Donald A. Robin

Investigating the Functional Heterogeneity of the Default Mode Network Using Coordinate-Based Meta-Analytic Modeling

The default mode network (DMN) comprises a set of regions that exhibit ongoing, intrinsic activity in the resting state and task-related decreases in activity across a range of paradigms. However, DMN regions have also been reported as task-related increases, either independently or coactivated with other regions in the network. Cognitive subtractions and the use of low-level baseline conditions have generally masked the functional nature of these regions. Using a combination of activation likelihood estimation, which assesses statistically significant convergence of neuroimaging results, and tools distributed with the BrainMap database, we identified core regions in the DMN and examined their functional heterogeneity. Meta-analytic coactivation maps of task-related increases were independently generated for each region, which included both within-DMN and non-DMN connections. Their functional properties were assessed using behavioral domain metadata in BrainMap. These results were integrated to determine a DMN connectivity model that represents the patterns of interactions observed in task-related increases in activity across diverse tasks. Subnetwork components of this model were identified, and behavioral domain analysis of these cliques yielded discrete functional properties, demonstrating that components of the DMN are differentially specialized. Affective and perceptual cliques of the DMN were identified, as well as the cliques associated with a reduced preference for motor processing. In summary, we used advanced coordinate-based meta-analysis techniques to explicate behavior and connectivity in the default mode network; future work will involve applying this analysis strategy to other modes of brain function, such as executive function or sensorimotor systems.

Perception of rhythmic and sequential pitch patterns by normally hearing adults and adult cochlear implant users

Objective: This study compares the musical perception of 17 adult recipients of the Nucleus cochlear implant using two different format extraction processing strategies (F0F1F2 and MPEAK). Design: Over a 12 mo period, participants were alternately switched between two strategies every 3 mo. Performance was evaluated using three measures of rhythmic and sequential pitch perception. Results: Three individuals performed significantly better with the MPEAK strategy on one particular rhythm task, 11 participants performed better with the MPEAK strategy on another rhythm task, and no significant differences were found between the two strategies on a sequential pitch pattern task. Conclusions: Neither strategy seems clearly superior for perception of either sequential pitch or rhythmic patterns.

Erratum: ″Personality change disorder in children and adolescents following traumatic brain injury,″ (Journal of the International Neuropsychological Society (2000) vol. 6(3) (279-289))

HIV infection often results in neuropsychological (NP) impairment. In order to assess the impact that HIV-related NP deficits may have on automobile driving, we evaluated 68 HIV-seropositive drivers using an NP battery and two PC-based driving simulations. Thirty-two participants were classified as NP impaired; most (72%) evidenced only mild impairment, and none met criteria for HIV-associated dementia. After controlling for degree of immunosuppression and disease stage, NP-impaired participants failed a previously validated driving simulation at a much higher rate than cognitively intact participants [OR = 5.3, 95% CI (1.7, 17.0), p = .006]. Similarly, on a simulation of city driving, NP impaired participants were more likely to fail based upon the number of accidents [OR = 6.1, 95% CI (1.5, 24.6), p = .01]. Simulator performance was predicted by functioning in a number of NP domains, with NP tests accounting for 13–30% of the variance on the simulations. Although it would be premature to extrapolate these findings to impairment in on-the-road driving, they do argue for greater attention to the impact that even mild HIV-related NP deficits may have on driving skills. ( JINS , 1999, 5 , 579–592.)

A study of the reproducibility and etiology of diffusion anisotropy differences in developmental stuttering: A potential role for impaired myelination

Several diffusion tensor imaging (DTI) studies have reported fractional anisotropy (FA) reductions within the left perisylvian white matter (WM) of persistent developmental stutterers (PSs). However, these studies have not reached the same conclusions in regard to the presence, spatial distribution (focal/diffuse), and directionality (elevated/reduced) of FA differences outside of the left perisylvian region. In addition, supplemental DTI measures (axial and radial diffusivities, diffusion trace) have yet to be utilized to examine the potential etiology of these FA reductions. Therefore, the present study sought to reexamine earlier findings through a sex- and age-controlled replication analysis and then to extend these findings with the aforementioned non-FA measures. The replication analysis showed that robust FA reductions in PSs were largely focal, left hemispheric, and within late-myelinating associative and commissural fibers (division III of the left superior longitudinal fasciculus, callosal body, forceps minor of the corpus callosum). Additional DTI measures revealed that these FA reductions were attributable to an increase in diffusion perpendicular to the affected fiber tracts (elevated radial diffusivity). These findings suggest a hypothesis that will be testable in future studies: that myelogenesis may be abnormal in PSs within left-hemispheric fiber tracts that begin a prolonged course of myelination in the first postnatal year.

Influence of order of stimulus presentation on speech motor learning: A principled approach to treatment for apraxia of speech

The present study was designed to examine whether applying principles of motor learning to a commonly used treatment approach for acquired apraxia of speech (AOS) would enhance relearning of speech production skills. In particular, we examined one main principle, random practice, and compared it to blocked practice. Of importance is the fact that many speech treatments utilize blocked practice, but the literature on motor learning clearly shows that blocked practice facilitates acquisition of target behaviours, but not retention and transfer. The latter two are considered true indices of learning. In two subjects with severe AOS, results showed that random practice facilitated retention whereas blocked practice did not. The present study provides preliminary evidence that these principles may have a similar effect on learning of skilled speech motor acts as they do on learning of limb movements. The results reported here are encouraging and provide justification and focus for further investigation.

Processing speed is correlated with cerebral health markers in the frontal lobes as quantified by neuroimaging.

We explored relationships between decline in cognitive processing speed (CPS) and change in frontal lobe MRI/MRS-based indices of cerebral integrity in 38 healthy adults (age 57-90 years). CPS was assessed using a battery of four timed neuropsychological tests: Grooved Pegboard, Coding, Symbol Digit Modalities Test and Category Fluency (Fruits and Furniture). The neuropsychological tests were factor analyzed to extract two components of CPS: psychomotor (PM) and psychophysical (PP). MRI-based indices of cerebral integrity included three cortical measurements per hemisphere (GM thickness, intergyral and sulcal spans) and two subcortical indices (fractional anisotropy (FA), measured using track-based spatial statistics (TBSS), and the volume of hyperintense WM (HWM)). MRS indices included levels of choline-containing compounds (GPC+PC), phosphocreatine plus creatine (PCr+Cr), and N-acetylaspartate (NAA), measured bilaterally in the frontal WM bundles. A substantial fraction of the variance in the PM-CPS (58%) was attributed to atrophic changes in frontal WM, observed as increases in sulcal span, declines in FA values and reductions in concentrations of NAA and choline-containing compounds. A smaller proportion (20%) of variance in the PP-CPS could be explained by bilateral increases in frontal sulcal span and increases in HWM volumes.

Putamen Lesions and the Development of Attention-Deficit/Hyperactivity Symptomatology

OBJECTIVE To investigate the association between focal stroke lesions of the putamen and either attention-deficit/hyperactivity disorder or traits of the disorder (ADHD/Traits). METHOD Twenty-five children with focal stroke lesions were studied with standardized psychiatric assessments and anatomic brain magnetic resonance imaging. The pattern of lesion overlap in subjects with ADHD/Traits was determined. RESULTS Fifteen of 25 subjects had ADHD/Traits. The densest area of overlapping lesions (n = 7) in subjects with ADHD/Traits included the posterior ventral putamen. The median lesion volume was 9.7 cm3, and the distribution was highly skewed. Lesion volume was not associated with ADHD/Traits. Therefore the following analyses focused on the 13 subjects with lesions < 10 cm3: ADHD/Traits were exhibited in 6/7 subjects with putamen lesionsversus 2/6 with no putamen lesions (Fisherexacttestp= .1). Half (4/8) of the subjects with ADHD/Traits had overlapping lesions encompassing the posterior ventral putamen. None of the 5 subjects without ADHD/Traits had lesions in this empirically derived region of interest (Fisher exact test p = .1). CONCLUSIONS Lesions within the dopamine-rich ventral putamen, which is part of the ventral or limbic striatum, tended to increase the risk of ADHD/Traits. ADHD/Traits may therefore be a disinhibition syndrome associated with dysfunction in this cortical-striato-thalamocortical loop.

Cognitive outcome in children and adolescents following severe traumatic brain injury: influence of psychosocial, psychiatric, and injury-related variables

Previous studies of childhood traumatic brain injury (TBI) have emphasized injury-related variables rather than psychiatric or psychosocial factors as correlates of cognitive outcomes. We addressed this concern by recruiting a consecutive series (N = 24) of children age 5 through 14 years who suffered a severe TBI, a matched group who sustained a mild TBI, and a second matched group who sustained an orthopedic injury. Standardized intellectual, memory, psychiatric, family functioning, family psychiatric history, neurological, and neuroimaging assessments were conducted at an average of 2 years following injury. Severe TBI, when compared to mild TBI and orthopedic injury, was associated with significant decrements in intellectual and memory function. A principal components analysis of independent variables that showed significant (p < .05) bivariate correlations with the outcome measures yielded a neuropsychiatric factor encompassing severity of TBI indices and postinjury psychiatric disorders and a psychosocial disadvantage factor. Both factors were independently and significantly related to intellectual and memory function outcome. Postinjury psychiatric disorders added significantly to severity indices and family functioning and family psychiatric history added significantly to socioeconomic status in explaining several specific cognitive outcomes. These results may help to define subgroups of children who will require more intensive services following their injuries.

Changes occur in resting state network of motor system during 4 weeks of motor skill learning.

We tested whether the resting state functional connectivity of the motor system changed during 4 weeks of motor skill learning using functional magnetic resonance imaging (fMRI). Ten healthy volunteers learned to produce a sequential finger movement by daily practice of the task over a 4 week period. Changes in the resting state motor network were examined before training (Week 0), two weeks after the onset of training (Week 2), and immediately at the end of the training (Week 4). The resting state motor system was analyzed using group independent component analysis (ICA). Statistical Parametric Mapping (SPM) second-level analysis was conducted on independent z-maps generated by the group ICA. Three regions, namely right postcentral gyrus, and bilateral supramarginal gyri were found to be sensitive to the training duration. Specifically, the strength of resting state functional connectivity in the right postcentral gyrus and right supramarginal gyrus increased from Week 0 to Week 2, during which the behavioral performance improved significantly, and decreased from Week 2 to Week 4, during which there was no more significant improvement in behavioral performance. The strength of resting state functional connectivity in left supramarginal gyrus increased throughout the training. These results confirm changes in the resting state network during slow-learning stage of motor skill learning, and support the premise that the resting state networks play a role in improving performance.

Changes in regional activity are accompanied with changes in inter-regional connectivity during 4 weeks motor learning

Structural equation modeling (SEM) and fMRI were used to test whether changes in the regional activity are accompanied by changes in the inter-regional connectivity as motor practice progresses. Ten healthy subjects were trained to perform finger movement task daily for 4 weeks. Three sessions of fMRI images were acquired within 4 weeks. The changes in inter-regional connectivity were evaluated by measuring the effective connectivity between the primary motor area (M1), supplementary motor area (SMA), dorsal premotor cortex (PMd), basal ganglia (BG), cerebellum (CB), and posterior ventrolateral prefrontal cortex (pVLPFC). The regional activities in M1 and SMA increased from pre-training to week 2 and decreased from week 2 to week 4. The inter-regional connectivity generally increased in strength (with SEM path coefficients becoming more positive or negative) as practice progressed. The increases in the strength of the inter-regional connectivity may reflect long-term reorganization of the skilled motor network. We suggest that the performance gain was achieved by dynamically tuning the inter-regional connectivity in the motor network.