Behavioral and Electrophysiological Evidence of Motor Cortex Activation Related to an Amputated Limb: a Multisensorial Approach

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Behavioral and Electrophysiological Evidence of Motor Cortex Activation Related to an Amputated Limb: A Multisensorial Approach

Pascale Touzalin-Chretien1, Solange Ehrler2, and André Dufour1 Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021

Abstract ■ Phantom limb sensations may be linked to motor activities frontally. Measurement of lateralized movement-related brain po- in the deafferented cortices of amputees, with artificial visual tentials showed that, under the lateral mirror condition, contra- feedback of an amputated limb leading to enhanced phantom lateral motor activity of the viewed hand was observed in both sensations. The present study was designed to verify if cortical normal subjects and trauma amputees. In contrast, this activity motor activity related to an amputated limb can be triggered by was not observed in subjects with congenital limb absence. These visual input using an objective behavioral measure and with a neu- findings suggest that, in traumatic amputees, motor enhance- rophysiological correlate. Trauma amputees and normally limbed ment due to visualization of the movements of the missing limb subjects showed superior performance in a mirror-drawing task reflects the effectiveness of motor commands to the missing when the mirror was placed sagittally (giving visual feedback of limb, strengthening the hypothesis of the functional survival of the amputated/inactive limb) compared with when it was placed deafferented cortical motor areas. ■

INTRODUCTION 1996; Ramachandran, Stewart, & Rogers-Ramachandran, Almost immediately after the loss of a limb, more than 1992), body representation appears to be relatively main- 90% of patients experience vivid phantom sensations in tained throughout life, even after drastic changes such as the amputated limb (Ramachandran & Hirstein, 1998). limb amputation. This phantom limb phenomenon refers to the illusory Studies using a mirror box (Ramachandran & Rogers- impression that an amputated limb is still present: The Ramachandran, 1996) also provide evidence for mainte- specificity of normal somatosensory sensations associ- nance of motor representation of a missing limb in the ated with phantom limbs is preserved, as is the ability brains of amputees. In those studies, a mirror is oriented at times to move the missing limb. Although the neuro- at the midsagittal plane, with the reflective surface facing logical cause of this illusion is unclear, understanding of the intact limb. Thus, the hand in the mirror occupies the this perceptual phenomenon may provide valuable in- place of the opposite hand in normally limbed subjects. sight into the mechanisms underlying body representa- For amputees, the reflection provides visual feedback of tion in relation to its neurobiological substrate. Recent the missing limb. This illusion can have positive conse- brain-mapping studies using fMRI, PET, ERP, and TMS indi- quences in some amputees with painful paralyzed phan- cate that the cortical representation of a missing limb may tom limbs. Vision of the missing limb provides congruent survive in the brains of amputees. Indeed, TMS (Mercier, motor (including proprioception) and visual information Reilly, Vargas, Aballea, & Sirigu, 2006) and fMRI and PET about that limb. In normally limbed subjects, studies fo- scan studies (Roux et al., 2003) have shown that the cor- cusing on the interactions between these two sensory in- tical area previously devoted to a now-amputated hand puts have shown that stimulation in one modality can have could retain its original function of controlling hand (or significant effects on the perception in a second modality phantom hand) movements, despite the absence of mus- (Berberovic & Mattingley, 2003; Michel, Pisella, et al., cles normally targeted by the cortical outputs. Thus, de- 2003; Michel, Rossetti, Rode, & Tilikete, 2003; Rossetti, spite dramatic reorganization at the neural level (Karl, Koga, & Mano, 1993; Hay, Pick, & Ikeda, 1965). Clinical Birbaumer, Lutzenberger, Cohen, & Flor, 2001; Flor et al., data in amputees may reflect the persistence of this visuo- 1998; Pascual-Leone, Peris, Tormos, Pascual, & Catala, proprioceptive integration related to the missing arm, as seen in the mirror. At a neural level, this could reflect activation of motor areas (including proprioceptive areas) re- 1Laboratoire dʼImagerie et de Neurosciences Cognitives, Stras- lated to the missing limb. This hypothesis was supported bourg, France, 2Centre de Réadaptation Fonctionnelle Clémenceau, by the behavioral and physiological observation of pa- Strasbourg, France tients with brachial plexus avulsion (Giraux & Sirigu, 2003).

© 2009 Massachusetts Institute of Technology Journal of Cognitive Neuroscience 21:11, pp. 2207–2216 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 A visuomotor training program in which the patients were In addition, and to further confirm the hypothesis of mo- required to match “voluntary” movements of the paralyzed/ tor activation related to the seen limb, we also examined phantom limb with movements of a virtual hand reduced lateralized brain motor activity while subjects performed phantom pain sensations. These changes were correlated motor tasks using frontal or lateral visual feedback as de- with increased activity in the contralateral M1 region. scribed above. To determine whether vision influenced Brain mapping and clinical studies with amputees sug- motor preparation, we analyzed the ERP component gest that activation of sensorimotor cerebral regions may called the lateralized readiness potential (LRP), which re- be triggered by visual feedback or mental imagery of the flects preparation of the responding hand. We anticipated amputated limb and account for phantom limb sensations that visual feedback from the responding hand would lead (Mercier et al., 2006; Roux et al., 2003; Ramachandran & to cortical activity contralateral to the missing/inactive Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 Rogers-Ramachandran, 1996). In these studies, however, hand in normally limbed and trauma amputee subjects activation of cortical motor areas was examined solely in but not in congenital limb absence subjects. relation to sensed or imagined movements of the missing limb, with no information on behavioral performance in amputated patients. The aim of the present study was EXPERIMENT 1 to determine (a) whether cortical motor areas can be acti- vated by visual inputs from the corresponding limb, and We focused on the objective measures of possible visuo- therefore (b) whether cortical activations corresponding proprioceptive persistence in the missing limb of trauma to the missing limb can affect motor performances of amputees, independent of any factor that could influence the remaining limb. On the basis of studies indicating analysis such as phantom sensations, pain, medication, or that the image of the body and its neurobiological sub- presence of prosthesis. Hence, we measured motor per- strate develops only with experience (Montoya et al., formances of the remaining hand in a mirror-drawing task. 1998; Melzack, 1990), we also expected neurofunctional and motor differences between trauma amputees and subjects with congenital limb absence, in which cortical Methods motor areas in relation to their missing limb are not or Participants are less functional. Research on plasticity in somatosen- Four subjects with traumatic upper-limb loss and four sory and motor areas has emphasized the role of critical subjects with congenital upper-limb absence were en- periods during early developmental stages. Animal stud- rolled. Demographic and clinical data are summarized ies suggest that the formation of cortical and subcortical in Table 1. A third group of 26 normally limbed subjects maps may be altered by peripheral damage of a limb dur- was also enrolled (20 men and 6 women, mean age = ing the prenatal period (Rhoades, Chiaia, Bennett-Clarke, 33.64 years). All participants were naive to the purpose Janas, & Fisher, 1994) as well as lesions or deprivation dur- of the study. Subjects gave informed consent before par- ing development (Killackey, Rhoades, & Bennett-Clarke, ticipation, in accordance with the guidelines of our local 1995). ethics committee, which approved the study. We have described a method to assess functional survival and activation of deafferented cortical motor areas using a visuomotor performance test based on visual feed- Materials back from the missing limb. Using a mirror, amputees re- ceived visual feedback of an intact hand while performing The mirror-drawing apparatus was a wooden box with a a motor task. The mirror was placed either in front of vertical mirror facing a star pattern. Metallic plates were the subject, generating an inverted vision of the drawing placed side by side on each of the 12 segments of the hand, or in the midsagittal plane, giving the illusion that star (see Figure 1). Drawing was performed with a digital the missing hand was performing the motor task, as de- pen, which did not leave a visible trace, connected to a scribed in the mirror-box paradigm (Ramachandran & computer. A cover prevented direct vision of the drawing Rogers-Ramachandran, 1996). hand. The following data were collected: (a) the total We anticipated that visual feedback of the missing time necessary to complete the star pattern (12 segments; hand through a midsagittally oriented mirror would acti- segment width = 0.5 cm, segment length = 3.6 cm); (b) vate proprioception of the missing/inactive hand in trau- the number of errors, recorded each time the digital ma amputees and normally limbed subjects, who should pen touched the metallic plates surrounding the star seg- perform the task better than when receiving visual feed- ments; and (c) the total time the digital pen was in contact back of the performing hand when the mirror is oriented with the metallic plates (another indicator of error). frontally. By contrast, we anticipated that, in subjects with congenital limb absence who have never experienced Procedure sight of the missing limb, a lateral mirror view of their drawing hands should not facilitate drawing performance Subjects participated in two successive sessions, each when compared with a frontal mirror view. lasting approximately 5 minutes. Participants were seated

2208 Journal of Cognitive Neuroscience Volume 21, Number 11 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 Table 1. Clinical Features of the Amputee Groups for Experiments 1 and 2

Side of Year of Handedness Subjects, Sex Age (Years) Amputation Amputation before Amputation Sensations Pain Prothesis

A. Main clinical features of the two amputee groups enrolled in the mirror-drawing task FV, M 29 Left hand 1998 Right-handed Yes Yes Aesthetic SS, M 50 Right arm 2003 Right-handed Yes Yes No EP, M 44 Right arm 1998 Right-handed Yes Sometimes No Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 DT, M 50 Left arm 1997 Right-handed Sometimes Sometimes Myoelectric SR, F 30 Right arm Congenital – Never Never No LF, F 22 Left forearm Congenital – Never Never No NT, F 34 Left forearm Congenital – Never Never No TO, F 28 Right arm Congenital – Sometimes Never Aesthetic

B. Main clinical features of trauma amputee and congenital limb absence groups enrolled in the electrophysiological experiment NB, F 37 Right hand 2000 Right-handed Yes Sometimes Aesthetic FV, M 29 Left hand 1998 Right-handed Yes Yes Aesthetic JM, M 46 Left arm 1978 Right-handed Yes Sometimes Aesthetic GS, M 59 Right arm 1968 Right-handed Yes Sometimes No LF, F 22 Left forearm Congenital – Never Never No MA, M 33 Right forearm Congenital – Sometimes Never No NT, F 34 Left forearm Congenital – Never Never No SR, F 30 Right arm Congenital – Never Never No

at a table in front of the mirror-drawing apparatus. In the tions, whereas the other half completed the first session first session, the mirror was oriented in the midsagittal under frontal feedback conditions. plane (lateral feedback). In the second session, the mirror was oriented in the frontal plane (frontal feedback). While viewing the image through the mirror, subjects Results were instructed to trace the six-pointed star pattern as rapidly and as accurately as possible with their intact/ Normally Limbed Subjects dominant hand. Half the participants within each group A greater number of normally limbed subjects (compared completed the first session under lateral feedback condi- with trauma amputees and congenital limb absence subjects)

Figure 1. The experimental setup for the mirror-drawing task. (A) The subject faced the mirror to obtain frontal visual feedback of the drawing hand. (B) The mirror was placed sagittally and provided a view of the nondrawing/missing hand. An opaque box positioned over the star pattern prevented the subject from having a direct view of the performing hand.

Touzalin-Chretien, Ehrler, and Dufour 2209 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 were recruited to test a possible order effect between the two experimental conditions. Previous research has shown that, in a mirror-drawing task with the mirror in the frontal plane, scores improve from the first to the second trial (Lajoie et al., 1992). Although in this study the two successive trials were not performed under equivalent conditions (i.e., lateral vs. frontal mirror placement), the training effects remain an issue and, more importantly, the training effects may differ according to which mirror position is used first. Results from normally limbed Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 subjects showed that mirror order presentation had no effect on drawing time, t(24) = 1.51, p = .14, or error frequency, t(24) = −0.82, p = .42.

Time and Error Indices Drawing performances were evaluated in terms of time and errors. The total number of errors was weighted for error duration for each subject. Hence, a high error score may reflect either a large number of brief touches or a small number of long touches of the star borders.

Data Transformation The difference between the total time needed to complete the drawing under frontal and lateral feedback conditions (Δt) was calculated; a positive Δt value indicated that the time to complete the task was longer with frontal feedback than with lateral feedback. Error index was calculated similarly, yielding a single Δe value for each subject. These performance evolution indices were preferred Figure 2. Performances. (A) Mean drawing time differences (Δt) to raw data for two major reasons. First, the sample sizes under frontal and lateral feedback conditions (raw data are given of normally limbed and amputee subjects differed. Var- for each condition). Positive (negative) differences indicate longer iance homogeneity and normality could, therefore, not (shorter) completion times under frontal feedback than under be tested, and nonparametric tests appeared to be more lateral feedback. (B) Mean differences between error indices under Δ appropriate for evaluating the significance of perfor- frontal and lateral feedback conditions ( e = error frequency × error duration). mance differences. However, interactions cannot be evaluated using nonparametrical tests, only between- or within-group effects. Second, time performances in the Δt values were similar for normally limbed and trauma mirror-drawing task were highly variable within each amputee groups. The robustness of the feedback condition group. Hence, transforming two scores into a single effect was confirmed by analysis of individual data. All signed score resulted in a lower degree of freedom and four trauma amputees had shorter task completion times a greater statistical power. with lateral compared with frontal feedback. Conversely, The mean Δt values for each group are shown in Fig- all four congenital limb absence subjects had shorter task ure 2A. Trauma amputees and normally limbed subjects completion times with frontal compared with lateral feed- showed positive Δt values, indicating that the task took back. Eighteen of the 26 normally limbed subjects had longer under frontal rather than lateral feedback condi- shorter task completion times with lateral compared with tions. We also found that Δt values differed among the frontal feedback ( p = .02, binomial test). three groups [H(2,34) = 8.47, p = .014, Kruskal–Wallis Mean Δe values for each group are shown in Figure 2B. ANOVA]. Paired comparisons (Mann–Whitney test) showed Mean Δe values differed between the three groups, H(2) = that Δt values differed significantly between normally 6.02, p = .048, Kruskal–Wallis ANOVA. Although paired limbed and congenital limb absence subjects (z =2.56, comparisons (Mann–Whitney test) suggested different p = .01) and between trauma amputees and congenital Δe values between normally limbed and congenital limb limb absence subjects (z = −2.31, p = .02). This latter absence subjects (z = 1.89, p = .058) and between con- probability is close to the adjusted threshold of 0.017 genital limb absence subjects and trauma amputees (z = for three comparisons (Bonferroni correction). In contrast, −1.73, p = .083), Δe values did not differ between normally

2210 Journal of Cognitive Neuroscience Volume 21, Number 11 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 limbed subjects and trauma amputees. Individual Δe values subjects had a visual feedback of the hand in the sagittally showed the same distribution as individual Δt values. placed mirror (giving an image of the left/missing hand). Although the same hand is performing under both conditions, if vision of the performing hand influences mo- EXPERIMENT 2 tor activity, a lateralized cortical motor activity should The findings shown above indicate that a view of the emerge from this comparison. Conversely, if vision does missing or inactive hand can improve mirror-drawing task not influence motor activity, the two waveforms should performances in trauma amputees and healthy controls. be identical because the motor task is identical and no We hypothesized that this enhancement may be due to LRP should emerge. activation of the motor cortex of the seen hand. Thus, The LRP component reflects response preparation, thus Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 in both groups, ipsilateral motor-cortical activity of the commencing before muscle contraction begins, and can active/intact hand would be anticipated because move- occur in the absence of an overt response (Minelli, Marzi, ment is seen in a sagittally positioned mirror. In the same & Girelli, 2007; Galdo-Alvarez & Carrillo-de-la-Pena, 2004; manner, individuals with congenital limb absence did Miller & Hackley, 1992; de Jong, Wierda, Mulder, & Mulder, not show enhanced performance when the mirror was 1988). This component is, therefore, applicable to ampu- placed in the sagittal plane. Thus, we hypothesized that, tees. If cortical motor representation survives in their in these subjects, vision of the missing hand would not brains, an LRP should be recorded, even in the absence generate activity of the motor cortex ipsilateral of the of muscles targeted by the cortical outputs, and motor performing hand. To test these hypotheses, we examined performances of the responding hand, as shown in Exper- LRP, a measurement reflecting contralateral hand prepa- iment 1, would be enhanced under lateral visual feed- ration. LRP was chosen because neuroanatomical evidence back conditions by cortical motor activity of the inactive/ from surface and depth electrode recordings has shown amputated hand. That is, we anticipated lateralized mo- that this component is generated, at least in part, in the tor preparation initiated by a mirror-reflected view of the primary motor cortex (Gemba, Sasaki, & Tsujimoto, 1990; nonresponding/missing hand. Okada, Williamson, & Kaufman, 1982; Vaughan, Costa, & Ritter, 1968). LRP corresponds to an increasing negative asymmetric scalp potential over the hemisphere contra- Methods lateral to the movement side. This premovement later- Participants alized negativity reflects differential involvement of the Four subjects with traumatic upper-limb loss and four sub- left and right motor cortices in preparing to execute uni- jects with congenital upper-limb absence were enrolled. manual motor acts. Because motor asymmetry may be overlapped by a variety of asymmetries related to other Demographic and clinical data are summarized in Table 1. A third group of eight normally limbed subjects (four functional or structural differences between hemispheres, men, mean age = 31.5 years) was also enrolled. All nor- motor asymmetry has been defined as that part of the total potential recorded between opposite scalp locations mally limbed subjects except one were right-handed according to self-reporting. Subjects gave informed consent above the motor cortex that reverses when the response before participation, in accordance with the guidelines of hand is reversed and everything else is kept constant. Thus, asymmetry of motor-cortical activation can be obtained our local ethics committee, which approved the study. by summing total activation asymmetry of the two cerebral hemispheres obtained for right- and left-hand responses: Materials and Procedure (C3 − C4) right-hand response + (C4 − C3) left-hand response. This is equivalent to subtracting the opposite Subjects performed a forced-choice task unimanually un- asymmetry obtained for the left hand from the asym- der three different conditions defined by different views metry obtained for the right hand: (C3 − C4) right-hand of the responding hand. Subjects were seated at a table response − (C3 − C4) left-hand response, with C3 and and, using the intact/right hand, were asked to press as C4 corresponding to the electrode site above the hand area quickly as possible one of two response keys placed be- of the left and right motor cortices, respectively. side two light-emitting diodes that were switched on ran- Although LRP is usually computed from tasks involving domly for 200 msec. The two light-emitting diodes were both hands, we computed LRP from a task involving only placed 3 cm apart on the table (Figure 3). Conditions one hand with a direct visual feedback of that hand and a were identical except for the type of visual feedback of visual feedback given by a sagittally placed mirror, which the responding hand. gave the impression of seeing the opposite/missing hand. Although traditional LRP was computed as the difference (1) In the “direct view” condition, participants performed between right- and left-hand cortical activities, we com- the task with a direct view of the performing hand puted LRP by comparing right/intact hand cortical activ- (intact/right hand). ities while subjects had a direct view of their right/intact (2) In the “sagittal mirror view” condition, subjects per- hand with right/intact hand cortical activity and while formed the task with a mirror placed sagittally, which

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Figure 3. Experimental setup for the mirror task in Experiment 2. (A) Lateral mirror condition: The mirror placed sagittally provided a view of the nonmoving/missing hand, hidden behind the mirror. (B) Frontal mirror condition: The mirror provided a frontal visual feedback of the performing hand. An opaque cover (not shown in the figure) positioned over the performing hand prevented the subject from having a direct view.

gave the impression of a direct view of the missing/ The artifact rejection and the duration of averaging inactive hand. epoch were from 200 msec before stimulus onset to (3) In the “frontal mirror view” condition, the mirror was 500 msec afterward. After rejection of invalid trials (con- placed frontally giving visual frontal feedback of the taminated by ocular, muscular, and cerebral artifacts), performing hand. data analyses were performed on a mean of 186.4 trials per condition and subject. All normally limbed subjects performed the task with the right hand under the direct view, the sagittal mirror view, and the frontal mirror view conditions. In addition, EEG Analysis to compute a reference LRP (i.e., obtained with both To calculate response-specific lateralization according to hands), normally limbed subjects performed the task under the viewed hand, ERPs were computed separately for a fourth condition—they performed the motor task with each of the four conditions defined by the visual feed- thelefthandwithadirectview(directleftviewcondition). back of the performing hand, with all potentials sub- An opaque cover was used to prevent direct vision of jected to a two-step subtraction procedure. This double the performing hand in all conditions involving the mir- subtraction method accounted for unilateral motor activ- ror (sagittal and frontal mirror-view conditions). Two hun- ity evoked by a voluntary movement. First, the difference dred trials randomly spaced from 2600 to 3000 msec were in waveforms between the contralateral and the ipsilat- performed under each condition. eral central electrodes with respect to the performing hand was calculated for each trial and condition. Second, Electrophysiological Recording from the average waveform for the direct view condition trials, we subtracted the average waveform for the sagittal EEG were recorded using Ag/AgCl electrodes mounted in mirror view, the frontal mirror view, and the direct left an elastic cap. The electrodes were placed at C3 and C4 view condition trials. For a classic LRP, the formula for sites according to the 10/20 system (Klem, Luders, Jasper, normally limbed subjects is & Elger, 1999), above the hand area of the left and right motor cortices, and sampled at a rate of 500 Hz (band- ¼ð − Þ − LRP C3 C4 right hand ðdirect view conditionÞ pass filter = 0.01–500 Hz, with off-line digital smooth- ð − Þ : ing, 10 Hz cutoff). Impedances were maintained at less C3 C4 left hand ðdirect left view conditionÞ than 5 kΩ. Vertical, horizontal EOG and muscular potentials were This formula computes the difference of the contralateral- recorded from bipolar derivations using Ag/AgCl electrodes minus-ipsilateral difference for right-hand response and (band-pass filter = 0.01–200Hz)tomonitorocularartifacts ipsilateral-minus-contralateral difference for left-hand re- and EMG activity from the muscles of the intact hand in sponse. This corresponds to the total potential recorded amputees and of the right and left hands in normally between opposite scalp locations above the motor cortex limbed subjects. that reverses when the response hand is reversed, elim-

2212 Journal of Cognitive Neuroscience Volume 21, Number 11 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 inating any overall differences between the left and right tivation in the opposite hemisphere. Thus, the response hemispheres (independent of hand) and any overall dif- potential will be less lateralized and will yield a smaller ferences between the left and right hands (independent global negativity (LRP). Even when motor preparation of hemisphere). All that remains is the extent to which was observed in the hemisphere contralateral to the the response is generally larger over the hemisphere con- viewed hand, no actual movements were executed by tralateral to the hand being prepared, regardless of which that hand (opposite hand placed behind the mirror), as hand is being prepared or which hemisphere is being shown by EMG records (Figure 4D). recorded. In the trauma amputee group, an LRP was also ob- Using this analytical design, a comparison of the direct served when electrophysiological activity under lateral view and direct left view conditions should be indicative mirror view conditions was subtracted from activity un- Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 of the classic LRP in normally limbed subjects. A compar- der direct view conditions (direct view vs. sagittal mirror ison between the direct view and the sagittal mirror view view conditions; Figure 4B). As observed in normally conditions should be indicative of an LRP due to hand limbed subjects, the frontal mirror condition did not in- vision. Finally, no LRP was expected when the waveforms duce any LRP in the trauma amputee group (control from the direct view and the frontal mirror view condi- potential). The mean LRP amplitude induced by the lat- tions were compared because both conditions involved eral mirror differed significantly from the control poten- the same lateralized view of the performing hand. Thus, tial (z =1.82,p = .06, Wilcoxon test). LRP amplitudes subtracting a negative waveform from a similar negative induced by the lateral mirror relative to those of the con- waveform should result in a baseline waveform, which trol potential were similar for both normally limbed sub- was termed the control potential. jects and trauma amputees (z = 1.02, p = .31). LRPs were not observed in congenital limb absence subjects, neither under lateral mirror nor frontal mirror Results conditions (Figure 4C). ERP amplitudes were analyzed for 200 msec from LRP on- A posteriori examination of LRP onsets revealed signif- set. Onset of LRP was estimated for each subject using a icant differences between conditions. In the normally segmented regression method, based on average ERP limbed group, the LRP began at a mean of 123 msec fol- amplitudes (Mordkoff & Gianaros, 2000). This method de- lowing stimulus onset. This latency period was statisti- fined the LRP onset as the point of intersection between cally shorter than for the lateral mirror view (mean = two straight lines that were fitted to the LRP waveform. 186 msec, z = 2.38, p = .02, Wilcoxon paired test). Dif- One line was fitted to the putative preonset segment of ferences in stimulus-locked LRP onset are caused by pre- the LRP, whereas the other line was fitted to the segment motor processes (Mordkoff & Gianaros, 2000) and may that rose to the peak. be explained by the same reasons as those proposed In the normally limbed group, right and left hands un- for amplitude differences: Subjects had to inhibit move- der direct view yielded an LRP (direct view vs. direct left ment of the real left hand. This inhibition process, prob- view conditions). In addition, an LRP in the normally ably taking place in the motor cortex, may explain the limbed group was observed when electrophysiological observed differences in onset latency. activity under lateral mirror view conditions was sub- In the trauma amputee group, the mean onset laten- tracted from activity under direct view conditions (direct cy estimated using the segmented regression procedure view vs. sagittal mirror view conditions). The averaged was 124 msec. This latency did not differ from the LRP LRPs for the normally limbed group are shown in Fig- involving the two hands in normally limbed subjects ure 4A. These results indicate that a right-hand response (123 msec). Thus, in trauma amputees, the LRP induced was associated with activation of the left-hand primary by the lateral mirror view of the hand had the same tem- motor cortex (right hemisphere). When we compared poral characteristics as LRPs in normally limbed subjects the mean amplitudes of the two LRP waveforms with performing the task with both hands. Unlike normal- the control potential, we found that the mean amplitudes ly limbed subjects, amputees do not have to inhibit an for both the direct and lateral mirror-view LRPs differed actual movement, even if the motor command is sent, from the control potential (z = 2.52, p = .012 and z = because the muscles that are targeted are absent, dimin- 2.38, p = .017, respectively, Wilcoxon test). There was ishing any incongruence between what is seen (missing also a difference between direct and lateral mirror view hand) and what has to be done (movement with the in- LRPs (z = 2.52, p = .012). This difference in amplitude tact hand). may reflect the incongruence between the motor preparation of the viewed hand and the motor preparation of the responding hand in the LRP induced by the lateral DISCUSSION mirror. Although vision of the reflected hand may lead to motor preparation in the hemisphere contralateral to the We have investigated whether activation of deafferented seen hand (Kilner, Vargas, Duval, Blakemore, & Sirigu, cortical motor areas could be revealed by visuomotor 2004), the actual moving hand will also generate motor ac- performances when visual feedback of the amputated

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Figure 4. Electrophysiological and EMG activity. (A) Grand average waveforms depicting the voltage differences between the scalp electrodes (C3 and C4) for the three subtraction procedures in control subjects. (B and C) Grand average waveforms for the two subtraction procedures in trauma amputees and congenital limb absence subjects, respectively. (D) EMG activity from the muscles of the performing hand for all three groups and of the nonmoving left hand in normally limbed subjects for the “sagittal mirror view” condition.

limb was provided. Using performance and physiological tal visual feedback. These findings indicate that, under measures, we found that a view of one hand could gen- lateral feedback conditions, the discordance between vi- erate cortical motor preparation in the nonresponding sion and proprioception is reduced in normal and trauma hand. Our performance test results indicate that normal- amputee subjects but is enhanced in subjects with con- ly limbed subjects and trauma amputees deal with in- genital upper-limb loss. Thus, trauma amputees likely congruent visuoproprioceptive information in a similar conserve proprioceptive inputs for their missing limbs, manner. Both of these groups had more difficulties with and this proprioceptive information is used to perform the task when the mirror was placed in the frontal plane visuomotor activities. rather than in the lateral plane, whereas the opposite was Our results are consistent with clinical rehabilitation stud- true for congenital upper-limb loss subjects. For trauma ies using the “mirror-box illusion” to restore appropriate amputees, the image of the missing hand provided by a visual feedback to proprioceptive sensations in upper-limb lateral mirror facilitated motor actions of the remaining/ amputees (Ramachandran & Rogers-Ramachandran, 1996). drawing hand; a finding also observed in normally limbed This study found that proprioceptive sensations could subjects. Conversely, congenital loss subjects who had emerge from the missing limb when the remaining limb never experienced the missing hand either visually or was viewed through a mirror, even several years after am- proprioceptively showed reduced motor performances putation. Generally, research on phantom limbs has been for the remaining hand when visual feedback was given based on subjective measurement, that is, descriptions of in the position of the missing hand compared with fron- sensations in the patientsʼ phantom limbs (Ramachandran

2214 Journal of Cognitive Neuroscience Volume 21, Number 11 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 & Hirstein, 1998; Melzack, 1990). In the present study, cor- iological studies showing that observing an action is suf- tical motor activity in M1 permitted an objective measure of ficient to induce changes in the sensory-motor cortex. kinesthetics, supplementing the performance data. Indeed, lateralized activity is observed in fMRI images on Our performance test results were consistent with the the contralateral side to the observed movement (Oouchida results of physiological studies using fMRI or TMS show- et al., 2004). Moreover, that cortical activity depends on ing that motor commands to the missing limb remain ef- hand orientation, with a significant lateralized activation fective and that cortical activity was present in motor of the precentral gyrus when the observed movement is areas previously devoted to the missing limb when per- in the first-person perspective (Jackson, Meltzoff, & Decety, forming “virtual” movements with the amputated limb 2006). (Mercier et al., 2006; Roux et al., 2003). Although those The present results are also in agreement with previ- Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 studies referred only to proprioception (kinesthetic as- ous studies, highlighting perceptual differences between pect), functional integration of visual and kinesthetic traumatic amputees and individuals who have born with- information is likely preserved. In healthy subjects, in- out a limb (Flor et al., 1998; Ramachandran & Hirstein, tegrative areas of converging visual and proprioceptive 1998). Phantom sensations are rare in congenital am- information have been localized essentially to the premo- putees (Flor et al., 1998; Montoya et al., 1998). In the tor cortex (Balslev, Nielsen, Paulson, & Law, 2005), and present study, the absence of cortical motor activity in these cerebral regions may still receive converging inputs congenital subjects compared with traumatic amputees from both systems in trauma amputees. and normal individuals reflects a functional difference, Our electrophysiological results correlate with the per- consistent with the assumption that congenital subjects formance results. A view of the missing hand in trauma have not developed somatosensory and motor maps amputees and the inactive hand in normally limbed sub- due to limb deprivation during critical periods of devel- jects was found to enhance motor performance in a dif- opment. However, there are some reports indicating that ficult task such as mirror drawing. We hypothesized that congenital subjects may have such sensations (Brugger better performances correspond to motor activation that et al., 2000; Ramachandran & Hirstein, 1998; Simmel, is related to the viewed hand (amputated/inactive) ow- 1962). The present data do not allow us to interpret this ing to the integration of visual feedback and a proprio- paradox. However, these cases have often been cited as ceptively possible position of the hand. To determine evidence that the body schema has an innate component whethervisioninfluencesmotorpreparationinanRT (Melzack, 1990) as well as a possible role related to action task, we analyzed LRP, which reflects preparation of the observation (Ramachandran & Hirstein, 1998). responding hand. As expected, a reliable LRP was ob- Thus, the present experimental findings indicate the served when the seen hand was not the responding stability of body representation in trauma amputees and hand, indicating that motor preparation depends, at least suggest that the organization of visuomotor behavior de- partially, on the available visual information. This LRP was pends on body representation established through prior observed in both trauma amputees and normally limbed experience. On the basis of studies showing that LRP is individuals, but not in the congenital group, in accor- an on-line measure of response preparation (Coles, 1989), dance with the performance findings. Our LRP data, thus, the presence of this component in the hemisphere con- provide an objective physiological measure of visuopro- tralateral to the amputation indicates neural activity in the prioception persistence in the missing limb of trauma primary motor cortex with respect to the amputated hand. amputees. Moreover, studying proprioception through Using visual feedback of the missing limb via a sagittally vision using motor performances circumvents the prob- placed mirror, our findings demonstrate a model in which lem of virtual movements by amputees recorded in fMRI the LRP and the performance indices can be used to reliably (Roux et al., 2003). Factors that can influence the final measure cortical motor activity related to an amputated/ analysis (such as speed of phantom movement and am- inactive hand. plitude and type of movement) can only be determined based on patient descriptions of phantom-limb movement, an extremely subjective measure (Roux et al., 2003). Reprint requests should be sent to Pascale Touzalin-Chretien, Laboratoire dʼImagerie et de Neurosciences Cognitives, UMR The recording of an LRP in the lateral mirror condition 7191, CNRS-ULP, 21 rue Becquerel, 67087 Strasbourg, France, supports the hypothesis that the motor cortices of trau- or via e-mail: [email protected]. ma amputees still respond to the missing hand and that the visual and the motor systems in humans are tightly related. These results are consistent with previous elec- REFERENCES trophysiological studies in healthy subjects, showing that observation of a movement leads to a cortical motor ac- Balslev, D., Nielsen, F. A., Paulson, O. B., & Law, I. (2005). tivation, even without an actual movement (Kilner et al., Right temporoparietal cortex activation during visuoproprioceptive conflict. Cerebral Cortex, 15, 166–169. 2004). The findings shown here also indicate that this Berberovic, N., & Mattingley, J. B. (2003). Effects of prismatic motor activation is lateralized, depending on the visual adaptation on judgements of spatial extent in peripersonal feedback. These findings are also in accordance with phys- and extrapersonal space. Neuropsychologia, 41, 493–503.

Touzalin-Chretien, Ehrler, and Dufour 2215 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/jocn.2009.21218 by guest on 28 September 2021 Brugger, P., Kollias, S. S., Muri, R. M., Crelier, G., Michel, C., Rossetti, Y., Rode, G., & Tilikete, C. (2003). Hepp-Reymond, M. C., & Regard, M. (2000). Beyond After-effects of visuo-manual adaptation to prisms on body re-membering: Phantom sensations of congenitally absent posture in normal subjects. Experimental Brain Research, limbs. Proceedings of the National Academy of Sciences, 148, 219–226. U.S.A., 97, 6167–6172. Miller, J., & Hackley, S. A. (1992). Electrophysiological Coles, M. G. (1989). Modern mind-brain reading: evidence for temporal overlap among contingent mental Psychophysiology, physiology, and cognition. processes. Journal of Experimental Psychology: General, Psychophysiology, 26, 251–269. 121, 195–209. de Jong, R., Wierda, M., Mulder, G., & Mulder, L. J. (1988). Use Minelli, A., Marzi, C. A., & Girelli, M. (2007). Lateralized of partial stimulus information in response processing. readiness potential elicited by undetected visual stimuli. Journal of Experimental Psychology: Human Perception Experimental Brain Research, 179, 683–690. Downloaded from http://mitprc.silverchair.com/jocn/article-pdf/21/11/2207/1759861/jocn.2009.21218.pdf by guest on 18 May 2021 and Performance, 14, 682–692. Montoya, P., Ritter, K., Huse, E., Larbig, W., Braun, C., Topfner, Flor, H., Elbert, T., Muhlnickel, W., Pantev, C., Wienbruch, C., & S., et al. (1998). The cortical somatotopic map and phantom Taub, E. (1998). Cortical reorganization and phantom phenomena in subjects with congenital limb atrophy and phenomena in congenital and traumatic upper-extremity traumatic amputees with phantom limb pain. European amputees. Experimental Brain Research, 119, 205–212. Journal of Neuroscience, 10, 1095–1102. Galdo-Alvarez, S., & Carrillo-de-la-Pena, M. T. (2004). ERP Mordkoff, J. T., & Gianaros, P. J. (2000). Detecting the onset evidence of MI activation without motor response execution. of the lateralized readiness potential: A comparison of NeuroReport, 15, 2067–2070. available methods and procedures. Psychophysiology, 37, Gemba, H., Sasaki, K., & Tsujimoto, T. (1990). Cortical field 347–360. potentials associated with hand movements triggered by Okada, Y. C., Williamson, S. J., & Kaufman, L. (1982). Magnetic warning and imperative stimuli in the monkey. Neuroscience field of the human sensorimotor cortex. International Letters, 113, 275–280. Journal of Neuroscience, 17, 33–38. Giraux, P., & Sirigu, A. (2003). Illusory movements of the Oouchida, Y., Okada, T., Nakashima, T., Matsumura, M., Sadato, paralyzed limb restore motor cortex activity. Neuroimage, N., & Naito, E. (2004). Your hand movements in my 20(Suppl. 1), S107–S111. somatosensory cortex: A visuo-kinesthetic function in human Hay, J. C., Pick, H. L., Jr., & Ikeda, K. (1965). Visual capture area 2. NeuroReport, 15, 2019–2023. produces by prism spectacles. Psychonomic Science, 2, Pascual-Leone, A., Peris, M., Tormos, J. M., Pascual, A. P., & 215–216. Catala, M. D. (1996). Reorganization of human cortical motor Jackson, P. L., Meltzoff, A. N., & Decety, J. (2006). Neural output maps following traumatic forearm amputation. circuits involved in imitation and perspective-taking. NeuroReport, 7, 2068–2070. Neuroimage, 31, 429–439. Ramachandran, V. S., & Hirstein, W. (1998). The perception Karl, A., Birbaumer, N., Lutzenberger, W., Cohen, L. G., & Flor, of phantom limbs. The D. O. Hebb lecture. Brain, 121, H. (2001). Reorganization of motor and somatosensory 1603–1630. cortex in upper extremity amputees with phantom limb Ramachandran, V. S., & Rogers-Ramachandran, D. (1996). pain. Journal of Neuroscience, 21, 3609–3618. Synaesthesia in phantom limbs induced with mirrors. Killackey, H. P., Rhoades, R. W., & Bennett-Clarke, C. A. (1995). Proceedings of the Royal Society of London, Series B, The formation of a cortical somatotopic map. Trends in Biological Sciences, 263, 377–386. Neurosciences, 18, 402–407. Ramachandran, V. S., Stewart, M., & Rogers-Ramachandran, Kilner, M. J., Vargas, C., Duval, S., Blakemore, S. J., & Sirigu, A. D. C. (1992). Perceptual correlates of massive cortical (2004). Motor activation prior to observation of a predicted reorganization. NeuroReport, 3, 583–586. movement. Nature Neuroscience, 7, 1299–1301. Rhoades, R. W., Chiaia, N. L., Bennett-Clarke, C. A., Janas, G. J., Klem, G. H., Luders, H. O., Jasper, H. H., & Elger, C. (1999). & Fisher, C. M. (1994). Alterations in brainstem and cortical The ten-twenty electrode system of the International organization of rats sustaining prenatal vibrissa follicle Federation. The International Federation of Clinical lesions. Somatosensory & Motor Research, 11, 1–17. Neurophysiology. Electroencephalography and Clinical Rossetti, Y., Koga, K., & Mano, T. (1993). Prismatic Neurophysiology, 52(Suppl.),3–6. displacement of vision induces transient changes in the Lajoie, Y., Paillard, J., Teasdale, N., Bard, C., Fleury, M., Forget, timing of eye-hand coordination. Perception & R., et al. (1992). Mirror drawing in a deafferented patient Psychophysics, 54, 355–364. and normal subjects: Visuoproprioceptive conflict. Roux, F. E., Lotterie, J. A., Cassol, E., Lazorthes, Y., Sol, J. C., & Neurology, 42, 1104–1106. Berry, I. (2003). Cortical areas involved in virtual movement Melzack, R. (1990). Phantom limbs and the concept of a of phantom limbs: Comparison with normal subjects. neuromatrix. Trends in Neurosciences, 13, 88–92. Neurosurgery, 53, 1342–1352; discussion 1352–1353. Mercier, C., Reilly, K. T., Vargas, C. D., Aballea, A., & Sirigu, A. Simmel, M. L. (1962). Phantom experiences following (2006). Mapping phantom movement representations in amputation in childhood. Journal of Neurology, the motor cortex of amputees. Brain, 129, 2202–2210. Neurosurgery and Psychiatry, 25, 69–78. Michel, C., Pisella, L., Halligan, P. W., Luaute, J., Rode, G., Vaughan, H. G., Jr., Costa, L. D., & Ritter, W. (1968). Boisson, D., et al. (2003). Simulating unilateral neglect in Topography of the human motor potential. normals using prism adaptation: Implications for theory. Electroencephalography and Clinical Neurophysiology, Neuropsychologia, 41, 25–39. 25, 1–10.

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