The impact of cardiac phases on multisensory integration

The brain continuously processes information coming from both the external environment and visceral signals generated by the body. This constant information exchange between the body and the brain allows signals originating from the oscillatory activity of the heart, among others, to influence perception. Here, we investigated how the cardiac phase modulates multisensory integration, which is the process that allows information from multiple senses to combine non-linearly to reduce environmental uncertainty. Forty healthy participants completed a Simple Detection Task with unimodal (Auditory, Visual, Tactile) and bimodal (Audio-Tactile, Audio-Visual, Visuo-Tactile) stimuli presented 250 ms and 500 ms after the R-peak of the electrocardiogram, that is, systole and diastole, respectively. First, we found a nonspecific effect of the cardiac cycle phases on detection of both unimodal and bimodal stimuli. Reaction times were faster for stimuli presented during diastole, compared to systole. Then, applying the Race Model Inequality approach to quantify multisensory integration, Audio-Tactile and Visuo-Tactile, but not Audio-Visual stimuli, showed higher integration when presented during diastole than during systole. These findings indicate that the impact of the cardiac phase on multisensory integration may be specific for stimuli including somatosensory (i.e., tactile) inputs. This suggests that the heartbeat-related noise, which according to the interoceptive predictive coding theory suppresses somatosensory inputs, also affects multisensory integration during systole. In conclusion, our data extend the interoceptive predictive coding theory to the multisensory domain. From a more mechanistic view, they may reflect a reduced optimization of neural oscillations orchestrating multisensory integration during systole.