Physiological identification of cortico-striatal projection neurons for song control in Bengalese finches

The avian song system is a group of brain areas specialized for vocal learning and production of song. A major cortical control area, HVC, projects both to a motor output circuit and to a striatal area in the anterior forebrain pathway. These projections are made by two groups of neurons, with mainly distinct roles in either programming vocal production or regulating vocal plasticity. In order to distinguish these two types of projection neurons in singing birds, we recorded unit activity in HVC of anesthetized birds, while stimulating in the anterior forebrain nucleus Area X. HVC units identified in this way had a distinct spike waveform, with a much longer duration positive peak than an initial negative one. We further found that units with a very similar spike waveform were phasically active during singing, firing at specific points of a limited number of song syllables. These units were also less active when birds only heard their own song, during the same syllables. While similar results from anesthetized and awake recordings have been reported in previous studies, the combination of both types of experiments here may be useful as a basis for identifying HVC neurons projecting to Area X based on their spike waveforms, and aid further study of their role in song learning and control.