Constrained by our connections: white matter's key role in interindividual variability in visual working memory capacity.
Visual working memory (VWM) plays an essential role in many perceptual and higher-order cognitive processes. Despite its reliance on a broad network of brain regions, VWM has a capacity limited to a few objects. This capacity varies substantially across individuals and relates closely to measures of overall cognitive function (Luck and Vogel, 2013). The mechanisms underlying these properties are not completely understood, although the amplitude of neural signal oscillations (Vogel and Machizawa, 2004) and brain activation in specific cortical regions (Todd and Marois, 2004) have been implicated. Variability in VWM performance may also reflect variability in white matter structural properties. However, data based primarily on diffusion tensor imaging approaches remain inconclusive. Here, we investigate the relationship between white matter and VWM capacity in human subjects using an advanced diffusion imaging technique, diffusion kurtosis imaging. Diffusion kurtosis imaging provides several novel quantitative white mater metrics, among them the axonal water fraction (f(axon)), an index of axonal density and caliber. Our results show that 59% of individual variability in VWM capacity may be explained by variations in f(axon) within a widely distributed network of white matter tracts. Increased f(axon) associates with increased VWM capacity. An additional 12% in VWM capacity variance may be explained by diffusion properties of the extra-axonal space. These data demonstrate, for the first time, the key role of white matter in limiting VWM capacity in the healthy adult brain and suggest that white matter may represent an important therapeutic target in disorders of impaired VWM and cognition.
Department of Radiology, New York University School of Medicine, New York, New York 10016.
Ali M
http://orcid.org/0000-0003-1989-4705
AM
Golestani
Department of Radiology, New York University School of Medicine, New York, New York 10016.
Laura
L
Miles
Department of Radiology, New York University School of Medicine, New York, New York 10016.
James
J
Babb
Department of Radiology, New York University School of Medicine, New York, New York 10016, Department of Child and Adolescent Psychiatry, New York University School of Medicine, New York, New York 10016, Nathan Kline Institute for Psychiatric Research, Orangeburg, New York 10962, and.
F Xavier
http://orcid.org/0000-0001-9192-9437
FX
Castellanos
Department of Child and Adolescent Psychiatry, New York University School of Medicine, New York, New York 10016, Department of Psychiatry, New York University School of Medicine, New York, New York 10016.
Dolores
D
Malaspina
Department of Radiology, New York University School of Medicine, New York, New York 10016, mariana.lazar@nyumc.org.
Mariana
http://orcid.org/0000-0001-9285-8124
M
Lazar
D000328:Adult; D001369:Axons / Q000502:physiology; D002540:Cerebral Cortex / Q000166:cytology / Q000502:physiology*; D006801:Humans; D008297:Male; D008570:Memory, Short-Term; D008875:Middle Aged; D014796:Visual Perception; D066127:White Matter / Q000166:cytology / Q000502:physiology*
axonal density; diffusion kurtosis imaging; individual differences; microstructure; visual working memory capacity; white matter