Fear conditioning to discontinuous auditory cues requires perirhinal cortical function

Area of Science:

• Neuroscience
• Behavioral Neuroscience
• Auditory Processing

Background:

• The perirhinal cortex (PR) is implicated in associative learning and memory.
• Previous research indicates PR lesions impair fear conditioning to ultrasonic vocalizations (USVs).
• The specific features of USVs that engage PR-dependent fear conditioning remain unclear.

Purpose of the Study:

• To investigate which stimulus features of USVs necessitate perirhinal cortex (PR) involvement in fear conditioning.
• To differentiate the roles of temporal patterning versus spectral complexity in PR-dependent auditory fear conditioning.

Main Methods:

• Rats underwent fear conditioning using three auditory stimuli: a multicall 19-kHz USV, a 19-kHz discontinuous tone mimicking the USV's temporal pattern, and a 19-kHz continuous tone.
• Neurotoxic lesions were targeted to the PR cortex in a subset of rats.
• Fear conditioning performance was assessed for each stimulus type and the training context.

Main Results:

• PR lesions significantly impaired fear conditioning to the USV and the discontinuous tone.
• PR lesions also impaired fear conditioning to the training context.
• Conditioning to the continuous 19-kHz tone was unaffected by PR lesions.
• The discontinuous tone replicated the temporal structure of the USV but lacked its frequency modulations.

Conclusions:

• The perirhinal cortex (PR) is essential for fear conditioning to auditory stimuli with complex temporal structures, even when spectral complexity is absent.
• PR lesions do not impair fear conditioning to simple, continuous tones.
• These findings support the hypothesis that the PR cortex plays a critical role in binding disparate stimulus elements into coherent, unitary representations for associative learning.