Adult neuroplasticity in the song control system of seasonal songbirds is largely driven by photoperiod-induced increases in testosterone. Prior studies of the relationships between testosterone, song performance and neuroplasticity used invasive techniques, which prevent analyzing the dynamic changes over time and often focus on pre-defined regions-of-interest instead of examining the entire brain. Here, we combined (i) in vivo diffusion tensor imaging (DTI) to assess structural neuroplasticity with (ii) repeated monitoring of song and (iii) measures of plasma testosterone concentrations in thirteen female photosensitive starlings (Sturnus vulgaris) who received a testosterone implant for 3 weeks. We observed fast (days) and slower (weeks) effects of testosterone on song behavior and structural neuroplasticity and determined how these effects correlate on a within-subject level, which suggested separate contributions of the song motor and anterior forebrain pathways in the development of song performance. Specifically, the increase in testosterone correlated with a rapid increase of song rate and RA volume, and with changes in Area X microstructure. After implant removal, these variables rapidly reverted to baseline levels. In contrast, the more gradual improvement of song quality was positively correlated with the fractional anisotropy values (DTI metric sensitive to white matter changes) of the HVC-RA tract and of the lamina mesopallialis, which contains fibers connecting the song control nuclei. Thus, we confirmed many of the previously reported testosterone-induced effects, like the increase in song control nuclei volume, but identified for the first time a more global picture of the spatio-temporal changes in brain plasticity.

中文翻译：

---

体内在线监测雌性鸣禽中睾丸激素诱导的神经可塑性。

季节性鸣禽的歌曲控制系统中的成人神经可塑性在很大程度上受光周期诱导的睾丸激素增加的驱动。先前对睾丸激素，歌曲演奏和神经可塑性之间关系的研究使用了侵入性技术，这种技术无法分析随时间变化的动态变化，并且通常侧重于预先定义的目标区域，而不是检查整个大脑。在这里，我们结合了（i）体内扩散张量成像（DTI）来评估结构神经可塑性，（ii）重复监测歌曲，以及（iii）接受睾丸激素植入的13只雌性八哥雌性八哥（Sturnus vulgaris）血浆睾酮浓度的测量3个星期。我们观察到睾丸激素对歌曲行为和结构神经可塑性的快速（几天）和较慢（几周）的影响，并确定了这些影响在受试者内水平上的相关性，这表明歌曲运动和前脑前路在歌曲发展中的独立贡献性能。具体而言，睾丸激素的增加与歌曲速度和RA音量的快速增加以及X区域微结构的变化相关。去除种植体后，这些变量迅速恢复到基线水平。相反，歌曲质量的逐步改善与HVC-RA片段和中隔层板（包含连接歌曲控制核的纤维）的分数各向异性值（对白质变化敏感的DTI度量）呈正相关。从而，