RARE TARGET PROBABILITY ENHANCES CM–PF ERP AMPLITUDES WHILE REDUCING BEHAVIORAL RESPONSES IN RATS PERFORMING A THREE-CLASS AUDITORY ODDBALL PARADIGM

The three-class auditory oddball paradigm, in which participants must respond to rare target tones amongst frequent standard and rare distractor tones, enables the study of sensory processing, attentional control, and decision-making processes. The thalamic centromedian-parafascicular (CM-Pf) complex regulates attention and salience by acting as a filter for 'important events'. This study examined how intertrial interval (ITI) length and target tone presentation probability influence behavior and neural response of the CM-Pf.
Male Sprague–Dawley rats (n=10) were trained to respond to rare target tones (5000 Hz) while ignoring rare distractor (1500 Hz) and frequent standard tones (3000 Hz). Following training, electrodes were implanted in a stereotaxic surgery under anesthesia into the CM-Pf to record local field potentials (LFPs) and extract ERPs. Experimental sessions varied in the proportion of target tones (5% vs. 20%) and in the length of the ITI (short: ~0.1sec vs. long: ~9sec). CM-Pf LFPs were recorded during behavioral testing.
Correct response rate to targets was lower when the targets were rare (5%) than when they were more frequent (20%) among the standard tones (p<0.05). Low performance was accompanied by higher early and late ERP amplitudes in the CM-Pf (p<0.05). Behavioral performance was best with long ITI accompanied by 20% target probability (p<0.05) with no effect on early and late ERP amplitude.
Our findings indicate that target occurrence and ITI length modulates behavioral performance and neural processing within the CM-Pf. Together, these results provide a translational framework for probing neurophysiological mechanisms of attention and stimulus evaluation.