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The dynamic and flexible nature of memories is evident in our ability to adopt multiple visual perspectives. Although autobiographical memories are typically encoded from the visual perspective of our own eyes they can be retrieved from the perspective of an observer looking at our self. Here, we examined the neural mechanisms of shifting visual perspective during long-term memory retrieval and its influence on online and subsequent memories using functional magnetic resonance imaging (fMRI). Participants generated specific autobiographical memories from the last five years and rated their visual perspective. In a separate fMRI session, they were asked to retrieve the memories across three repetitions while maintaining the same visual perspective as their initial rating or by shifting to an alternative perspective. Visual perspective shifting during autobiographical memory retrieval was supported by a linear decrease in neural recruitment across repetitions in the posterior parietal cortices. Additional analyses revealed that the precuneus, in particular, contributed to both online and subsequent changes in the phenomenology of memories. Our findings show that flexibly shifting egocentric perspective during autobiographical memory retrieval is supported by the precuneus, and suggest that this manipulation of mental imagery during retrieval has consequences for how memories are retrieved and later remembered. •Memories are shaped by retrieval from alternative egocentric frameworks.•Posterior parietal cortices underlie shifts in visual perspective during memory retrieval.•Precuneus predicts online and subsequent changes in memories due to perspective shifting.

Objectives Although motor control exercises have been shown to be effective in the management of low back pain (LBP) the mechanism of action is unclear. The current study investigated the relationship between the ability to recruit transversus abdominis and clinical outcomes of participants in a clinical trial. Methods Ultrasonography was used to assess the ability to recruit transversus abdominis in a nested design: a sample of 34 participants with chronic LBP was recruited from participants in a randomised controlled trial comparing the efficacy of motor control exercise, general exercise and spinal manipulative therapy. Perceived recovery, function, disability and pain were also assessed. Results Participants with chronic LBP receiving motor control exercise had a greater improvement in recruitment of transversus abdominis (7.8%) than participants receiving general exercise (4.9% reduction) or spinal manipulative therapy (3.7% reduction). The effect of motor control exercise on pain reduction was greater in participants who had a poor ability to recruit transversus abdominis at baseline. There was a significant, moderate correlation between improved recruitment of transversus abdominis and a reduction in disability (r = −0.35; 95% CI 0.02 to 0.62). Conclusion These data provide some support for the hypothesised mechanism of action of motor control exercise and suggest that the treatment may be more effective in those with a poor ability to recruit transversus abdominis.

There is limited evidence that preprogrammed feedforward adjustments, which are modified in people with neurological and musculoskeletal conditions, can be trained and whether this depends on the type of training. As previous findings demonstrate consistent delays in feedforward activation of the deep abdominal muscle, transversus abdominis (TrA), in people with recurrent low back pain (LBP), we investigated whether training involving voluntary muscle activation can change feedforward mechanisms, and whether this depends on the manner in which the muscle is trained. Twenty-two volunteers with recurrent LBP were randomly assigned to undertake either training of isolated voluntary activation of TrA or sit-up training to activate TrA in a non-isolated manner to identical amplitude. Subjects performed a trunk perturbation task involving arm movement prior to and after training, and surface and fine-wire electromyography (EMG) recordings were made from trunk and arm muscles. Following a single session of training of isolated voluntary activation of TrA, onset of TrA EMG was earlier during rapid arm flexion and extension, to more closely resemble the responses in pain-free individuals. The magnitude of change in TrA EMG onset was correlated with the quality of isolated training. In contrast, all of the abdominal muscles were recruited earlier during arm flexion after sit-up training, while onset of TrA EMG was further delayed during arm extension. The results provide evidence that training of isolated muscle activation leads to changes in feedforward postural strategies, and the magnitude of the effect is dependent on the type and quality of motor training.

Age-related changes in motor unit activation properties remain unclear for locomotor muscles such as quadriceps muscles, although these muscles are preferentially atrophied with aging and play important roles in daily living movements. The present study investigated and compared detailed motor unit firing characteristics for the vastus lateralis muscle during isometric contraction at low to moderate force levels in the elderly and young. Fourteen healthy elderly men and 15 healthy young men performed isometric ramp-up contraction to 70 % of the maximal voluntary contractions (MVC) during knee extension. Multichannel surface electromyograms were recorded from the vastus lateralis muscle using a two-dimensional grid of 64 electrodes and decomposed with the convolution kernel compensation technique to extract individual motor units. Motor unit firing rates in the young were significantly higher (~+29.7 %) than in the elderly ( p  < 0.05). There were significant differences in firing rates among motor units with different recruitment thresholds at each force level in the young ( p  < 0.05) but not in the elderly ( p  > 0.05). Firing rates at 60 % of the MVC force level for the motor units recruited at <20 % of MVC were significantly correlated with MVC force in the elderly ( r  = 0.885, p  < 0.0001) but not in the young ( r  = 0.127, p  > 0.05). These results suggest that the motor unit firing rate in the vastus lateralis muscle is affected by aging and muscle strength in the elderly and/or age-related strength loss is related to motor unit firing/recruitment properties.

To compare muscle recruitment, maximal force, and rate of force development changes following different resistance exercise protocols with a constant volume-load. Within-subjects randomized crossover trial. Fourteen (n=14) resistance trained male participants completed three different resistance exercise protocols involving 20 squat repetitions, prescribed at 80% of 1-repetition-maximum. Protocol A consisted of 5 sets of 4 repetitions with 3min inter-set rest intervals, protocol B was 5 sets of 4 repetitions with 20s inter-set rest intervals, and the rest-pause method was an initial set to failure with subsequent sets performed with a 20s inter-set rest interval. Maximal squat isometric force output and rate of force development (RFD) were measured before, immediately upon completion (IP), and 5min (5P) following each protocol. Muscle activity from 6 different thigh and hip muscles was measured with surface electromyography (EMG) at each time point, and during every squat repetition. Participants completed the rest-pause method in 2.1±0.4 sets, with a total protocol duration of 103s compared to 140s and 780s for protocols B and A, respectively. All protocols elicited similar decreases (p<0.05) in maximal force and RFD at IP, with full recovery at 5P. Increased motor unit recruitment was observed during the rest-pause method compared to both protocols A and B for all muscles measured (p<0.05). As a result of the increased EMG during exercise and no greater post-exercise fatigue, it was concluded that the rest-pause method may be an efficacious training method for resistance-trained individuals.

The purpose of this investigation was to evaluate the effects of repeated, high‐ (HT: 70% MVIC) versus low‐torque (LT: 30% MVIC) isometric exercise performed to failure on motor unit (MU) recruitment and firing behavior of the vastus lateralis. Eighteen resistance‐trained males (23.1 ± 3.8 years) completed familiarization, followed by separate experimental sessions in which they completed either HT or LT exercise to failure in random order. LT exercise resulted in a greater time to task failure and a more dramatic decline in the muscle's force capacity, but the total work completed was similar for HT and LT exercise. An examination of the firing trains from 4670 MUs recorded during exercise revealed that firing rates generally increased during HT and LT exercise, but were higher during HT than LT exercise. Furthermore, recruitment thresholds (RT) did not significantly change during HT exercise, whereas the RT of the smallest MUs increased and the RT for the moderate to large MUs decreased during LT exercise. Both HT and LT exercise resulted in the recruitment of additional higher threshold MUs in order to maintain torque production. However, throughout exercise, HT required the recruitment of larger MUs than did LT exercise. In a few cases, however, MUs were recruited by individuals during LT exercise that were similar in size and original (pre) RT to those detected during HT exercise. Thus, the ability to achieve full MU recruitment during LT exercise may be dependent on the subject. Consequently, our data emphasize the task and subject dependency of muscle fatigue. This study expands on recent work examining the motor unit control scheme during muscle fatigue by examining the effect of varying torque levels on motor unit behavior. Our data suggest that as excitation to the motor neuron pool increases during fatigue, motor unit firing rates increase during both high‐ and low‐torque exercise. However, changes in motor unit recruitment thresholds were dependent on torque level. Our data also suggest that the net output of the motor neuron pool during fatigue at low‐torques may be constrained in comparison to high‐torques, although the degree to which this was true was dependent on the subject.

The aim of the study was to investigate the effect of chronic administration of paroxetine (selective serotonin reuptake inhibitor: SSRI) on motor cortex excitability in healthy subjects by means of transcranial magnetic stimulation (TMS), functional magnetic resonance imaging (fMRI) and behavioral motor tests. In a randomized, double-blind, crossover study, twenty-one right-handed subjects received 20 mg daily of either paroxetine or a placebo over a period of 30 days separated by a period of 3 months wash-out. The TMS study is presented here correlated with some results of the motor behavior study (finger tapping test) and the fMRI study (primary sensorimotor cortex (S1M1) volume of activation). TMS was used to test motor threshold (MT), motor evoked potential recruitment curve (RC), cortical silent period (CSP) and paired-pulse intracortical inhibition and facilitation (ICI, ICF). Chronic administration of paroxetine did not modulate ICI or CSP but induced a significant enhancement of mean ICF (ANOVA P = 0.04), which significantly correlated with increase of speed in a finger tapping test ( P = 0.02). This suggests a modulation of cortical interneuronal excitatory pathways without changes in the excitability of cortical inhibitory GABAergic interneurons. A decrease of RC (ANOVA P = 0.05) was also observed after 30 days intake of paroxetine in comparison with placebo and was associated with changes of fMRI activation intensity (left S1M1 hypoactivation, Loubinoux, I., Tombari, D., Pariente, J., Gerdelat, A., Pastor, J., Cassol, E., Rascol, O. and Chollet, F., Modulation of behavior and cortical motor activity in healthy subjects by a chronic administration of a serotonin enhancer. NeuroImage (in press)), without changes of S1M1 activation volume. Finally, the different modulation of RC and ICF after chronic administration of paroxetine compared to single dose (opposite effects) emphasizes the different pharmacological action of the drug at cortical level depending on its acute or long-term administration.

Introduction The needle electromyography (EMG) serves to supply additional information in patients with suspected neuromuscular disorders. We aimed to provide motor unit potential (MUP) data by concentric needle EMG in the erector spinae (ES) in comparison with biceps brachii (BB) and lateral vastus (LV). Methods Electromyography MUP data (n) were obtained in ES (517), BB (539), and LV (627) in 32 healthy volunteers (16f). Results Motor unit potential data: amplitude (μV) 393 ± 174 (ES), 375 ± 162 (BB), and 577 ± 304 (LV); duration (ms) 10.4 ± 2.4 (ES), 10.1 ± 2.1 (BB), and 11.1 ± 2.3 (LV), area (μV × ms) 585 ± 327 (ES), 538 ± 267 (BB), and 881 ± 492 (LV); phase number 3.23 ± 0.94 (ES), 2.98 ± 0.76 (BB), and 3.19 ± 0.81 (LV); size index 0.60 ± 0.56 (ES), 0.51 ± 0.53 (BB), and 0.96 ± 0.55 (LV). LV displayed higher values (p at least <.001) for MUP amplitude, duration, area, and size index as compared to both, BB and ES. Conclusion Concentric needle EMG investigations in healthy adult human subjects revealed similar MUP parameters in the ES and BB muscles, while in the LV muscle MUP amplitude, duration, area, and size index were significantly larger. Different neuromuscular disorders display a predominant involvement of proximally located muscles such as truncal muscles. The present results given here may facilitate the diagnosis of neuromuscular disorders. The needle electromyography (EMG) serves to supply additional information in patients with suspected neuromuscular disorders. We aimed to provide motor unit potential data by concentric needle EMG in the erector spinae in comparison with biceps brachii and lateral vastus. The present results given here may facilitate the diagnosis of neuromuscular disorders.

There has been a recent proliferation of functional magnetic resonance imaging (fMRI) studies that interpret between-group or within-group differences in brain response patterns as evidence for compensatory neural recruitment. However, it is currently a challenge to determine whether these observed differences are truly attributable to compensatory neural recruitment or whether they are indicative of some other cognitive or physiological process. Therefore, the need for a standardized set of criteria for interpreting whether differences in brain response patterns are compensatory in nature is great. Focusing on studies of aging and potentially prodromal Alzheimer’s disease conditions (genetic risk, mild cognitive impairment), we critically review the functional neuroimaging literature purporting evidence for compensatory neural recruitment. Finally, we end with a comprehensive model set of criteria for ascertaining the degree to which a ‘compensatory’ interpretation may be supported. This proposed model addresses significant brain region, activation pattern, and behavioral performance considerations, and is therefore termed the Region-Activation-Performance model (RAP model).

Low back pain (LBP) may be associated with inadequate multifidus muscle function. Varying the frequency and timing of feedback may enhance acquisition and retention of multifidus muscle recruitment during exercise. Subjects without LBP (n=30) were randomly assigned to a constant (CON) or variable (VAR) feedback group. Twenty-eight subjects (mean age=28 years, SD=8.0; mean body mass index=24 kg/m(2), SD=0.70) completed training, and 23 completed retention testing. Eight training sessions over 4 weeks included multifidus muscle exercise with rehabilitative ultrasound imaging (RUSI) feedback. Retention was assessed at 1 week and >or=1 month. At the start, both groups had similar performances of multifidus muscle recruitment (Fisher exact test, P=.26). Early in training, the CON group had good success (mean=80%) that was maintained at session 8 (mean=84%), with no difference between sessions 1 and 8 (Wilcoxon signed rank test, P=.19, 95% confidence interval [CI]=-9%, 42%). The VAR group gradually increased success (Wilcoxon signed rank test, P=.002, 95% CI=17%, 59%) between sessions 1 and 8. Both groups sustained their session 8 success when tested for short-term retention at 1 week (CON group: Wilcoxon signed rank test, P=.79; VAR group: Wilcoxon signed rank test, P=.36). At the long-term retention test, the VAR group outperformed the CON group (Wilcoxon score test, P=.04), indicating superior motor learning. Variable feedback provided by RUSI resulted in greater success in lumbar multifidus muscle recruitment up to 3 to 4 months after training.