Developmental and evolutionary changes in sensorimotor integration to maintain coordination of corollary discharge and afferent input in electric fish.

Nervous systems generate predictions using internal copies of motor commands, termed corollary discharge (CD). CD modulates sensory neurons to distinguish self-generated sensory inputs (reafference) from external inputs (exafference). As behavior changes throughout development and evolution, these predictions must update as reafference changes. However, mechanisms that synchronize CD to reafferent input remain unknown. Mormyrid fish communicate using electric organ discharges (EODs). To distinguish reafferent and exafferent EODs, a CD inhibits sensory neurons whenever a reafferent EOD is produced. EOD duration varies across and within species, and a yet-unknown mechanism precisely time-locks inhibition with reafference. Likewise, seasonal increases in testosterone reversibly elongate male EODs in some species, and testosterone shifts CD timing to match changing reafference. To identify the neural substrates of hormonal CD shifts, we treated Brienomyrus brachyistius with testosterone and recorded field potentials from six nuclei linking electromotor, CD, and electrosensory pathways. Testosterone delayed and elongated field potentials in the mesencephalic command-associated nucleus (MCA) of the CD pathway, which shifted downstream activity. We identified substrates of evolutionary and age-related shifts in two species of Campylomormyrus with dramatically different EODs: one with short-duration EODs and one with long EODs that can elongate as individuals age. Both inter- and intraspecies EOD variation was associated with the onset and duration of MCA field potentials. We find distinct processes-hormonal plasticity over days, age-related changes over years, and evolutionary divergence-converge on a common substrate to synchronize CD with reafference. This suggests that sensorimotor systems can evolve a shared solution for temporal coordination across timescales.