Research Reports - Working memory in patients with mild traumatic brain injury: Functional MR imaging analysis

Radiology. 2012 Sep;264(3):844-51

Chen CJ, Wu CH, Liao YP, Hsu HL, Tseng YC, Liu HL, Chiu WT

Purpose: To analyze brain activation patterns in response to tests of working
memory after a mild traumatic brain injury (MTBI). Materials and Methods:
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. Results: 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). Conclusion: 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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