Blast in Context: The Neuropsychological and Neurocognitive Effects of Long-Term Occupational Exposure to Repeated Low-Level Explosives on Canadian Armed Forces\u27 Breaching Instructors and Range Staff

Currently, there is strong interest within the military to better understand the effects of long-term occupational exposure to repeated low-level blast on health and performance. To gain traction on the chronic sequelae of blast, we focused on breaching—a tactical technique for gaining entry into closed/blocked spaces by placing explosives and maintaining a calculated safe distance from the detonation. Using a cross-sectional design, we compared the neuropsychological and neurocognitive profiles of breaching instructors and range staff to sex- and age-matched Canadian Armed Forces (CAF) controls. Univariate tests demonstrated that breaching was associated with greater post-concussive symptoms (Rivermead Post Concussion Symptoms Questionnaire) and lower levels of energy (RAND SF-36). In addition, breaching instructors and range staff were slower on a test that requires moving and thinking simultaneously (i.e., cognitive-motor integration). Next, using a multivariate approach, we explored the impact of other possible sources of injury, including concussion and prior war-zone deployment on the same outcomes. Concussion history was associated with higher post-concussive scores and musculoskeletal problems, whereas deployment was associated with higher post-concussive scores, but lower energy and greater PTSD symptomatology (using PCL-5). Our results indicate that although breaching, concussion, and deployment were similarly correlated with greater post-concussive symptoms, concussion history appears to be uniquely associated with altered musculoskeletal function, whereas deployment history appears to be uniquely associated with lower energy and risk of PTSD. We argue that the broader injury context must, therefore, be considered when studying the impact of repetitive low-level explosives on health and performance in military members

An fMRI examination of the neural processing of periodic motion trajectories

Perception of periodic or closed-circuit motion trajectories plays a crucial role in our ability to learn and perform many common skilled actions. For example, periodic trajectories are a key component of many types of biological movements when viewed relative to body translation. In the current fMRI study, we used a novel visual stimulus consisting of a target moving along a closed trajectory defined by a radial frequency (RF) pattern (i.e., a sinusoidal variation of trajectory radius relative to a circular trajectory) to determine which brain regions encode these periodic movement paths. Multivoxel pattern analyses permitted prediction of the shapes of different periodic trajectories within regions V2 and V3 indicating that these regions play a role in the processing of periodic visual motion. In addition, blood oxygen level dependent (BOLD) responses associated with the presentation of targets moving along RF trajectories compared with nonperiodic motion and static RF shapes revealed significantly greater activity in visual areas V1, V2, V3, V3A, and V4. To our knowledge, the results of this study represent the first examination of the functional brain activity underlying periodic motion processing and should inform further study

Regions of interest localized across all participants.

<p>Regions of interest localized across all participants.</p

Kinematic measures of arm movements in AVG players and non-players.

<p>Mean arm movement velocity profiles after the “Go” signal for the AVG players (dashed burgundy line) and non-players (solid blue line). Velocity profiles are pooled for the Standard and Non-standard visuomotor conditions. Error bars represent SEM.</p

Relationship between preparatory BOLD signal and time spent playing.

<p>Linear regression results for mean instructed-delay epoch BOLD signal beta weights versus estimates of time spent playing action video games in regions of interest with significantly lower amplitude BOLD signal in the AVG player group compared with the non-player group. Regions of interest are displayed on each regression plot as overlays on the mean T1-weighted anatomical images for all participants. The Standard visuomotor mapping is represented by green squares and solid green lines. The Non-Standard visuomotor mapping is represented by orange triangles and dashed orange lines. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0189110#pone.0189110.t002" target="_blank">Table 2</a> for specific <i>p</i>-values.</p

Mean values of kinematic measures collected in Experiment 2 in the AVG player and non-player groups for the standard and non-standard visuomotor mapping conditions.

<p>Mean values of kinematic measures collected in Experiment 2 in the AVG player and non-player groups for the standard and non-standard visuomotor mapping conditions.</p

Linear regression of the timing of mean peak beta weights versus estimated time spent playing action video games each week.

<p>Linear regression of the timing of mean peak beta weights versus estimated time spent playing action video games each week.</p

Translational and rotational head movement.

<p>Group mean composite (x, y, and z directions) translational head motion (left panel) and rotational head motion (right panel). Data from the action video game (AVG) player group are represented by dashed burgundy lines and non-player data are represented by solid blue lines. Standard deviations are shown in paler colours around main plotted lines. Comparisons of estimates of area under the curve (using Riemann sums) for the gamer (hatched burgundy) and non-gamer (blue) groups are shown inset at the top left of each panel. Error bars represent standard deviation. No significant group differences in area under the curve were detected indicating that the overall amount of head motion in the scanner did not significantly differ between the AVG player and non-player groups.</p

Linear regression of mean beta weights during the instructed-delay period versus estimated time spent playing video games each week.

<p>Linear regression of mean beta weights during the instructed-delay period versus estimated time spent playing video games each week.</p