The fovea is a neural specialization that endows humans and other primates with the sharpest vision among mammals. This performance originates in the foveal cones, which are extremely narrow and long to form a high-resolution pixel array. Puzzlingly, this form is predicted to impede electrical conduction to an extent that appears incompatible with vision. We observe the opposite: signal flow through even the longest cones (0.4-mm axons) is essentially lossless. Unlike in most neurons, amplification and impulse generation by voltage-gated channels are dispensable. Rather, sparse channel activity preserves intracellular current, which flows as if unobstructed by organelles. Despite these optimizations, signaling would degrade if cones were lengthier. Because cellular packing requires that cone elongation accompanies foveal expansion, this degradation helps explain why the fovea is a constant, miniscule size despite multiplicative changes in eye size through evolution. These observations reveal how biophysical mechanisms tailor form-function relationships for primate behavioral performance.

中央凹是一种神经特化，赋予人类和其他灵长类动物在哺乳动物中最敏锐的视觉。这种性能源于中央凹锥体，它们极窄且长，以形成高分辨率像素阵列。令人费解的是，预计这种形式会在与视觉不相容的程度上阻碍电传导。我们观察到相反的情况：即使是最长的锥体（0.4 毫米轴突）的信号流也基本上是无损的。与大多数神经元不同，电压门控通道的放大和脉冲生成是可有可无的。相反，稀疏的通道活动保留了细胞内电流，其流动就像不受细胞器阻碍一样。尽管进行了这些优化，但如果视锥细胞更长，则信号会降低。因为细胞堆积要求锥体伸长伴随中央凹扩张，这种退化有助于解释为什么尽管眼睛大小在进化过程中发生了倍增的变化，但中央凹仍然是一个恒定的、微小的大小。这些观察结果揭示了生物物理机制如何为灵长类动物的行为表现定制形式-功能关系。