Neural mechanisms of intersensory switching: Evidence for delayed sensory processing and increased cognitive demands.

Intersensory switching (IS), the ability to shift attention between different sensory systems, is essential for cognitive flexibility, yet leads to slower responses compared to repeating the same sensory modality. The underlying neural mechanisms of IS remain largely unknown. In this study, high-density EEG was used to investigate these mechanisms in healthy adults (n = 53; mean age 26±7.39; 30 female) performing a speeded reaction time (RT) task involving visual and auditory stimuli. Trials were categorized as Repeat (same preceding modality) or Switch (different preceding modality). Switch trials showed slower RTs and delayed sensory responses (N1 and P2 components). Furthermore, across both Repeat and Switch trials, RT correlated with the latency of these neural responses. Additionally, lower alpha-band inter-trial phase coherence (ITPC) in primary sensory regions was noted for Switch compared to Repeat trials, suggesting reduced efficiency of sensory processing. Greater induced theta activity over fronto-central scalp regions in Switch trials suggested increased cognitive control demands. These findings support a model where the prior stimulus primes the sensory cortex for faster processing of Repeat trials, while Switch trials lead to heightened cognitive resources for adjustment, likely reflecting attentional reallocation mediated by the anterior cingulate cortex (ACC). The consistent effects across auditory and visual modalities indicate that IS relies on a core, modality-independent mechanism grounded in fundamental principles of sensory and attentional reorganization.