A long held view in the spinal cord injury field is that corticospinal terminal sprouting is needed for new connections to form, that then mediate behavioral recovery. This makes sense, but tells us little about the relationship between corticospinal sprouting extent and recovery potential. The inference has been that more extensive axonal sprouting predicts greater recovery, though there is little evidence to support this. Here we addressed this by comparing behavioral data from monkeys that had received one of two established deafferentation spinal injury models in monkeys (Darian-Smith et al., 2014, Fisher et al., 2019, 2020). Both injuries cut similar afferent pools supplying the thumb, index and middle fingers of one hand but each resulted in a very different corticospinal tract (CST) sprouting response. Following a cervical dorsal root lesion, the somatosensory CST retracted significantly, while the motor CST stayed largely intact. In contrast, when a dorsal column lesion was combined with the DRL, somatosensory and motor CSTs sprouted dramatically within the cervical cord. How these two responses relate to the behavioral outcome was not clear. Here we analyzed the behavioral outcome for the two lesions, and provide a clear example that sprouting extent does not track with behavioral recovery.

脊髓损伤领域长期持有的观点是，新连接的形成需要皮质脊髓末端萌芽，然后介导行为恢复。这是有道理的，但几乎没有告诉我们皮质脊髓萌芽程度和恢复潜力之间的关系。推论是更广泛的轴突发芽预示着更大的恢复，尽管几乎没有证据支持这一点。在这里，我们通过比较猴子的行为数据来解决这个问题，这些猴子接受了两种已建立的猴子传入神经阻断性脊髓损伤模型之一（Darian-Smith 等人，2014 年；Fisher 等人，2019 年、2020 年）。两种损伤都切断了类似的传入池，为一只手的拇指、食指和中指提供能量，但每种损伤都导致了截然不同的皮质脊髓束 (CST) 萌芽反应。在颈椎背根损伤后，体感 CST 明显收缩，而运动 CST 基本保持完好。相反，当背柱损伤与 DRL 相结合时，体感和运动 CST 在颈髓内显着萌芽。这两种反应如何与行为结果相关尚不清楚。在这里，我们分析了两个病变的行为结果，并提供了一个明显的例子，即发芽程度不随行为恢复而变化。