Sensory feedback independent pre-song vocalizations correlate with current state of motor preparation

Many self-initiated, learned, motor sequences begin by repeating a simple movement, like ball-bouncing before a tennis serve, and this repetition is thought to represent motor preparation. Do these simple movements provide real-time sensory feedback used by the brain for getting ready or do they simply reflect internal neural preparatory processes? Here, we addressed this question by examining the introductory notes (INs) that zebra finches repeat before starting their learned song sequence. INs progress from a variable initial state to a stereotyped final state before each song and are thought to represent motor preparation before song. Here, we found that the mean number of INs before song and the progression of INs to song were not affected by removal of two sensory feedback pathways (auditory and proprioceptive). In both feedback-intact and feedback-deprived birds, the presence of calls (other non-song vocalizations), just before the first IN, was correlated with fewer INs before song and an initial state closer to song. Finally, the initial IN state correlated with the time to song initiation. Overall, these results show that INs do not provide real-time sensory feedback for preparing the motor system. Rather, repetition of INs, and possibly, other such simple movements, may reflect the ″current″ state of internal neural preparatory processes involved in getting the brain ready to initiate a learned movement sequence.