The Potential for Individual Mapping of Working Memory Using the N-Back fMRI Task

Background. Individual activation maps based on brain functional magnetic resonance imaging (fMRI) data cannot yet be applied to refine a patient's diagnosis and prognosis. However, tracking activation dynamics in the same patient during the course of treatment or rehabilitation can be useful for assessing their efficacy. Population-based studies often fail to identify clinically significant activation parameters and to aid interpretation. To address this gap, we propose the examination of individual differences in activation in correspondence with the state of the mental process of interest.
Objective: to analyze individual differences in brain activation evoked by the n-back task (working memory updating) in young and elderly healthy participants related to accuracy and response times in this task.
Material and methods. fMRI was recorded in 16 young (18–35 years) and 16 elderly (60–75 years) healthy right-handed participants while they performed the n-back task. Group-level activation was assessed in the 2-back versus 0-back conditions. The effects of age (young/elderly), material type (verbal/nonverbal), accuracy and response times were assessed.
Results. In all participants, regardless of age, less effective performance in the 2-back task was accompanied by more pronounced activation. Lower accuracy was coupled with higher activation in the visual cortex bilaterally and in the right inferior frontal gyrus, while a higher response time was associated with greater activation in the right frontal components of the frontoparietal network and the right frontal pole.
Conclusion. Our findings explain a very small portion of the variance in activation patterns in the working memory tasks, so they cannot yet be used to interpret individual activation maps. However, they could pave the way for assessing dynamics of individual patterns over time if successfully replicated in a longitudinal study.

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