ABSTRACT: Verbal learning and strategic processing deficits are common sequelae of traumatic brain injury (TBI); however, the neurophysiological mechanisms underlying such deficits remain poorly understood.
We performed functional magnetic resonance imaging (fMRI) in 25 individuals with chronic TBI (>1 year after injury) and 20 matched healthy controls. Subjects were scanned while encoding word lists, with free recall and recognition assessed after each scanning run. To vary the strategic processing load, participants learned semantically unrelated words (Unrelated condition), semantically related words under null instruction conditions (Spontaneous condition), and semantically related words following training on the use of a semantic clustering strategy (Directed condition).
Behavioral performance on recall, recognition, and semantic clustering improved significantly as follows: Unrelated < Spontaneous < Directed. Individuals with TBI exhibited impaired yet parallel behavioral performance relative to control participants. The fMRI measures of brain activity during verbal encoding revealed decreased activity in participants with TBI relative to controls in left dorsolateral prefrontal cortex (DLPFC; BA 9) and in a region spanning the left angular and supramarginal gyri (BA 39/40). Functional connectivity analysis revealed evidence of a functional-but not anatomical-breakdown in the connectivity between the DLPFC and other regions specifically when participants with TBI were directed to use the semantic encoding strategy.
After TBI, the DLPFC appears to be decoupled from other active brain regions specifically when strategic control is required. We hypothesize that approaches designed to help re-couple DLPFC under such conditions may aid TBI cognitive rehabilitation.
Neurorehabilitation and neural repair 01/2009; 23(3):226-36. · 4.49 Impact Factor
ABSTRACT: To evaluate the ability of functional magnetic resonance imaging (fMRI) measures collected from people with traumatic brain injury (TBI) to provide predictive value for rehabilitation outcomes over and above standard predictors.
Academic medical center.
Persons (N=54) with TBI greater than 1 year postinjury.
A novel 12-session group rehabilitation program focusing on internal strategies to improve memory.
The Hopkins Verbal Learning Test-Revised (HVLT-R) delayed recall score.
fMRI measures were collected while participants performed a strategically directed word memorization task. Prediction models were multiple linear regressions with the following primary predictors of outcome: age, education, injury severity, preintervention HVLT-R, and task-related fMRI activation of the left dorsolateral and left ventrolateral prefrontal cortex (VLPFC). Baseline HVLT-R was a significant predictor of outcome (P=.007), as was injury severity (for severe vs mild, P=.049). We also found a significant quadratic (inverted-U) effect of fMRI in the VLPFC (P=.007).
This study supports previous evidence that left prefrontal activity is related to strategic verbal learning, and the magnitude of this activation predicted success in response to cognitive memory rehabilitation strategies. Extreme under- or overactivation of VLPFC was associated with less successful learning after rehabilitation. Further study is necessary to clarify this relationship and to expand and optimize the possible uses of functional imaging to guide rehabilitation therapies.
Archives of physical medicine and rehabilitation 06/2008; 89(5):974-81. · 2.18 Impact Factor
ABSTRACT: Gray and white matter volume deficits have been reported in a number of studies of children with attention-deficit/hyperactivity disorder (ADHD); however, there is a paucity of structural magnetic resonance imaging (MRI) studies of adults with ADHD. This structural MRI study used an a priori region of interest approach.
Twenty-four adults with DSM-IV ADHD and 18 healthy controls comparable on age, socioeconomic status, sex, handedness, education, IQ, and achievement test performance had an MRI on a 1.5T Siemens scanner. Cortical and sub-cortical gray and white matter were segmented. Image parcellation divided the neocortex into 48 gyral-based units per hemisphere. Based on a priori hypotheses we focused on prefrontal, anterior cingulate cortex (ACC) and overall gray matter volumes. General linear analyses of the volumes of brain regions, adjusting for age, sex, and total cerebral volumes, were used to compare groups.
Relative to controls, ADHD adults had significantly smaller overall cortical gray matter, prefrontal and ACC volumes.
Adults with ADHD have volume differences in brain regions in areas involved in attention and executive control. These data, largely consistent with studies of children, support the idea that adults with ADHD have a valid disorder with persistent biological features.
Biological Psychiatry 12/2006; 60(10):1071-80. · 8.28 Impact Factor
ABSTRACT: To evaluate the effects of participation in a memory group intervention focusing on internal strategy use on persons with traumatic brain injury-related memory impairment.
Ninety-four adults with traumatic brain injury (54 in the experimental group and 40 controls) and resulting memory impairment, with severities ranging from mild to severe. All participants were at least 18 years of age at the time of injury and at least 1 year post injury at the time of study.
Non randomized pre/posttest group comparison design.
Hopkins Verbal Learning Test-Revised and Rivermead Behavioral Memory Test II.
Participation in the memory group intervention was associated with improved memory performance immediately postintervention, and improvements were maintained 1 month postintervention. Severe injury was associated with less improvement in memory outcomes than mild and moderate injuries. Age and preinjury education were not related to outcome.
Individuals with traumatic brain injury may benefit from memory group intervention focusing on internal strategy use. Study hypotheses should be retested using a randomized, controlled design, and further research is needed to better delineate influences on intervention candidacy and outcomes.
The Journal of head trauma rehabilitation 25(1):43-51. · 2.39 Impact Factor