Examining working memory task acquisition in a disrupted neural network

Abstract

There is mounting literature that examines brain activation during tasks of working memory in individuals with neurological disorders such as traumatic brain injury. These studies represent a foundation for understanding the functional brain changes that occur after moderate and severe traumatic brain injury, but the focus on topographical brain-'activation' differences ignores potential alterations in how nodes communicate within a distributed neural network. The present study makes use of the most recently developed connectivity modelling (extended-unified structural equation model) to examine performance during a well-established working-memory task (the n-back) in individuals sustaining moderate and severe traumatic brain injury. The goal is to use the findings observed in topographical activation analysis as the basis for second-level effective connectivity modelling. Findings reveal important between-group differences in within-hemisphere connectivity during task acquisition, with the control sample demonstrating rapid within-left hemisphere connectivity increases and the traumatic brain injury sample demonstrating consistently elevated within-right hemisphere connectivity. These findings also point to important maturational effects from 'early' to 'late' during task performance, including diminished right prefrontal cortex involvement and an anterior to posterior shift in connectivity with increased task exposure. We anticipate that this approach to functional imaging data analysis represents an important future direction for understanding how neural plasticity is expressed in brain disorders.

Neural Underpinnings of Working Memory in Adult Survivors of Childhood Brain Tumors

“…Hillary and colleagues suggest that in the context of brain injury, increased BOLD King-Working Memory in Brain Tumor Survivors 20 in the prefrontal cortex is not due to a compensatory mechanism or brain reorganization but rather attempts of the neurological group to increase cognitive control in the context of poorer performance (Hillary et al, 2011). Our findings are in line with this allocation of latent resources theory of the prefrontal lobe which is observed when prefrontal BOLD response increases with greater task demands.…”

“…However, on average the nback and other neuropsychological performance was comparable to the performance reported in other fMRI studies (Hillary et al, 2011;Medaglia et al, 2012;Robinson, Pearson, Cannistraci, Anderson, Kuttesch, Wymer, Smith, & Compas, 2014). The current control group was carefully selected from a larger control sample that was consistent with the state of Georgia census for ethnicity and also included first-generation college students which makes it more consistent with community samples.…”

“…The left hemisphere findings are consistent with prior letter n-back tasks (Owen et al, 2005;Robinson, Pearson, Cannistraci, Anderson, Kuttesch, Wymer, Smith, & Compas, 2014). However, some researchers have suggested the importance of the right prefrontal lobe due to the novelty of the task demands (Hillary et al, 2011).…”

Hyperconnectivity is a fundamental response to neurological disruption.

“…These findings are an important reminder that the typical measures of connectivity isolated in this literature capture only the most robust effects leaving unknown transient shifts in network connectivity. By modeling stochasticity in time series data (e.g., via sliding time windows) one can determine the timing and variability of observable connections to better understand how neural networks adapt to challenge and disruption (Gates & Molenaar, 2012;Hillary et al, 2011a;Jones et al, 2012;Kiviniemi et al, 2011;Leonardi et al, 2013).…”

Neural correlates of working memory in children and adolescents with agenesis of the corpus callosum: An fMRI study

“…In typically developing (TD) children and adolescents, a core bilateral fronto-parietal network is known to underpin verbal and visuo-spatial WM (e.g., Kwon et al, 2002;O'Hare et al, 2008;Spencer-Smith et al, 2013;van den Bosch et al, 2014). Intrahemispheric as well as interhemispheric connectivity, mostly supported by the CC, is likely to play a crucial role in WM processes by promoting efficient functional integration between brain areas (Hillary et al, 2011;Koshino et al, 2005;Schlösser et al, 2006). Indeed, in typically developing children, a significant correlation between visual WM performance and development of white matter in the anterior corpus callosum has been described (Nagy et al, 2004).…”