Strange Bedfellows? Protein Degradation and Neurological Dysfunction

as well as why brain areas are differentially activated song system is likely to yield important insights into during these behaviors, is not clear. One possibility is the mechanisms underlying the differences observed that the differential activation of the anterior pathway between directed and undirected singing. More gener-during undirected and directed song may serve to coor-ally, important mechanistic insight into the functioning dinate other motor behaviors that are generally associ-of the song system is likely to emerge from a deeper ated with these different song types. For example, when understanding of the mammalian cortical–basal ganglia the male directs his song to a female, the anterior path-pathway and its role in motor control and function, while, way may well be optimized to coordinate, or bind, song conversely, work on the mammalian basal ganglia will motor activity with other motor behaviors such as the likely benefit from a deeper understanding of the song courtship dance, which is only observed during directed system. singing. The use of immediate-early genes, such as ZENK, as Marc F. Schmidt markers for neural activity, provides a powerful tool that Division of Biology can be used in identifying new ways in which neural California Institute of Technology circuits may be organized. As the authors point out, Pasadena, California 91125 however, interpreting the relationship between ZENK expression and neural activity should be done cau-Selected Reading tiously. A case in point is the pattern of ZENK expression observed in nucleus RA. ing neural activity in birds singing under different behav