Working Memory in Patients with Mild Traumatic Brain Injury: Functional MR Imaging Analysis

Department of Radiology, Taipei Medical University/Shuang Ho Hospital, New Taipei City, Taiwan.
Radiology (Impact Factor: 6.87). 07/2012; 264(3):844-51. DOI: 10.1148/radiol.12112154
Source: PubMed


To analyze brain activation patterns in response to tests of working memory after a mild traumatic brain injury (MTBI).
Research ethics committee approval and patient written informed consent were obtained. Brain activation patterns in response to n-back working memory tasks (n = 1, 2, 3) were assessed with functional magnetic resonance (MR) imaging in 20 patients with MTBI within 1 month after their injury and in 18 healthy control subjects. In n-back working memory tasks, participants monitored a series of number stimuli and were to indicate when the presented number was the same as that presented n back previously. Nine (45%) MTBI patients underwent follow-up functional MR imaging studies 6 weeks later. Digit span, a memory test for how many numbers a person can remember in sequence, and continuous performance test (CPT), a test that measures a person's sustained and selective attention and impulsivity, were also performed before functional MR imaging studies and outside the imager for each participant. Clinical data were analyzed by using t and χ(2) tests. Within-group, between-group, and initial and follow-up differences of functional MR imaging data were analyzed by using one-sample, two-sample, and paired t tests, respectively.
Groups were similar for sex (P = .75), years of education (P = .069), digit span (P = .37 for total score), CPT (P = .31, .27, and .43 for omission error, commission error, and hit reaction time, respectively), and accuracy of n-back working memory performance (P = .90, .11, and .39 for one-, two-, and three-back tasks, respectively). Brain activation patterns differed between MTBI patients and controls in response to increasing working memory loads (P < .01, uncorrected). Control subjects maintained their ability to increase activation in the working memory circuitry with each increase in working memory load. In contrast, MTBI patients were impaired in their ability to increase activation in working memory circuitry under both moderate and high working memory load conditions. However, MTBI patients did show cerebral plasticity, as evidenced by more activation in some areas outside and inside the working memory circuitry as compared with control subjects (P < .01, uncorrected). In the 6-week follow-up study, compared with baseline, MTBI patients showed an improvement of activation in response to increasing working memory loads (P < .05, uncorrected).
MTBI-induced differences in working memory functional activity were observed even though differences in behavioral performance between MTBI patients and controls were absent, which suggests that this approach may increase sensitivity to MTBI compared with neuropsychological evaluation alone.

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Available from: Yen-Peng Liao
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    • "Summarizing across tasks, the data presented here suggest that participants with mTBI and ongoing PCS have limited working memory capacity (lower BOLD increase in left IFG/MFG), and compensate for this by greater attention and performance monitoring (greater BOLD increase in ACC) and reduction of activity in task-irrelevant areas (medial temporal lobe and DMN). These functional changes are observed even in the absence of behavioral differences (Fig. 3), as has been seen in previous studies (McAllister et al. 2001; Stulemeijer et al. 2010; Witt et al. 2010; Chen et al. 2012) indicating that fMRI may be more sensitive to subtle changes after mTBI. It has previously been suggested that a large scale disorder of attention underlies the symptoms seen after TBI (Ghajar and Ivry 2008), with enhanced top-down control of attention necessary to compensate for microstructural damage causing variability in white matter transmission speed. "
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    • "Improvements in balance and, to a lesser extent, in gait outcomes were also found in these two patients. In another study of 20 patients at 1 month after mild TBI (mTBI) and 18 healthy controls, Chen et al. (2012) demonstrated that brain activation patterns differed between mTBI patients and controls in response to increasing working memory loads (P < 0.01, uncorrected). mTBI patients were impaired in their ability to increase activation in working memory circuitry under both moderate and high working memory load conditions in contrast with controls. "
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    • "It causes 1.1 million emergency visits, 235,000 hospitalisations, and 50,000 deaths in the United States every year [5, 6]. The socioeconomic impacts and burden of diseases for disability following TBI are potentially long term or lifelong [2–5, 7–14]. While the epidemiology, natural history, risk factors, and outcomes of TBI have been established [1–17], TBI treatment and rehabilitation are still crucial problems of global concern. "
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