Singing in the Brain: Investigating the Role of Adult Neurogenesis in Long-Term Memory Preservation

Neurogenesis refers to the process of adding new neurons in the brain. It is typically a perinatal phenomenon. However, it can occur in very specific regions of the adult vertebrate brain, usually related to memory. The role of neurogenesis in memory is not yet clear. Some evidence suggests that neurogenesis facilitates new learning, but there is also a case for neurogenesis promoting long-term memory (Alvarez-Buylla and Kirn, 1997, Pytte et al., 2012). The zebra finch brain contains a set of discrete regions specialized for different aspects of song learning, production, and memory. Several of these regions receive new neurons throughout life. This makes the zebra finch an excellent animal model for studying memory in vertebrates. Juveniles learn their songs from adult song tutors. The region of interest in this study is the caudomedial nidopallium (NCM), which is thought to play a dominant role in song perception, especially in memory of the tutor's song. Preliminary studies have used immediate early gene (IEG) expression and electrophysiological techniques to show that NCM preferentially responds to the tutor's song (Bolhuis et al., 2000, Phan et al., 2006). Little is known regarding the function of adult-born neurons in NCM. Could they be involved in this maintenance of the tutor song memory, a song that pre-dates them? In order to address this question, I measured the responsiveness of new neurons to playbacks of tutor song, compared with the responsiveness of the general neuronal population. My research investigated if and how the response properties of new neurons differ from those of the general population when the bird hears its tutor's song for the first time since early life. Neuronal response properties were assessed by way of a triple-labeling protocol that included immediate early gene (IEG) expression to identify cells that were active during song playback, as well as a neuronal marker and a birth marker to identify newly added cells. My research aimed to clarify the differences between neurons added at different points within the zebra finch's development and, more generally, provide a better understanding of the role of neurogenesis and whether it is involved in the formation of new memories, the preservation of old ones, or perhaps both. Preliminary results confirm that newly added neurons can indeed express immediate early genes. However, these new neurons appear to respond to the tutor song in a manner opposing that of the general neuronal population.