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Movement preparation is affected by tissue damage in multiple sclerosis: Evidence from EEG event-related desynchronization
Clinical Neurophysiology 116 (2005) 1515–1519 www.elsevier.com/locate/clinph
Movement preparation is affected by tissue damage in multiple sclerosis: Evidence from EEG event-related desynchronization L. Leocani*, M. Rovaris, F. Martinelli-Boneschi, P. Annovazzi, M. Filippi, B. Colombo, V. Martinelli, G. Comi Department of Neurology, Clinical Neurophysiology and Neurorehabilitation, Scientific Institute, Hospital San Raffaele, University Vita-Salute, Via Olgettina 60, 20132 Milan, Italy Accepted 26 February 2005 Available online 26 April 2005
Abstract Objective: To investigate the impact of brain tissue damage in Multiple Sclerosis (MS) on the efficiency of programming of voluntary movement, assessed using event-related desynchronization of the EEG. Methods: The onset latency of mu ERD (percent desyncronization of the mu rhythm preceding movement onset) to hand movement was studied in 34 MS patients. ERD onset was compared with normative data and correlated with T1 and T2 total lesion volume (TLV) at magnetic resonance imaging (MRI). Results: ERD onset latency was significantly correlated with T1-TLV (rZ0.53, PZ0.001) and T2 lesion load (rZ0.5, PZ0.003), even after correcting for disability. Patients with higher T1-TLV had significantly delayed ERD onset compared with normal subjects and with patients with lower T1-TLV; patients with higher T2-TLV had significantly delayed ERD compared with normal subjects only. ERD onset latency was not correlated to clinical disability. Conclusions: Our finding of delayed ERD onset in patients with more severe measures of brain damage, independently from clinical disability, suggests that functional cortico-cortical and cortico-subcortical connections underlying the expression of ERD during programming of voluntary movement are disrupted by the MS related pathological process. Further, studies are needed to evaluate the role of specific anatomical cortico-subcortical circuits in determining this abnormality. Significance: The extent of brain lesion load in multiple sclerosis affects cortical changes related to motor preparation, detected by analysis of onset latency of event-related desynchronization (ERD) of the mu rhythm to self-paced movement. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Multiple sclerosis; Voluntary movement; Magnetic resonance imaging; EEG; Event-related desynchronization
1. Introduction Multiple sclerosis (MS) is a demyelinating disease of the central nervous system of unknown etiology. Converging evidence suggests that the MS-related brain damage is related to disruption of neural connections among cortical associative areas and between cortical and subcortical structures, leading to the impairment of cognitive functions (Comi et al., 1993; Rao, 1990). The amount of subcortical brain lesions has been previously related to global
* Corresponding author. Tel.: C39 02 26433092; fax: C39 02 26433085. E-mail address: [email protected] (L. Leocani).
impairment of functional cortico-cortical connections in MS patients as measured from the resting EEG (Leocani et al., 2000). The extent of brain tissue damage in MS patients also correlates with the pattern of activation to voluntary movement at functional magnetic resonance imaging (MRI), interpreted as the expression of cortical reorganization partially limiting the consequences of MS injury in the brain and spinal cord (Filippi and Rocca, 2003). Another functional correlate of brain activity to voluntary movement is the event-related desynchronization (ERD; Pfurtscheller, 1977) of the electroencephalogram (EEG). Reduced expression of the mu and beta rhythms, observed over the contralateral sensorimotor cortex 1–2 s prior to voluntary movement (Leocani et al., 1997;
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.02.026
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Pfurtscheller, 1977) is considered an indicator of cortical activation. Delayed mu ERD onset, reported in basal ganglia disorders such as Parkinson’s disease (Defebvre et al., 1994, 1996; Magnani et al., 1998, 2002), has been related to involvement of cortical circuits related to motor programming. The aim of this study was to investigate the impact of accumulated brain damage in MS patients, assessed at conventional MRI measures of lesion load, on the efficiency of brain circuits involved in motor planning, assessed by mu ERD preceding voluntary movement.
2. Methods 2.1. Patients Thirty-four right-handed patients (14 males, 20 females; mean age [GSD]: 35.3G7.0 years, mean disease duration: 9.2G6.1 years), followed-up in the MS Clinic of our Institution, were included. Twenty-three had the relapsingremitting and 11 the secondary progressive form of MS, according to consensus criteria (Lublin et al. 1996). Their median Expanded Disability Status Scale (EDSS) score (Kurtzke, 1983) was 3.5 (range: 0–6.5; mean: 3.1G1.9), with the following Functional Systems (Kurtzke, 1983) scores: pyramidal: 2.3G1.5; brainstem 1.1G1; cerebellar 1.2G1.3; somatosensory 0.9G0.8; sphyncteric 0.8G0.9; visual 0.3G0.7; mental 0.5G0.8. Patients with a history of affective disorders, drug or alcohol abuse, or treated in the previous month with steroids or other psychoactive drugs, were not included, as well as patients with upper limb motor impairment, possibly interfering with performance at the electrophysiological examination. All patients gave their informed consent to participate in the study, which was approved by the local ethic committee.
2.3. Image analysis MS lesions were first outlined by agreement by two experienced observers, unaware of patients’ clinical characteristics, on proton density (PD)-weighted and T1-weighted MPRAGE image hardcopies; T2-weighted scans were always used to increase confidence in lesion identification. Only areas with signal intensity close to that of the CSF and corresponding hyperintensities on PD and T2-weighted images were considered as hypointense lesions. Total T2-hyperintense and T1-hypointense lesion volume (T2 TLV and T1 TLV, respectively) measurements were then performed by a trained technician, who was also unaware of patients’ clinical characteristics. A local thresholding technique (LTT) was used for lesion segmentation on computer-displayed images, keeping the marked hardcopies as a reference. The LTT is based on the assumption that, on MR images, MS lesions have a different signal intensity compared with the normal-appearing brain tissue. Using a mouse-controlled cursor, the rater first chooses a point on the lesion boundary and the algorithm starts contouring the lesion, following from the strongest edge point in the neighbourhood (i.e. by searching it over a 5!5 pixel square area with the manually-selected point in its center). Once the starting point has been found, the program searches in all directions and chooses the next contour point, which must have at least as strong a gradient as the starting one. By following the same principle from the most recent point, the contour is complete when it traces back to the starting point. Lesions are delineated as regions of interest (ROIs) and for each sequence the lesion volume can be simply calculated by multiplying the total ROI area for the slice thickness. Further, details about this image analysis method are extensively reported elsewhere (Rovaris et al., 1997). 2.4. EEG recording
2.2. Image acquisition On a 1.5 T scanner, each patient underwent dual echo turbo spin echo (TSE) (TRZ3300, TEZ16/98, echo train lengthZ5) brain MRI scans. Twenty-four axial 5-mm thick contiguous interleaved slices were obtained, with rectangular 188!250 mm field of view and 194!256 image matrix, thus obtaining approximately a 1!1 mm in-plane resolution. T1-weighted magnetization-prepared rapid acquisition gradient echo (MP-RAGE) scans were also obtained in the same session (TRZ10, TEZ4, TIZ700, flip angleZ 108, number of acquisitionsZ1), with the acquisition of a 3D sagittal slab (194!256!160 image matrix, 250 mm field of view) covering the entire brain. The original MPRAGE data were reformatted to obtain 24 axial contiguous 5-mm thick slices, with the same orientation and offsets as the corresponding TSE slices. Patients were positioned in the scanner following published guidelines for MS studies (Miller et al., 1991).
Patients performed about 60 self-paced extensions of the right thumb at a rate of one every 5–10 s, while seated on an armchair in an electrically and sound-shielded room, their hands pronated and resting on a pillow. Twenty-nine EEG channels with binaural reference were recorded with scalp electrodes mounted on an elastic cap (Electro-cap International, Eaton, OH) according to the 10–20 international system of electrode placement, with additional electrodes placed along the longitudinal axis (FC3, FCz, FC4, CP3, CPz, CP4, FT3, FT4, TP3, TP4) and bipolar electrooculogram. The EEG signal was amplified (Synamps Amplifiers, Neuroscan, Inc., Herndon, VA), filtered (DC to 50 Hz), and digitized (250 Hz sampling frequency). Bilateral bipolar EMG from the right extensor pollicis brevis muscle was recorded to detect movement onset and to monitor for contralateral complete relaxation. Subjects were asked to perform brisk movements while keeping their eyes open and fixated on a point in front of them.
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2.5. EEG analysis
3. Results
The recordings were visually inspected and EMG onset was marked as the first abrupt change in the background. Non brisk movements, or accompanied by changes in EMG background in the contralateral muscle, or separated by an EMG pause of less than 5 s, were excluded from the analysis. EEG artifacts were firstly excluded using an automatic detection threshold (amplitude exceeding 50 mV) and then checked visually to avoid excluding epochs with alpha amplitude exceeding 50 mV or channel saturations. The frequency band of the mu rhythm was individually selected as the 3 Hz interval centered on the frequency falling within the alpha band (8–13 Hz) displaying the highest power decrease during movement (from K0.5 to C0.5 s with respect to EMG onset) compared to a 1 s epoch starting K2.5 before EMG onset. After Laplacian computation for obtaining reference-free data (Lutzenberger et al., 1987), the EEG was bandpass filtered (2 Hz interval centered on the selected frequency) and rectified to obtain polarity-free amplitude values. Percent ERD was calculated over successive 50 ms time intervals between K2 and 1.3 s with respect to EMG onset, according to the formula by Pfurtscheller and Berghold (1989): (X-baseline)!100/baseline, in which baseline was set from K2.5 to K2 s before EMG onset. Since the earliest ERD during motor preparation starts about 1.5 s before movement over the contralateral sensorimotor area (electrode C3), while it appears ipsilaterally only close to movement execution (Defebvre et al., 1994; Leocani et al., 1997; Pfurtsheller et al., 1977), the onset latency of mu ERD was measured for each subject at the electrode overlying electrode C3, as the latency (from EMG onset) at which percent power of the mu rhythm started to decrease steadily (i.e. remained negative up to movement execution or later).
Movement performance was similar in MS patients and normal subjects, as the amount of rectified EMG activity did not significantly differ between the two groups. The amount of ERD over C3 and C4 did not significantly differ between the whole group of MS patients and normal subjects (Fig. 1), as well as ERD onset over C3 (MS: K1298.2G639.2 ms; controls: K1593.7G407.8 ms; PZ0.12; Fig. 2). When subdividing MS patients according to their median value of brain TLV (cut-off: 5.15 for T1-TLV, 18.2 for T2-TLV), we obtained a subgroup with higher T1 TLV (mean: 15.5G9.5; range 5.2–35.6), lower T1 TLV (mean: 1.9G1.6; range 0–5.1), higher T2 TLV (mean: 41.8G19.1; range 18.4–73.7) and lower T2 TLV (mean: 2.5G3.2; range 0.2–18). Patients with higher T1 TLV had a significantly delayed ERD onset (mean: K1044G687.1 ms) both compared with patients with lower T1 TLV (mean: K1552.3G483.1 ms; PZ0.02) and with normal subjects (mean: K1593.8G 407.8; PZ0.02) (Fig. 2). ERD onset latency in patients with higher T2 TLV (mean: K1094.1G689.1) was greater than in those with lower T2 TLV (mean: K1502.4G528.5; PZ0.058) and than normal subjects (PZ0.01) (Fig. 2). No significant differences in ERD onset were found between patients with lower T1 TLV or T2 TLV and normal subjects. EDSS was significantly higher in patients with higher T2 TLV (3.8G2.0) than in those with lower T2 TLV
2.6. Statistical analysis The relationship between cortical activation to movement preparation (ERD onset latency) and the amount of brain lesions (T1 and T2 TLV) was investigated using the Spearman’s rank correlation coefficient (rS) for crude correlations and Pearson’s correlation coefficient (rP) when correcting for other variables. Patients were divided in two subgroups according to the amount of TLV (i.e. higher versus lower T1 TLV; higher versus lower T2 TLV), using the median value of the overall distribution as the cut-off value. Differences in ERD onset latency between these subgroups, as well as between the whole patient cohort and a group of healthy normal volunteers (6 males, 10 females, mean age 28G5 years) were analysed using the Mann–Whitney U test.
Fig. 1. Average of percent ERD (event-related desynchronization) of mu oscillations to movement preparation and execution in normal subjects (continuous line) and in MS patients (dotted line) with respect to baseline (between K2.5 and 2.5 s prior to movement, occurring a time 0). Data from the sensorimotor regions contralateral (electrode C3) and ipsilateral (electrode C4) are shown.
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4. Discussion
Fig. 2. Mean ERD onset latency (in ms) with respect to EMG activity, in normal subjects compared with the whole MS group (left pair of columns) and in the MS subgroups obtained by subdividing patients according to their EDSS and to their median value of T2 TLV and of T1 TLV.
(2.5G1.6; PZ0.047), as well as in patients with higher T1-TLV (3.9G2.1) than in those with lower T1-TLV (2.3G1.5; PZ0.02). ERD onset latency was significantly, positively correlated with both T1 TLV (rSZ0.53, PZ0.001; Fig. 3) and T2 TLV (rSZ0.50, PZ0.003; Fig. 3), but not with patients’ EDSS (rSZ0.27; PZ0.13). The correlation between T2 TLV and T1 TLV and the ERD onset latency was not substantially modified after adjustment with the EDSS score (T1 TLVERD: rP after adjustment: 0.50, P: 0.003 versus crude rP: 0.55, PZ0.001; T2 TLV-ERD: rP after adjustment: 0.43, PZ0.01 versus crude rP: 0.49, PZ0.003). This was also confirmed by the fact that the ERD onset latency did not significantly differ when subdividing patients into two subgroups according to EDSS (lower EDSS: range 0–3.0; higher EDSS: range 3.5–6.5), respectively, K1502.5C503.5 versus K1116.7C703.7; PZ0.14) (Fig. 2).
Fig. 3. Brain MRI lesion load and ERD onset latency (in ms) with respect to EMG onset. Negative values in the abscissa indicate ERD latency preceding EMG onset. Dots and broken line represent T2-TLV values and the regression line with ERD onset latency, respectively. Triangles and continuous line represent T1-TLV values and the regression line with ERD onset latency, respectively.
In the present study, we found a correlation between delayed latency of mu ERD preceding voluntary movement and measures of brain damage in MS such as T1 and, to a lesser extent, T2 total lesion load. This correlation was present also when correcting for EDSS, which conversely was not found significantly related with ERD onset latency. Event-related desynchronization (ERD) of the EEG has been interpreted as an electrophysiological correlate of activated cortical areas involved in sensory and motor processing (Pfurtscheller and Lopes da Silva, 1999), based on the observation that increased excitability in thalamo-cortical networks results in a low amplitude desynchronized EEG (Steriade and Llinas, 1988). During preparation of voluntary movement, ERD of the mu rhythm begins over the contralateral sensorimotor area 1.5–2 s before movement (Leocani et al., 1997; Pfurtscheller, 1977), and is considered a correlate of activation of cortical motor circuits preceding movement, even though it may not be considered a direct indicator of the subsequent corticospinal activation (Chen et al., 1998). Several studies (Defebvre et al., 1994, 1996; Magnani et al., 1998, 2002) have shown delayed ERD onset over the contralateral sensorimotor area (electrode C3) during movement preparation in Parkinson’s disease (PD), a disorder in which abnormal motor preparation has been suggested (Marsden, 1982). The evidence that delayed ERD onset to simple self-paced movement is related to dysfunction of cortical circuits involved in motor planning is indirect but several pieces of evidence suggest this view. First, in untreated hemiparkinsonian patients, the ERD onset is more delayed for movements of the affected side (Defebvre et al., 1996). Moreover, the delay or reduced expression of premotor ERD improve after chronic (Defebvre et al., 1998) and acute (Magnani et al., 2002; Wang et al., 1999) L-DOPA treatment and during subthalamic nucleus stimulation (Devos et al., 2004), all factors related to improved clinical motor symptoms. The implications of the latter findings cannot be directly transferred to our results, but the finding that the more MS lesions the patient has (i.e. the more severe the tissue damage), the more delayed the ERD, is consistent with the view that delayed sensorimotor ERD is dysfunctional, at least in relation to a simple motor task performed by naive subjects, as in our experiment. Measurement of T2 and T1 LL partially lacks pathological specificity. Conventional T2-weighted MRI scans have a high sensitivity in revealing MS lesions, but they lack specificity to further characterize the stages of the pathological process in individual lesions. Edema, demyelination, gliosis and axonal loss (McDonald et al., 1992) all lead to a similar appearance of hyperintensity on T2-weighted images. On the other hand, pathological studies have confirmed that hypointense lesions on chronic hypointense areas on unenhanced T1-weighted images show severe tissue disruption, corresponding to areas of tissue disorganization due to demyelination and/or axonal loss (van Walderveen et al., 1998). The potential of
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T1-weighted MRI abnormalities as pathologically specific MRI markers of MS severity has been emphasized by crosssectional (van Walderveen et al., 1998) and longitudinal (Truyen et al., 1997) studies. Even though lesion hypointensity may also occur acutely and transiently in the case of inflammatory edema (with subsequent return to isointensity), the latter condition is unlikely to have contributed to the measures obtained from patients included in our study, being all of them relapse-free for at least a month. The stronger relationship between delayed ERD and T1-TLV compared with T2-TLV suggests that abnormal motor programming revealed by ERD analysis is more related to the severity of tissue loss rather than to other consequences of inflammation. Movement preparation involves complex functional interactions between basal ganglia, supplementary motor area and primary motor cortex (Jurgens, 1984). Our finding of delayed ERD onset in patients with more severe measures of brain damage suggests that functional cortico-cortical and cortico-subcortical connections underlying the expression of ERD during programming of voluntary movement are disrupted by the MS related pathological process. Further studies are needed in order to define the impact of more specific measures of tissue damage and to evaluate the role of specific anatomical cortico-subcortical circuits in determining this abnormality. Acknowledgements This study was supported by a grant from the ‘Fondazione Italiana Sclerosi Multipla’ (project 2001/R/37). We would like to thank Andrea Nossa, R.EEGT, for EEG recordings. References Chen R, Yaseen Z, Cohen LG, Hallett M. Time course of corticospinal excitability in reaction time and self-paced movements. Ann Neurol 1998;44:317–25. Comi G, Filippi M, Martinelli V, Sirabian G, Visciani A, Campi A, Mammi S, Rovaris M, Canal N. Brain magnetic resonance imaging correlates of cognitive impairment in multiple sclerosis. J Neurol Sci 1993;115:66–73. Defebvre L, Bourriez JL, Dujardin K, Derambure P, Destee A, Guieu JD. Spatiotemporal study of Bereitschaftspotential and event-related desynchronization during voluntary movement in Parkinson’s disease. Brain Topogr 1994;6:237–44. Defebvre L, Bourriez JL, Destee A, Guieu JD. Movement-related desynchronisation pattern preceding voluntary movement in untreated Parkinson’s disease. J Neurol Neurosurg Psychiatry 1996;60:307–12. Defebvre L, Bourriez JL, Derambure P, Duhamel A, Guieu JD, Destee A. Influence of chronic administration of L-DOPA on event-related desynchronization of mu rhythm preceding voluntary movement in Parkinson’s disease. Electroencephalogr Clin Neurophysiol 1998;109: 161–7.
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Devos D, Labyt E, Derambure P, Bourriez JL, Cassim F, Reyns N, Blond S, Guieu JD, Deste´e A, Defebvre L. Subthalamic nucleus stimulation modulates motor cortex oscillatory activity in Parkinson’s disease. Brain 2004;127:408–19. Filippi M, Rocca MA. Disturbed function and plasticity in multiple sclerosis as gleaned from functional magnetic resonance imaging. Curr Opin Neurol 2003;16:275–82. Jurgens U. The efferent and afferent connections of the supplementary motor area. Brain Res 1984;300:63–87. Kurtzke JF. Rating neurologic impairment in multiple sclerosis: an expanded disability status scale (EDSS). Neurology 1983;33:1444–52. Leocani L, Toro C, Manganotti P, Zhuang P, Hallett M. Event-related coherence and event-related desynchronization/synchronization in the 10 Hz and 20 Hz EEG during self-paced movements. Electroencephalogr Clin Neurophysiol 1997;104:199–206. Leocani L, Locatelli T, Martinelli V, Rovaris M, Falautano M, Filippi M, Magnani G, Comi G. Electroencephalographic coherence analysis in multiple sclerosis: correlation with clinical, neuropsychological, and MRI findings. J Neurol Neurosurg Psychiatry 2000;69:192–8. Lublin FD, Reingold SC. Defining the clinical course of multiple sclerosis: results of an international survey. National Multiple Sclerosis Society (USA). Advisory Committee on Clinical Trials of New Agents in Multiple Sclerosis. Neurology 1996;46:907–11. Lutzenberger W, Elbert T, Rockstroh B. A brief tutorial on the implications of volume conduction for the interpretation of the EEG. J. Psychophysiol 1987;1:81–9. Magnani G, Cursi M, Leocani L, Volonte` MA, Locatelli T, Elia A, Comi G. Event-related desynchronization to contingent negative variation and self-paced movement paradigms in Parkinson’s disease. Mov Disord 1998;13:653–60. Magnani G, Cursi M, Leocani L, Volonte` MA, Comi G. Acute effects of Ldopa on event-related desynchronization in Parkinson’s disease. Neurol Sci 2002;23:91–7. Marsden CD. The mysterious motor function of the basal ganglia: the Robert Wartenberg lecture. Neurology 1982;32:514–39. McDonald WI, Miller DH, Barnes D. The pathological evolution of multiple sclerosis. Neuropathol Appl Neurobiol 1992;18:319–34. Miller DH, Barkhof F, Berry I, Kappos L, Scotti G, Thompson AJ. Magnetic resonance imaging in monitoring the treatment of multiple sclerosis: concerted action guidelines. J Neurol Neurosurg Psychiatry 1991;54:683–8. Pfurtscheller G. Graphical display and statistical evaluation of event-related desynchronization (ERD). Electroenceph Clin Neurophysiol 1977;43: 757–60. Pfurtscheller G, Lopes da Silva FH. Event-related EEG/MEG synchronization and desynchronization: basic principles. Clin Neurophysiol 1999; 110:1842–57. Rao SM. Multiple sclerosis. In: Cummings JL, editor. Subcortical dementia. New York, NY: Oxford University Press; 1990. p. 164–80. Rovaris M, Filippi M, Calori G, Rodegher M, Campi A, Colombo B, Comi G. Intra-observer reproducibility in measuring new putative markers of demyelination and axonal loss in multiple sclerosis: a comparison with conventional T2-weighted images. J Neurol 1997;244: 266–70. Steriade M, Llinas R. The functional states of the thalamus and the associated neuronal interplay. Phys Rev 1988;68:649–742. van Walderveen MA, Kamphorst W, Scheltens P, van Waesberghe JH, Ravid R, Valk J, Polman CH, Barkhof F. Histopathologic correlate of hypointense lesions on T1-weighted spin-echo MRI in multiple sclerosis. Neurology 1998;50:1282–8. Wang H-C, Lees AJ, Brown P. Impairment of EEG desynchronisation before and during movement and its relation to bradykinesia in Parkinson’s disease. J Neurol Neurosurg Psychiatry 1999;66:442–6.
Movement preparation is affected by tissue damage in multiple sclerosis: Evidence from EEG event-related desynchronization L. Leocani*, M. Rovaris, F. Martinelli-Boneschi, P. Annovazzi, M. Filippi, B. Colombo, V. Martinelli, G. Comi Department of Neurology, Clinical Neurophysiology and Neurorehabilitation, Scientific Institute, Hospital San Raffaele, University Vita-Salute, Via Olgettina 60, 20132 Milan, Italy Accepted 26 February 2005 Available online 26 April 2005
Abstract Objective: To investigate the impact of brain tissue damage in Multiple Sclerosis (MS) on the efficiency of programming of voluntary movement, assessed using event-related desynchronization of the EEG. Methods: The onset latency of mu ERD (percent desyncronization of the mu rhythm preceding movement onset) to hand movement was studied in 34 MS patients. ERD onset was compared with normative data and correlated with T1 and T2 total lesion volume (TLV) at magnetic resonance imaging (MRI). Results: ERD onset latency was significantly correlated with T1-TLV (rZ0.53, PZ0.001) and T2 lesion load (rZ0.5, PZ0.003), even after correcting for disability. Patients with higher T1-TLV had significantly delayed ERD onset compared with normal subjects and with patients with lower T1-TLV; patients with higher T2-TLV had significantly delayed ERD compared with normal subjects only. ERD onset latency was not correlated to clinical disability. Conclusions: Our finding of delayed ERD onset in patients with more severe measures of brain damage, independently from clinical disability, suggests that functional cortico-cortical and cortico-subcortical connections underlying the expression of ERD during programming of voluntary movement are disrupted by the MS related pathological process. Further, studies are needed to evaluate the role of specific anatomical cortico-subcortical circuits in determining this abnormality. Significance: The extent of brain lesion load in multiple sclerosis affects cortical changes related to motor preparation, detected by analysis of onset latency of event-related desynchronization (ERD) of the mu rhythm to self-paced movement. q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. Keywords: Multiple sclerosis; Voluntary movement; Magnetic resonance imaging; EEG; Event-related desynchronization
1. Introduction Multiple sclerosis (MS) is a demyelinating disease of the central nervous system of unknown etiology. Converging evidence suggests that the MS-related brain damage is related to disruption of neural connections among cortical associative areas and between cortical and subcortical structures, leading to the impairment of cognitive functions (Comi et al., 1993; Rao, 1990). The amount of subcortical brain lesions has been previously related to global
* Corresponding author. Tel.: C39 02 26433092; fax: C39 02 26433085. E-mail address: [email protected] (L. Leocani).
impairment of functional cortico-cortical connections in MS patients as measured from the resting EEG (Leocani et al., 2000). The extent of brain tissue damage in MS patients also correlates with the pattern of activation to voluntary movement at functional magnetic resonance imaging (MRI), interpreted as the expression of cortical reorganization partially limiting the consequences of MS injury in the brain and spinal cord (Filippi and Rocca, 2003). Another functional correlate of brain activity to voluntary movement is the event-related desynchronization (ERD; Pfurtscheller, 1977) of the electroencephalogram (EEG). Reduced expression of the mu and beta rhythms, observed over the contralateral sensorimotor cortex 1–2 s prior to voluntary movement (Leocani et al., 1997;
1388-2457/$30.00 q 2005 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.clinph.2005.02.026
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Pfurtscheller, 1977) is considered an indicator of cortical activation. Delayed mu ERD onset, reported in basal ganglia disorders such as Parkinson’s disease (Defebvre et al., 1994, 1996; Magnani et al., 1998, 2002), has been related to involvement of cortical circuits related to motor programming. The aim of this study was to investigate the impact of accumulated brain damage in MS patients, assessed at conventional MRI measures of lesion load, on the efficiency of brain circuits involved in motor planning, assessed by mu ERD preceding voluntary movement.
2. Methods 2.1. Patients Thirty-four right-handed patients (14 males, 20 females; mean age [GSD]: 35.3G7.0 years, mean disease duration: 9.2G6.1 years), followed-up in the MS Clinic of our Institution, were included. Twenty-three had the relapsingremitting and 11 the secondary progressive form of MS, according to consensus criteria (Lublin et al. 1996). Their median Expanded Disability Status Scale (EDSS) score (Kurtzke, 1983) was 3.5 (range: 0–6.5; mean: 3.1G1.9), with the following Functional Systems (Kurtzke, 1983) scores: pyramidal: 2.3G1.5; brainstem 1.1G1; cerebellar 1.2G1.3; somatosensory 0.9G0.8; sphyncteric 0.8G0.9; visual 0.3G0.7; mental 0.5G0.8. Patients with a history of affective disorders, drug or alcohol abuse, or treated in the previous month with steroids or other psychoactive drugs, were not included, as well as patients with upper limb motor impairment, possibly interfering with performance at the electrophysiological examination. All patients gave their informed consent to participate in the study, which was approved by the local ethic committee.
2.3. Image analysis MS lesions were first outlined by agreement by two experienced observers, unaware of patients’ clinical characteristics, on proton density (PD)-weighted and T1-weighted MPRAGE image hardcopies; T2-weighted scans were always used to increase confidence in lesion identification. Only areas with signal intensity close to that of the CSF and corresponding hyperintensities on PD and T2-weighted images were considered as hypointense lesions. Total T2-hyperintense and T1-hypointense lesion volume (T2 TLV and T1 TLV, respectively) measurements were then performed by a trained technician, who was also unaware of patients’ clinical characteristics. A local thresholding technique (LTT) was used for lesion segmentation on computer-displayed images, keeping the marked hardcopies as a reference. The LTT is based on the assumption that, on MR images, MS lesions have a different signal intensity compared with the normal-appearing brain tissue. Using a mouse-controlled cursor, the rater first chooses a point on the lesion boundary and the algorithm starts contouring the lesion, following from the strongest edge point in the neighbourhood (i.e. by searching it over a 5!5 pixel square area with the manually-selected point in its center). Once the starting point has been found, the program searches in all directions and chooses the next contour point, which must have at least as strong a gradient as the starting one. By following the same principle from the most recent point, the contour is complete when it traces back to the starting point. Lesions are delineated as regions of interest (ROIs) and for each sequence the lesion volume can be simply calculated by multiplying the total ROI area for the slice thickness. Further, details about this image analysis method are extensively reported elsewhere (Rovaris et al., 1997). 2.4. EEG recording
2.2. Image acquisition On a 1.5 T scanner, each patient underwent dual echo turbo spin echo (TSE) (TRZ3300, TEZ16/98, echo train lengthZ5) brain MRI scans. Twenty-four axial 5-mm thick contiguous interleaved slices were obtained, with rectangular 188!250 mm field of view and 194!256 image matrix, thus obtaining approximately a 1!1 mm in-plane resolution. T1-weighted magnetization-prepared rapid acquisition gradient echo (MP-RAGE) scans were also obtained in the same session (TRZ10, TEZ4, TIZ700, flip angleZ 108, number of acquisitionsZ1), with the acquisition of a 3D sagittal slab (194!256!160 image matrix, 250 mm field of view) covering the entire brain. The original MPRAGE data were reformatted to obtain 24 axial contiguous 5-mm thick slices, with the same orientation and offsets as the corresponding TSE slices. Patients were positioned in the scanner following published guidelines for MS studies (Miller et al., 1991).
Patients performed about 60 self-paced extensions of the right thumb at a rate of one every 5–10 s, while seated on an armchair in an electrically and sound-shielded room, their hands pronated and resting on a pillow. Twenty-nine EEG channels with binaural reference were recorded with scalp electrodes mounted on an elastic cap (Electro-cap International, Eaton, OH) according to the 10–20 international system of electrode placement, with additional electrodes placed along the longitudinal axis (FC3, FCz, FC4, CP3, CPz, CP4, FT3, FT4, TP3, TP4) and bipolar electrooculogram. The EEG signal was amplified (Synamps Amplifiers, Neuroscan, Inc., Herndon, VA), filtered (DC to 50 Hz), and digitized (250 Hz sampling frequency). Bilateral bipolar EMG from the right extensor pollicis brevis muscle was recorded to detect movement onset and to monitor for contralateral complete relaxation. Subjects were asked to perform brisk movements while keeping their eyes open and fixated on a point in front of them.
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3. Results
The recordings were visually inspected and EMG onset was marked as the first abrupt change in the background. Non brisk movements, or accompanied by changes in EMG background in the contralateral muscle, or separated by an EMG pause of less than 5 s, were excluded from the analysis. EEG artifacts were firstly excluded using an automatic detection threshold (amplitude exceeding 50 mV) and then checked visually to avoid excluding epochs with alpha amplitude exceeding 50 mV or channel saturations. The frequency band of the mu rhythm was individually selected as the 3 Hz interval centered on the frequency falling within the alpha band (8–13 Hz) displaying the highest power decrease during movement (from K0.5 to C0.5 s with respect to EMG onset) compared to a 1 s epoch starting K2.5 before EMG onset. After Laplacian computation for obtaining reference-free data (Lutzenberger et al., 1987), the EEG was bandpass filtered (2 Hz interval centered on the selected frequency) and rectified to obtain polarity-free amplitude values. Percent ERD was calculated over successive 50 ms time intervals between K2 and 1.3 s with respect to EMG onset, according to the formula by Pfurtscheller and Berghold (1989): (X-baseline)!100/baseline, in which baseline was set from K2.5 to K2 s before EMG onset. Since the earliest ERD during motor preparation starts about 1.5 s before movement over the contralateral sensorimotor area (electrode C3), while it appears ipsilaterally only close to movement execution (Defebvre et al., 1994; Leocani et al., 1997; Pfurtsheller et al., 1977), the onset latency of mu ERD was measured for each subject at the electrode overlying electrode C3, as the latency (from EMG onset) at which percent power of the mu rhythm started to decrease steadily (i.e. remained negative up to movement execution or later).
Movement performance was similar in MS patients and normal subjects, as the amount of rectified EMG activity did not significantly differ between the two groups. The amount of ERD over C3 and C4 did not significantly differ between the whole group of MS patients and normal subjects (Fig. 1), as well as ERD onset over C3 (MS: K1298.2G639.2 ms; controls: K1593.7G407.8 ms; PZ0.12; Fig. 2). When subdividing MS patients according to their median value of brain TLV (cut-off: 5.15 for T1-TLV, 18.2 for T2-TLV), we obtained a subgroup with higher T1 TLV (mean: 15.5G9.5; range 5.2–35.6), lower T1 TLV (mean: 1.9G1.6; range 0–5.1), higher T2 TLV (mean: 41.8G19.1; range 18.4–73.7) and lower T2 TLV (mean: 2.5G3.2; range 0.2–18). Patients with higher T1 TLV had a significantly delayed ERD onset (mean: K1044G687.1 ms) both compared with patients with lower T1 TLV (mean: K1552.3G483.1 ms; PZ0.02) and with normal subjects (mean: K1593.8G 407.8; PZ0.02) (Fig. 2). ERD onset latency in patients with higher T2 TLV (mean: K1094.1G689.1) was greater than in those with lower T2 TLV (mean: K1502.4G528.5; PZ0.058) and than normal subjects (PZ0.01) (Fig. 2). No significant differences in ERD onset were found between patients with lower T1 TLV or T2 TLV and normal subjects. EDSS was significantly higher in patients with higher T2 TLV (3.8G2.0) than in those with lower T2 TLV
2.6. Statistical analysis The relationship between cortical activation to movement preparation (ERD onset latency) and the amount of brain lesions (T1 and T2 TLV) was investigated using the Spearman’s rank correlation coefficient (rS) for crude correlations and Pearson’s correlation coefficient (rP) when correcting for other variables. Patients were divided in two subgroups according to the amount of TLV (i.e. higher versus lower T1 TLV; higher versus lower T2 TLV), using the median value of the overall distribution as the cut-off value. Differences in ERD onset latency between these subgroups, as well as between the whole patient cohort and a group of healthy normal volunteers (6 males, 10 females, mean age 28G5 years) were analysed using the Mann–Whitney U test.
Fig. 1. Average of percent ERD (event-related desynchronization) of mu oscillations to movement preparation and execution in normal subjects (continuous line) and in MS patients (dotted line) with respect to baseline (between K2.5 and 2.5 s prior to movement, occurring a time 0). Data from the sensorimotor regions contralateral (electrode C3) and ipsilateral (electrode C4) are shown.
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4. Discussion
Fig. 2. Mean ERD onset latency (in ms) with respect to EMG activity, in normal subjects compared with the whole MS group (left pair of columns) and in the MS subgroups obtained by subdividing patients according to their EDSS and to their median value of T2 TLV and of T1 TLV.
(2.5G1.6; PZ0.047), as well as in patients with higher T1-TLV (3.9G2.1) than in those with lower T1-TLV (2.3G1.5; PZ0.02). ERD onset latency was significantly, positively correlated with both T1 TLV (rSZ0.53, PZ0.001; Fig. 3) and T2 TLV (rSZ0.50, PZ0.003; Fig. 3), but not with patients’ EDSS (rSZ0.27; PZ0.13). The correlation between T2 TLV and T1 TLV and the ERD onset latency was not substantially modified after adjustment with the EDSS score (T1 TLVERD: rP after adjustment: 0.50, P: 0.003 versus crude rP: 0.55, PZ0.001; T2 TLV-ERD: rP after adjustment: 0.43, PZ0.01 versus crude rP: 0.49, PZ0.003). This was also confirmed by the fact that the ERD onset latency did not significantly differ when subdividing patients into two subgroups according to EDSS (lower EDSS: range 0–3.0; higher EDSS: range 3.5–6.5), respectively, K1502.5C503.5 versus K1116.7C703.7; PZ0.14) (Fig. 2).
Fig. 3. Brain MRI lesion load and ERD onset latency (in ms) with respect to EMG onset. Negative values in the abscissa indicate ERD latency preceding EMG onset. Dots and broken line represent T2-TLV values and the regression line with ERD onset latency, respectively. Triangles and continuous line represent T1-TLV values and the regression line with ERD onset latency, respectively.
In the present study, we found a correlation between delayed latency of mu ERD preceding voluntary movement and measures of brain damage in MS such as T1 and, to a lesser extent, T2 total lesion load. This correlation was present also when correcting for EDSS, which conversely was not found significantly related with ERD onset latency. Event-related desynchronization (ERD) of the EEG has been interpreted as an electrophysiological correlate of activated cortical areas involved in sensory and motor processing (Pfurtscheller and Lopes da Silva, 1999), based on the observation that increased excitability in thalamo-cortical networks results in a low amplitude desynchronized EEG (Steriade and Llinas, 1988). During preparation of voluntary movement, ERD of the mu rhythm begins over the contralateral sensorimotor area 1.5–2 s before movement (Leocani et al., 1997; Pfurtscheller, 1977), and is considered a correlate of activation of cortical motor circuits preceding movement, even though it may not be considered a direct indicator of the subsequent corticospinal activation (Chen et al., 1998). Several studies (Defebvre et al., 1994, 1996; Magnani et al., 1998, 2002) have shown delayed ERD onset over the contralateral sensorimotor area (electrode C3) during movement preparation in Parkinson’s disease (PD), a disorder in which abnormal motor preparation has been suggested (Marsden, 1982). The evidence that delayed ERD onset to simple self-paced movement is related to dysfunction of cortical circuits involved in motor planning is indirect but several pieces of evidence suggest this view. First, in untreated hemiparkinsonian patients, the ERD onset is more delayed for movements of the affected side (Defebvre et al., 1996). Moreover, the delay or reduced expression of premotor ERD improve after chronic (Defebvre et al., 1998) and acute (Magnani et al., 2002; Wang et al., 1999) L-DOPA treatment and during subthalamic nucleus stimulation (Devos et al., 2004), all factors related to improved clinical motor symptoms. The implications of the latter findings cannot be directly transferred to our results, but the finding that the more MS lesions the patient has (i.e. the more severe the tissue damage), the more delayed the ERD, is consistent with the view that delayed sensorimotor ERD is dysfunctional, at least in relation to a simple motor task performed by naive subjects, as in our experiment. Measurement of T2 and T1 LL partially lacks pathological specificity. Conventional T2-weighted MRI scans have a high sensitivity in revealing MS lesions, but they lack specificity to further characterize the stages of the pathological process in individual lesions. Edema, demyelination, gliosis and axonal loss (McDonald et al., 1992) all lead to a similar appearance of hyperintensity on T2-weighted images. On the other hand, pathological studies have confirmed that hypointense lesions on chronic hypointense areas on unenhanced T1-weighted images show severe tissue disruption, corresponding to areas of tissue disorganization due to demyelination and/or axonal loss (van Walderveen et al., 1998). The potential of
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T1-weighted MRI abnormalities as pathologically specific MRI markers of MS severity has been emphasized by crosssectional (van Walderveen et al., 1998) and longitudinal (Truyen et al., 1997) studies. Even though lesion hypointensity may also occur acutely and transiently in the case of inflammatory edema (with subsequent return to isointensity), the latter condition is unlikely to have contributed to the measures obtained from patients included in our study, being all of them relapse-free for at least a month. The stronger relationship between delayed ERD and T1-TLV compared with T2-TLV suggests that abnormal motor programming revealed by ERD analysis is more related to the severity of tissue loss rather than to other consequences of inflammation. Movement preparation involves complex functional interactions between basal ganglia, supplementary motor area and primary motor cortex (Jurgens, 1984). Our finding of delayed ERD onset in patients with more severe measures of brain damage suggests that functional cortico-cortical and cortico-subcortical connections underlying the expression of ERD during programming of voluntary movement are disrupted by the MS related pathological process. Further studies are needed in order to define the impact of more specific measures of tissue damage and to evaluate the role of specific anatomical cortico-subcortical circuits in determining this abnormality. Acknowledgements This study was supported by a grant from the ‘Fondazione Italiana Sclerosi Multipla’ (project 2001/R/37). We would like to thank Andrea Nossa, R.EEGT, for EEG recordings. References Chen R, Yaseen Z, Cohen LG, Hallett M. Time course of corticospinal excitability in reaction time and self-paced movements. Ann Neurol 1998;44:317–25. Comi G, Filippi M, Martinelli V, Sirabian G, Visciani A, Campi A, Mammi S, Rovaris M, Canal N. Brain magnetic resonance imaging correlates of cognitive impairment in multiple sclerosis. J Neurol Sci 1993;115:66–73. Defebvre L, Bourriez JL, Dujardin K, Derambure P, Destee A, Guieu JD. Spatiotemporal study of Bereitschaftspotential and event-related desynchronization during voluntary movement in Parkinson’s disease. Brain Topogr 1994;6:237–44. Defebvre L, Bourriez JL, Destee A, Guieu JD. Movement-related desynchronisation pattern preceding voluntary movement in untreated Parkinson’s disease. J Neurol Neurosurg Psychiatry 1996;60:307–12. Defebvre L, Bourriez JL, Derambure P, Duhamel A, Guieu JD, Destee A. Influence of chronic administration of L-DOPA on event-related desynchronization of mu rhythm preceding voluntary movement in Parkinson’s disease. Electroencephalogr Clin Neurophysiol 1998;109: 161–7.
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