David J. Arpin

Stride-time variability and sensorimotor cortical activation during walking

The time it takes between consecutive foot contacts from the same leg is referred to as the stride-time interval. Several investigations have shown that the variations that are present in the stride time intervals are linked to walking balance. In this study, functional near infrared spectroscopy (fNIRS) was utilized to evaluate whether activation in the medial sensorimotor cortices reflects the amount of variations seen in the stride-time intervals. Thirteen healthy adults (Age=23.7 ± 1.4 yrs.) walked forwards and backwards on a programmable treadmill. Each walking condition consisted of two sessions, with each being comprised of five alternating blocks of standing still or walking at 0.45 m/s. Activation in the medial sensorimotor cortices was measured using an fNIRS system, which consisted of a 4 × 4 grid of infrared optode emitter/detector pairs. The optodes were positioned on the participants head using the International 10/20 system with Cz located beneath the center of the front two rows of optodes. We evaluated the block-wise changes in the amount of oxygenated (oxyHb) and deoxygenated hemoglobin (deoxyHb) in the channels that were located over the supplementary motor area, pre-central gyrus, post-central gyrus and superior parietal lobule. Throughout the experiment, a footswitch system was used to concurrently measure the amount of variation present in the stride-time intervals. Our results showed that oxyHb was greater in the supplementary motor area, pre-central gyrus, and superior parietal lobule when participants walked backwards rather than forwards, which suggests that backward walking presents more of a challenge to the nervous system as it controls the stepping pattern. Additionally, there was a significant decrease in the amount of deoxyHb present in the supplementary motor area while walking backward. Consistent with previous investigations, we noted that the amount of variability present in the stride-time intervals was greater during backward walking compared to forward walking. In addition, the amount of variation in the stride-time intervals while walking forward was positively correlated with the maximum oxyHb response found in the pre-central gyrus and supplementary motor area, which has not been previously shown. This neurobehavioral relationship supports the notion that the subtle variations found in the stride-time intervals are partly associated with processing demands by the motor cortices for regulating the forward temporal kinematics.

Differences in the dynamic gait stability of children with cerebral palsy and typically developing children

The aim of this investigation was to evaluate the differences in the dynamic gait stability of children with cerebral palsy (CP) and typically developing (TD) children. The participants walked on a treadmill for 2 min as a motion capture system assessed the walking kinematics. Floquet analysis was used to quantify the rate of dissipation of disturbances that were present in the walking kinematics, and the variability measures were used to assess the magnitude of the disturbances present in the step length and width. The Floquet multipliers, step width and length values were correlated with Sections D and E of the Gross Motor Function Measure (GMFM). The children with CP had a larger Floquet multiplier and used a wider step width than the TD children. The magnitude of the maximum Floquet multiplier was positively correlated with the step width. Furthermore, the magnitude of the maximum Floquet multiplier and the step width were negatively correlated with the score on Section E of the GMFM. Lastly, the children with CP used a more variable step length than the TD children. These results suggest that children with CP have poor dynamic gait stability because they require more strides to dissipate the disturbances that are present in their walking pattern. In effort to stabilize these disturbances, the children with CP appear to utilize a wider step width and modulate their step length. Overall the inability to effectively dissipate the gait disturbances may be correlated with the childs ability to perform a wide range of gross motor skills (e.g., step over obstacles, jump, walk up stairs).

Functional specialization within the supplementary motor area: A fNIRS study of bimanual coordination

Bimanual movements can be performed by flexing and extending the target effectors (e.g., hand muscles) in unison, or by flexing units on one side in unison with extension of the same units on the opposite side. The former movement patterns are generally referred to as in-phase or parallel, whereas the latter patterns are often termed anti-phase movements. It is well known that anti-phase patterns are unstable and tend to spontaneously transition to in-phase movements at higher repetition rates, but the mechanisms and brain regions involved are not fully understood. In the current study, we utilized functional near-infrared spectroscopy (fNIRS) to evaluate whether anterior/posterior subdivisions of the supplementary motor complex (SMA) have distinct functional roles in maintaining in-phase and anti-phase movement patterns. Twelve healthy adult participants completed a bimanual coordination task comprised of anti-phase and in-phase trials as 24-channel fNIRS data was recorded from dorsal-medial motor areas. We examined the relative concentrations of oxygenated and deoxygenated hemoglobin in the channels that were located over the anterior SMA (e.g., pre-SMA) and the SMA proper. Our most interesting results indicated that oxygenated hemoglobin responses were greater in the anterior SMA during performance of anti-phase compared to in-phase movements. In the SMA proper, oxygenated hemoglobin responses did not differ between the two movement patterns. These data suggest that the anterior SMA is critical to programming and maintaining the less stable anti-phase movement patterns, and support the conceptual framework of an anterior-directed gradient of progressively more complex functionality in the SMA.

Aberrant synchrony in the somatosensory cortices predicts motor performance errors in children with cerebral palsy

Cerebral palsy (CP) results from a perinatal brain injury that often results in sensory impairments and greater errors in motor performance. Although these impairments have been well catalogued, the relationship between sensory processing networks and errors in motor performance has not been well explored. Children with CP and typically developing age-matched controls participated in this investigation. We used high-density magnetoencephalography to measure event-related oscillatory changes in the somatosensory cortices following tactile stimulation to the bottom of the foot. In addition, we quantified the amount of variability or errors in the isometric ankle joint torques as these children attempted to match a target. Our results showed that neural populations in the somatosensory cortices of children with CP were desynchronized by the tactile stimulus, whereas those of typically developing children were clearly synchronized. Such desynchronization suggests that children with CP were unable to fully integrate the external stimulus into ongoing sensorimotor computations. Our results also indicated that children with CP had a greater amount of errors in their motor output when they attempted to match the target force, and this amount of error was negatively correlated with the degree of synchronization present in the somatosensory cortices. These results are the first to show that the motor performance errors of children with CP are linked with neural synchronization within the somatosensory cortices.

Motor control of the lower extremity musculature in children with cerebral palsy

The aim of this investigation was to quantify the differences in torque steadiness and variability of the muscular control in children with cerebral palsy (CP) and typically developing (TD) children. Fifteen children with CP (age=14.2±0.7 years) that had a Gross Motor Function Classification System (GMFCS) score of I-III and 15 age and gender matched TD children (age=14.1±0.7 years) participated in this investigation. The participants performed submaximal steady-state isometric contractions with the ankle, knee, and hip while surface electromyography (sEMG) was recorded. An isokinetic dynamometer was used to measure the steady-state isometric torques while the participants matched a target torque of 20% of the subjects maximum voluntary torque value. The coefficient of variation was used to assess the amount of variability in the steady-state torque, while approximate entropy was used to assess the regularity of the steady-state torque over time. Lastly, the distribution of the power spectrum of the respective sEMG was evaluated. The results of this investigation were: 1) children with CP had a greater amount of variability in their torque steadiness at the ankle than TD children, 2) children with CP had a greater amount of variability at the ankle joint than at the knee and hip joint, 3) the children with CP had a more regular steady-state torque pattern than TD children for all the joints, 4) the ankle sEMG of children with CP was composed of higher harmonics than that of the TD children.

Cue-related temporal factors modulate movement-related beta oscillatory activity in the human motor circuit

In humans, there is a strong beta (15–30 Hz) event-related desynchronization (ERD) that begins before movement, which has been tentatively linked to motor planning operations. The dynamics of this response are strongly modulated by whether a pending movement is cued and the inherent parameters of the cue. However, previous studies have focused on the information content of cues and not on parameters such as the timing of the cue relative to other events. Variations in such timing are critical, as they directly impact the amount of time that participants have to plan pending movements. In this study, participants performed finger-tapping sequences during magnetoencephalography, and we manipulated the amount of time (i.e., “long” vs. “short”) between the presentation of the to-be-executed sequence and the cue to initiate the sequence. We found that the beta ERD was stronger immediately after the cue to move in the contralateral postcentral gyrus and bilateral parietal cortices during the short compared with long planning time condition. During movement execution, the beta ERD was stronger in the premotor cortex and the SMA in the short relative to long condition. Finally, peak latency in the SMA significantly correlated with RT, such that the closer the peak beta ERD was to the cue to move, the quicker the participant responded. The results of this study establish that peri-movement beta ERD activity across the cortical motor circuit is highly sensitive to cue-related temporal factors, with a direct link to motor performance.

Neurorehabilitation Strategies Focusing on Ankle Control Improve Mobility and Posture in Persons With Multiple Sclerosis.

Background and Purpose: The neuromuscular impairments seen in the ankle plantarflexors have been identified as a primary factor that limits the mobility and standing postural balance of individuals with multiple sclerosis (MS). However, few efforts have been made to find effective treatment strategies that will improve the ankle plantarflexor control. Our objective was to determine whether an intensive 14-week neurorehabilitation protocol has the potential to improve the ankle plantarflexor control of individuals with MS. The secondary objectives were to determine whether the protocol would also improve postural control, plantarflexion strength, and mobility. Methods: Fifteen individuals with MS participated in a 14-week neurorehabilitation protocol, and 20 healthy adults served as a comparison group. The primary measure was the amount of variability in the submaximal steady-state isometric torque, which assessed plantarflexor control. Secondary measures were the Sensory Organization Test composite score, maximum plantarflexion torque, and the spatiotemporal gait kinematics. Results: There was less variability in the plantarflexion torques after the neurorehabilitation protocol (preintervention, 4.15% ± 0.5%; postintervention, 2.27% ± 0.3%). In addition, there were less postural sway (preintervention, 51.87 ± 0.2 points; postintervention, 67.8 ± 0.5 points), greater plantarflexion strength (preintervention, 0.46 ± 0.04 Nm/kg; postintervention, 0.57 ± 0.05 Nm/kg), and faster walking speeds (preferred preintervention, 0.71 ± 0.05 m/s; preferred postintervention, 0.81 ± 0.05 m/s; fast-as-possible preintervention, 0.95 ± 0.06 m/s; postintervention, 1.11 ± 0.07 m/s). All of the outcome variables matched or trended toward those seen in the controls. Discussion and Conclusions: The outcomes of this exploratory study suggest that the neurorehabilitation protocol employed in this investigation has the potential to promote clinically relevant improvements in the ankle plantarflexor control, standing postural balance, ankle plantarflexion strength, and the mobility of individuals with MS. Video Abstract available for more insights from the authors (see Video, Supplemental Digital Content 1, http://links.lww.com/JNPT/A110).

An fNIRS exploratory investigation of the cortical activity during gait in children with spastic diplegic cerebral palsy

OBJECTIVE The primary aim of this exploratory investigation was to determine if there are differences in cortical activation of children with spastic diplegic cerebral palsy (CP) and typically developing children during gait. METHODS Functional near-infrared spectroscopy was used to measure the concentration of oxygenated hemoglobin that was present in the supplementary motor area, pre-central gyrus, post-central gyrus and superior parietal lobule as the children walked on a treadmill. A sagittal plane video was concurrently collected and later digitized to quantify the temporal gait variations. RESULTS (1) The children with CP had an increased amount of activation in the sensorimotor cortices and superior parietal lobule during gait, (2) the children with CP had a greater amount of variability or error in their stride time intervals, and (3) an increased amount of error in the temporal gait kinematics was associated with an increased amount of activity across the cortical network. CONCLUSION Our results suggest that the perinatal damage and subsequent neural reorganization that occurs with spastic diplegic CP may impact the functional cortical activity for controlling gait. Furthermore, our results imply the increased cortical activity of the somatosensory cortices and superior parietal cortices may underlie the greater amount of error in the temporal gait kinematics.

Developmental Trajectory of Beta Cortical Oscillatory Activity During a Knee Motor Task

There is currently a void in the scientific literature on the cortical beta oscillatory activity that is associated with the production of leg motor actions. In addition, we have limited data on how these cortical oscillations may progressively change as a function of development. This study began to fill this vast knowledge gap by using high-density magnetoencephalography to quantify the beta cortical oscillatory activity over a cross-section of typically developing children as they performed an isometric knee target matching task. Advanced beamforming methods were used to identify the spatiotemporal changes in beta oscillatory activity during the motor planning and motor action time frames. Our results showed that a widespread beta event-related desynchronization (ERD) was present across the pre/postcentral gyri, supplementary motor area, and the parietal cortices during the motor planning stage. The strength of this beta ERD sharply diminished across this fronto-parietal network as the children initiated the isometric force needed to match the target. Rank order correlations indicated that the older children were more likely to initiate their force production sooner, took less time to match the targets, and tended to have a weaker beta ERD during the motor planning stage. Lastly, we determined that there was a relationship between the child’s age and the strength of the beta ERD within the parietal cortices during isometric force production. Altogether our results suggest that there are notable maturational changes during childhood and adolescence in beta cortical oscillatory activity that are associated with the planning and execution of leg motor actions.

Overground Body-Weight-Supported Gait Training for Children and Youth with Neuromuscular Impairments

ABSTRACT The aim of this investigation was to determine if body-weight-supported (BWS) overground gait training has the potential to improve the walking abilities of children and youth with childhood onset motor impairments and intellectual disabilities. Eight participants (mean age of 16.3 years) completed 12 weeks of BWS overground gait training that was performed two times a week. BWS was provided during the training sessions by an overhead harness system that rolls overground. There was a significant improvement in the preferred walking speed after the training (p < .01; pre = 0.51 ± 0.2 m/s; post = 0.67 ± 0.3 m/s; Cohens d = 0.80) and cadence (p = .04; pre = 37 ± 7 steps/min; post = 43 ± 8 steps/min; Cohens d = 0.94). Our results indicate that overground BWS gait training may be an effective treatment strategy for improving the preferred walking speed of children and youth with motor impairments.