Three important concepts for us to consider are cognitive work capacity, cognitive work demand, and cognitive reserve, the person’s residual functional capacity.
As a person is evaluated to return to work after experiencing a brain injury, a comparison will be made between his or her available work capacity and the job’s demands. If there is cognitive reserve, return to work can be readily undertaken. Without reserve, accommodations are necessary.
If the client has a focused impairment such as that occasioned by a small caliber gunshot wound or stabbing or a localized stroke, it may be possible to modify the job’s demands so that cognitive reserve is reestablished. If the job’s demands cannot be modified, it still may be possible to provide rehabilitation that restores adequate reserves, harnessing neurogenesis and neuroplasticity (Satz, Cole, Hardy, & Rassovsky, 2011).
White matter linkages between the parietal lobe and frontal lobe appear to be causally linked to cognitive capacity; greater linkage demonstrated by diffusion tensor imaging is related to higher levels of cognitive capacity as measured by tests of intelligence (Haut et al., 2007). These findings point to the importance of distinguishing global or diffuse brain injuries from focal brain injuries as we consider cognitive work capacity.
- Haut, M., Moran, M., Lancaster, M., Kuwabara, H., Parsons, M., & Puce, A. (2007). White matter correlates of cognitive capacity studied with diffusion tensor imaging: Implications for cognitive reserve. Brain Imaging and Behavior, 1, 83–92.
- Satz, P., Cole, M. A., Hardy, D. J., & Rassovsky, Y. (2011). Brain and cognitive reserve: Mediator(s) and construct validity, a critique. J Clin Exp Neuropsychol, 33(1), 121–130.
During childhood and adolescence, the development of executive functions such as working memory follows the development of white matter tracts and associations among cortical and sub-cortical structures in the human brain (Nagy, Westerberg, & Klingberg, 2004). Full integration of white matter and gray matter does not conclude until early adulthood, with males and females differing in the trajectories of development in different brain areas (Schmithorst, Holland, & Dardzinski, 2008). This improvement in function may be due to greater axonal coherence (Barnea-Goraly et al., 2005) stimulated by experience (O’Hare, Lu, Houston, Bookheimer, & Sowell, 2008).
Experience-based development has important consequences for the rehabilitation of teenagers and young adults with brain injury. On the one hand, this supports the notion that practice with working memory is crucial for its development, with the implication that practice provided in rehabilitation after a brain injury can be expected to improve working memory and, potentially, other executive functions. On the other hand, the natural age-linked development of executive functions may be due to genetic factors so that there will be a temporary ceiling effect during middle and late adolescence. Still another consideration is the potential for a critical period in the development of the various executive functions that requires practice during childhood and adolescence in order to achieve full function in adulthood.
Until we better understand the dynamics of the development of executive function, the best approach is to provide appropriate challenges and practice opportunities to adolescents and young adults with brain injury.
- Barnea-Goraly, N., Menon, V., Eckert, M., Tamm, L., Bammer, R., Karchemskiy, A., et al. (2005). White matter development during childhood and adolescence: A cross-sectional diffusion tensor imaging study. Cereb Cortex, 15(12), 1848–1854.
- Nagy, Z., Westerberg, H., & Klingberg, T. (2004). Maturation of white matter is associated with the development of cognitive functions during childhood. J Cogn Neurosci, 16(7), 1227–1233.
- O’Hare, E. D., Lu, L. H., Houston, S. M., Bookheimer, S. Y., & Sowell, E. R. (2008). Neurodevelopmental changes in verbal working memory load-dependency: An fmri investigation. Neuroimage, 42(4), 1678–1685.
- Schmithorst, V. J., Holland, S. K., & Dardzinski, B. J. (2008). Developmental differences in white matter architecture between boys and girls. Hum Brain Mapp, 29(6), 696–710.