Brown, Liana E

Mild sauna dehydration and fluid abstinence were investigated as weight loss strategies for lightweight rowers. Rowers (N=12) performed a power test, an incremental VO2max test, and a visuomotor battery: once euhydrated, once following sauna dehydration (SAU), and once following fluid abstinence and then sauna dehydration (FA). The percent body mass change (%BMC) achieved, %BMC attributable to sauna dehydration, and %BMC attributable to fluid abstinence were used within linear mixed effects models to predict hydration and performance variables. Sauna and overnight dehydration exerted indistinguishable effects on plasma osmolality, urine osmolality and thirst (p > .05). Fluid abstinence but not sauna dehydration was related to lower power production on the power test (b = 12.14W / 1%BMC, FA = 673.46 ± 79.50, SAU = 683.33 ± 72.08, p = .029), a lower total wattage produced on the incremental VO2max test (b = 4261.51W / 1%BMC, FA = 71029.58 ± 16256.56, SAU = 74001.50 ± 14936.56, p = .006), lower wattages at 2 mmol/L (b = 27.84W / 1%BMC, FA = 180.74 ± 40.27, SAU = 190.82 ± 50.79, p < .001) and 4 mmol/L (b = 20.45W / 1%BMC, FA = 221.90 ± 52.62, SAU = 238.89 ± 40.78, p = .002) blood lactate, and slower movement time on a visuomotor task (b = -38.06ms / 1%BMC, p = .004). Mild fluid abstinence but not sauna dehydration reduces rowing performance when two-hour rehydration is allowed.

Author Keywords: crew, fluid, hydration, lightweight, sauna, weight

Evidence suggests that visuomotor system behaviour may be more sensitive to the prolonged effects of mild brain injuries than neuropsychological tests. We evaluated whether participants with a mild closed head injury (CHI) would show lingering visuomotor deficits, but not cognitive deficits, up to three years post-injury compared to participants with an orthopaedic injury and healthy controls. All three groups completed a tablet-based visuomotor assessment tool and a brief neuropsychological test battery. The CHI participants scored comparable to the control groups on the neuropsychological tests, but when assessed for visuomotor function requiring adjustment to a changing stimulus, CHI participants showed poorer performance than the control groups. Combined, these findings add to the evidence that CHI can lead to persistent visuomotor deficits that extend beyond those of neuropsychological tests. Therefore, visuomotor assessment should be included in brain injury and recovery evaluation, and this can be accomplished easily using tablet-based tasks.

Author Keywords: closed head injury, neuropsychological assessment, recovery, tablet, traumatic brain injury, visuomotor

Typically task interference is studied using reaching adaptation tasks (visuomotor rotation and/or force-field learning). Participants in these experiments are already experts at the base task (point-to-point, planar reaching) and their ability to adapt reaching to the imposed perturbation is studied. The pattern of data induced by the perturbation is used to make inferences about the nature and neural correlates of our learning and memory for reaching perturbations, specifically, and motor performance in general. We wanted to see if it is possible to demonstrate this same interference pattern using a novel vegetable-chopping task, where we can easily recreate natural performance settings using a task for which we can easily identify non-experts. Participants performed a chopping task in which they are asked to chop a sweet potato into 5 mm-wide slices, matching the beat of a metronome (120 bpm). Following this initial learning, participants were exposed to an interference condition. Participants then performed trials of the original task again. Interference was inferred if the second performance of the original task was impaired, compared to initial performance. Experiment 1 involved novice choppers, and either the force or frequency of chops was manipulated. Only the altered frequency task produced interference effects. In Experiment 2, competent and expert choppers had to manage either a faster or slower frequency. We found evidence for interference in competents, but not experts. These results support the idea that the vulnerability to interference of motor memory changes with practice, and so any inferences made about memory structure must take into account not only expert performance, but every level of skill.

Author Keywords: expertise, interference, motor learning, reaching adaptation

It is universally accepted that human motor performance is variable in both its timing and spatial qualities. However, it is unclear to what extent motor variability impedes performance when learning a new skill and to what extent it enables our ability to learn. The first experiment examined whether performance during a test task depended on whether participants practiced to constrain or vary the task-relevant parameter. Participants used their right hand to make simple point-to-point movements. Results demonstrated the importance of paying attention to test task demands to evaluate which form of practice is most beneficial. The second experiment examined whether levels of variability could be manipulated using a reward-based paradigm to enhance learning when adapting to a perturbation of a simple visually-guided reaching movement. A reward-based feedback task was designed to encourage exploration along the task-relevant dimension, specifically movement direction variability. Overall, I did not find any significant results.

Author Keywords: Adaptation, Motor Control, Motor Learning, Reaching

We investigated whether hand-proximity effects arise from the recruitment of visual-tactile bimodal cells. In Experiment 1, we executed right-hand open-loop reaching movements to targets, presented either near or far from the resting left-hand, and after applying repetitive transcranial magnetic stimulation (rTMS) to suppress neuronal activity in the PMd and AIP, in Experiment 2. Results from Experiment 1, indicated that near-hand targets improved accuracy and reduced variability. In Experiment 2, suppressing PMd showed similar near-hand effects as above. In contrast, applying rTMS to AIP disrupted the representation of target location, indicating less accuracy and greater error. Near-hand proximity effects possibly arise from the recruitment of visual-tactile bimodal cells within the human AIP.

Author Keywords: anterior intraparietal sulcus, peripersonal space, repetitive transcranial magnetic stimulation (rTMS), , rTMS, anterior intraparietal sulcus, AIP., visual-tactile bimodal neurons