Reproducability of corticomuscular coherence:A comparison between static and perturbed tasks

Corticomuscular coherence (CMC) is used to quantify functional corticomuscular coupling during a static motor task. Although the reproducibility of CMC characteristics such as peak strength and frequency within one session is good, reproducibility of CMC between sessions is limited (Pohja et al. 2005, NeuroImage). Reproducible CMC characteristics are required in order to assess changes in corticomuscular coupling in a longitudinal study design, for example during rehabilitation. We recently demonstrated that the presence of CMC in the population in substantially increased when position perturbations are applied during an isotonic force task. Here, we assessed the reproducibility of perturbed CMC compared to unperturbed CMC. Subjects (n=10) performed isotonic wrist flexion contractions against the handle of a wrist manipulator (WM) while EEG (64 channels) and EMG of the m.flexor carpi radialis were recorded in two experimental sessions separated by at least one week. The handle of the WM either kept a neutral angle (baseline task) or imposed a small angle perturbation (perturbed task). In the baseline task, 3 subjects had significant CMC in both the first and the second sessions. In the other 7 subjects no significant CMC was found in both sessions. Between sessions, significant CMC was always found in overlapping frequency bands and generally on overlapping electrodes. In the subjects with CMC a significant cross correlation coefficient between the spectra in the two sessions was present (mean 0.57; 0.3 - 0.79). In the perturbed task CMC was present in 8 subjects in both sessions and absent in 1 subject in the two sessions. One subject had CMC only in the second session. For the subjects with CMC, the correlation coefficient between the spectra of the two sessions was significantly larger than zero with a mean of 0.68 (range 0.38 - 0.88). The presence and absence of CMC within subjects could be reproduced very well between the sessions. This was also demonstrated by the significant correlation between the spectra in the two sessions ; the degree of correlation was variable over subjects both in the baseline and the perturbed task. The reproducibility characteristics of CMC in a perturbed task are comparable or slightly better with respect to an unperturbed task. However, comparison is limited by the small number of subjects with CMC in the baseline task. Perturbed CMC is present in more subjects, which is crucial when developing methods to track corticomuscular coupling over multiple sessions, for example during rehalibitation.handles MIMO systems, and can deal with short measurement time

Stretch Evoked Potentials in Healthy Subjects and After Stroke: A Potential Measure for Proprioceptive Sensorimotor Function

Sensory feedback is of vital importance in motor control, yet rarely assessed in diseases with impaired motor function like stroke. Muscle stretch evoked potentials (StrEPs) may serve as a measure of cortical sensorimotor activation in response to proprioceptive input. The aim of this study is: 1) to determine early and late features of the StrEP and 2) to explore whether StrEP waveform and features can be measured after stroke. Consistency of StrEP waveforms and features was evaluated in 22 normal subjects. StrEP features and similarity between hemispheres were evaluated in eight subacute stroke subjects. StrEPs of normal subjects had a consistent shape across conditions and sessions (mean cross correlation waveforms > 0.75). Stroke subjects showed heterogeneous StrEP waveforms. Stroke subjects presented a normal early peak (40 ms after movement onset) but later peaks had abnormal amplitudes and latencies. No significant differences between stroke subjects with good and poor motor function were found (P > 0.14). With the consistent responses of normal subjects the StrEP meets a prerequisite for potential clinical value. Recording of StrEPs is feasible even in subacute stroke survivors with poor motor function. How StrEP features relate to clinical phenotypes and recovery needs further investigatio

Participatory action research in two communities in Bolivia and the United States

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66665/2/10.1177_002087289203500214.pd

Quantifying connectivity via efferent and afferent pathways in motor control using coherence measures and joint position perturbations

The applicability of corticomuscular coherence (CMC) as a connectivity measure is limited since only 40–50 % of the healthy population presents significant CMC. In this study, we applied continuous joint position perturbations to obtain a more reliable measure of connectivity in motor control. We evaluated the coherence between joint position perturbations and EEG (position-cortical coherence, PCC) and CMC. Healthy subjects performed two isotonic force tasks against the handle of a wrist manipulator. The baseline task was isometric; in the perturbed task, the handle moved continuously with small amplitude. The position perturbation signal covered frequencies between 5 and 29 Hz. In the perturbed task, all subjects had significant PCC and 86 % of the subjects had significant CMC, on both stimulus and non-stimulus frequencies. In the baseline task, CMC was present in only 45 % of the subjects, mostly on beta-band frequencies. The position perturbations during an isotonic force task elicited PCC in all subjects and elicited CMC in most subjects on both stimulus and non-stimulus frequencies. Perturbed CMC possibly arises by two separate processes: an intrinsic process, similar to the process in an unperturbed task, involving both efferent and afferent pathways; and a process related to the excitation of the afferent and efferent pathways by the perturbation. These processes cannot be separated. PCC, however, reflects connectivity via the afferent pathways only. As PCC was present in all healthy subjects, we propose this coherence as a reliable measure for connectivity in motor control via the afferent pathways

Poor motor function is associated with reduced sensory processing after stroke

Pathofysiological analysis of movement disorders in relation to functio

Position-cortical coherence as a marker for somatosensory integrity early post-stroke, a prospective cohort study

Introduction: Neurophysiological assessments in addition to clinical scales can potentially elucidate the role of somatosensory function in post-stroke motor recovery. Main objective:To investigate the longitudinal construct validity of positioncortical coherence (PCC), the agreement between evoked wrist perturbations and EEG, as a measure of afferent integrity, with respect to longitudinal recovery of sensorimotor function. Methods: PCC was measured serially in 48 patients after a fi rst-ever ischemic stroke, in addition to Fugl-Meyer motor assessment of the upper extremity (FM-UE) and Erasmus modifi cation of the Nottingham Sensory Assessment (EmNSA), within 3, 5, 12 and 26 weeks post-stroke. Change in PCC over time represented by: percentage presence of PCC (%PCC), mean amplitude of PCC over the affected hemisphere (Amp-A) were addressed as well as their association with FM-UE and EmNSA. Patients were classifi ed into: expectedfi tters (FM-UE-baseline=18 points), unexpected-fi tters (FM-UE-baseline<18 points) and non-fi tters (FM-UE-baseline<18 points), to the proportional recovery model. Results and discussion: %PCC increased from baseline to 12 weeks post-stroke (ß:1.6%, CI:0.32-2.86%, P=0.01), which was no longer signifi cant after adjusting for EmNSA and FM-UE. A signifi cant positive association was found between %PCC, Amp-A and EmNSA. Unexpected fi tters (N=8) showed longitudinally signifi cantly higher %PCC than those expected to fi t the proportional recovery model (N=23). Conclusion: We demonstrated the longitudinal construct validity of %PCC and Amp-A as a measure of afferent pathway integrity. A high %PCC in unexpected fi tters suggests that this marker contains information above afferent integrity, i.e. cortical excitability. More work is needed to improve clinical prediction models for functional outcome post-stroke

Position-Cortical Coherence as a Marker of Afferent Pathway Integrity Early Poststroke: A Prospective Cohort Study

Background. Addressing the role of somatosensory impairment, that is, afferent pathway integrity, in poststroke motor recovery may require neurophysiological assessment. Objective. We investigated the longitudinal construct validity of position-cortical coherence (PCC), that is, the agreement between mechanically evoked wrist perturbations and electroencephalography (EEG), as a measure of afferent pathway integrity. Methods. PCC was measured serially in 48 patients after a first-ever ischemic stroke in addition to Fugl-Meyer motor assessment of the upper extremity (FM-UE) and Nottingham Sensory Assessment hand-finger subscores (EmNSA-HF, within 3 and at 5, 12, and 26 weeks poststroke. Changes in PCC over time, represented by percentage presence of PCC (%PCC), mean amplitude of PCC over the affected (Amp-A) and nonaffected hemisphere (Amp-N) and a lateralization index (L-index), were analyzed, as well as their association with FM-UE and EmNSA-HF. Patients were retrospectively categorized based on FM-UE score at baseline and 26 weeks poststroke into high- and low-baseline recoverers and non-recoverers. Results. %PCC increased from baseline to 12 weeks poststroke (β = 1.6%, CI = 0.32% to 2.86%, P = .01), which was no longer significant after adjusting for EmNSA-HF and FM-UE. A significant positive association was found between %PCC, Amp-A, and EmNSA-HF. Low-baseline recoverers (n = 8) showed longitudinally significantly higher %PCC than high-baseline recoverers (n = 23). Conclusions. We demonstrated the longitudinal construct validity of %PCC and Amp-A as a measure of afferent pathway integrity. A high %PCC in low-baseline recoverers suggests that this measure also contains information on cortical excitability. Use of PCC as an EEG-based measure to address the role of somatosensory integrity to motor recovery poststroke requires further attention

Poor motor function is associated with reduced sensory processing after stroke

Abstract The possibility to regain motor function after stroke depends on the intactness of motor and sensory pathways. In this study, we evaluated afferent sensory pathway information transfer and processing after stroke with the coherence between cortical activity and a position perturbation (position-cortical coherence, PCC). Eleven subacute stroke survivors participated in this study. Subjects performed a motor task with the affected and non-affected arm while continuous wrist position perturbations were applied. Cortical activity was measured using EEG. PCC was calculated between position perturbation and EEG at the contralateral and ipsilateral sensorimotor area. The presence of PCC was quantified as the number of frequencies where PCC is larger than zero across the sensorimotor area. All subjects showed significant contralateral PCC in affected and non-affected wrist tasks. Subjects with poor motor function had a reduced presence of contralateral PCC compared with subjects with good motor function in the affected wrist tasks. Amplitude of significant PCC did not differ between subjects with good and poor motor function. Our results show that poor motor function is associated with reduced sensory pathway information transfer and processing in subacute stroke subjects. Position-cortical coherence may provide additional insight into mechanisms of recovery of motor function after stroke.Biomechanical EngineeringMechanical, Maritime and Materials Engineerin