Department of Psychology, College of Arts and Science, Vanderbilt Vision Research Center, Center for Integrative and Cognitive Neuroscience, Vanderbilt University, Nashville, TN 37235
Princeton Neuroscience Institute, Princeton University, Princeton, NJ 09540.
eNeuro. 2021 Apr 8;8(2). doi: 10.1523/ENEURO.0364-20.2020. Print 2021 Mar-Apr.
The lateral geniculate nucleus (LGN) of the dorsal thalamus is the primary recipient of the two eyes' outputs. Most LGN neurons are monocular in that they are activated by visual stimulation through only one (dominant) eye. However, there are both intrinsic connections and inputs from binocular structures to the LGN that could provide these neurons with signals originating from the other (non-dominant) eye. Indeed, previous work introducing luminance differences across the eyes or using a single-contrast stimulus showed binocular modulation for single unit activity in anesthetized macaques and multiunit activity in awake macaques. Here, we sought to determine the influence of contrast viewed by both the non-dominant and dominant eyes on LGN single-unit responses in awake macaques. To do this, we adjusted each eye's signal strength by independently varying the contrast of stimuli presented to the two eyes. Specifically, we recorded LGN single unit spiking activity in two awake macaques while they viewed drifting gratings of varying contrast. We found that LGN neurons of all types [parvocellular (P), magnocellular (M), and koniocellular (K)] were significantly suppressed when stimuli were presented at low contrast to the dominant eye and at high contrast to the non-dominant eye. Further, the inputs of the two eyes showed antagonistic interaction, whereby the magnitude of binocular suppression diminished with high contrast in the dominant eye, or low contrast in the non-dominant eye. These results suggest that the LGN represents a site of precortical binocular processing involved in resolving discrepant contrast differences between the eyes.
背外侧膝状体（LGN）是双眼输出的主要接收者。大多数 LGN 神经元是单眼的，因为它们仅通过一只（主导）眼睛的视觉刺激而被激活。然而，LGN 中存在内在连接和来自双眼结构的输入，这些输入可以为这些神经元提供来自另一只（非主导）眼睛的信号。事实上，之前的工作表明，在麻醉猕猴中，通过跨眼引入亮度差异或使用单对比度刺激，可以在单单元活动中观察到双眼调制，在清醒猕猴中观察到多单元活动。在这里，我们试图确定非主导眼和主导眼所看到的对比度对清醒猕猴 LGN 单单元反应的影响。为此，我们通过独立改变向两只眼睛呈现的刺激对比度来调整每只眼睛的信号强度。具体来说，我们在两只清醒的猕猴中记录了 LGN 单单元的尖峰活动，同时它们观看了变化对比度的漂移光栅。我们发现，当主导眼的对比度较低，而非主导眼的对比度较高时，所有类型的 LGN 神经元（小细胞（P）、大细胞（M）和 koniocellular（K））均受到显著抑制。此外，两只眼睛的输入表现出拮抗相互作用，即主导眼的对比度增加或非主导眼的对比度降低，双眼抑制的幅度减小。这些结果表明，LGN 代表了参与解决眼睛之间差异对比度差异的皮质前双眼处理的一个部位。
