Working memory in patients with mild traumatic brain injury: functional MR imaging analysis.
ABSTRACT 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.
Full-textDOI: · Available from: Yen-Peng Liao, May 30, 2015
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ABSTRACT: To compare the frequency of microbleeds identified by susceptibility-weighted MRI (SWMRI) in patients with mild traumatic brain injury (mTBI) and normal controls, and correlate these findings with neuropsychological tests. Research ethics committee approval and patient written informed consents were obtained. One hundred eleven patients with mTBI without parenchymal hemorrhage on CT and conventional MRI received SWMRI as well as a digit span and continuous performance test. One hundred eleven healthy volunteers without history of traumatic brain injury were enrolled as the control group and received conventional MRI with additional SWMRI study. We analyzed the number and location of microbleeds in both groups. Twenty-six patients with mTBI and 12 control subjects presented microbleeds on SWMRI (p = 0.0197). Sixty microbleeds were found in 26 patients with mTBI and 15 microbleeds in 12 control subjects. The mTBI group showed notably more microbleeds in the cortex/subcortical region (52 microbleeds, 86.7%, vs 3 microbleeds, 20%; p < 0.0001). Conversely, the control group showed more microbleeds in the central brain (9 microbleeds, 60%, vs 3 microbleeds, 5%; p < 0.0001). There was no statistical difference in number of microbleeds in the cerebellum and brainstem (p = 0.2598 and p = 0.4932, respectively). Patients with mTBI who had detected microbleeds had lower digit span scores than the patients with negative SWMRI findings (p = 0.017). Presence of mTBI-related microbleeds showed a neuropsychological defect on short-term memory function, indicating that the presence of microbleeds could be a possible severity biomarker for mTBI. Addition of the SWMRI technique to the MRI protocol for patients with mTBI is recommended. © 2015 American Academy of Neurology.Neurology 01/2015; 84(6). DOI:10.1212/WNL.0000000000001237 · 8.30 Impact Factor
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ABSTRACT: The N-back task is often used in functional brain imaging studies to activate working memory networks; however, limited information is available on its association to clinical outcomes in children or cancer survivors. A total of 137 survivors of acute lymphoblastic leukemia (ALL; mean current age = 14.3 years, SD = 4.8; time since diagnosis = 7.6 years, SD = 1.6) completed the N-back task and comprehensive neurocognitive testing, including standardized measures of attention, processing speed, and working memory. Results indicated that females demonstrated significantly slower reaction times (0-back p = .02; 1-back p = .03) than males. Survivors <15 years old at the time of testing demonstrated a significant decrease in accuracy as working memory load increased compared to survivors ≥15 years old (p < .001). Performance on the N-back task was associated with nonverbal working memory (rs = .56, p < .001) in survivors ≥15 years of age. For younger survivors, N-back performance was more strongly associated with attention skills. Results suggest the N-back assesses different cognitive constructs at younger compared to older childhood ages. These age differences should be considered in interpreting functional brain imaging results.Journal of Clinical and Experimental Neuropsychology 09/2014; 36(9):1-12. DOI:10.1080/13803395.2014.957168 · 2.16 Impact Factor
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ABSTRACT: Persistent postconcussion syndrome (PCS) occurs in around 5-10% of individuals after mild traumatic brain injury (mTBI), but research into the underlying biology of these ongoing symptoms is limited and inconsistent. One reason for this could be the heterogeneity inherent to mTBI, with individualized injury mechanisms and psychological factors. A multimodal imaging study may be able to characterize the injury better. To look at the relationship between functional (fMRI), structural (diffusion tensor imaging), and metabolic (magnetic resonance spectroscopy) data in the same participants in the long term (>1 year) after injury. It was hypothesized that only those mTBI participants with persistent PCS would show functional changes, and that these changes would be related to reduced structural integrity and altered metabolite concentrations. Functional changes associated with persistent PCS after mTBI (>1 year postinjury) were investigated in participants with and without PCS (both n = 8) and non-head injured participants (n = 9) during performance of working memory and attention/processing speed tasks. Correlation analyses were performed to look at the relationship between the functional data and structural and metabolic alterations in the same participants. There were no behavioral differences between the groups, but participants with greater PCS symptoms exhibited greater activation in attention-related areas (anterior cingulate), along with reduced activation in temporal, default mode network, and working memory areas (left prefrontal) as cognitive load was increased from the easiest to the most difficult task. Functional changes in these areas correlated with reduced structural integrity in corpus callosum and anterior white matter, and reduced creatine concentration in right dorsolateral prefrontal cortex. These data suggest that the top-down attentional regulation and deactivation of task-irrelevant areas may be compensating for the reduction in working memory capacity and variation in white matter transmission caused by the structural and metabolic changes after injury. This may in turn be contributing to secondary PCS symptoms such as fatigue and headache. Further research is required using multimodal data to investigate the mechanisms of injury after mTBI, but also to aid individualized diagnosis and prognosis.01/2015; 5(1):45-61. DOI:10.1002/brb3.292