A fMRI investigation of the interactions between memory and material-sensitivity

Multiple studies of memory in animals and humans have demonstrated that prefrontal and medial temporal brain regions are engaged in memory processes. Brain regions in inferotemporal cortex respond preferentially to some categories of material (words, faces, houses, etc.) versus other categories of material, which is a phenomenon referred to as material-sensitivity. Functional magnetic resonance imaging (fMRI) experiments were designed to examine the interactions between memory and material-sensitivity by addressing three main questions: (1) Are there functional regions within human prefrontal cortex that preferentially process different types of stimulus information? (2) Is activity in the medial temporal lobe differentially influenced by the processing of distinct categories of stimuli? (3) Are material-sensitive inferotemporal regions solely engaged by perceptual processes, or are they also engaged by memory processes? Experiment 1 examined how prefrontal, medial temporal, and lateral temporal regions are preferentially engaged by the encoding of verbal versus non-verbal stimuli. Three patterns of encoding-related activation in inferior prefrontal and lateral temporal structures were revealed that appeared to vary depending on whether visuo-spatial/visuo-object, phonological/lexical, or semantic attributes were processed. Stimulus type also influenced medial temporal lobe activity. Experiment 2 used cortical reconstruction techniques and a meta-analysis of fMRI encoding studies to explore the number, location, and function of inferior prefrontal regions engaged by stimulus encoding. Evidence for a consistent pattern of anatomically distinct functional regions within inferior prefrontal cortex was found both within individual subjects and across fMRI encoding studies. Experiment 3 used a paired-association paradigm to determine whether functional activity in inferotemporal regions that demonstrate material-sensitive responses can be influenced by the formation of paired-associations. Activity in these areas was impacted by memory processes, which demonstrated that these regions are not exclusively involved in stimulus perception. Together, these studies provided evidence for interactions between memory and material-sensitive processes in prefrontal, medial temporal, and inferotemporal regions.