Karlsgodt 2011 ACNP
Presented at ACNP, December 2011: Capacity-Based Differences in Structural Connectivity and Functional Network Activation Associated With Spatial Working Memory Katherine H. Karlsgodt, Eliza Congdon, Russell A. Poldrack, Angelica A. Bato, Fred W. Sabb, Edythe London, Robert Bilder, Tyrone D. Cannon
Background: Working memory is a core cognitive function that is thought to play a role in a number of more complex, higher-level processes. However, working memory capacity varies substantially even across healthy individuals. While there are indications that white matter structure, grey-matter integrity, neural signaling changes, and other factors may contribute to this variation, the roots of these individual differences are still under investigation. It is of particular interest to probe what neural signatures differentiate high-performing individuals, as this information may help us understand how to improve functioning in individuals who have lower performance either due to natural variation or to effects of neurocognitive disorders. Here we sought to assess differences in functional activation in a large sample of healthy individuals with a wide range of behavioral performance using functional magnetic resonance imaging (fMRI) during a spatial working memory task.
Methods: As a part of the Consortium for Neuropsychiatric Phenomics project at UCLA, we assessed 117 healthy community participants aged 21-50 years. We administered a Sternberg-style spatial working memory task with 4 levels of difficulty during fMRI. To quantify performance differences, we calculated each subject’s working memory capacity using Cowan’s formula. We then performed a voxel-wise analysis, corrected for age and sex, to determine which activation patterns were correlated and anti-correlated with individual working memory capacity.
Results: Across the entire group, the task elicited activation in regions previously associated with working memory, namely the superior frontal lobes, superior parietal lobes, anterior cingulate, and striatum. In addition, there was significantly decreased activation in regions associated with the default mode network, including medial prefrontal cortex (mPFC), posterior cingulate cortex (PCC), and superior temporal lobes. Notably, voxel-wise regression of working memory capacity predicting functional activation across the whole task revealed that the primary difference in activation associated with higher capacity was a more pronounced decrease in mPFC activation during task performance.
Discussion: Individuals with higher working memory capacity were characterized by more successful disengagement of areas associated with the default mode network during task performance. This effect suggests that the hallmark of high performance is dexterous coordination of interactive neural networks rather than simply increased or decreased activation in isolated task-related nodes. The finding has implications for our understanding of why certain healthy individuals have higher and lower working memory abilities. It also can inform our conceptualization of working memory deficits in patient populations, particularly those associated with neural connectivity deficits, such as schizophrenia.
