Time-dependent changes in learning audiovisual associations: A single-trial fMRI study

Functional imaging studies of learning and memory have primarily focused on stimulus material presented within a single modality (see review by Gabrie li, 1998, Annu. Rev. Psychol. 49: 87-115). In the present study we investig ated mechanisms for learning material presented in visual and auditory moda lities, using single-trial functional magnetic resonance imaging. We evalua ted time-dependent learning effects under two conditions involving presenta tion of consistent (repeatedly paired in the same combination) or inconsist ent (items presented randomly paired) pairs. We also evaluated time-depende nt changes for bimodal (auditory and visual) presentations relative to a co ndition in which auditory stimuli were repeatedly presented alone. Using a time by condition analysis to compare neural responses to consistent versus inconsistent audiovisual pairs, we found significant time-dependent learni ng effects in medial parietal and right dorsolateral prefrontal cortices. I n contrast, time-dependent effects were seen in left angular gyrus, bilater al anterior cingulate gyrus, and occipital areas bilaterally. A comparison of paired (bimodal) versus unpaired (unimodal) conditions was associated wi th time-dependent changes in posterior hippocampal and superior frontal reg ions for both consistent and inconsistent pairs. The results provide eviden ce that associative learning for stimuli presented in different sensory mod alities is supported by neural mechanisms similar to those described for ot her kinds of memory processes. The involvement of posterior hippocampus and superior frontal gyrus in bimodal learning for both consistent and inconsi stent pairs supports a putative function for these regions in associative l earning independent of sensory modality. (C) 2000 Academic Press.