Jenny Haefeli

Temporal and spatial patterns of cortical activation during assisted lower limb movement

Human gait is a complex process in the central nervous system that results from the integrity of various mechanisms, including different cortical and subcortical structures. In the present study, we investigated cortical activity during lower limb movement using EEG. Assisted by a dynamic tilt table, all subjects performed standardized stepping movements in an upright position. Source localization of the movement-related potential in relation to spontaneous EEG showed activity in brain regions classically associated with human gait such as the primary motor cortex, the premotor cortex, the supplementary motor cortex, the cingulate cortex, the primary somatosensory cortex and the somatosensory association cortex. Further, we observed a task-related power decrease in the alpha and beta frequency band at electrodes overlying the leg motor area. A temporal activation and deactivation of the involved brain regions as well as the chronological sequence of the movement-related potential could be mapped to specific phases of the gait-like leg movement. We showed that most cortical capacity is needed for changing the direction between the flexion and extension phase. An enhanced understanding of the human gait will provide a basis to improve applications in the field of neurorehabilitation and brain–computer interfaces.

Preparation and performance of obstacle steps: interaction between brain and spinal neuronal activity

This study investigated the interactions of supraspinal with spinal neuronal circuits during obstacle steps by recordings of electroencephalography (EEG), reflex activity and limb muscle electromyography (EMG). Subjects walking with reduced vision on a treadmill were acoustically informed about an approaching obstacle and received feedback about task performance. Only following a task‐relevant acoustic signal, spinal reflex responses, evoked by tibial nerve stimulation during mid‐stance, were enhanced in proximal arm and leg flexor muscles prior to obstacle compared to normal swing, reflecting the neuronal preparation of the task. During swing over the obstacle, limb muscle EMG activity was greater than in normal swing. Both the preparation and the performance (i.e. ascending movement slope of the obstacle‐crossing leg) were associated with an enhanced EEG signal mainly in the prefrontal cortex of the right hemisphere. Adaptational changes in performance, reflex activity and muscle activation during repetitive obstacle stepping were not reflected in the EEG activity, probably due to an insufficient resolution of the EEG. The observations suggest that drive from supraspinal centers initiates and maintains spinal neuronal activity underlying obstacle task preparation and performance.

Increased baseline temperature improves the acquisition of contact heat evoked potentials after spinal cord injury.

OBJECTIVE To investigate the effect of increasing the skin surface baseline temperature for contact heat evoked potentials (CHEPs). METHODS CHEPs were studied in healthy subjects and subjects with chronic cervical spinal cord injury (SCI) using a conventional 35°C (condition 1) or increased 42-45°C baseline temperature (condition 2). A third condition was used to standardize the contact heat stimulus duration from the different baseline temperatures. Changes in peak latency and N2P2 amplitude of the CHEPs and rating of perceived intensity were examined between conditions. RESULTS In healthy subjects, increasing the baseline temperature for contact heat stimulation significantly increased the rating of perceived intensity (conditions 2 and 3), as well as the amplitude of CHEPs (condition 2 only). Following SCI, an increased baseline temperature facilitated perception of contact heat stimulation and evoked potentials could be recorded from dermatomes that were insensitive to contact heat from a conventional baseline temperature. CONCLUSIONS Enhancing the acquisition of CHEPs can be achieved by increasing the baseline temperature. This effect can be attributed, in part, to shortening the stimulation duration. SIGNIFICANCE After SCI, increasing the baseline temperature for CHEPs in dermatomes with absent or diminished sensation improved the neurophysiological resolution of afferent sparing.

Test-retest reliability of contact heat-evoked potentials from cervical dermatomes.

Summary The purpose of this study was to investigate the test–retest reliability of contact heat-evoked potentials (CHEPs) in neurologically healthy subjects from cervical dermatomes (C4–C8). Seventeen individuals underwent test–retest examination of cervical CHEPs. Peak latencies and peak-to-peak amplitude of N2–P2 and ratings of perceived intensity were analyzed using test–retest reliability statistics (intraclass correlation coefficients [ICCs] and Bland–Altman confidence parameters). For comparison, a group of similar age and gender was also examined with dermatomal somatosensory-evoked potentials (dSSEPs, n = 17). The ICC values for CHEP latency and amplitude parameters were significant (P < 0.05) and corresponded to at least “fair” reliability, while peak-to-peak amplitude demonstrated “substantial” (≥0.81) reliability for all dermatomes. The coefficients of repeatability (i.e., 2SD of the difference between examinations) confirm that CHEPs and dSSEPs are reliable according to measures of latency. Superior peak-to-peak amplitude test–retest reliability was found for CHEPs. In conclusion, the test–retest reliability of dSSEP and CHEP parameters supports the fact that these outcomes can be used to objectively track changes in spinal conduction in the dorsal column and spinothalamic tract, respectively. The reliable acquisition of CHEPs may depend on the intensity of the sensation reported by the subject for a given area of skin stimulated.

Improved diagnosis of spinal cord disorders with contact heat evoked potentials

Objective: To evaluate the sensitivity of contact heat evoked potentials (CHEPs) compared with dermatomal somatosensory evoked potentials (dSSEPs) and clinical sensory testing in myelopathic spinal cord disorders (SCDs). Methods: In a prospective cohort study, light-touch (LT) and pinprick (PP) testing was complemented by dermatomal CHEPs and dSSEPs in patients with a confirmed SCD as defined by MRI. Patients with different etiologies (i.e., traumatic and nontraumatic) and varying degrees of spinal cord damage (i.e., completeness) were included. SCD was distinguished into 3 categories according to MRI pattern and neurologic examination: a) complete, b) incomplete-diffuse, and c) central or anterior cord damage. Results: Seventy-five patients were included (complete n = 7, incomplete-diffuse n = 33, central/anterior n = 35). In total, 319 dermatomes were tested with combined CHEPs and dSSEPs. CHEPs, dSSEPs, and clinical sensory testing were comparably sensitive to detect the myelopathy in complete (CHEPs 100%, dSSEPs 91%, PP and LT 82%) and incomplete-diffuse (CHEPs 92%, dSSEPs and PP 86%, LT 81%, p > 0.05 for all comparisons) cord damage. In central/anterior cord damage, CHEPs showed a significantly higher sensitivity than dSSEPs (89% compared with 24%, p < 0.001) and clinical sensory testing (PP 62%, LT 57%, p < 0.05). A subclinical sensory impairment was detected more frequently by CHEPs than dSSEPs (60% compared with 29%, p = 0.001). Conclusions: Assessment of spinothalamic pathways with CHEPs is reliable and revealed the highest sensitivity in all SCDs. Specifically in incomplete lesions that spare dorsal pathways, CHEPs are sensitive to complement the clinical diagnosis.

Improving the acquisition of nociceptive evoked potentials without causing more pain

Summary Causing a greater subjective pain experience is not necessary for improving the objective assessment of pain using contact heat‐evoked potentials. ABSTRACT Following nociceptive heat or laser stimulation, an early contralateral and later vertex potential can be recorded. Although more indicative of the nociceptive input, the acquisition of the contralateral N1 after contact heat stimulation (contact heat‐evoked potentials [CHEPs]) remains difficult. An advantage of contact heat is that the baseline skin temperature preceding peak stimulation can be controlled. Increasing the baseline temperature may represent a novel strategy to improve the acquisition of CHEPs without resulting in more subjective pain to stimulation. A study was undertaken in 23 healthy subjects to examine the effects of increasing the baseline temperature but not the perceived intensity of contact heat stimulation. A combined standard averaging and single‐trial analysis was performed to disclose how changes in averaged waveforms related to latency jitter and individual trial amplitudes. By increasing the baseline temperature, the acquisition of N1 was improved among subjects with a low‐amplitude response (greater than −4 μV) following 35°C baseline temperature stimulation (P < .05). Based on standard averaging, N2/P2 amplitudes were also significantly increased with and without an accompanying change in the rating of perceived pain when the baseline temperature was increased (P < .05). In contrast, automated single‐trial averaging revealed no significant difference in N2 amplitude when the baseline temperature was increased to 42°C and the peak temperature reduced. These findings suggest that 2 mechanisms underlie the improved acquisition of CHEPs: increased synchronization of afferent volley, yielding larger‐amplitude evoked potentials in response to the same rating of intensity; and reduced inter‐trial variability.

Assessment of Spinothalamic Tract Function Beyond Pinprick in Spinal Cord Lesions A Contact Heat Evoked Potential Study

Background. Although a mainstay of clinical sensory examination after damage in the spinal cord, pinprick sensation represents only one afferent modality conveyed in the spinothalamic tract. As an objective outcome, complementary information regarding spinothalamic tract conduction may be elucidated by measuring contact heat evoked potentials (CHEPs). Objective. To assess the value of CHEPs to measure spinothalamic tract function in spinal cord disorders compared with pinprick scoring. Methods. CHEPs were examined using a standard (35°C) and increased baseline (42°C) contact heat temperature. Pinprick sensation was rated as absent, impaired, or normal according to the International Standards for the Neurological Classification of Spinal Cord Injury. Results. Fifty-nine dermatomes above, at, and below the sensory level of impairment were analyzed in 37 patients with defined spinal cord disorder. In dermatomes with absent or impaired pinprick sensation, CHEPs using a standard baseline temperature were mainly abolished (3/16 and 8/35, respectively). However, when applying an increased baseline temperature, CHEPs became recordable (absent: 11/16; impaired: 31/35). Furthermore, CHEPs with increased baseline temperature allowed discerning between dermatomes with absent, impaired, and normal pinprick sensation when using an objective measure (ie, N2P2 amplitude). In contrast, the pain perception to contact heat stimulation was independent of pinprick scores. Conclusion. Applying pinprick testing is of limited sensitivity to assess spinothalamic tract function in spinal cord disorders. The application of CHEPs (using standard and increased baseline temperatures) as an objective readout provides complementary information of spinothalamic tract functional integrity beyond pinprick testing.

Refined sensory measures of neural repair in human spinal cord injury: bridging preclinical findings to clinical value

Sensory input from the periphery to the brain can be severely compromised or completely abolished after an injury to the spinal cord. Evidence from animal models suggests that endogenous repair processes in the spinal cord mediate extensive sprouting and that this might be further attenuated by targeted therapeutic interventions. However, the extent to which sprouting can contribute to spontaneous recovery after human spinal cord injury (SCI) remains largely unknown, in part because few measurement tools are available in order to non-invasively detect subtle changes in neurophysiology. The proposed application of segmental sensory evoked potentials (e.g., dermatomal contact heat evoked potentials and somatosensory evoked potentials) to assess conduction in ascending pathways (i.e., spinothalamic and dorsal column, respectively) differs from conventional approaches in that individual spinal segments adjacent to the level of lesion are examined. The adoption of these approaches into clinical research might provide improved resolution for measuring changes in sensory impairments and might determine the extent by which spontaneous recovery after SCI is mediated by similar endogenous repair mechanisms in humans as in animal models.

Effects of Pain and Pain Management on Motor Recovery of Spinal Cord–Injured Patients: A Longitudinal Study

Background. Approximately 60% of patients suffering from acute spinal cord injury (SCI) develop pain within days to weeks after injury, which ultimately persists into chronic stages. To date, the consequences of pain after SCI have been largely examined in terms of interfering with quality of life. Objective. The objective of this study was to examine the effects of pain and pain management on neurological recovery after SCI. Methods. We analyzed clinical data in a prospective multicenter observational cohort study in patients with SCI. Using mixed effects regression techniques, total motor and sensory scores were modelled at 1, 3, 6, and 12 months postinjury. Results. A total of 225 individuals were included in the study (mean age: 45.8 ± 18 years, 80% male). At 1 month postinjury, 28% of individuals with SCI reported at- or below-level neuropathic pain. While pain classification showed no effect on neurological outcomes, individuals administered anticonvulsant medications at 1 month postinjury showed significant reductions in pain intensity (2 points over 1 year; P < .05) and greater recovery in total motor scores (7.3 points over 1 year; P < .05). This drug effect on motor recovery remained significant after adjustment for injury level and injury severity, pain classification, and pain intensity. Conclusion. While initial pain classification and intensity did not reveal an effect on motor recovery following acute SCI, anticonvulsants conferred a significant beneficial effect on motor outcomes. Early intervention with anticonvulsants may have effects beyond pain management and warrant further studies to evaluate the therapeutic effectiveness in human SCI.

Differences in spinothalamic function of cervical and thoracic dermatomes: insights using contact heat evoked potentials.

Introduction: After spinal cord injury, contact heat evoked potentials (CHEPs) may represent a means to refine the clinical assessment of sensory function from each spinal cord segment by quantifying nociception, including conduction along the spinothalamic tract. Methods: The influence of stimulation site (i.e., dermatomes) on CHEPs and thermal thresholds in 19 healthy subjects (mean age, 45.2 ± 18.3 years) divided into 2 age classes (younger subjects, n = 10; mean age, 28.8 ± 5.2 years; older subjects, n = 9; mean age, 63.4 ± 3.4 years) at 5 different dermatomes (C4, C5, C6, C8, and T4) was assessed. Results: In terms of distance from the body midline (i.e., spinal cord entry), there was a reduction in CHEP amplitudes from proximal (C4 and T4) to distal (C6 and C8) dermatomes with a corresponding reduction in nociceptive perception (i.e., pain threshold and rating). Within primary and secondary cortical sensory areas, including areas associated with affective noxious processing, the cortical source density analysis showed a similar current density distribution between C4 and C8 dermatomes but consistent higher current densities for C4. Conclusions: The study supports CHEPs as a feasible tool for assessing discrete dermatomes corresponding to spinal cord segments. The results suggest that the proximodistal pattern in the intensity of perceived pain and CHEP amplitudes is likely attributable to the distribution of heat nociceptors and the increase in conduction distance from proximal to distal dermatomes. The present findings emphasize on the importance that if patients are assessed segment by segment, the underlying topographical differences need to be accounted for.