Neural processing of auditory stimuli in rats: Translational aspects using auditory oddball paradigms.

Background: The three-class oddball paradigm allows to investigate the processing of behaviorally relevant and irrelevant auditory stimuli. In humans, event-related potentials (ERPs) are used as neural correlate of behavior. We recorded local field potentials (LFPs) within the medial prefrontal cortex (mPFC) in rats during three-class and passive two-class oddball paradigms and analyzed the ERPs focusing on similarities to human recordings.

New Method: Rats were trained in a three-class auditory oddball paradigm to respond by nose poke to an infrequent Target tone that was rewarded, while ignoring an infrequent Distractor and frequent Standard tone of different frequencies. After reaching a success criterion of correct responses to the Target and correct rejection of the Standard and Distractor (80 %, each), electrodes were stereotaxically implanted into the mPFC. The recording of the neuronal activity took place in the three-class oddball paradigm as well as in a passive two-class oddball paradigm with unfamiliar frequencies.

Results: Correct responding to the Target tone was accompanied by a higher amplitude of the ERP in comparison to the Standard and Distractor tones (p < 0.05). Target Miss, or incorrect responding to Distractor or Standard led to reduced, respectively enhanced peak latency. In the two-class oddball paradigm, the amplitude of the Distractor ERP was enhanced as compared to that after Standard (p < 0.05).

Conclusion: ERPs derived from mPFC LFPs of rats show key characteristics similar to that derived from human EEGs. This model allows to investigate the processing of behaviorally important and irrelevant auditory stimuli in subcortical brain regions in a translational approach.