Department of Zoology, University of British Columbia, 4200-6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada.
Department of Zoology, University of British Columbia, 4200-6270 University Boulevard, Vancouver, BC V6T 1Z4, Canada; Department of Biological Sciences, University of Alberta, CW 405 Biological Sciences Building, Edmonton, AB T6G 2E9, Canada; Structure and Motion Laboratory, Royal Veterinary College, University of London, Hatfield AL9 7TA, UK.
Curr Biol. 2022 Jun 20;32(12):2772-2779.e4. doi: 10.1016/j.cub.2022.04.076. Epub 2022 May 23.
All visual animals experience optic flow-global visual motion across the retina, which is used to control posture and movement. The midbrain circuitry for optic flow is highly conserved in vertebrates, and these neurons show similar response properties across tetrapods. These neurons have large receptive fields and exhibit both direction and velocity selectivity in response to large moving stimuli. Hummingbirds deviate from the typical vertebrate pattern in several respects. Their lentiformis mesencephali (LM) lacks the directional bias seen in other tetrapods and has an overall bias for faster velocities. This led Ibbotson to suggest that the hummingbird LM may be specialized for hovering close to visual structures, such as plants. In such an environment, even slight body motions will translate into high-velocity optic flow. A prediction from this hypothesis is that hummingbird LM neurons should be more responsive to large visual features. We tested this hypothesis by measuring neural responses of hummingbirds and zebra finches to sine wave gratings of varying spatial and temporal frequencies. As predicted, the hummingbird LM displayed an overall preference for fast optic flow because neurons were biased to lower spatial frequencies. These neurons were also tightly tuned in the spatiotemporal domain. We found that the zebra finch LM specializes along another domain: many neurons were initially tuned to high temporal frequencies followed by a shift in location and orientation to slower velocity tuning. Collectively, these results demonstrate that the LM has distinct and specialized tuning properties in at least two bird species.
所有有视觉的动物都能体验到光流——视网膜上的全局视觉运动，这有助于控制姿势和运动。脊椎动物的中脑光流回路高度保守，这些神经元在四足动物中表现出相似的反应特性。这些神经元具有较大的感受野，并对大运动刺激表现出方向和速度选择性。蜂鸟在几个方面偏离了典型的脊椎动物模式。它们的中脑 Lentiformis（LM）缺乏其他四足动物中看到的方向偏差，整体上对更快的速度有偏向。这导致 Ibbotson 提出，蜂鸟的 LM 可能专门用于在视觉结构（如植物）附近悬停。在这样的环境中，即使是轻微的身体运动也会转化为高速光流。这一假设的一个预测是，蜂鸟的 LM 神经元应该对大的视觉特征更敏感。我们通过测量蜂鸟和斑马雀对不同空间和时间频率正弦光栅的神经反应来验证这一假设。正如预测的那样，蜂鸟的 LM 由于神经元偏向较低的空间频率，因此整体上偏好快速光流。这些神经元在时空域也被紧密调谐。我们发现，斑马雀的 LM 沿着另一个领域专业化：许多神经元最初对高时间频率敏感，然后位置和方向发生变化，对较慢的速度调谐。总之，这些结果表明，LM 在至少两种鸟类中具有独特而专门的调谐特性。
