Acoustic Context Modulates Natural Sound Discrimination in Auditory Cortex through Frequency-Specific Adaptation

Area of Science:

• Neuroscience
• Auditory Processing
• Animal Communication

Background:

• Sound discrimination is crucial for survival in many species, including bats, which use echolocation for navigation and communication calls for social interactions.
• The bat auditory cortex processes both echolocation and communication sounds, but how neurons respond to sequences of these sounds (acoustic transitions) is not well understood.

Purpose of the Study:

• To investigate how acoustic context, specifically sequences of sounds preceding a target sound, influences neuronal responses in the bat auditory cortex.
• To determine if neuronal selectivity for echolocation versus communication calls changes based on the preceding acoustic environment.

Main Methods:

• Recorded neuronal activity in the auditory cortex of awake bats of both sexes.
• Presented sequences of sounds (context) followed by a target sound (echolocation or communication call).
• Developed and utilized a computational neuron model based on stimulus-specific adaptation to replicate and predict observed neuronal responses.

Main Results:

• Acoustic context significantly altered neuronal selectivity: nonselective neurons became category-selective, while some selective neurons became nonselective.
• Context induced stimulus-specific response suppression, with stronger suppression when context and target sounds belonged to the same category.
• A computational model successfully replicated these findings, predicting stimulus-specific adaptation and long-lasting context effects (up to 1.5 s).

Conclusions:

• Two distinct neuronal populations exist in the bat auditory cortex: those that discriminate well between social and echolocation sounds, and those that respond similarly to both.
• Acoustic context plays a critical role in shaping natural sound selectivity in the auditory cortex, in ways not predictable from responses to isolated sounds.
• A computational model incorporating segregated inputs, synaptic depression, and postsynaptic adaptation can explain context-dependent neuronal processing of natural sounds in bats.