Hyper-Adaptation in the Human Brain: Functional and Structural Changes in the Foot Section of the Primary Motor Cortex in a Top Wheelchair Racing Paralympian.

The human brain has the capacity to drastically alter its somatotopic representations in response to congenital or acquired limb deficiencies and dysfunctions. The main purpose of the present study was to elucidate such extreme adaptability in the brain of an active top wheelchair racing Paralympian (participant P1) who has congenital paraplegia (dysfunction of bilateral lower limbs). Participant P1 has undergone long-term wheelchair racing training using bilateral upper limbs and has won a total of 19 medals in six consecutive summer Paralympic games as of 2021. We examined the functional and structural changes in the foot section of the primary motor cortex (M1) in participant P1 as compared to able-bodied control participants. We also examined the functional and structural changes in three other individuals (participants P2, P3, and P4) with acquired paraplegia, who also had long-term non-use period of the lower limbs and had undergone long-term training for wheelchair sports (but not top athletes at the level of participant P1). We measured brain activity in all the participants using functional magnetic resonance imaging (MRI) when bimanual wrist extension-flexion movement was performed, and the structural MRI images were collected. Compared to 37 control participants, participant P1 showed significantly greater activity in the M1 foot section during the bimanual task, and significant local GM expansion in this section. Significantly greater activity in the M1 foot section was also observed in participant P4, but not in P2 and P3, and the significant local GM expansion was observed in participant P2, but not in P3 and P4. Thus, functional or structural change was observed in an acquired paraplegic participant, but was not observed in all the paraplegic participants. The functional and structural changes typically observed in participant P1 may represent extreme adaptability of the human brain. We discuss the results in terms of a new idea of hyper-adaptation.

Augmented activity of the forearm extensor muscles induced by vibratory stimulation of the palm of the hand in individuals with subacute post-stroke hemiplegia.

PRIMARY OBJECTIVE: To examine whether vibration to the palm of the hand induces motor activity in the forearm muscles of individuals with post-stroke and healthy young adults. We hypothesized that the vibration would induce antagonistic muscle activities via the motor cortex. RESEARCH DESIGN: Observational study using the between- and within-subjects mixed design. METHODS AND PROCEDURES: Vibratory stimulation was applied to the palm of the paretic and non-paretic hands in seven post-stroke hemiplegia, and of the right hand in 22 healthy young adults in the eyes-closed and eyes-open conditions. Surface electromyography (sEMG) was recorded from the forearm extensors and flexors and the sEMG amplitudes were analyzed. MAIN OUTCOMES AND RESULTS: The extensor activities were significantly larger than that of the flexors in all hands. Especially, the extensor activities were augmented when the eyes were open in the paretic and non-paretic hands. Moreover, there was greater muscle activity in the non-paretic hand compared with the paretic hand. CONCLUSIONS: These novel findings revealed that vibration to the palm augmented the activity of the antagonistic forearm extensors, especially in the paretic hand, which was induced via top-down cortical modulation. Thus, it can be utilized to improve the impaired forearm extensors in post-stroke rehabilitation.

The centre of pressure position determined by capacity of weight-shifting in stride stances in individuals with post-stroke.

BACKGROUND: The dynamics of shifting the centre-of-pressure in stride stances are essential for postural control during the double-limb support phase of gait. Impaired loading onto a paretic limb following stroke causes a biased self-centred position (defined as the centre-of-pressure position in a static stride stance) between legs, which may be related to the capacity of the centre-of-pressure movements. This study investigated anteroposterior centre-of-pressure movements relative to two different positions in stride stances and determine their relationship with the self-centred position and clinical measures after stroke. METHODS: Sixteen chronic post-stroke individuals performed anteroposterior weight-shifting in stride stances with the anterior and posterior paretic foot on a plantar pressure platform. The maximum anterior and posterior centre-of-pressure movements in stride stances were quantified relative to the self-centred position and the origin of the platform. FINDINGS: The self-centred position was biased towards the non-paretic limb to maintain identical anterior and posterior centre-of-pressure movements between stride stances with the anterior and posterior paretic foot. Furthermore, the self-centred position was related to the capacity of anteroposterior centre-of-pressure movements in stride stances. Especially, impaired balance function was associated with the self-centred position and decreased posterior centre-of-pressure movement in stride stance with the posterior paretic foot. INTERPRETATIONS: The assessment of the self-centred position in stride stances can be beneficial in understanding the capability to control weight-shifting. In particular, the improvement of balance control in stride stance with the posterior paretic foot would help to improve postural control during the double-limb support phase following stroke.

Bimanual digit training improves right-hand dexterity in older adults by reactivating declined ipsilateral motor-cortical inhibition.

Improving deteriorated sensorimotor functions in older individuals is a social necessity in a super-aging society. Previous studies suggested that the declined interhemispheric sensorimotor inhibition observed in older adults is associated with their deteriorated hand/finger dexterity. Here, we examined whether bimanual digit exercises, which can train the interhemispheric inhibitory system, improve deteriorated hand/finger dexterity in older adults. Forty-eight healthy, right-handed, older adults (65-78 years old) were divided into two groups, i.e., the bimanual (BM) digit training and right-hand (RH) training groups, and intensive daily training was performed for 2 months. Before and after the training, we evaluated individual right hand/finger dexterity using a peg task, and the individual state of interhemispheric sensorimotor inhibition by analyzing ipsilateral sensorimotor deactivation via functional magnetic resonance imaging when participants experienced a kinesthetic illusory movement of the right-hand without performing any motor tasks. Before training, the degree of reduction/loss of ipsilateral motor-cortical deactivation was associated with dexterity deterioration. After training, the dexterity improved only in the BM group, and the dexterity improvement was correlated with reduction in ipsilateral motor-cortical activity. The capability of the brain to inhibit ipsilateral motor-cortical activity during a simple right-hand sensory-motor task is tightly related to right-hand dexterity in older adults.

Influencing kinetic energy using ankle-foot orthoses to help improve walking after stroke: a pilot study.

BACKGROUND: An ankle-foot orthosis with an oil damper (AFO-OD) may improve kinetics and kinematics for efficient walking after stroke. Yet it is unknown whether hemiplegic walking behaves like "inverted-pendulum" gait and how it is modulated by using AFO-ODs for efficiency. OBJECTIVES: This study examined whether the use of AFO-ODs improves the kinetics of total vertical ground reaction force (vGRF) and kinematics of vertical pelvic displacement (vPD) in different walking phases, and gait speed following stroke. Also, the relationship between those gait parameters was examined to assess efficient walking. STUDY DESIGN: Observational study within subject. METHODS: Eight participants with hemiplegia walked at self-selected speed without and with AFO-ODs over the walkway and gait speed was measured. Force plates were used to measure total vGRF during the double-limb support phase with the paretic leading limb and with the paretic trailing limb (DSPT). The vPD in the paretic and nonparetic stance phases was measured by a three-dimensional motion analysis system. RESULTS: Without AFO-ODs, reduced total vGRF during DSPT was related to greater vPD in the subsequent nonparetic stance. Using AFO-ODs significantly increased gait speed and total vGRF during double-limb support phase with the paretic leading limb and during DSPT, which were significantly correlated. Vertical pelvic displacement in the nonparetic stance was higher than the paretic stance in both conditions. CONCLUSIONS: Decreased total vGRF during DSPT was compensated by excessive vPD in the nonparetic stance phase without AFO-ODs, indicating inefficient walking. However, the use of AFO-ODs improved the kinetic energy of total vGRF during the double-limb support phase, contributing to efficient walking. CLINICAL RELEVANCE STATEMENT: The AFO-ODs can be used to improve kinetic energy and to modulate functions in the weight transition during the double-limb support phase, with faster walking speed. Thus, AFO-ODs can be considered to be therapeutic AFOs to acquire efficient walking performance in poststroke rehabilitation.

Existence of Interhemispheric Inhibition between Foot Sections of Human Primary Motor Cortices: Evidence from Negative Blood Oxygenation-Level Dependent Signal.

Interhemispheric inhibition (IHI) between the left and right primary motor cortices (M1) plays an important role when people perform an isolated unilateral limb movement. Moreover, negative blood oxygenation-level dependent signal (deactivation) obtained from the M1 ipsilateral to the limb could be a surrogate IHI marker. Studies have reported deactivation in the hand section of the ipsilateral M1 during simple unilateral hand movement. However, deactivation in the foot section during unilateral foot movement has not been reported. Therefore, IHI between the foot sections of the bilateral M1s has been considered very weak or absent. Thirty-seven healthy adults performed active control of the right foot and also passively received vibration to the tendon of the tibialis anterior muscle of the right foot, which activates the foot section of the contralateral M1, with brain activity being examined through functional magnetic resonance imaging. The vibration and active tasks significantly and non-significantly, respectively, deactivated the foot section of the ipsilateral M1, with a corresponding 86% and 60% of the participants showing decreased activity. Thus, there could be IHI between the foot sections of the bilateral M1s. Further, our findings demonstrate between-task differences and similarities in cross-somatotopic deactivation.

The Effect Of Visual Dual-Tasking Interference On Walking In Healthy Young Adults.

BACKGROUND: Visual dual-task skills are essential for stable ambulation in everyday life such as walking while reading text. Gait analysis in a virtual environment can provide insight into altered walking performance while visual dual-tasking. RESEARCH QUESTION: How visual dual-tasking including cognitive load of reading text and altered optical flow influences walking speed and stability in healthy adults? Also, is there a relationship between the mediolateral centre of mass(CoM) displacement and mediolateral trunk movement? METHODS: Nineteen able-bodied young adults performed self-selected walking on a treadmill in a virtual environment under the following three conditions; single-task walking, walking while viewing scrolling lines, and walking while reading text scrolling on the screen. Three-dimensional motion analysis was used to measure the effect of dual-tasking on gait velocity, step length, mediolateral CoM displacement, and mediolateral thorax inclination. RESULTS: The effect of visual dual-tasking showed significantly increased walking speed and longer step length compared to single-tasking. The cognitive load of reading text while walking had a significant impact on reduced step length variability and greater mediolateral CoM displacement. This was related to the mediolateral thorax inclination. SIGNIFICANCE: A visual dual-task influences gait through altered optical flow and a cognitive load effect. Altered optical flow increased walking speed whilst the visual attention to read text affected foot placement and upright trunk posture, together with greater mediolateral CoM displacement. Thus, dual-tasking of reading text in a virtual environment substantially affected walking stability in healthy young people. This paradigm is therefore useful for assessment of walking stability in daily life and in the clinical setting.