Adolescents demonstrate increasing mastery of motor actions with age. One prevailing hypothesis is that maturation of the somatosensory system during adolescence contributes to the improved motor control. However, limited efforts have been made to determine if somatosensory cortical processing is different in adolescents during movement. In this study, we used magnetoencephalographic brain imaging to begin addressing this knowledge gap by applying an electrical stimulation to the tibial nerve as adolescents (Age = 14.8 ± 2.5 yrs.) and adults (Age = 36.8 ± 5.0 yrs.) produced an isometric ankle plantarflexion force, or sat with no motor activity. Our results showed strong somatosensory cortical oscillations for both conditions in the alpha-beta (8–30 Hz) and gamma (38–80 Hz) ranges that occurred immediately after the stimulation (0–125 ms), and a beta (18–26 Hz) oscillatory response shortly thereafter (300–400 ms). Compared with the passive condition, all of these frequency specific cortical oscillations were attenuated while producing the ankle force. The attenuation of the alpha-beta response was greater in adolescents, while the adults had a greater attenuation of the beta response. These results imply that altered attenuation of the somatosensory cortical oscillations might be central to the under-developed somatosensory processing and motor performance characteristics in adolescents.
Magnetoencephalography data were acquired during a leg force task in pre‐/post‐practice sessions in adolescents and adults. Strong peri‐movement alpha and beta oscillations were mapped to the cortex. Following practice, performance improved and beta oscillations were altered. Beta oscillations decreased in the sensorimotor cortex in adolescents after practice, but increased in adults. No pre‐/post‐practice differences were detected for alpha oscillations.
There is considerable evidence that there are motor performance and practice differences between adolescents and adults. Behavioural studies have suggested that these motor performance differences are simply due to experience. However, the neurophysiological nexus for these motor performance differences remains unknown. The present study investigates the short‐term changes (e.g. fast motor learning) in the alpha and beta event‐related desynchronizations (ERDs) associated with practising an ankle plantarflexion motor action. To this end, we utilized magnetoencephalography to identify changes in the alpha and beta ERDs in healthy adolescents (
- NSF-PAR ID:
- 10459673
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Journal of Physiology
- Volume:
- 597
- Issue:
- 12
- ISSN:
- 0022-3751
- Page Range / eLocation ID:
- p. 3203-3216
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Key points Visual attention involves discrete multispectral oscillatory responses in visual and ‘higher‐order’ prefrontal cortices.
Prefrontal cortex laterality effects during visual selective attention are poorly characterized.
High‐definition transcranial direct current stimulation dynamically modulated right‐lateralized fronto‐visual theta oscillations compared to those observed in left fronto‐visual pathways.
Increased connectivity in right fronto‐visual networks after stimulation of the left dorsolateral prefrontal cortex resulted in faster task performance in the context of distractors.
Our findings show clear laterality effects in theta oscillatory activity along prefrontal–visual cortical pathways during visual selective attention.
Abstract Studies of visual attention have implicated oscillatory activity in the recognition, protection and temporal organization of attended representations in visual cortices. These studies have also shown that higher‐order regions such as the prefrontal cortex are critical to attentional processing, but far less is understood regarding prefrontal laterality differences in attention processing. To examine this, we selectively applied high‐definition transcranial direct current stimulation (HD‐tDCS) to the left or right dorsolateral prefrontal cortex (DLPFC). We predicted that HD‐tDCS of the left
versus right prefrontal cortex would differentially modulate performance on a visual selective attention task, and alter the underlying oscillatory network dynamics. Our randomized crossover design included 27 healthy adults that underwent three separate sessions of HD‐tDCS (sham, left DLPFC and right DLPFC) for 20 min. Following stimulation, participants completed an attention protocol during magnetoencephalography. The resulting oscillatory dynamics were imaged using beamforming, and peak task‐related neural activity was subjected to dynamic functional connectivity analyses to evaluate the impact of stimulation site (i.e. left and right DLPFC) on neural interactions. Our results indicated that HD‐tDCS over the left DLPFC differentially modulated right fronto‐visual functional connectivity within the theta band compared to HD‐tDCS of the right DLPFC and further, specifically modulated the oscillatory response for detecting targets among an array of distractors. Importantly, these findings provide network‐specific insight into the complex oscillatory mechanisms serving visual selective attention. -
more » « less
Abstract Neural oscillations may be sensitive to aspects of brain maturation such as myelination and synaptic density changes. Better characterization of developmental trajectories and reliability is necessary for understanding typical and atypical neurodevelopment. Here, we examined reliability in 110 typically developing children and adolescents (aged 9–17 years) across 2.25 years. From 10 min of magnetoencephalography resting-state data, normalized source spectral power and intraclass correlation coefficients were calculated. We found sex-specific differences in global normalized power, with males showing age-related decreases in delta and theta, along with age-related increases in beta and gamma. Females had fewer significant age-related changes. Structural magnetic resonance imaging revealed that males had more total gray, subcortical gray, and cortical white matter volume. There were significant age-related changes in total gray matter volume with sex-specific and frequency-specific correlations to normalized power. In males, increased total gray matter volume correlated with increased theta and alpha, along with decreased gamma. Split-half reliability was excellent in all frequency bands and source regions. Test–retest reliability ranged from good (alpha) to fair (theta) to poor (remaining bands). While resting-state neural oscillations can have fingerprint-like quality in adults, we show here that neural oscillations continue to evolve in children and adolescents due to brain maturation and neurodevelopmental change.
-
more » « less
Abstract Background Ankle-targeting resistance training for improving plantarflexion function during walking increases rehabilitation intensity, an important factor for motor recovery after stroke. However, understanding of the effects of resisting plantarflexion during stance on joint kinetics and muscle activity—key outcomes in evaluating its potential value in rehabilitation—remains limited. This initial study uses a unilateral exosuit that resists plantarflexion during mid-late stance in unimpaired individuals to test the hypotheses that when plantarflexion is resisted, individuals would (1) increase plantarflexor ankle torque and muscle activity locally at the resisted ipsilateral ankle, but (2) at higher forces, exhibit a generalized response that also uses the unresisted joints and limb. Further, we expected (3) short-term retention into gait immediately after removal of resistance.
Methods Ten healthy young adults walked at 1.25 m s−1for four 10-min discrete bouts, each comprising baseline, exposure to active exosuit-applied resistance, and post-active sections. In each bout, a different force magnitude was applied based on individual baseline ankle torques. The peak resistance torque applied by the exosuit was 0.13 ± 0.01, 0.19 ± 0.01, 0.26 ± 0.02, and 0.32 ± 0.02 N m kg−1, in the LOW, MED, HIGH, and MAX bouts, respectively.
Results (1) Across all bouts, participants increased peak ipsilateral biological ankle torque by 0.13–0.25 N m kg−1(p < 0.001) during exosuit-applied resistance compared to corresponding baselines. Additionally, ipsilateral soleus activity during stance increased by 5.4–11.3% (p < 0.05) in all but the LOW bout. (2) In the HIGH and MAX bouts, vertical ground reaction force decreased on the ipsilateral limb while increasing on the contralateral limb (p < 0.01). Secondary analysis found that the force magnitude that maximized increases in biological ankle torque without significant changes in limb loading varied by subject. (3) Finally, peak ipsilateral plantarflexion angle increased significantly during post-exposure in the intermediate HIGH resistance bout (p < 0.05), which corresponded to the greatest average increase in soleus activity (p > 0.10).
Conclusions Targeted resistance of ankle plantarflexion during stance by an exosuit consistently increased local ipsilateral plantarflexor effort during active resistance, but force magnitude will be an important parameter to tune for minimizing the involvement of the unresisted joints and limb during training.
-
more » « less
Key points Maximum fascicle shortening/rotation was significantly decreased in paretic medial gastrocnemius (MG) muscles compared to non‐paretic MG muscles.
The fascicle gear ratio on both sides decreased as the ankle became dorsiflexed, but the slope of the fascicle gear ratio over ankle joint angle was significantly lower on the paretic side.
The side‐to‐side slope difference was strongly correlated with the relative maximum joint torque and with the relative shear wave speed, suggesting that variable gearing may explain muscle weakness after stroke.
Abstract The present study aimed to understand variable fascicle gearing during voluntary isometric contractions of the medial gastrocnemius (MG) muscle in chronic stroke survivors. Using ultrasonography, we characterized fascicle behaviour on both paretic and non‐paretic sides during plantarflexion contractions at different intensities and at different ankle joint angles. Shear wave speed was also recorded from the MG muscle belly under passive conditions. Fascicle gear ratios were then calculated as the ratio of muscle belly shortening velocity to fascicle shortening velocity, and variable fascicle gearing was quantified from the slope of gear ratio
vs . joint angle relations. This slope was used to establish associations with maximum joint torques and with shear wave speeds. At all measured angles, we found a significant reduction in both maximum fascicle shortening and maximum fascicle rotation on the paretic side compared to the non‐paretic side on our stroke survivor cohort. The fascicle rotation per fascicle shortening on the paretic side was also significantly smaller than on the non‐paretic side, especially at plantarflexed positions. Furthermore, the fascicle gear ratio on both sides decreased as the ankle became dorsiflexed, but the change in the fascicle gear ratio was significantly lower on the paretic side. The side‐to‐side difference in the gear ratio slope was also strongly correlated with the relative maximum joint torque and with the relative shear wave speed, suggesting that variable gearing may explain muscle weakness after stroke. Further studies are needed to investigate how muscular changes after stroke may impede variable gearing and adversely impact muscle performance.
