In neural networks that store information in their connection weights, there is a tradeoff between sensitivity and stability^1,2. Connections must be plastic to incorporate new information, but if they are too plastic, stored information can be corrupted. A potential solution is to allow plasticity only during epochs when task-specific information is rich, on the basis of a ‘when-to-learn’ signal³. We reasoned that dopamine provides a when-to-learn signal that allows the brain’s spatial maps to update when new spatial information is available—that is, when an animal is moving. Here we show that the dopamine neurons innervating the Drosophila head direction network are specifically active when the fly turns to change its head direction. Moreover, their activity scales with moment-to-moment fluctuations in rotational speed. Pairing dopamine release with a visual cue persistently strengthens the cue’s influence on head direction cells. Conversely, inhibiting these dopamine neurons decreases the influence of the cue. This mechanism should accelerate learning during moments when orienting movements are providing a rich stream of head direction information, allowing learning rates to be low at other times to protect stored information. Our results show how spatial learning in the brain can be compressed into discrete epochs in which high learning rates are matched to high rates of information intake.

在将信息存储在连接权重中的神经网络中，需要在灵敏度和稳定性之间进行权衡^1,2。连接必须是塑料的才能容纳新信息，但如果塑料太强，存储的信息可能会被损坏。一个潜在的解决方案是，基于“何时学习”信号，仅在特定任务信息丰富的时期允许可塑性³。我们推断，多巴胺提供了何时学习的信号，使大脑的空间图能够在新的空间信息可用时（即当动物移动时）进行更新。在这里，我们展示了支配果蝇的多巴胺神经元当苍蝇转向改变其头部方向时，头部方向网络特别活跃。此外，它们的活动随着转速的瞬时波动而变化。将多巴胺释放与视觉提示配对会持续增强提示对头部方向细胞的影响。相反，抑制这些多巴胺神经元会降低提示的影响。当定向运动提供丰富的头部方向信息流时，这种机制应该会加速学习，从而允许在其他时间较低的学习率以保护存储的信息。我们的结果表明，大脑中的空间学习如何被压缩成离散的时期，其中高学习率与高信息摄入率相匹配。