How neuronal recognition of songbird calls unfolds over time

Songbirds use distinct vocal calls to convey different types of information, such as communicating hunger or warning about a nearby predator. Using a large database of zebra finch sounds, Elie and Theunissen previously showed that when one bird hears another's calls, neurons in the auditory region of its brain respond differently to different calls, depending on the different meanings of those calls.

Now, the researchers have investigated how that process of neuronal recognition of different call meanings unfolds over time. Using a mathematical framework known as information theory, they developed a novel method for studying the response of sensory systems to stimuli that must be classified into different categories. They applied it to analyze recordings taken of neuronal activity in finches while they listened to others' calls.

The analysis showed that, for a given recording of a single neuron's activity in response to a call, the initial response contains some information about the call's meaning, but additional information continues to accumulate for up to 600 milliseconds. The onset phase and the sustained response phase capture a similar amount of information about the meaning of the call. The researchers also identified individual neurons that may play a bigger role than others in categorizing the meaning of a given call.

"We found a new method to calculate how information about a behaviorally meaningful category of sounds unfolds in time while an individual is processing communication signals, performing the necessary transformations from sound to meaning," Elie says.

She and Theunissen plan to continue using experimental and computational methods to explore how songbirds' brains process the meanings of different calls. Meanwhile, the novel information theory approach they developed could be applied to other sensory and motor systems in other species to better understand how information processing unfolds over time at the neuronal level.