Peter William Stubbs

Short-Latency Crossed Inhibitory Responses in the Human Soleus Muscle

Even though interlimb coordination is critical in bipedal locomotion, the role of muscle afferent mediated feedback is unknown. The aim of this study was to establish if ipsilateral muscle generated afferent feedback can influence contralateral muscle activation patterns in the human lower limb and to elucidate the mechanisms involved. The effect of ipsilateral tibial nerve stimulation on contralateral soleus (cSOL) responses were quantified. Three interventions were investigated, 1) electrical stimulation applied to the tibial nerve at stimulation intensities from 0 to 100% of maximal M-wave (M-max) with the cSOL contracted from 5 to 15% of maximal voluntary contraction (MVC) and 15 to 30% MVC, 2) ispsilateral tibial nerve stimulation at 75% M-max prior to, during, and following the application of ischemia to the ipsilateral thigh. 3) Electrical stimulation applied to the ipsilateral sural (SuN) and medial plantar nerves at stimulation intensities from 1 to 3 times perceptual threshold. A short-latency depression in the cSOL electromyogram (EMG; onset: 37-41 ms) was observed following ipsilateral tibial nerve stimulation. The magnitude of this depression increased (P = 0.0005 and P = 0.000001) with increasing stimulus intensities. Ischemia delayed the time of the minimum of the cSOL depression (P = 0.04). SuN and medial plantar nerve stimulation evoked a longer latency depression [average; 91.2 ms (SuN); 142 ms (medial plantar nerve)] and therefore do not contribute to the response. This is the first study to demonstrate a short-latency depression in the cSOL following ipsilateral tibial nerve stimulation. Due to its short latency, the response is spinally mediated. The involvement of crossed spinal interneurons receiving input from low-threshold muscle afferents is discussed.

Phase Modulation of the Short-Latency Crossed Spinal Response in the Human Soleus Muscle

Short-latency spinally mediated interlimb reflex pathways were recently reported between the left and right soleus muscles in the human lower-limb during sitting. The aim of the current study was to establish if these pathways were observed during a functional motor task such as human gait and modulated by the gait cycle phase and/or electrical stimulation intensity. The second aim was to elucidate on the afferents involved. Two interventions were investigated. First was ipsilateral tibial nerve (iTN) stimulation at motor threshold (MT), 35% of the maximal peak-to-peak M-wave(M-Max) and 85% M-Max (85M-Max) with stimuli applied at 60%, 70%, 80%, 90%, and 100%of the gait cycle of the ipsilateral leg. Second was ipsilateral sural nerve (SuN) and medial plantar nerve (MpN) stimulation at 1, 2, and 3X perceptual threshold at 90% of the gait cycle [corrected]. The root mean squared (RMS) of the contralateral soleus (cSOL) responses were analyzed in a time window, 40-55 ms (or 45-60 ms for subjects >50 y/o) following iTN stimulation. The most consistent responses occurred at 90 and 100% of the gait cycle at higher stimulation intensities of the iTN. Significantly inhibitory responses (P = 0.006) were reported at 60 versus 80% (P = 0.03), 90% (P = 0.006), and 100% (P = 0.002) and 70 versus 90% (P = 0.02) and 100% (P = 0.009) of the gait cycle at 85M-Max. The responses became more inhibitory with increasing stimulation intensities at 80% (P = 0.01), 90% (P = 0.001), and 100% (P = 0.004) of the gait cycle. Stimulation of the MpN and SuN at all stimulation intensities demonstrated no short-latency responses. Therefore, it is unlikely that afferents within these nerves contribute to the response. This is the first study to show short-latency spinally mediated responses in the cSOL following iTN stimulation, during walking. It provides evidence for a new spinal pathway contributing to motor control and demonstrates that the response likely has functional relevance.

Crossed spinal soleus muscle communication demonstrated by H-reflex conditioning

Introduction: A conditioning volley to the ipsilateral tibial nerve (iTN) inhibits contralateral soleus (cSOL) electromyographic activity at latencies of 37–41 ms. This is evidence for spinal muscular communication in opposing limbs. The aim of our study was to determine whether the cSOL H‐reflex would be inhibited in a similar manner. Methods: Thirteen subjects participated in two experiments: (1) stimuli delivered to the iTN at 85% of the maximal peak‐to‐peak M‐wave (85% M‐max) with a pre‐contracted cSOL; (2) 510 stimuli delivered at 85% M‐max to the iTN with a test volley delivered to the contralateral tibial nerve at interstimulus intervals of −6 to 100 ms. Results: Significant inhibition was observed in the cSOL H‐reflex when conditioning stimuli were delivered 3–33 ms before the test H‐reflex. Conclusions: The activity of this spinal pathway can be quantified using H‐reflex conditioning to provide a controlled model for further studies of this response. Muscle Nerve, 2011

Short-latency crossed spinal responses are impaired differently in sub-acute and chronic stroke patients

OBJECTIVE Investigate if patients with supraspinal lesions have impaired interlimb spinal reflex pathways. The short-latency crossed spinal response will be investigated during sitting from the non-paretic to paretic and paretic to non-paretic extremities at different stimulation intensities in chronic and sub-acute stroke patients. METHODS The ipsilateral tibial nerve of the paretic and non-paretic extremities were stimulated at motor threshold, 35% M-max and 85% M-max of the ipsilateral soleus while the contralateral soleus was contracted from 5% to 15% of the maximum voluntary contraction of the paretic soleus. RESULTS Chronic patients (from both extremities) had significantly less prominent inhibitory responses than healthy controls (post hoc tests: P<.01-P<.05). The responses were significantly modulated by stimulus intensity in healthy controls and chronic patients (P<.001-P<.05) but not sub-acute patients (P>.05). Some sub-acute patients had significantly more variable responses than chronic patients and healthy controls (P<.001-P⩽.05). CONCLUSIONS Short-latency interlimb reflexes are impaired differently in sub-acute vs. chronic patients, are impaired from the non-paretic and paretic extremity, and abnormal when compared to healthy controls. SIGNIFICANCE The inappropriate coordination could result in an inability to quickly avoid obstacles following a mechanical disturbance to the ipsilateral extremity. It also indicates that bilateral descending projections affect the response.

Using EFA and FIM rating scales could provide a more complete assessment of patients with acquired brain injury

Abstract Purpose: In some hospitals, patients exhibit significant heterogeneity of function at admission and discharge. The current study aims to assess if concurrent usage of the Early Functional Assessment (EFA) and Functional Independence Measure (FIM®) is warranted and practical in rehabilitation centers with diverse patient groups and outcomes. Methods: This retrospective study examined a data set of all patients with concurrent EFA and FIM scores admitted to a single rehabilitation center (4076 scores from 1251 patients). The patients had acquired brain injury of multiple etiologies and a range of severities. Results: The EFA scale was more able to characterize the function of lower functioning patients according to the FIM while the FIM scale was more able to characterize the function of higher functioning patients according to the EFA. This was highlighted by 21% of assessments with the lowest FIM score (18) having corresponding EFA scores of 22–76 and 27% of assessments with the highest EFA score (>90) having corresponding FIM scores of 38–126. Conclusions: In rehabilitation centers with diverse patient groups and outcomes, the FIM and EFA scale could be used to characterize the heterogeneity of function in patients with acquired brain injury. The EFA/FIM scale could be used concurrently in certain patients providing a more complete view of patients throughout the rehabilitation process. Implications for Rehabilitation Rehabilitation scales can be administered on multiple occasions to track the progress of a patient throughout the rehabilitation process; however, a lot of popular scales (such as the FIM®) are limited containing ceiling and floor effects for higher and lower functioning patients, respectively. In rehabilitation centers with diverse patient groups and outcomes, the FIM and EFA scale could be used to characterize the heterogeneity of function in patients with acquired brain injury. Concurrent usage of the scales could be indicated for some patients and each scale could provide information that the other scale does not provide however the FIM and EFA scales should be administered solely for EFA scores >90 (FIM administered solely) and the lowest FIM scores (EFA administered solely).

Microstructural changes in the thalamus after mild traumatic brain injury: A longitudinal diffusion and mean kurtosis tensor MRI study.

Abstract Primary objective: The primary aim of this study was to assess microstructural changes in the thalamus, hippocampus and corpus callosum with a fast mean kurtosis tensor (MKT) technique, in the acute and sub-acute phase after mTBI. It was hypothesized that MKT would differ between baseline and follow-up in patients. The secondary aim was to relate diffusion measures to symptoms of mTBI. Research design: A longitudinal case-control study. Methods and procedures: Twenty-seven patients with mTBI and 27 age- and gender-matched healthy controls were enrolled in the study. Patients were scanned within 2 weeks and 3 months after mTBI, while the controls were scanned once. Main outcomes and results: MKT decreased significantly (p = 0.02) from baseline to follow-up in the thalamus in patients. Compared to healthy subjects, thalamic MKT values were significantly larger in patients at baseline (p = 0.048). Secondary analysis revealed a significant decrease (p = 0.01) in fractional anisotropy in the splenium of corpus callosum from baseline to follow-up. Conclusions: The current study indicates microstructural changes in the thalamus and corpus callosum from within 14 days to 3 months after mTBI and suggests MKT as a potential biomarker after mTBI.

Motor adaptation following split-belt treadmill walking.

Malone L, Vasudevan E, and Bastian A (J Neurosci 31: 15136-15143, 2011) investigated the effects of different training paradigms on the day-by-day retention of learned motor patterns. In this Neuro Forum, a description and assessment of the methods used will be presented. The interpretation of the findings will be extended and the possible implications will be discussed. Finally, alternative explanations of the possible regions involved in motor pattern relearning will be provided.

Effect of transcranial direct current stimulation on neuroplasticity in corticomotor pathways of the tongue muscles

The aim of this study is to investigate effects of transcranial direct current stimulation (tDCS) on neuroplasticity in corticomotor pathways related to tongue muscles evoked by a training task using the tongue drive system (TDS). Using a crossover design, 13 healthy participants completed two sessions of tDCS while performing 30 min of TDS training. Sessions were spaced at least 2 weeks apart and participants randomly received anodal and sham tDCS stimulation in the first session and the other condition in the second session. Single and paired pulse transcranial magnetic stimulation was used to elicit motor evoked potentials (MEPs) of the tongue at three time-points: before, immediately after and 30 min after training. Participant-based reports of fun, pain, fatigue and motivation, level of difficulty and effort were evaluated on numerical rating scales. There was no consistent significant effect of anodal and sham stimulation on single or paired pulse stimulation MEP amplitude immediately or 30 min after TDS training. Irrespective of tDCS type, training with TDS induced cortical plasticity in terms of increased MEP amplitudes for higher stimulus intensities after 30 min compared with before and immediately after training. Participant-based reports revealed no significant difference between tDCS conditions for level of fun, fatigue, motivation, difficulty and level of effort but a significant increase in pain in the anodal condition, although pain level was low for both conditions. In conclusion, tongue MEP amplitudes appear to be sensitive to training with the tongue using TDS; however, anodal tDCS does not have an impact on training-evoked neuroplasticity of tongue corticomotor pathways.

The effect of strengthening interventions on strength and physical performance in people with cerebral palsy (PEDro synthesis)

BACKGROUND Muscle weakness is a common motor impairment that affects the performance of activities of daily living in children and adults with cerebral palsy. Strengthening interventions in people with cerebral palsy produce patient-perceived improvements in strength, walking ability and activity participation. Inspite of this, previous systematic reviews demonstrate that the effects of strengthening interventions on strength and physical performance are still uncertain. 5

Impaired heel to toe progression during gait is related to reduced ankle range of motion in people with Multiple Sclerosis

Background: Gait impairment in people with Multiple Sclerosis results from neurological impairment, muscle weakness and reduced range of motion. Restrictions in passive ankle range of motion can result in abnormal heel‐to‐toe progression (weight transfer) and inefficient gait patterns in people with Multiple Sclerosis. The purpose of this study was to determine the associations between gait impairment, heel‐to‐toe progression and ankle range of motion in people with Multiple Sclerosis. Methods: Twelve participants with Multiple Sclerosis and twelve healthy age‐matched participants were assessed. Spatiotemporal parameters of gait and individual footprint data were used to investigate group differences. A pressure sensitive walkway was used to divide each footprint into three phases (contact, mid‐stance, propulsive) and calculate the heel‐to‐toe progression during the stance phase of gait. Findings: Compared to healthy controls, people with Multiple Sclerosis spent relatively less time in contact phase (7.8% vs 25.1%) and more time in the mid stance phase of gait (57.3% vs 33.7%). Inter‐limb differences were observed in people with Multiple Sclerosis between the affected and non‐affected sides for contact (7.8% vs 15.3%) and mid stance (57.3% and 47.1%) phases. Differences in heel‐to‐toe progression remained significant after adjusting for walking speed and were correlated with walking distance and ankle range of motion. Interpretation: Impaired heel‐to‐toe progression was related to poor ankle range of motion in people with Multiple Sclerosis. Heel‐to‐toe progression provided a sensitive measure for assessing gait impairments that were not detectable using standard spatiotemporal gait parameters. HIGHLIGHTSHeel‐to‐toe progression was measured in people with and without Multiple Sclerosis.In people with Multiple Sclerosis, heel‐to‐toe progression was severely compromised.Impaired heel‐to‐toe progression was related to poor ankle range of motion.The new test revealed functionally and clinically important inter‐limb differences.Heel‐to‐toe progression is a sensitive measure to detect gait abnormalities.