Exploring the neural basis of cognitive reserve.

There is epidemiologic and imaging evidence for the presence of cognitive reserve, but the neurophysiologic substrate of CR has not been established. In order to test the hypothesis that CR is related to aspects of neural processing, we used fMRI to image 19 healthy young adults while they performed a nonverbal recognition test. There were two task conditions. A low demand condition required encoding and recognition of single items and a titrated demand condition required the subject to encode and then recognize a larger list of items, with the study list size for each subject adjusted prior to scanning such that recognition accuracy was 75%. We hypothesized that individual differences in cognitive reserve are related to changes in neural activity as subjects moved from the low to the titrated demand task. To test this, we examined the correlation between subjects' fMRI activation and NART scores. This analysis was implemented voxel-wise in a whole brain fMRI dataset. During both the study and test phases of the recognition memory task we noted areas where, across subjects, there were significant positive and negative correlations between change in activation from low to titrated demand and the NART score. These correlations support our hypothesis that neural processing differs across individuals as a function of CR. This differential processing may help explain individual differences in capacity, and may underlie reserve against age-related or other pathologic changes.