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Using Sympathetic Skin Responses in Individuals With Spinal Cord Injury as a Quantitative Evaluation of Motor Imagery Abilities

  1. Murielle Grangeon,
  2. Kathleen Charvier,
  3. Aymeric Guillot,
  4. Gilles Rode and
  5. Christian Collet
  1. M. Grangeon, PhD, Laboratoire de la Performance Motrice, Université de Lyon, Université Claude Bernard Lyon 1, CRIS EA 647 (P3M), Mentale et du Matériel 27–29, Boulevard du 11 Novembre 1918, 69622 Villeurbanne Cedex, France, and Centre de Recherche Interdisciplinaire en Réadaptation du Grand Montréal (CRIR), Institut de Réadaptation Gingras–Lindsay de Montréal, Laboratoire de Pathokinésiologie, 6300 Avenue Darlington, Montreal, Quebec, Canada, H3S 2J4.
  2. K. Charvier, MD, Service de Médecine Physique et Réadaptation Neurologique, Hôpital Henry Gabrielle, St Genis-Laval, France.
  3. A. Guillot, PhD, Claude Bernard University, CRIS EA 647 (P3M), Villeurbanne, France, and Institut Universitaire de France, Paris, France.
  4. G. Rode, MD, PhD, Claude Bernard University, INSERM-UMRS 534, Bron, France.
  5. C. Collet, PhD, Claude Bernard University, CRIS EA 647 (P3M), Villeurbanne, France.
  1. Address all correspondence to Dr Grangeon at: murielle.grangeon{at}umontreal.ca.

Abstract

Background Motor imagery (MI) ability should be evaluated in selected individuals with spinal cord injury (SCI) who can benefit from MI training in their rehabilitation program. Electrodermal activity seems to be a reliable indicator for assessing MI ability. However, individuals with SCI have a variety of autonomic dysfunctions.

Objective This study aimed to investigate electrodermal responses (EDRs) elicited by MI.

Design A cost-utility analysis of EDR above and below the lesion level in individuals with complete or incomplete SCI (n=30) versus a control group of individuals who were healthy (n=10) was used.

Method The EDR was recorded above and below the lesion level during MI of a drinking action. Duration, latency, and amplitude of EDR were the outcome measures.

Results Hand and foot EDR in the control group occurred with the same pattern and similar latencies, suggesting a common efferent sympathetic pathway to sweat glands of the hand and foot mediating a sympathetic skin response. Individuals with SCI elicited responses above the lesion level. The EDR amplitude was correlated to the lesion level and autonomic dysreflexia history. No foot response was recorded in individuals with complete cervical and thoracic motor lesions. Foot response with a lower amplitude and higher latency occurred in participants with incomplete motor lesion, suggesting a link between the descending motor pathway and sympathetic function.

Limitations The small sample of individuals with incomplete SCI limits the generalization of the results obtained at the foot site.

Conclusions Electrodermal response above the lesion level may be a reliable index for assessing MI ability in individuals with SCI. It is a noninvasive, user-friendly method for clinicians to consider before enrolling individuals in MI training.

Motor imagery (MI) is defined as a dynamic state during which an action is mentally simulated from the first-person perspective with no associated overt body movement.1 The first-person perspective implies imagining action from an internal perspective as if the person is actually performing the movement. It is considered to have a large kinesthetic component, causing an individual to feel as if he or she is performing the imagined movement.1,2 Because systematic reviews have shown the positive effects of MI on motor recovery in people with stroke,3,4 mental practice might be an effective additional therapy for people with spinal cord injury (SCI).5 People who benefit from mental training should exhibit high MI ability. It is essential, therefore, to evaluate the ability of individuals to create mental representations before integrating mental practice into the rehabilitation process. Due to the concealed nature of MI, its ability and quality remain difficult to evaluate.

According to Jeannerod,6 MI represents the process of accessing the intention to perform a movement that may be carried out unconsciously during movement preparation. Motor imagery and motor preparation, therefore, share common mechanisms and can be viewed as functionally equivalent processes.7 As a result, it is not surprising that movement execution and MI reveal a high overlap of active brain regions. Brain imaging methods, such as functional magnetic resonance imagery (fMRI) and positron emission tomography, may identify areas in the brain that are activated during MI with high spatial resolution and provide objective results regarding MI ability.8 In an fMRI study of individuals with SCI, Alkadhi et al9 found significant correlations between enhanced activation in the primary motor cortex and other mesial frontal motor areas (known to be involved in motor planning and preparation)10 during MI of foot movements and the vividness of MI, as assessed by an interview. However, the authors selected only participants deemed to have good MI ability prior to the experiment using the Vividness Motor Imagery Questionnaire (VMIQ).11 The VMIQ mainly measures visual imagery rather than MI (ie, no mention of kinesthetic sensations in the instructions and an anchored rating scale in terms of vision). Furthermore, the poor temporal resolution of fMRI, which relies on physiological phenomena, makes it difficult to investigate the functional organization of the regions of cortical activation involved in MI. Scalp-recorded electroencephalograms (magnetoencephalography) also have been used extensively to investigate MI,12,13 providing information on the dynamic aspect of movement-related activity of the involved areas in real time due to its high temporal resolution. However, these techniques have too poor spatial resolution to provide information on the anatomical structure of the neural networks involved during MI. The use of multimodal brain techniques may hold promise for investigating MI ability; however, these methods are expensive and nonambulatory, making them difficult for the therapist to use during the rehabilitation program.

Other clinical techniques that are easier to use have been used in the last few years. Several psychological questionnaires that are better directed toward measuring MI compared with the VMIQ are proposed to evaluate the vividness of MI,14 such as the Movement Imagery Questionnaire–Revised15 in people who are healthy and the Kinesthetic and Visual Imagery Questionnaire16 in individuals with stroke. However, psychological tests often are considered too subjective because participants report their own representation of MI accuracy and need to be correlated with more quantitative tools. Mental chronometry is a reliable measure to estimate an individual's ability to preserve the temporal structure of movement during MI because an isochrony between the actual movement and the MI of the same movement is found.17–19 A similar temporal equivalence has been established through a large variety of motor tasks, albeit not systematic yet still dependent on many external influencing factors such as movement duration20 and instructions,21 as well as movement difficulty.22 Although the chronometric method is a reliable tool for assessing MI ability, interpretation of the results is not always straightforward, and imagery vividness is not considered when looking at imagery times.

The use of physiological measures that indicate psychophysiological parameter changes during MI as well as during actual execution may effectively complement assessment of MI ability.23 Peripheral physiological indicators from the autonomic nervous system (ANS) are an inference of cognitive processes, thus guaranteeing a valuable procedure to control efficient mental work.24–26 Representation of an action is accompanied not only by activation of cortical structures but also by peripheral responses originating from the central commands of the ANS.27 Cerebral function may be investigated through ANS effector activity at the peripheral level.28 Among ANS effectors, sweat glands are innervated by sympathetic endings only; thus electrodermal variations (ie, skin resistance) are not elicited by the antagonist effect of vagal endings. The electrodermal response (EDR) is mediated by neural networks involving prefrontal, insular, parietal cortices and limbic structures.29 Thus, EDR is a sensitive psycho-physiological index of changes involved in autonomic sympathetic arousal that are integrated with sensorimotor, emotional, and cognitive states.30,31 Increase in an individual's arousal level elicits the release of sweat within the sweat gland ducts. This physiological reaction induces a decrease in skin resistance. As soon as an individual starts to generate a mental representation of movement, EDR is evoked. Because EDR during MI resembles EDR during actual execution (ie, similar duration and latency and slightly lower amplitude during MI), this is a reliable method for assessing the quality of arousal and for focusing attention during the mental representation of actions.24,32

However, SCI causes serious dysfunctions of the sympathetic nervous system, which controls ANS effectors, including the sweat glands.33 Individuals with SCI could exhibit particular electrodermal activity during MI, thereby making it difficult to use EDR as an index of MI quality. The objective of this study was to investigate whether EDR might be recorded above or below the lesion level while individuals with SCI were performing MI. We hypothesized that there would be intact responses above the lesion level in individuals with SCI compared with a control group. We also expected a damaged EDR or lack of response below the lesion level in individuals with SCI linked to the neurological characteristics.

Materials and Method

Participants

Ten volunteers who were healthy (mean age=36.4 years, SD=10.4, range=19–57) and 30 patients with SCI (mean age=37.9 years, SD=12.3, range=19–60) took part in the study after giving informed consent. To be included in the experimental group, individuals with SCI had to be admitted to and follow their physical therapy protocol at the rehabilitation hospital after having sustained a traumatic SCI. Time from injury ranged from 6 to 360 months, with an average delay of 100 months. The participants' sex was not a selection criterion (at the time of the experiment, only male patients were in the hospital). All individuals with SCI included in the study were able to perform a grasping task with the dominant upper limb. Patients with severe spasticity34 and phantom limb pain35 were excluded. The control group comprised only male individuals recruited through postings at the rehabilitation hospital. None of the participants were taking any medication with known autonomic effects. Individuals with psychiatric complications were excluded. All participants had to be right-handed after the accident (by their own admission and confirmed by the Edinburgh Handedness Inventory Questionnaire36).

A detailed neurological examination was performed by a physician familiar with this procedure. Individuals with SCI were divided into 3 groups according to the degree of completeness and height of the lesion (Tab. 1) using the American Spinal Injury Association (ASIA) impairment scale (AIS).37 Group 1 represented individuals with cervical SCI classified as AIS A, group 2 represented individuals with thoracic and lumbar SCI classified as AIS A, and group 3 represented individuals with SCI classified as AIS B, C, and D. Unfortunately, group 3 could not be divided according to the lesion level due to the small sample of individuals with incomplete SCI. Twelve individuals had previous autonomic dysreflexia (AD) as specified in their medical record. Autonomic dysreflexia is a sympathetic dysfunction mainly observed in patients with high-level SCI. It is a result of the disconnection of spinal sympathetic nuclei from supraspinal centers, eliciting sustained sympathetic outflow with profuse sweating below the lesion level.38 However, none of patients with high-level SCI experienced AD during the experiment. Demographic and diagnostic information is summarized in Table 1.

View this table:
Table 1.

Participant Characteristics

Procedure

Participants were asked to physically perform a self-paced drinking movement with their dominant hand before simulating the same sequence mentally. The glass used was empty and adapted for individuals with SCI (ie, small and lightweight). The height of the table was adjusted to fit the anthropometric features of each participant (ie, slightly below the elbow level when sitting). This position allowed the arm and the forearm to rest on the table in a relaxed position while waiting for a stimulus. The glass was positioned 15 cm from the starting point to ensure that the participants performed the movement under the same conditions (ie, comparable elbow extension among participants). Participants were asked to grasp the glass on the table and simulate drinking before returning the glass to the starting position. During the MI trials, participants were instructed to mentally imagine the movement they had just performed, paying particular attention to movement accuracy and mental image vividness (ie, sensations and visual cues). They had to perform MI in the first-person perspective. The participants were required to produce no concomitant body movements and had to keep their eyes closed during MI. During the experiment, special care was taken to maintain ambient room temperature (24°–26°C). Additionally, all participants were protected from external influences known to have an effect on electrodermal activity or MI performance (eg, stress, noise, shock, bright lights).

EDR

Electrodermal activity was recorded using in-house instrumentation (see eAppendix for details pertaining to the recording system). Skin resistance was used to analyze the EDR. Skin resistance was recorded using a constant-current method39 with two 50-mm2 unpolarizable silver/silver chloride electrodes (Clark Electromedical Instruments, Edenbridge, United Kingdom). It is an exosomatic technique in which a very small current is injected between 2 electrodes and skin resistance is measured during its passage. In the study, resistance was measured with 10-μA direct current; current density was 0.2 μA/mm2. A conductive paste was applied to improve skin/electrode contact, and the electrodes were held in place by adhesive tape. These electrodes were placed above the lesion level. They were positioned on the second phalanx of the second and third digits (palmar side) of the nondominant hand40 of participants in the control group and of individuals with SCI below T1. Electrodes were positioned on the neck of individuals with SCI above T1, based on the data by Matsunaga et al,41 who recorded a similar EDR response from nonpalmar and nonplantar sites. Only latency was significantly shorter at the hand site compared with the other sites. Therefore, EDR recorded on the neck site was considered as reliable as EDR recorded on the hand site. Electrodes also were placed below the lesion level on the third metatarsal and on the dorsal area of the third metatarsal in all participants. Resistance measurements were carried out using a high-rate common rejection mode differential amplifier. Similarly, recorder inputs were in differential mode, and resistance circuit supply was of the floating type. Skin resistance to the current that passed between the 2 electrodes corresponded to the EDR. A significant decrease in EDR was associated with an increase in attention and arousal.

Six actual trials and 12 MI trials were performed in a counterbalanced order. The participants were blinded to the type of trial (actual trial versus MI trial) so that they could not anticipate which type of trial they would perform next, thus avoiding a learning effect. Each trial was separated from the next trial by a rest period, which never lasted less than 15 seconds in order for the physiological measure to recover its basal level (ie, 1 standard deviation).

Outcome Measures

The following EDR parameters were analyzed: ohmic perturbation duration (OPD) (representing response duration), response amplitude, and latency. Response amplitude and OPD were measured at the beginning of the sudden drop of the EDR curve elicited by MI or actual movement and ended when the minimum of the curve was reached following this stimulation42 (further information is presented in the eAppendix). Response latency was the average time between the stimulus and the sudden slope drop. Because it had been shown that response amplitude depended on the prestimulation value (or tonic level),43,44 amplitude ratios were calculated by dividing the response value (ie, the minimum of the curve) by the prestimulation value (ie, corresponding to the skin resistance value just before the sudden drop). Therefore, a great amplitude response corresponded to a low amplitude ratio (see the eAppendix for calculation details). All responses longer than 1 to 3 seconds following stimulus were considered not to be elicited by that stimulus and were excluded.45

Data Analysis

Shapiro-Wilk tests were carried out first to verify whether the data from our sample of participants followed a normal distribution. The null hypothesis that the data came from a population with normal distribution was verified. All participants elicited an EDR above the lesion level. Consequently, a 2-factor, repeated-measures analysis of variance (ANOVA) was performed to identify differences across groups and tasks above the lesion level, followed by a Tukey post hoc test (α=.05). Pearson correlation coefficients were computed to associate the lesion level and AIS to the EDR. Foot responses were obtained in only 9 individuals with SCI and in all control participants. Therefore, a 2-factor, repeated-measures ANOVA followed by a Tukey post hoc test (α=.05) was computed to compare EDR recorded above the lesion level and EDR recorded below the lesion level across tasks and participants who elicited foot EDR. Statistical analyses were performed using SPSS version 17.0 software for Windows (SPSS Inc, Chicago, Illinois).

Results

Mean values (standard deviation) above and below the lesion level in each group are presented in Table 2.

View this table:
Table 2.

Mean Values (Standard Deviation) Above and Below the Lesion Level in Each Groupa

Comparison of EDR Recorded Above the Lesion Level Among Groups

With respect to EDR latency, no group effect (F3,36=0.77, P=.52), no task effect (F1,36=0.75, P=.39), and no group × task interaction (F3,36=0.61, P=.44) were found. The response latency of individuals with SCI did not significantly differ from that of the control group, irrespective of the task. As for OPD, no group effect (F3,36=0.53, P=.66), no task effect (F1,36=0.85, P=.36), and no group × task interaction (F3,36=2.20, P=.10) were found. The neurological impairment did not seem to modify EDR latency and response duration above the lesion level.

In terms of EDR amplitude, there was no task effect (F1,36=0.85, P=.36) and no group × task interaction (F3,36=2.00, P=.17), but a significant group effect (F3,36=4.79, P=.007) was observed. A Tukey honestly significant difference test showed that the EDR amplitude ratio was lower for the control group than for group 1 (P=.008) and group 3 (P=.03), irrespective of the task. No significant difference was found between group 2 and the other groups. Thus, EDR amplitude was lower in group 1 and group 3. A significant correlation between the lesion level and EDR amplitude ratio was found during MI trials (r21,38=.31, P<.001) and actual task trials (r21,38=.26, P=.001). The EDR amplitude tended to decrease with the height of the lesion level (Fig. 1). A significant correlation between AD and EDR amplitude was revealed during the MI (r21,38=.12, P=.026) and the actual task (r21,38=.12, P=.032). The EDR amplitude also tended to decrease in individuals with SCI and previous AD. No significant correlation was revealed between EDR amplitude and AIS during MI trials (r21,38=.09, P=.06) and actual task trials (r21,38=.004, P=.71).

Figure 1.
Figure 1.

Effect of the lesion level (A) and the severity (B) of spinal cord injury on the amplitude of the electrodermal response recorded above the lesion level. Great amplitude ratio=low amplitude response, r2=determination coefficient, AIS=American Spinal Injury Association (ASIA) impairment scale, CTL=control group.

Comparison of EDR According to Recording Site

Foot responses were recorded in all participants in the control group. Foot site EDRs also were elicited in 2 individuals with complete lumbar SCI (group 2) and individuals with incomplete SCI (group 3), with the exception of 3 participants with SCI classified as AIS B. Individuals with a complete cervical or thoracic motor lesion (groups 1 and 2) had no foot responses (Fig. 2). Interestingly, responses below the lesion level were absent in almost all participants who had AD prior to the study. Among individuals with SCI and previous AD, the only participant who elicited foot responses was also the only one with an incomplete motor lesion.

Figure 2.
Figure 2.

Example of electrodermal response recording during motor imagery (MI) of the drinking movement performed by an individual with a complete C6 spinal cord injury. Although a response was observed on the neck site, no response was recorded on the foot site. Electrodermal response values (kΩ) are on the vertical axis. Time (seconds) is on the horizontal axis.

Repeated-measures ANOVAs were performed to compare EDR among the recording sites across tasks in individuals with SCI who elicited foot responses and in the control group. In the control group, no task effect (F1,18=2.99, P=.09), no site effect (F1,18=1.79, P=.19), and no task × site interaction (F1,18=0.94, P=.40) were found for EDR latency. As for EDR amplitude, no task effect (F1,18=0.66, P=.43), no site effect (F1,18=1.02, P=.37), and no task × site interaction (F1,18=0.80, P=.46) were found. As regards OPD, no task effect (F1,18=0.43, P=.53), no site effect (F1,18=1.56, P=.23), and no task × site interaction (F1,18=0.32, P=.26) were revealed. Similar responses were observed irrespective of the recording site and tasks.

Among individuals with SCI, there was no task effect (F1,16=0.43, P=.53) and no task × site interaction (F1,16=1.33, P=.26), but a site effect (F1,16=49.47, P<.001) for EDR latency was noted. With respect to EDR amplitude, no task effect (F1,16=0.43, P=.53) and no task × site interaction (F1,16=1.33, P=.26) was observed, but a site effect (F1,16=49.47, P<.001) was found. As for OPD, no task effect (F1,16=3.31, P=.09) and no task × site interaction (F1,16=1.30, P=.29) was observed, but a site effect (F1,16=6.01, P=.02) was found. Longer latency, lower amplitude, and shorter duration at the foot site were observed during MI and actual movement compared with the hand site.

Discussion

Comparisons Between Individuals With SCI and the Control Group

The purpose of this study was to assess EDR in individuals with SCI while performing MI compared with a control group. First, EDR occurred with the same pattern and similar latency for both hand and foot sites in the control group. These findings confirm the results of previous studies that showed EDR may be elicited from different recording sites in individuals who are healthy41,46,47 and that MI may be an effective supraspinal stimulus to assess EDR.27,48 Thus, a common sympathetic supraspinal efferent pathway to sweat glands of hand and foot is believed to mediate EDR. Moreover, the similarity in EDR between MI and actual task suggests that ANS activity is not inhibited during MI, whereas motor command is inhibited. This finding suggests activation of the anticipated function of the ANS to perform the movement during MI. It supposes a relative independence of somatic and autonomic commands at the level of the central motor system, or at least, a dissociation of somatic and autonomic coprogramming during MI. Although further studies should confirm this hypothesis, these results confirm that ANS activity assessed by EDR may be an effective index of cognitive processes accompanying MI and, therefore, may be a quantitative measure for evaluating MI ability in individuals who are healthy.23

Second, an EDR was obtained in all individuals with SCI above the lesion level (neck or hand). Because the sympathetic skin response is a somato-sympathetic reflex with spinal, bulbar, and suprabulbar components,49 which is supposed to be intact above the lesion, an intact EDR was expected from the neck or palmar sites. However, there may be differences in EDR amplitude depending on the lesion level because individuals with a high lesion level tend to have low EDR amplitude. These results corroborate those of Nicotra et al,50 who found palmar EDR amplitude <50% of control participants in individuals with SCI at T1–T4 and mostly ≥50% in those with SCI at T6–T11. The significant correlation found between AD and responses may explain this result because all participants diagnosed with prior AD had sustained a high complete or incomplete cervical lesion and exhibited a lower reflex activity of sympathetic response. Nevertheless, further studies on this phenomenon with a larger sample should be done to confirm this link between AD and low sympathetic activity.51

Below the lesion level, the results suggest a link with sympathetic function impairment (assessed using MI, AIS, and AD history). All participants with a complete cervical and thoracic motor lesion (AIS A and B) who had AD prior to the study did not elicit foot EDRs. All participants with an incomplete motor lesion (AIS C or D), including the participant with prior AD, elicited foot EDRs, suggesting a link between the descending motor pathway and sympathetic function in individuals with SCI. Additionally, the lower amplitude and greater latency in foot responses compared with those of the control group might suggest that the foot responses perhaps were not conducted through the same neurological pathways as those of the control group. Furthermore, the foot responses elicited in 2 individuals with a complete lumbar SCI suggest that sympathetic pathways pass mainly through the T8–T12 segments to the lower limb.

These results coincide with those of a study by Cariga et al,52 who observed a plantar EDR to supraspinal stimuli in an individual with a complete lesion at L1. Thus, lumbar lesions may not disturb the sympathetic outflow mediating the electrodermal activity to the lower limbs.51 However, a possible explanation is that the SCI was not complete in these individuals and the response in the foot was mediated by residual spinal fibers, which escaped the clinical and electrophysiological testing procedures. Nevertheless, in the current study, the foot responses during MI found in individuals with SCI coincide with the findings of previous studies that used supraspinal stimuli to elicit EDR52,53 and suggest that connections with supraspinal structures are essential for evoking EDR. The spinal cord below the lesion level may be isolated from its supraspinal reflex center in a complete cervical or thoracic motor lesion.

Lastly, the main principle governing the use of electrodermal activity to assess MI ability is that autonomic response patterns during MI should resemble those recorded during actual execution, making EDR a psychophysiological marker of mental rehearsal. This principle held true for responses above the lesion level in the control group and in individuals with SCI. It has long been known that imagery ability is subject to a wide range of individual differences54 and may influence the degree of improvement achieved following MI. This is why it is imperative to measure imagery ability prior to an imagery experiment or imagery training program. Electrodermal response should be used to follow the effectiveness of mental rehearsal. Combining electrodermal activity with psychological and chronometric tests to compare MI ability of individuals with SCI with that of individuals who are healthy will yield relevant information for the integration of MI in rehabilitation programs. Additionally, more information on individual MI ability can be obtained by using the ratio between responses during actual movement and responses during MI. Because the objective of the present study was not to assess MI ability but to confirm the use of EDR as an indicator of MI ability in individuals with SCI despite their impairment, ratios were not calculated.

Limitations of the Study and Potential Clinical Research

Although this study provided a preliminary, population-specific benchmark for investigating physiological measures in individuals with SCI during MI, there are some limitations that should be taken into consideration for future studies. The sample of individuals with incomplete SCI was too small and there might be a confusing effect to take all levels in the incomplete lesion group, suggesting that the generalization of results obtained in this group is limited. Further studies with a larger sample should be done to confirm the conductivity of autonomic pathways below the lesion level in individuals with incomplete SCI. However, because rather normal EDRs were recorded above the lesion level in all individuals with SCI, clinicians may use the neck or hand as reliable recording sites. Our results represent a first step toward the integration of MI in rehabilitation programs. Because its use as an adjunct therapy among individuals with SCI is relatively new, strategies and guidelines for clinical assessment are still being developed. Additionally, further studies with a larger sample should be done to assess the habituation of the response and reliability of MI as stimuli, although some of our results corroborated the findings of previous studies that used physiological stimuli (eg, inspiratory gasp)55,56 or electrical stimulation.52,53,57

Lastly, the lack of correlation between AIS and sympathetic skin responses underscored the need to expand the impairment classification to include ANS dysfunctions. Normell58 has already suggested that sympathetic and sensory function after SCI might be different in level by 1 to 2 dermatomes. Thus, it is possible that the extent of sympathetic nerve damage does not always follow that of somatic nerve dysfunction. To our knowledge, this is the first time that sympathetic skin responses in individuals with SCI have been investigated during MI. Other factors such ASIA motor and sensitive scores and time from injury may complement this study.

Conclusion

One of the main questions resulting from experiments involving imagined movements is how well MI is performed. No external control is available to verify whether individuals mentally perform the task according to the instructions. As there is no unique way to evaluate MI ability, it is important to use complementary methods to evaluate an individual's ability to create vivid and accurate motor images. This study demonstrates that electrodermal activity may be an effective and quantitative tool to assess MI ability in individuals with SCI. The next step would be to incorporate this method into MI questionnaires and mental chronometry to provide clinical assessment of MI ability in individuals with SCI.

The Bottom Line

What do we already know about this topic?

Patients who benefit from mental training should have high motor imagery (MI) ability. Therefore, MI ability should be evaluated in select individuals with spinal cord injury (SCI) who might potentially benefit from MI training in their rehabilitation program. Although there is no unique way to evaluate MI ability, complementary methods can be used to evaluate an individual's ability to create vivid and accurate motor images. However, to date, clinicians lack an easy-to-use quantitative method for assessing MI ability.

What new information does this study offer?

This study shows that recording electrodermal activity above the level of the spinal cord lesion, a noninvasive and user-friendly method, may be useful in assessing MI ability. This article also presents new information about the sympathetic skin responses in relation to MI among people with SCI.

Footnotes

  • Dr Grangeon, Dr Guillot, and Dr Collet provided concept/idea/research design, writing, and data analysis. Dr Grangeon provided data collection. Dr Charvier and Dr Collet provided project management and consultation (including review of manuscript before submission). Dr Charvier and Dr Rode provided participants. Dr Charvier, Dr Rode, and Dr Collet provided facilities/equipment. Dr Rode and Dr Collet provided institutional liaisons.

  • The experimental procedure was approved by the Ethics Committee of Henry Gabrielle Hospital.

  • Received October 17, 2011.
  • Accepted March 2, 2012.

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