Perimenopausal women show modulation of excitatory and inhibitory neuromuscular mechanisms.

BACKGROUND: Menopausal transition exposes women to an early decline in muscle force and motor function. Changes in muscle quality and function, especially in lower limbs, are crucial, as they expose individuals to increased risk of falls. To elucidate some of the related neuromuscular mechanisms, we investigated cortical inhibition and peripheral muscle twitch force potentiation in women during the early and late stages of perimenopause. METHODS: Participants were 63 women aged 48-55 years categorized as early (EP, n = 25) or late (LP, n = 38) perimenopausal according to serum follicle-stimulating hormone (FSH) levels and menstrual diaries. EP women had an irregular menstrual cycle and FSH < 25 IU/L, while LP women had an irregular cycle and > 25 IU/L. We examined motor evoked potential (MEP) and silent period (SP) elicited by transcranial magnetic stimulation (TMS), in the tibialis anterior muscle at 20%, 40%, and 60% of maximal voluntary contraction (MVC) levels, and twitch force potentiation in plantar flexors. RESULTS: EP group showed a longer SP duration in 40% MVC condition and larger motor evoked potential amplitude in 20% MVC condition compared to the LP group. No group difference was detected in twitch force potentiation; however, it correlated negatively with FSH levels. Other factors, such as age, height, body mass index, or physical activity did not explain group differences. CONCLUSIONS: Our preliminary results indicate subtle modulation in both TMS-induced inhibitory and excitatory mechanisms and twitch force potentiation in women already in the late perimenopausal stage. This suggests that the reduction of estrogens may have an accelerating role in the aging process of neuromuscular control.

Bilateral activations in operculo-insular area show temporal dissociation after peripheral electrical stimulation in healthy adults.

Interhemispheric transfer is necessary for sensory integration and coordination of body sides. We studied how somatosensory input from one body side may reach both body sides. First, we investigated with 17 healthy adults in which uni- and bilateral brain areas were involved in consecutive stages of automatic sensory processing of non-nociceptive peripheral stimulation. Somatosensory evoked fields (SEFs) to electrical stimulation were recorded with 306-channel magnetoencephalography in two conditions. First, SEFs were registered following sensory radial nerve (RN) stimulation to dorsal surface of the right hand and second, following median nerve (MN) stimulation at the right wrist. Cortical activations were located in contralateral postcentral gyrus after MN and RN stimulations and in bilateral operculo-insular area after RN stimulation. First component occurred earlier after MN than RN stimulation. Middle latency components had similar latencies with stronger activation in contralateral postcentral gyrus after MN than RN stimulation. Interestingly, long latency components located in bilateral operculo-insular area after RN stimulation showed latency difference between hemispheres, i.e. activation peaked earlier in contralateral than in ipsilateral side. Additional experiments comparing novel intracutaneous nociceptive, RN and MN electrical stimuli confirmed bilateral long latency activation elicited by each stimulus type and highlighted latency differences between hemispheres. Variations in activation of bilateral operculo-insular areas may corroborate their role in pain network and in multisensory integration. Our findings imply that these areas present a relay station in multisensory stimulus detection.

Somatosensory Brain Function and Gray Matter Regional Volumes Differ According to Exercise History: Evidence from Monozygotic Twins.

Associations between long-term physical activity and cortical function and brain structure are poorly known. Our aim was to assess whether brain functional and/or structural modulation associated with long-term physical activity is detectable using a discordant monozygotic male twin pair design. Nine monozygotic male twin pairs were carefully selected for an intrapair difference in their leisure-time physical activity of at least three years duration (mean age 34 ± 1 years). We registered somatosensory mismatch response (SMMR) in EEG to electrical stimulation of fingers and whole brain MR images. We obtained exercise history and measured physical fitness and body composition. Equivalent electrical dipole sources of SMMR as well as gray matter (GM) voxel counts in regions of interest indicated by source analysis were evaluated. SMMR dipolar source strengths differed between active and inactive twins within twin pairs in postcentral gyrus, medial frontal gyrus and superior temporal gyrus and in anterior cingulate (AC) GM voxel counts differed similarly. Compared to active twins, their inactive twin brothers showed greater dipole strengths in short periods of the deviant-elicited SMMR and larger AC GM voxel counts. Stronger activation in early unattended cortical processing of the deviant sensory signals in inactive co-twins may imply less effective gating of somatosensory information in inactive twins compared to their active brothers. Present findings indicate that already in 30's long-term physical activity pattern is linked with specific brain indices, both in functional and structural domains.

Ten-year resistance training background modulates somatosensory P3 cognitive brain resonse in older men: A magnetoencephalograpy study.

The brain electrophysiological component P3, associated with good cognitive abilities, deteriorates during healthy aging. Both cognitive functions and P3 component amplitude respond positively to exercise, but the effects of resistance training on P3 are much less studied. Short-term resistance training interventions in older adults indicate modulation towards larger P3 amplitude, but this association has not been studied with a longitudinal study design. We investigated magnetoencephalographically recorded P3 (P3m) in a unique study design of nine aged men (mean age 77.7 y) with quasi-supervised resistance training background over a 10-year period and eight controls of similar age (mean age 77.5 y) with no training background. We elicited P3m utilizing lower limb electrical stimulation, as the resistance training program was mostly directed to lower limbs. Somatosensory oddball paradigm was performed with the right foot's fourth toe as standard (90%) and hallux as deviant (10%). Participants were asked to respond to deviants with a button press using their left index finger. Topographic maps showed bilateral temporoparietal activation for P3m in both groups. No amplitude differences were found in active P3m regions between groups. However, the groups differed in hemispheric activity of P3m. The exercise group showed stronger activation in the right frontotemporal and parietal sensor-groups compared to the left sensor-groups, and the control group showed stronger activation in right frontotemporal sensor-group compared to left. The control group showed shorter P3m latency in the right temporal sensor-group than the exercise group, but the latencies in other sensor-groups were similar. In aging, the brain utilizes compensatory areas to perform cognitive tasks. Our results suggest modulation in topographic distribution of P3m activity in aging men with long-term resistance training background compared to their controls. This might arise from a difference in age-related compensatory mechanisms in P3m generation.

Acute Exercise Modulates Pain-induced Response on Sensorimotor Cortex ∼20 Hz Oscillation.

Exercise affects positively on self-reported pain in musculoskeletal pain conditions possibly via top-down pain inhibitory networks. However, the role of cortical activity in these networks is unclear. The aim of the current exploratory study was to investigate the effects of acute exercise on cortical nociceptive processing and specifically the excitability in the human sensorimotor cortex. Five healthy adults (mean age 32.8 years) were recorded with a whole-head 306-channel magnetoencephalography (MEG, Elekta Neuromag® Triux™). Participant's right hand third fingertip was stimulated electrically with an intracutaneous non-magnetic copper tip electrode before and immediately after an exercise task. Stimulus intensity was set individually so that the stimulation was subjectively rated as moderately painful, 6-7 on a visual analog scale. The acute exercise task was an isometric three-minute fatiguing left hand contraction with force-level at 30% of maximum voluntary contraction. Data analysis was conducted as event-related evoked field and frequency analysis. Early cortical activations after stimulation were localized in the primary and secondary somatosensory cortices. The main result demonstrated modulation of cortical nociceptive processing in the sensorimotor cortex ∼20 Hz rhythm immediately after the acute exercise. In conclusion, acute exercise may have an effect on nociceptive processing in the sensorimotor cortex on oscillatory level. Research on cortical oscillations analyzing interaction between nociception and exercise is limited. This study presents results indicating brain oscillatory activity as a feasible research target for examining mechanisms interacting between exercise and cortical nociceptive processing.

Twin studies on the association of physical activity with cognitive and cerebral outcomes.

Regular physical activity (PA) offers positive effects on the human body. However, the effects of PA on cognition and in the brain are less clear. In this paper, we narratively review the relationship of PA with cognition and dementia, first from general perspective and then through genetically informed studies on the topic. Then we move on to imaging studies on exercise and brain anatomy first by presenting an overall picture of the topic and then discussing brain imaging studies addressing PA and brain structure in twins in more detailed way. Regarding PA and cognition or dementia, genetically informed studies are uncommon, even though the relationship between PA and cognitive ageing has been extensively studied. It is challenging to find twin pairs discordant for PA and dementia. Concerning brain imaging studies, among PA discordant young adult twin pairs, the more active co-twins showed larger gray matter volumes in striatal, prefrontal, and hippocampal regions and in electrophysiological studies automatic deviance-detection processes differed in brain regions involved with sensorimotor, visual and memory functions.

MicroRNAs in Extracellular Vesicles in Sweat Change in Response to Endurance Exercise.

BACKGROUND: To date, microRNAs (miRs) carried in extracellular vesicles (EVs) in response to exercise have been studied in blood but not in non-invasively collectable body fluids. In the present study, we examined whether six exercise-responsive miRs, miRs-21, -26, -126, -146, -221, and -222, respond to acute endurance exercise stimuli of different intensities in sweat. METHODS: We investigated the response of miRs isolated from sweat and serum EVs to three endurance exercise protocols: (1) maximal aerobic capacity (VO2 max ), (2) anaerobic threshold (AnaT), and (3) aerobic threshold (AerT) tests. Sauna bathing was used as a control test to induce sweating through increased body temperature in the absence of exercise. All protocols were performed by the same subjects (n = 8, three males and five females). The occurrence of different miR carriers in sweat and serum was investigated via EV markers (CD9, CD63, and TSG101), an miR-carrier protein (AGO2), and an HDL-particle marker (APOA1) with Western blot. Correlations between miRs in sweat and serum (post-sample) were examined. RESULTS: Of the studied miR carrier markers, sweat EV fractions expressed CD63 and, very weakly, APOA1, while the serum EV fraction expressed all the studied markers. In sweat EVs, miR-21 level increased after AerT and miR-26 after all the endurance exercise tests compared with the Sauna (p < 0.050). miR-146 after AnaT correlated to sweat and serum EV samples (r = 0.881, p = 0.004). CONCLUSION: Our preliminary study is the first to show that, in addition to serum, sweat EVs carry miRs. Interestingly, we observed that miRs-21 and -26 in sweat EVs respond to endurance exercise of different intensities. Our data further confirmed that miR responses to endurance exercise in sweat and serum were triggered by exercise and not by increased body temperature. Our results highlight that sweat possesses a unique miR carrier content that should be taken into account when planning analyses from sweat as a substitute for serum.

Motor Action Execution in Reaction-Time Movements: Magnetoencephalographic Study.

OBJECTIVE: Reaction-time movements are internally planned in the brain. Presumably, proactive control in reaction-time movements appears as an inhibitory phase preceding movement execution. We identified the brain activity of reaction-time movements in close proximity to movement onset and compared it with similar self-paced voluntary movements without external command. DESIGN: We recorded 18 healthy participants performing reaction-time and self-paced fast index finger abductions with 306-sensor magnetoencephalography and electromyography. Reaction-time movements were performed as responses to cutaneous electrical stimulation delivered on the hand radial nerve area. Motor field and movement-evoked field 1 corresponding to the sensorimotor cortex activity during motor execution and afferent feedback after the movement were analyzed with Brainstorm's scouts using regions of interest analysis. RESULTS: Primary motor and somato sensory cortices were active before and after movement onset. During reaction-time movements, primary motor and somato sensory cortices showed higher activation compared with self-paced movements. In primary motor cortex, stronger preparatory activity was seen in self-paced than in reaction time task. CONCLUSIONS: Both primary motor and somato sensory cortices participated in the movement execution and in the prediction of sensory consequences of movement. Cutaneous stimulation facilitated cortical activation during motor field after reaction-time movements, implying the applicability of cutaneous stimulation in motor rehabilitation.

Detecting differences with magnetoencephalography of somatosensory processing after tactile and electrical stimuli.

BACKGROUND: Deviant stimuli within a standard, frequent stimulus train induce a cortical somatosensory mismatch response (SMMR). The SMMR reflects the brain's automatic mechanism for the detection of change in a somatosensory domain. It is usually elicited by electrical stimulation, which activates nerve fibers and receptors in superficial and deep skin layers, whereas tactile stimulation is closer to natural stimulation and activates uniform fiber types. We recorded SMMRs after electrical and tactile stimuli. METHOD: 306-channel magnetoencephalography recordings were made with 16 healthy adults under two conditions: electrical (eSMMR) and tactile (tSMMR) stimulations. The SMMR protocol consisted of 1000 stimuli with 10% deviants to fingers. RESULTS: Sensor-level analysis revealed stronger activation after deviant stimulation in bilateral channel locations approximately corresponding to parietal cortical areas within both stimulation conditions. Between conditions, deviant tSMMR showed stronger activation in the ipsilateral channels. Based on sensor-level results, two components, M50 and SMMR (40-58 and 110-185 ms), were compared at the source-level. Deviant stimulation elicited stronger contralateral SI activation during M50 component in both conditions. SMMR was observed with both conditions, activating contralateral SII after deviant stimulation. However, only tSMMR showed long latency activation in bilateral SI cortices. This suggests that there is an integration of both body sides during the automatic stages of tactile processing in SI cortices. CONCLUSIONS: This study indicates that tactile stimulation (tSMMR) is a feasible method for investigating the brain's mechanism for detecting somatosensory changes; this may extend the clinical utility of tSMMR for assessing disorders involving altered somatosensory processing.

Long-Term Physical Activity May Modify Brain Structure and Function: Studies in Young Healthy Twins.

BACKGROUND: Physical activity (PA) is said to be beneficial to many bodily functions. However, the effects of PA in the brain are still inadequately known. The authors aimed to uncover possible brain modulation linked with PA. Here, they combine 4 of their studies with monozygotic twins, who were within-pair discordant in PA for a minimum of 1 year. METHODS: The authors performed brain imaging, brain electrophysiology, and cardiovascular and body composition assessments, and collected questionnaire-based data. The present synopsis elucidates the differences associated with differing PA history in conditions without genetic variability. They present new structural and electrophysiological results. Participants, healthy, 45 male monozygotic twins (mean age 34.5 [1.5] y) differed in aerobic capacity and fat percentage (P < .001). RESULTS: More active co-twins showed larger gray matter volumes in striatal, prefrontal, and hippocampal regions, and smaller gray matter volumes in the anterior cingulate area than less active co-twins. Functionally, visual and somatosensory automatic change detection processes differed between more and less active co-twins. CONCLUSIONS: In monozygotic twins, who differed in their PA history, differences were observed in identifiable anatomic brain locations involved with motor control and memory functions, as well as in electrophysiological measures detecting brain's automatic processes. Better aerobic capacity may modify brain morphology and sensory function.

Chronic diseases and objectively monitored physical activity profile among aged individuals - a cross-sectional twin cohort study.

INTRODUCTION: High physical activity (PA) at old age indicates good functional capacity enabling independent living. We investigated how different disease conditions are associated with measured PA indicators in old women and men, and whether they recognize this association. MATERIALS AND METHODS: This cross-sectional twin cohort study in Finland comprised 779 individuals (276 complete twin pairs, including 117 monozygotic pairs), who participated in hip-worn accelerometer monitoring of PA and responded to questions on diseases and mobility limitations at mean age of 73 (range 71-75). RESULTS: Of the participants, 23.2% reported having a disease restricting mobility. With sex and age in the regression model, the reported disease restricting mobility explained 11.8% of the variation in moderate-to-vigorous PA (MVPA) and 10.4% of the variation in daily steps. Adding stepwise other self-reported diseases and body mass index to the model increased the explanatory power for MVPA up to 18.5% and 25.5%, and for daily steps up to 16.0% and 20.7%, respectively. In the co-twin control analysis the PA differences were smaller in disease-discordant monozygotic than dizygotic pairs. CONCLUSIONS: Chronic disease conditions are associated with low PA, which individuals may not always recognize. Shared genetic factors may explain part of the associations. Key messages Among community-dwelling older men and women one-fourth of the variation in objectively measured moderate-to-vigorous physical activity is accounted for by age, sex, body mass index and self-reported diseases. Occurrence of chronic diseases is associated with low physical activity and individuals do not always recognize this. Healthcare professionals should pay attention to the low physical activity and mobility of individuals with chronic disease conditions before these result in limitations in independent living.

Long-term leisure-time physical activity and other health habits as predictors of objectively monitored late-life physical activity - A 40-year twin study.

Moderate-to-vigorous physical activity (MVPA) in old age is an important indicator of good health and functional capacity enabling independent living. In our prospective twin cohort study with 616 individuals we investigated whether long-term physical activity assessed three times, in 1975, 1982 and 1990 (mean age 48 years in 1990), and other self-reported health habits predict objectively measured MVPA measured with a hip-worn triaxial accelerometer (at least 10 hours per day for at least 4 days) 25 years later (mean age of 73 years). Low leisure-time physical activity at younger age, higher relative weight, smoking, low socioeconomic status, and health problems predicted low MVPA in old age in individual-based analyses (altogether explaining 20.3% of the variation in MVPA). However, quantitative trait modeling indicated that shared genetic factors explained 82% of the correlation between baseline and follow-up physical activity. Pairwise analyses within monozygotic twin pairs showed that only baseline smoking was a statistically significant predictor of later-life MVPA. The results imply that younger-age physical activity is associated with later-life MVPA, but shared genetic factors underlies this association. Of the other predictors mid-life smoking predicted less physical activity at older age independent of genetic factors.