Mirror neurons in humans and other primates fire both when a given action is either performed or observed (see the 'mirror neuron' category in the left column of this blog.) Now Prather et al. have found similar neurons in the swamp sparrow, which like humans depends on auditory experience to learn its vocal repertoire. These forebrain neurons are specialized for auditory-vocal monitoring and have virtually the same response to a given note sequence, whether performed or heard. They also innervate striatal structures important for song learning, raising the possibility that singing-related activity in these cells is compared to auditory feedback to guide vocal learning. Here is a graphic from a New and Views article on this work by Tchernichovski1 & Wallman in the same issue of Nature.
(click to enlarge) Figure legend: The neurons identified by Prather and colleagues could be involved in three sensorimotor processes. a, The delayed corollary discharge of song patterns can be simultaneously compared with auditory feedback of the bird's own song, allowing tuning. b, The auditory responses (in the mirroring neurons) to songs of a neighbour might be compared with the memory of the corollary discharge produced during singing. This might allow the bird to identify an imitation by that neighbour. c, Corollary discharges while singing might be compared with a memory of the mirroring neurons' response to the parent's song. The error may then feed back to the song generator and guide vocal learning during song development, in addition to guidance from auditory input during singing (lowest arrow).