Effect of Age on Working Memory Performance and Cerebral Activation after Mild Traumatic Brain Injury: A Functional MR Imaging Study.

PURPOSE: To evaluate the age effect on working memory (WM) performance and functional activation after mild traumatic brain injury (MTBI). MATERIALS AND METHODS: This study was approved by the local research ethics committee. All participants provided written informed consent. N-back WM cerebral activation was assessed with functional magnetic resonance (MR) imaging in 13 younger (mean age, 26.2 years ± 2.9; range, 21-30 years) and 13 older (mean age, 57.8 years ± 6.6; range, 51-68 years) patients with MTBI and 26 age- and sex-matched control subjects. Two functional MR images were obtained within 1 month after injury and 6 weeks after the initial study. Group comparison and regression analysis were performed among postconcussion symptoms, neuropsychologic tests, and WM activity in both groups. RESULTS: In younger patients, initial hyperactivation was seen in the right precuneus and right inferior parietal gyrus (P = .047 and P = .025, respectively) in two-back greater than one-back conditions compared with younger control subjects, whereas in older patients, hypoactivation was seen in the right precuneus and right inferior frontal gyrus (P = .013 and P =.019, respectively) compared with older control subjects. Increased WM activity was associated with increased postconcussion symptoms in the right precuneus (r = 0.57; P = .026) and right inferior frontal gyrus (r = 0.60; P = .019) and poor WM performance in the right precuneus (r = -0.55; P = .027) in younger patients at initial studies but not in older patients. At follow-up examinations, partial recovery of activation pattern and decreased postconcussion symptoms (P = .04) were observed in younger patients but not in older patients. CONCLUSION: The different manifestations of postconcussion symptoms at functional MR imaging between younger and older patients confirmed the important role of age in the activation, modulation, and allocation of WM processing resources after MTBI. These findings also supported that younger patients have better neural plasticity and clinical recovery than do older patients.

Sex Differences in Working Memory after Mild Traumatic Brain Injury: A Functional MR Imaging Study.

PURPOSE: To evaluate sex differences in mild traumatic brain injury (MTBI) with working memory functional magnetic resonance (MR) imaging. MATERIALS AND METHODS: Research ethics committee approval and patient written informed consent were obtained. Working memory brain activation patterns were assessed with functional MR imaging in 30 patients (15 consecutive men and 15 consecutive women) with MTBI and 30 control subjects (15 consecutive men and 15 consecutive women). Two imaging studies were performed in patients: the initial study, which was performed within 1 month after the injury, and a follow-up study, which was performed 6 weeks after the first study. For each participant, digit span and continuous performance testing were performed before functional MR imaging. Clinical data were analyzed by using Kruskal-Wallis, Mann-Whitney U, Wilcoxon signed rank, and Fisher exact tests. Within- and between-group differences of functional MR imaging data were analyzed with one- and two-sample t tests, respectively. RESULTS: Among female participants, the total digit span score was lower in the MTBI group than in the control group (P = .044). In initial working memory functional MR imaging studies, hyperactivation was found in the male MTBI group and hypoactivation was found in the female MTBI group compared with control male and female groups, respectively. At the 6-week follow-up study, the female MTBI group showed persistent hypoactivation, whereas the male MTBI group showed a regression of hyperactivation at visual comparison of activation maps. The male MTBI group was also found to have a higher initial ß value than the male control group (P = .040), and there was no significant difference between the male MTBI group and the male control group (P = .221) at follow-up evaluation, which was comparable to findings on activation maps. In the female MTBI group, average ß values at both initial and follow-up studies were lower compared with those in the female control group but were not statistically significant (P = .663 and P = .191, respectively). CONCLUSION: Female patients with MTBI had lower digit span scores than did female control subjects, and functional MR imaging depicted sex differences in working memory functional activation; hypoactivation with nonrecovery of activation change at follow-up studies may suggest a worse working memory outcome in female patients with MTBI.