Kristine M. Mosier

Regional Reproducibility of Pulsed Arterial Spin Labeling Perfusion Imaging at 3T

Arterial spin labeling (ASL) is a promising non-invasive magnetic resonance imaging (MRI) technique for measuring regional cerebral blood flow (rCBF) or perfusion in vivo. To evaluate the feasibility of ASL as a biomarker for clinical trials, it is important to examine test-retest reproducibility. We investigated both inter- and intra-session reproducibility of perfusion MRI using a pulsed ASL (PASL) sequence PICORE Q2TIPS with an echo-planar imaging (EPI) readout. Structural MRI regions of interest (ROIs) were extracted individually by automated parcellation and segmentation methods using FreeSurfer. These cortical and subcortical ROIs were used to assess regional perfusion stability. Our results indicated regional variability in grey matter rCBF. Although rCBF measurements were characterized by intersubject variation, our results also indicated relatively less within-subject variability estimated as within-subject standard deviation (SD(W)) (intersession SD(W): 2.0 to 8.8; intrasession SD(W): 2.8 to 9.6) and acceptable reliabilities as measured using intraclass correlation coefficient (ICC) (intersession ICC: 0.68 to 0.94; intrasession ICC: 0.66 to 0.95) for regional MRI perfusion measurements using the PICORE Q2TIPS technique. Overall, our findings suggest that PASL is a technique with good within and between session reproducibility. Further reproducibility studies in target populations relevant for specific clinical trials of neurovascular related agents will be important and the present results provide a framework for such assessments.

Reorganization of finger coordination patterns during adaptation to rotation and scaling of a newly learned sensorimotor transformation.

We examined how people organize redundant kinematic control variables (finger joint configurations) while learning to make goal-directed movements of a virtual object (a cursor) within a low-dimensional task space (a computer screen). Subjects participated in three experiments performed on separate days. Learning progressed rapidly on day 1, resulting in reduced target capture error and increased cursor trajectory linearity. On days 2 and 3, one group of subjects adapted to a rotation of the nominal map, imposed either stepwise or randomly over trials. Another group experienced a scaling distortion. We report two findings. First, adaptation rates and memory-dependent motor command updating depended on distortion type. Stepwise application and removal of the rotation induced a marked increase in finger motion variability but scaling did not, suggesting that the rotation initiated a more exhaustive search through the space of viable finger motions to resolve the target capture task than did scaling. Indeed, subjects formed new coordination patterns in compensating the rotation but relied on patterns established during baseline practice to compensate the scaling. These findings support the idea that the brain compensates direction and extent errors separately and in computationally distinct ways, but are inconsistent with the idea that once a task is learned, command updating is limited to those degrees of freedom contributing to performance (thereby minimizing energetic or similar costs of control). Second, we report that subjects who learned a scaling while moving to just one target generalized more narrowly across directions than those who learned a rotation. This contrasts with results from whole-arm reaching studies, where a learned scaling generalizes more broadly across direction than rotation. Based on inverse- and forward-dynamics analyses of reaching with the arm, we propose the difference in results derives from extensive exposure in reaching with familiar arm dynamics versus the novelty of the manual task.

Short-Term Violent Video Game Play by Adolescents Alters Prefrontal Activity During Cognitive Inhibition

Prior research has indicated an association between exposure to violent media and aggressive thoughts, feelings, and behavior, potentially as a result of effects on inhibitory mechanisms. However, the role of violence in video games in modulating subsequent neural activity related to cognitive inhibition has received little attention. To examine short-term effects of playing a violent video game, 45 adolescents were randomly assigned to play either a violent or a nonviolent video game for 30 minutes immediately prior to functional magnetic resonance imaging (fMRI). During the fMRI procedure, participants performed a go/no-go task that required them to press a button for each target stimulus and withhold the response for non-target stimuli. Participants who played the violent game demonstrated a lower BOLD response in right dorsolateral prefrontal cortex (DLPFC) when responses were appropriately inhibited. The DLPFC is involved with executive functioning, including suppression of unwanted thoughts and behaviors. In addition, responses in the DLPFC demonstrated stronger inverse connectivity with precuneus in the nonviolent game players. These results provide evidence that playing a violent video game can modulate prefrontal activity during cognitive inhibition.

Executive functioning characteristics associated with ADHD comorbidity in adolescents with disruptive behavior disorders

The nature of executive dysfunction in youth with disruptive behavior disorders (DBD) remains unclear, despite extensive research in samples of children with attention-deficit hyperactivity disorder (ADHD). To determine the relationship between DBD, ADHD, and executive function deficits in aggressive teens, adolescents with DBD and comorbid ADHD (DBD + ADHD; n = 25), DBD without ADHD (DBD-ADHD; n = 23), and healthy controls (HC; n = 25) were compared on neurocognitive tests and questionnaires measuring executive functioning. Teens with DBD + ADHD performed worse on both neurocognitive and questionnaire measures of executive function than the DBD-ADHD and HC groups. Results suggest that subgroups of DBD may exist depending on the presence or absence of comorbid ADHD, which may have implications for the selection and efficacy of treatment strategies.

Controlling instabilities in manipulation requires specific cortical-striatal-cerebellar networks

Dexterous manipulation requires both strength, the ability to produce fingertip forces of a specific magnitude, and dexterity, the ability to dynamically regulate the magnitude and direction of fingertip force vectors and finger motions. Although cortical activity in fronto-parietal networks has been established for stable grip and pinch forces, the cortical regulation in the dexterous control of unstable objects remains unknown. We used functional magnetic resonance imaging (fMRI) to interrogate cortical networks engaged in the control of four objects with increasing instabilities but requiring constant strength. In addition to expected activity in fronto-parietal networks we find that dexterous manipulation of increasingly unstable objects is associated with a linear increase in the amplitude of the BOLD signal in the basal ganglia (P = 0.007 and P = 0.023 for 2 compression tasks). A computational regression (connectivity) model identified independent subsets of cortical networks whose connection strengths were mutable and associated with object instability (P < 0.001). Our results suggest that in the presence of object instability, the basal ganglia may modulate the activity of premotor areas and subsequent motor output. This work, therefore, provides new evidence for the selectable cortical representation and execution of dynamic multifinger manipulation for grasp stability.

White matter abnormalities associated with disruptive behavior disorder in adolescents with and without attention-deficit/hyperactivity disorder.

Disruptive behavior disorders (DBD) are among the most commonly diagnosed mental disorders in children and adolescents. Some important characteristics of DBD vary based on the presence or absence of comorbid attention-deficit/hyperactivity disorder (ADHD), which may affect the understanding of and treatment decision-making related to the disorders. Thus, identifying neurobiological characteristics of DBD with comorbid ADHD (DBD+ADHD) can provide a basis to establish a better understanding of the condition. This study aimed to assess abnormal white matter microstructural alterations in DBD+ADHD as compared to DBD alone and healthy controls using diffusion tensor imaging (DTI). Thirty-three DBD (19 with comorbid ADHD) and 46 age-matched healthy adolescents were studied using DTI. Fractional anisotropy (FA), and mean diffusivity (MD), radial diffusivity (RD) and axial diffusivity (AD) were analyzed using tract-based spatial statistics (TBSS). Significantly lower FA and higher MD, RD and AD in many white matter fibers were found in adolescents with DBD+ADHD compared to controls. Moreover, lower FA and higher RD were also found in the DBD+ADHD versus the DBD alone group. Alterations of white matter integrity found in DBD patients were primarily associated with ADHD, suggesting that ADHD comorbidity in DBD is reflected in greater abnormality of microstructural connections.

Short Term Exposure to a Violent Video Game Induces Changes in Frontolimbic Circuitry in Adolescents

Despite evidence of effects of violent video game play on behavior, the underlying neuronal mechanisms involved in these effects remain poorly understood. We report a functional MRI (fMRI) study during two modified Stroop tasks performed immediately after playing a violent or nonviolent video game. Compared with the violent video game group, the nonviolent video game group demonstrated more activation in some regions of the prefrontal cortex during the Counting Stroop task. In contrast to the violent video game group, significantly stronger functional connectivity between left dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) was identified in the nonviolent video game group. During an Emotional Stroop task, the violent video game group showed more activity in the right amygdala and less activation in regions of the medial prefrontal cortex (MPFC). Furthermore, functional connectivity analysis revealed the negative coupling between right amygdala and MPFC in the nonviolent video game group. By contrast, no significant functional connectivity between right amygdala and MPFC was found in the violent video game group. These results suggest differential engagement of neural circuitry in response to short term exposure to a violent video game as compared to a nonviolent video game.

A method to map the visual cortex during an awake craniotomy

Much has been reported regarding the technique of performing an awake craniotomy with cortical mapping for the functional cortex responsible for sensorimotor activity and language. However, documentation for mapping the visual cortex during an awake craniotomy with a description of its technical details is rare. The authors report the case of a patient who underwent an awake craniotomy with mapping of the visual cortex to remove a glioma situated in the left medial occipital lobe. The techniques that made such a mapping procedure possible are discussed.

Learning Redundant Motor Tasks with and without Overlapping Dimensions: Facilitation and Interference Effects

Prior learning of a motor skill creates motor memories that can facilitate or interfere with learning of new, but related, motor skills. One hypothesis of motor learning posits that for a sensorimotor task with redundant degrees of freedom, the nervous system learns the geometric structure of the task and improves performance by selectively operating within that task space. We tested this hypothesis by examining if transfer of learning between two tasks depends on shared dimensionality between their respective task spaces. Human participants wore a data glove and learned to manipulate a computer cursor by moving their fingers. Separate groups of participants learned two tasks: a prior task that was unique to each group and a criterion task that was common to all groups. We manipulated the mapping between finger motions and cursor positions in the prior task to define task spaces that either shared or did not share the task space dimensions (x-y axes) of the criterion task. We found that if the prior task shared task dimensions with the criterion task, there was an initial facilitation in criterion task performance. However, if the prior task did not share task dimensions with the criterion task, there was prolonged interference in learning the criterion task due to participants finding inefficient task solutions. These results show that the nervous system learns the task space through practice, and that the degree of shared task space dimensionality influences the extent to which prior experience transfers to subsequent learning of related motor skills.

The interacting role of media violence exposure and aggressive-disruptive behavior in adolescent brain activation during an emotional Stroop task

Only recently have investigations of the relationship between media violence exposure (MVE) and aggressive behavior focused on brain functioning. In this study, we examined the relationship between brain activation and history of media violence exposure in adolescents, using functional magnetic resonance imaging (fMRI). Samples of adolescents with no psychiatric diagnosis or with disruptive behavior disorder (DBD) with aggression were compared to investigate whether the association of MVE history and brain activation is moderated by aggressive behavior/personality. Twenty-two adolescents with a history of aggressive behavior and diagnosis of either conduct disorder or oppositional-defiant disorder (DBD sample) and 22 controls completed an emotional Stroop task during fMRI. Primary imaging results indicated that controls with a history of low MVE demonstrated greater activity in the right inferior frontal gyrus and rostral anterior cingulate during the violent word condition. In contrast, in adolescents with DBD, those with high MVE exhibited decreased activation in the right amygdala, compared with those with low MVE. These findings are consistent with research demonstrating the importance of fronto-limbic structures for processing emotional stimuli, and with research suggesting that media violence may affect individuals in different ways depending on the presence of aggressive traits.