The neural correlates of picture encoding: fMRI investigations of age and cross -cultural differences.

Abstract

I investigate the effects of neurobiology and environment on plasticity in brain function, specifically seeking evidence for functional compensation with aging and culturally-distinct neural activation for picture encoding. Study one investigates the hypothesis that increased prefrontal activations in older adults are compensatory for decreases in medial temporal activations that occur with age. Because between-group comparisons of high- and low-performing elderly have yielded inconsistent results, it is unclear whether additional activations in older adults reflect compensation. We examined incidental encoding of scenes using functional MRI in a subsequent memory paradigm, which isolates successfully encoded (remembered) items. Younger and older adults both activated inferior frontal and lateral occipital regions bilaterally; however, older adults showed less activation than young in the parahippocampus and more activation than young in prefrontal cortex. Because the findings are unique for remembered but not forgotten items, these data suggest that prefrontal regions could serve a compensatory role for declines in medial temporal activations with age. Study two examines whether culturally-distinct modes of information processing are neurally distinguishable. Using an event-related fMRl design, we investigate the hypothesis that Westerners engage in object-based processing with less regard to the entire context as opposed to East Asians, who process objects in terms of relationships and contexts (Nisbett, 2003). American and East Asian participants incidentally encoded pictures of target objects, backgrounds, and the combination of the two. Consistent with our hypothesis, Americans activated left middle temporal cortex, which responds to presentation of objects and semantic knowledge about properties of objects, more than East Asians when pictures of objects on backgrounds were contrasted with those of backgrounds alone. Although both cultures similarly activated the fusiform region when complex pictures were contrasted with those of objects only, reflecting form and context processing, the more negative correlations between fusiform and middle temporal gyri for East Asians than Americans suggest that the region may be differently involved in task performance for the two cultures. These results suggest that fundamental differences exist cross-culturally in the type of information encoded from pictures, with Americans engaging additional object-based and semantic processing for pictures when salient central objects are present.