Optimized Cardiorespiratory State at Tone Onset Enhances Sensory Responses but Not Associative Learning in Healthy Adults.

Previous studies suggest that when a tone-conditioned stimulus (CS) predicting an airpuff towards the eye is presented at diastole during expiration, both sensory responses to the CS and trace eyeblink conditioning (TEBC) are enhanced. However, not all participants learn and individual variation in the body-brain relationship remains overlooked. We studied whether timing the CS based on an individually optimized bodily state enhances sensory responses and TEBC. We assumed so, as sensory response magnitude reflects attention and stimulus salience: A salient CS should facilitate TEBC. Forty-one young adults and 19 older adults completed a passive auditory task while electrocardiogram, respiration and electroencephalogram were recorded. The cardiorespiratory state associated with the largest N1-P2 response was identified individually. Optimal states varied across participants and did not differ between age groups. Participants underwent TEBC at their optimal state (Personalized) or at diastole during expiration (Control). As expected, the CS evoked a larger N1-P2 response in the Personalized than the Control group. However, conditioned responding, peak performance, and learning rate, or the proportion of good learners did not differ between groups. Older adults learned more slowly, made fewer conditioned responses, and were less aware of the tone-airpuff association than young adults. These findings tentatively suggest that enhancing early sensory processing of the CS may not improve TEBC, although the low reliability of the individually determined optimal state limits this conclusion. Future studies should examine whether timing external stimuli to specific bodily states effectively influences behaviour in tasks that rely on rapid sensory processing.