Traumatic brain injuries caused by knockout in Japanese amateur boxers: A questionnaire-based survey.

The aim of the present study is to conduct a trauma and disability survey in amateur boxers and show the actual conditions of injuries based on the current situations. We have obtained 663 valid responses from male and female boxers. In the questionnaire survey who was carried out on a Web questionnaire form. The questions involve that Face Sheet (gender, height, weight, athletic experience, etc.) and prepared 10 questions about trauma and impairment, 7 questions with concussion or damage on head. and, set 11 self-evaluations, which the boxers assessed their boxing skills. The subjects include amateur boxers who are all high school students (15 years old) and retired boxers. We had analyzed relation between the skills and the injuries. And, main outcome was that make a measure to setting whether or not questionnaires have been knockout (KO) as a variable, we applied a method of multiple logistic regression analysis. Moreover, as for the group who got KO in the past, we have also applied multiple regression analysis by using stepwise regression to factors affecting numbers of symptoms. The number of hits they experienced was smaller in international tournament matches, and the odds rate for KO was 0.669. And, KO experience group was compared with non-KO experience group, and the factors influencing the number of severity symptoms were examined. As a result, 2 factors were selected what "Seriousness in practice" and "Fighting spirit in games". It might be possible that the relation between the experience of being KO and self-assessment of boxing performance.

Corrigendum: Neuromuscular Fatigue in Unimanual Handgrip Does Not Completely Affect Simultaneous Bimanual Handgrip.

[This corrects the article DOI: 10.3389/fnhum.2021.763580.].

Neuromuscular Fatigue in Unimanual Handgrip Does Not Completely Affect Simultaneous Bimanual Handgrip.

Simultaneous bimanual movements are not merely the sum of two unimanual movements. Here, we considered the unimanual/bimanual motor system as comprising three components: unimanual-specific, bimanual-specific, and overlapping (mobilized during both unimanual and bimanual movements). If the force-generating system controlling the same limb differs between unimanual and bimanual movements, unimanual exercise would be expected to fatigue the unimanual-specific and overlapping parts in the force-generating system but not the bimanual-specific part. Therefore, we predicted that the decrease in bimanual force generation induced by unimanual neuromuscular fatigue would be smaller than the decrease in unimanual force generation. Sixteen healthy right-handed adults performed unimanual and bimanual maximal handgrip measurements before and after a submaximal fatiguing handgrip task. In the fatigue task, participants were instructed to maintain unimanual handgrip force at 50% of their maximal handgrip force until the time to task failure. Each participant performed this task in a left-hand fatigue (LF) condition and a right-hand fatigue (RF) condition, in a random order. Although the degree of neuromuscular fatigue was comparable in both conditions, as expected, the decrease in bimanual right handgrip force was significantly smaller than those during unimanual right performance in the RF condition, but not in the LF condition. These results indicate that for the right-hand, neuromuscular fatigue in unimanual handgrip does not completely affect simultaneous bimanual handgrip. Regarding the underlying mechanisms, we propose that although neuromuscular fatigue caused by unimanual handgrip reduces the motor output of unimanual-specific and overlapping parts in the force-generating system, when simultaneous bimanual handgrip is performed, the overlapping part (which is partially fatigued) and the bimanual-specific part (which is not yet fatigued) generate motor output, thus decreasing the force reduction.

Effects of Bilateral Transcranial Direct Current Stimulation on Simultaneous Bimanual Handgrip Strength.

Although the effects of transcranial direct current stimulation (tDCS) on contralateral unimanual movement have been well reported, its effects on coordinated multi-limb movements remain unclear. Because multi-limb coordination is often performed in daily activities and sports, clarifying the effects of tDCS on multi-limb coordination may have valuable implications. However, considering the neural crosstalk involved in bimanual movements, including the transcallosal pathway and ipsilateral motor pathway, the extent of tDCS-induced improvement may differ between unimanual and bimanual movement. We examined how tDCS affects simultaneous bimanual maximal voluntary contraction (MVC) by testing the effects of tDCS of the bilateral primary motor cortex (M1) on unimanual and bimanual handgrip strength. Twenty-one right-handed healthy adults underwent three bilateral tDCS protocols ("RaLc," with an anode on right M1 and a cathode on left M1, "RcLa," with an anode on left M1 and a cathode on right M1, and "Sham") in a randomized order. A 1.5 mA current was applied for 15 min during tDCS. Participants then performed maximal unimanual and bimanual handgrip tests. Bimanual handgrip force was higher in both hands in the RcLa condition than in the Sham condition. Similarly, unimanual handgrip force was higher in the RcLa condition than in the Sham condition. Stimulus responses were asymmetrical and were not observed in the RaLc condition. Our findings demonstrate that RcLa tDCS leads to neuromodulation that can produce greater unimanual and bimanual handgrip strength. This result provides basic evidence that tDCS may be useful in sports, particularly those involving bilateral coordination of upper limb movement.

Cathodal transcranial direct current stimulation over the Cz increases joint flexibility.

Joint flexibility depends on both mechanical and neural factors. However, the contribution of neural factors is not fully understood. To test the hypothesis that the sensorimotor cortex is involved in joint flexibility, we investigated whether transcranial direct current stimulation (tDCS) over the Cz modifies ankle and wrist flexibility in healthy human participants. In eight male participants, range of motion of the left ankle and wrist were measured during a passive-dorsiflexion test. We also assessed passive torque, which represents involuntary resistance to dorsiflexion at the ankle. Participants performed passive-dorsiflexion tests before and after anodal, cathodal, and sham tDCS over the Cz. The current was applied for 10min with an intensity of 2.0mA during anodal and cathodal tDCS. Cathodal tDCS resulted in a 10.5% increase in range of motion of the ankle, but no significant increase in range of motion of the wrist. Neither anodal nor sham tDCS had a significant effect. Cathodal tDCS over the Cz may have affected neural factors, such as perception of joint angle or pain, because the passive torque at 0°, 5°, 10°, and 15°, which indicates mechanical effects, did not change. These results suggest that the sensorimotor cortex is involved in joint flexibility.

Movement initiation-locked activity of the anterior putamen predicts future movement instability in periodic bimanual movement.

In periodic bimanual movements, anti-phase-coordinated patterns often change into in-phase patterns suddenly and involuntarily. Because behavior in the initial period of a sequence of cycles often does not show any obvious errors, it is difficult to predict subsequent movement errors in the later period of the cyclical sequence. Here, we evaluated performance in the later period of the cyclical sequence of bimanual periodic movements using human brain activity measured with functional magnetic resonance imaging as well as using initial movement features. Eighteen subjects performed a 30 s bimanual finger-tapping task. We calculated differences in initiation-locked transient brain activity between antiphase and in-phase tapping conditions. Correlation analysis revealed that the difference in the anterior putamen activity during antiphase compared within-phase tapping conditions was strongly correlated with future instability as measured by the mean absolute deviation of the left-hand intertap interval during antiphase movements relative to in-phase movements (r = 0.81). Among the initial movement features we measured, only the number of taps to establish the antiphase movement pattern exhibited a significant correlation. However, the correlation efficient of 0.60 was not high enough to predict the characteristics of subsequent movement. There was no significant correlation between putamen activity and initial movement features. It is likely that initiating unskilled difficult movements requires increased anterior putamen activity, and this activity increase may facilitate the initiation of movement via the basal ganglia-thalamocortical circuit. Our results suggest that initiation-locked transient activity of the anterior putamen can be used to predict future motor performance.

Resource-demanding versus cost-effective bimanual interaction in the brain.

When two hands require different information in bimanual asymmetric movements, interference can occur via callosal connections and ipsilateral corticospinal pathways. This interference could potentially work as a cost-effective measure in symmetric movements, allowing the same information to be commonly available to both hands at once. Using functional magnetic resonance imaging, we investigated supra-additive and sub-additive neural interactions in bimanual movements during the initiation and continuation phases of movement. We compared activity during bimanual asymmetric and symmetric movements with the sum of activity during unimanual right and left finger-tapping. Supra-additive continuation-related activation was found in the right dorsal premotor cortex and left cerebellum (lobule V) during asymmetric movements. In addition, for unimanual movements, the right dorsal premotor cortex and left cerebellum (lobule V) showed significant activation only for left-hand (non-dominant) movements, but not for right-hand movements. These results suggest that resource-demanding interactions in bimanual asymmetric movements are involved in a non-dominant hand motor network that functions to keep non-dominant hand movements stable. We found sub-additive continuation-related activation in the supplementary motor area (SMA), bilateral cerebellum (lobule VI) in symmetric movements, and the SMA in asymmetric movements. This suggests that no extra demands were placed on these areas in bimanual movements despite the conventional notion that they play crucial roles in bimanual coordination. Sub-additive initiation-related activation in the left anterior putamen suggests that symmetric movements place lower demands on motor programming. These findings indicate that, depending on coordination patterns, the neural substrates of bimanual movements either exhibit greater effort to keep non-dominant hand movements stable, or save neural cost by sharing information commonly to both hands.

Visuokinesthetic perception of hand movement is mediated by cerebro-cerebellar interaction between the left cerebellum and right parietal cortex.

Combination of visual and kinesthetic information is essential to perceive bodily movements. We conducted behavioral and functional magnetic resonance imaging experiments to investigate the neuronal correlates of visuokinesthetic combination in perception of hand movement. Participants experienced illusory flexion movement of their hand elicited by tendon vibration while they viewed video-recorded flexion (congruent: CONG) or extension (incongruent: INCONG) motions of their hand. The amount of illusory experience was graded by the visual velocities only when visual information regarding hand motion was concordant with kinesthetic information (CONG). The left posterolateral cerebellum was specifically recruited under the CONG, and this left cerebellar activation was consistent for both left and right hands. The left cerebellar activity reflected the participants' intensity of illusory hand movement under the CONG, and we further showed that coupling of activity between the left cerebellum and the "right" parietal cortex emerges during this visuokinesthetic combination/perception. The "left" cerebellum, working with the anatomically connected high-order bodily region of the "right" parietal cortex, participates in online combination of exteroceptive (vision) and interoceptive (kinesthesia) information to perceive hand movement. The cerebro-cerebellar interaction may underlie updating of one's "body image," when perceiving bodily movement from visual and kinesthetic information.

Hemispheric asymmetry of frequency-dependent suppression in the ipsilateral primary motor cortex during finger movement: a functional magnetic resonance imaging study.

Electrophysiological studies have suggested that the activity of the primary motor cortex (M1) during ipsilateral hand movement reflects both the ipsilateral innervation and the transcallosal inhibitory control from its counterpart in the opposite hemisphere, and that their asymmetry might cause hand dominancy. To examine the asymmetry of the involvement of the ipsilateral motor cortex during a unimanual motor task under frequency stress, we conducted block-design functional magnetic resonance imaging with 22 normal right-handed subjects. The task involved visually cued unimanual opponent finger movement at various rates. The contralateral M1 showed symmetric frequency-dependent activation. The ipsilateral M1 showed task-related deactivation at low frequencies without laterality. As the frequency of the left-hand movement increased, the left M1 showed a gradual decrease in the deactivation. This data suggests a frequency-dependent increased involvement of the left M1 in ipsilateral hand control. By contrast, the right M1 showed more prominent deactivation as the frequency of the right-hand movement increased. This suggests that there is an increased transcallosal inhibition from the left M1 to the right M1, which overwhelms the right M1 activation during ipsilateral hand movement. These results demonstrate the dominance of the left M1 in both ipsilateral innervation and transcallosal inhibition in right-handed individuals.

Cross-modal integration during vowel identification in audiovisual speech: a functional magnetic resonance imaging study.

To investigate the neural substrates of the perception of audiovisual speech, we conducted a functional magnetic resonance imaging study with 28 normal volunteers. We hypothesized that the constraint provided by visually-presented articulatory speech (mouth movements) would lessen the workload for speech identification if the two were concordant, but would increase the workload if the two were discordant. In auditory attention sessions, subjects were required to identify vowels based on auditory speech. Auditory vowel stimuli were presented with concordant or discordant visible articulation movements, unrelated lip movements, and without visual input. In visual attention sessions, subjects were required to identify vowels based on the visually-presented vowel articulation movements. The movements were presented with concordant or discordant uttered vowels and noise, and without sound. Irrespective of the attended modality, concordant conditions significantly shortened the reaction time, whereas discordant conditions lengthened the reaction time. Within the neural substrates that were commonly activated by auditory and visual tasks, the mid superior temporal sulcus showed greater activity for discordant stimuli than concordant stimuli. These findings suggest that the mid superior temporal sulcus plays an important role in the auditory-visual integration process underlying vowel identification.

Activity in the posterior parietal cortex mediates visual dominance over kinesthesia.

When both visual and kinesthetic information of a limb are available, vision is usually the dominant source of information used to perceive the spatial location. In this study, we conducted behavioral and functional magnetic resonance imaging (fMRI) experiments to examine the brain mechanisms underlying the visual dominance over kinesthesia in perceiving the position of a hand. We used tendon vibration to induce an illusory percept of flexion movement of an immobile hand, while the participants viewed a live image of either the vibrated or nonvibrated static hand through an on-line video camera. The intensity of illusory movement was significantly attenuated (for both the left and right hands) only when the participants viewed the static image of the vibrated hand. The fMRI study showed that the posterior parietal cortex (PPC) is specifically involved in the attenuation of illusory movement and that the activity of the PPC was associated with the degree of attenuation. This indicates that PPC is involved in the multisensory processing that occurs when vision overrules simultaneously available kinesthetic information for estimating the spatial location of a limb. It is thus suggested that the human parietal cortex may play a critical role in the maintenance of a coherent body image when the brain receives potentially conflicting multisensory information from the body.

Human limb-specific and non-limb-specific brain representations during kinesthetic illusory movements of the upper and lower extremities.

Sensing movements of the upper and lower extremities is important in controlling whole-body movements. We have shown that kinesthetic illusory hand movements activate motor areas and right-sided fronto-parietal cortices. We investigated whether illusions for the upper and lower extremities, i.e. right or left hand or foot, activate the somatotopical sections of motor areas, and if an illusion for each limb engages the right-sided cortices. We scanned the brain activity of 19 blindfolded right-handed participants using functional magnetic resonance imaging (fMRI) while they experienced an illusion for each limb elicited by vibrating its tendon at 110 Hz (ILLUSION). As a control, we applied identical stimuli to the skin over a nearby bone, which does not elicit illusions (VIBRATION). The illusory movement (ILLUSION vs. VIBRATION) of each immobile limb activated limb-specific sections of the contralateral motor cortex (along with somatosensory area 3a), dorsal premotor cortex (PMD), supplementary motor area (SMA), cingulate motor area (CMA), and the ipsilateral cerebellum, which normally participate in execution of movements of the corresponding limb. We found complex non-limb-specific representations in rostral parts of the bilateral SMA and CMA, and illusions for all limbs consistently engaged concentrated regions in right-sided fronto-parietal cortices and basal ganglia. This study demonstrated complete sets of brain representations related to kinesthetic processing of single-joint movements of the four human extremities. The kinesthetic function of motor areas suggests their importance in somatic perception of limb movement, and the non-limb-specific representations indicate high-order kinesthetic processing related to human somatic perception of one's own body.

Neural correlates of the spontaneous phase transition during bimanual coordination.

Repetitive bimanual finger-tapping movements tend toward mirror symmetry: There is a spontaneous transition from less stable asymmetrical movement patterns to more stable symmetrical ones under frequency stress but not vice versa. During this phase transition, the interaction between the signals controlling each hand (cross talk) is expected to be prominent. To depict the regions of the brain in which cortical cross talk occurs during bimanual coordination, we conducted event-related functional magnetic resonance imaging using a bimanual repetitive-tapping task. Transition-related activity was found in the following areas: the bilateral ventral premotor cortex, inferior frontal gyrus, middle frontal gyrus, inferior parietal lobule, insula, and thalamus; the right rostral portion of the dorsal premotor cortex and midbrain; the left cerebellum; and the presupplementary motor area, rostral cingulate zone, and corpus callosum. These regions were discrete from those activated by bimanual movement execution. The phase-transition-related activation was right lateralized in the prefrontal, premotor, and parietal regions. These findings suggest that the cortical neural cross talk occurs in the distributed networks upstream of the primary motor cortex through asymmetric interhemispheric interaction.

Sustained muscle contractions maintained by autonomous neuronal activity within the human spinal cord.

It is well known that muscle contraction can be easily evoked in the human soleus muscle by applying single-pulse electrical stimulation to the tibial nerve at the popliteal fossa. We herein reveal the unexpected phenomenon of muscle contractions that can be observed when train stimulation is used instead. We found, in 11 human subjects, that transient electrical train stimulation (1-ms pulses, 50 Hz, 2 s) was able to induce sustained muscle contractions in the soleus muscle that outlasted the stimulation period for greater than 1 min. Subjects were unaware of their own muscle activity, suggesting that this is an involuntary muscle contraction. In fact, the excitability of the primary motor cortex (M1) with the sustained muscle contractions evaluated by transcranial magnetic stimulation was lower than the excitability with voluntary muscle contractions even when both muscle contraction levels were matched. This finding indicates that M1 was less involved in maintaining the muscle contractions. Furthermore, the muscle contractions did not come from spontaneous activity of muscle fibers or from reverberating activity within closed neuronal circuits involving motoneurons. These conclusions were made based on the respective evidence: 1) the electromyographic activity was inhibited by stimulation of the common peroneal nerve that has inhibitory connections to the soleus motoneuron pool and 2) it was not abolished after stopping the reverberation (if any) for approximately 100 ms by inducing the silent period that followed an H-reflex. These findings indicate that the sustained muscle contractions induced in this study are most likely to be maintained by autonomous activity of motoneurons and/or interneurons within the human spinal cord.