FIGURE 6. HVCX neurons that express categorical auditory responses also express a precise and selective sensorimotor correspondence.

(A) Using the same approach as described in Figure 4, categorical responsiveness was detected in this HVCX neuron (different cell and different bird than in Figure 4). (B) A precise sensorimotor correspondence was also evident in this neuron (same cell as in panel A). That correspondence was evident as precise alignment activity of this cell when the bird sang the primary song type (top: singing-related action potentials; bottom: song spectrogram, 15-syllable trill clipped for clarity) and when the bird heard the primary song type played through a speaker (middle: auditory action potentials). This sort of sensorimotor correspondence was detected in all cells in which it was tested in swamp sparrows (7/7 cells in 3 birds) and Bengalese finches (7/7 cells in 2 birds) (Prather et al., 2008). Fujimoto and colleagues (2011) also found this sort of sensorimotor correspondence in HVCX cells of Bengalese finches. The prevalence of this correspondence is greater in our hands (100%) than in their data (31%), likely due to our assessment of each cell's auditory response using exactly the song that was recorded in association with singing-related activity in that cell. A detailed consideration of such features as the latency of action potentials in the hearing and singing states, as well as the production of single action potentials in the hearing state and bursts in the singing state can be found in our previous publication (Prather et al., 2008).