (V1) remains elusive. This study examined changes of neuronal excitability and contrast sensitivity in cat V1 cortex after top-down influence of area 7 (A7) was modulated by transcranial direct current stimulation (tDCS). The neuronal excitability in V1 cortex was evaluated by visually evoked field potentials (VEPs), and contrast sensitivity (CS) was assessed by the inverse of threshold contrast of neurons in response to visual stimuli at different performance accuracy. We found that the amplitude of VEPs in V1 cortex lowered after top-down influence suppression with cathode-tDCS in A7, whereas VEPs in V1 did not change after sham-tDCS in A7 and nonvisual cortical area 5 (A5) or cathode-tDCS in A5 and lesioned A7. Moreover, the mean CS of V1 neurons decreased after cathode-tDCS but not sham-tDCS in A7, which could recover after tDCS effect vanished. Comparisons of neuronal contrast-response functions showed that cathode-tDCS increased the stimulus contrast required to generate the half-maximum response, with a weakly-correlated reduction in maximum response but not baseline response. Therefore, top-down influence of A7 enhanced neuronal excitability in V1 cortex and improved neuronal contrast sensitivity by both contrast gain and response gain.
自上而下的影响如何影响初级视觉皮层 (V1) 的神经元活动和信息编码仍然难以捉摸。本研究通过经颅直流电刺激 (tDCS) 调节 7 区 (A7) 的自上而下的影响，检查了猫 V1 皮层的神经元兴奋性和对比敏感度的变化。通过视觉诱发电场电位 (VEPs) 评估 V1 皮层的神经元兴奋性，通过神经元对不同表现精度的视觉刺激的阈值对比度的倒数评估对比敏感度 (CS)。我们发现，用阴极 tDCS 抑制 A7 中的自上而下的影响后，V1 皮层中的 VEP 幅度降低，而用 A7 中的假 tDCS 和非视觉皮层 5 区 (A5) 或 A5 中的阴极 tDCS 以及损伤的 A7 后，V1 中的 VEP 没有变化。此外，A7 中的阴极 tDCS 后 V1 神经元的平均 CS 降低，但 A7 中的假 tDCS 后没有降低，并且在 tDCS 效应消失后可以恢复。对神经元对比反应功能的比较表明，阴极 tDCS 增加了产生半最大反应所需的刺激对比度，同时最大反应略有相关减少，但基线反应不变。因此，A7 的自上而下的影响增强了 V1 皮层的神经元兴奋性，并通过对比增益和响应增益提高了神经元的对比敏感度。
