Functional and structural plasticity induced by audiovisual associations and sensory experiences.

Crossmodal associations and correspondences play important roles in shaping perception and guiding our actions. However, we still have a limited understanding of association-induced changes in the adult human brain. An important question to address is to what extent passive exposure to crossmodal associations leads to functional and structural changes in the brain. Utilizing an audiovisual association paradigm in which motion stimuli presented in the left visual field were paired with auditory tones, we investigated experience-dependent crossmodal plasticity by examining resting-state functional connectivity and cortical thickness. Following the association phase, we observed widespread increases in functional connectivity between the trained region (e.g., right V1, V2, and V3) and higher-order frontal, temporal, and occipital areas. In contrast, functional connectivity changes in the untrained region (e.g., left V1, V2, and V3) were markedly reduced, indicating that the observed plasticity was largely specific to the cortical representation of the stimulated visual field. Consistent with the functional results, cortical thickness analysis revealed a clear hemispheric asymmetry, with significant changes observed exclusively in the right hemisphere. Moreover, both the functional and structural assessments showed widespread changes in high-level association cortices, whereas changes in low-level sensory areas were less pronounced. The overlap between functional and structural measures suggests that enhanced connectivity aligns with structural changes due to crossmodal associations. These results illustrate that associations formed without explicit training or feedback can lead to functional and structural changes in the adult human brain, providing important implications for perception and neural plasticity in daily life situations.