Abstract
In this fMRI study, the functions of the anterior cingulate cortex (ACC) were studied in a group of adolescents who had sustained a moderate to severe traumatic brain injury (TBI). A spatial working memory task with varying working memory loads, representing experimental conditions of increasing difficulty, was administered. In a cross-sectional comparison between the patients and a matched control group, patients performed worse than Controls, showing longer reaction times and lower response accuracy on the spatial working memory task. Brain imaging findings suggest a possible double-dissociation: activity of the ACC in the TBI group, but not in the Control group, was associated with task difficulty; conversely, activity of the left sensorimotor cortex (lSMC) in the Control group, but not in the TBI group, was correlated with task difficulty. In addition to the main cross-sectional study, a longitudinal study of a group of adolescent patients with moderate to severe TBI was done using fMRI and the same spatial working memory task. The patient group was studied at two time-points: one time-point during the post-acute phase and one time-point 12 months later, during the chronic phase. Results indicated that patients’ behavioral performance improved over time, suggesting cognitive recovery. Brain imaging findings suggest that, over this 12-month period, patients recruited less of the ACC and more of the lSMC in response to increasing task difficulty. The role of ACC in executive functions following a moderate to severe brain injury in adolescence is discussed within the context of conflicting models of the ACC functions in the existing literature.
Highlights
Anterior cingulate cortex (ACC) activity is reportedly related to task difficulty, in healthy subjects (Botvinick et al, 2004) as well as in clinical populations, such as patients with post-traumatic stress disorder (Shaw et al, 2009) or patients with traumatic brain injury (TBI) (Rasmussen et al, 2008; Kohl et al, 2009)
Cross-sectional study Behavioral results: within-group analysis Spearman correlation coefficients indicated a decline in both accuracy and response times (RTs) with increasing working memory load (WML) in the control group
A decline in accuracy with increasing WML was observed for the TBI group, but no such effects were noted for RT (Table 3)
Summary
Anterior cingulate cortex (ACC) activity is reportedly related to task difficulty, in healthy subjects (Botvinick et al, 2004) as well as in clinical populations, such as patients with post-traumatic stress disorder (Shaw et al, 2009) or patients with traumatic brain injury (TBI) (Rasmussen et al, 2008; Kohl et al, 2009). It has been suggested that it is diffuse axonal injury – commonly observed after TBI – that disrupts integrative networks and that is the main cause of executive functions impairment following TBI (Ghajar and Ivry, 2008; Niogi et al, 2008). This makes TBI a very interesting neuropsychological model for studying the role of ACC in executive functions. We expected patients in the longitudinal study to exhibit improvement of performance at Time 2 as compared to Time 1, as well as a change in brain imaging
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