Auditory

Hormonal Modulation of Auditory Processing

Induction of Egr-1 (also called ZENK) in two auditory areas in placebo (blank) treated and E2-treated females listening to song (yellow bars) or synthetic tones (blue bars). Among E2-treated females, those hearing song had more Egr-1 labeling in both brain regions than those hearing tones. Among the females hearing tones, E2-treated females had significantly fewer Egr-1 positive cells in the auditory forebrain than placebo treated females.

Research

There is mounting evidence in many species, including humans, that hormones modulate the perception of sensory cues by affecting sensory processing. To investigate how hormones might cause changes in the brain that alter perception, we are working with a seasonally breeding songbird in which hormone levels undergo dramatic changes between fall and spring. These hormones cycles are accompanied by equally dramatic changes in behavior, particularly responses to courtship signals. The female’s behavioral response to male song depends on her plasma levels of estradiol (E2), making this species an ideal model with which to study the effects of hormones on sensory functioning.

We are examining whether plasma E2 affects the female’s responses by changing the way her auditory system processes the songs. We have found that neurons at several levels of the auditory system respond to song more selectively in females that have been treated with E2 to simulate the breeding season. In E2-treated birds, hearing male song induced more synthesis of the protein Egr-1, a marker of new gene transcription, in the auditory system than did hearing frequency-matched synthetic tones. In placebo-treated control birds, however, the Egr-1 response to song and to tones was equivalent. We hypothesize that E2-dependent plasticity of auditory pathways and processing centers may promote recognition of and attention to courtship signals during the breeding season. Work with this model species serves as an example of how hormones alter neuronal function and plasticity in general, and is applicable to all vertebrates including humans.