A Novel Neural Circuit for Birdsong Learning
When I applied to graduate school in neuroscience back in the day, most of my cohort didn’t quite know which lab they wanted to join, but I was crystal clear about Richard Mooney’s birdsong lab at Duke University. I totally had a science crush. Ultimately, I didn’t get into Duke, yet I’ve remained a fan of Rich’s work (See this video from his interview as an Inscopix DECODE awardee). His group studies the neurobiology of communication in the zebra finch, a neuroscience model system rooted in natural animal behavior. Zebra finch males sing to court females, and they learn to sing from older, more experienced males. They have a specialized area in the brain that controls vocal learning and singing, making them an excellent model for understanding the interplay between motor and auditory systems during communication.
In an interview Inscopix had with Richard Mooney, he said his music drove his interest in the birdsong system. Rich plays classical guitar. And like a neuroscience rockstar, he and his lab continue to push the boundaries of what we understand about learning and sensorimotor integration. In this new paper, first author Todd Roberts and colleagues identify a novel neural circuit mechanism for a motor-to-auditory pathway important for vocal learning in zebra finches. They functionally characterize a circuit from HVC to Av or Avalanche, an analog of the mammalian secondary auditory cortex. Thus, this neural circuit transmits vocal motor signals to the auditory cortex. HVC has projection neurons going to a basal ganglia region Area X and song motor nucleus RA, both of which carry important information for song learning. This newly characterized projections from HVC to Av are distinct from those to Area X or RA, as shown by retrograde tracer studies. But what role does this circuit have in song learning?
The authors get at this question in several ways, one of which is to measure neural activity specifically in the HVC to Av projection neurons while a bird sings. To do so, the authors leverage the Inscopix nVista system for visualizing Ca2+ activity in hundreds of cells while the birds freely behave and sing. Rich described an advantage of using the Inscopix technology as giving an “unbiased screen of neural activity.” Indeed, with the head-mounted nVista miniature microscope, they are the first to see song motor-related signals in the HVC to Av projection neurons. They also show that genetic ablation of HVC to Av neurons in juvenile zebra finches impairs their ability to copy a tutor song. Ablation in adult birds indicates the HVC to Av circuit is necessary for temporal modification but not spectral features (like pitch) of the adult’s song. They show that HVC-->Av cells receive input from HVC-->RA cells, providing a source of premotor signals for song timing. But HVC cells do not receive input from HVC-->X cells. The authors explain how this selective organization could enable HVC-->Av cells to provide a direct source of song-timing information to the auditory system. They conclude this is the first song neural circuit to suggest a forward mechanism transmitting vocal motor-related information important to vocal learning.
Read the paper here in Nature Neuroscience.