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A method to monitor corticomotor excitability during passive rhythmic movement of the upper limb
Brain Research Protocols 8 (2001) 82–87 www.elsevier.com / locate / bres
Protocol
A method to monitor corticomotor excitability during passive rhythmic movement of the upper limb Gwyn N. Lewis*, Winston D. Byblow Human Motor Control Laboratory, Department of Sport and Exercise Science, University of Auckland, Private Bag 92019, Auckland, New Zealand Accepted 26 June 2001
Abstract A procedure is outlined in which the excitability of the corticomotor pathway is examined during rhythmic, passive upper limb movement. Using a custom built apparatus and software, wrist flexion–extension movements of a programmable frequency, amplitude and duration are induced while transcranial magnetic stimuli are delivered to the contralateral cortex over the area representing the flexor carpi radialis muscle. Stimuli are timed to occur during different phases of the movement cycle in order to examine the influence of ascending sensory input on the excitability of the corticospinal pathway. The protocol enables modulations in evoked responses to be analysed during movement of different frequencies and amplitudes, and permits alterations in cortical excitability to be examined by using paired pulse paradigms. The technique may also be utilised to examine hemispheric and segmental transfer if a stationary target limb is probed while the contralateral limb is passively moved. The protocol has potential use in examining corticomotor excitability in subjects with deficits in sensory and / or motor function, such as patients with Parkinson’s disease or individuals recovering from stroke. 2001 Elsevier Science B.V. All rights reserved. Theme: Motor systems and sensorimotor integration Topic: Control of posture and movement Keywords: Transcranial magnetic stimulation; Motor cortex; Passive movement; Ia Afferent
1. Type of research 1. Internationally codified basic principles and procedures for clinical applications on transcranial magnetic stimulation (TMS) in man [7]. 2. Investigation of corticomotor excitability during different phases of passive rhythmic movement of the upper limb [3,5]. 3. Investigation of corticomotor excitability during different phases of passive rhythmic movement of the contralateral upper limb [3].
2. Placement of electromyography (EMG) recording electrodes and reference cap: 15 min. 3. Determination of ‘hot spot’ and excitability thresholds: 15 min. 4. Test session of passive movement and static trials: 60–90 min depending on protocol. 5. Data processing and analysis: 50 min. 6. Total protocol: 150–180 min.
3. Materials
3.1. Subject information 2. Time required 1. Completion of handedness and TMS safety questionnaires: 10 min.
Edinburgh Handedness questionnaire [6] and TMS safety checklist.
3.2. Electromyography *Corresponding author. Tel.: 164-9-373-7599, ext. 3766; fax: 164-9373-7043. E-mail address: [email protected] (G.N. Lewis).
Ag /AgCl surface electrodes (Hydrospot, Physiometrix, MA, USA), amplifiers (Grass P511), MacLab 12 bit A / D
1385-299X / 01 / $ – see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S1385-299X( 01 )00093-9
G.N. Lewis, W.D. Byblow / Brain Research Protocols 8 (2001) 82 – 87
acquisition system (ADInstruments, NSW, Australia), PC with appropriate software (Scope, ADInstruments, NSW, Australia).
3.3. Magnetic stimulation Cotton cap with pre-marked grid for location of scalp stimulation sites, figure-of-eight stimulating coil (diameter 70 mm each), Magstim 200 stimulators and BiStim unit (Magstim, Whitland, Dyfed), subject chair with neck rest / head support and clamp system for holding stimulating coil.
3.4. Manipulanda Custom-built manipulandum consisting of a hand piece mounted on a steel framed table (61 cm wide344 cm deep373 cm high) and top plate (Fig. 1). The hand piece is a flat vertically-orientated plate with two adjustable posts on the dorsal side for securing the hand in position. The proximal end of the hand piece is mounted on a rotating shaft located coaxially with the wrist joint, enabling free rotation of the hand in the sagittal plane. The shaft of the hand piece is connected to a potentiometer with a 12-V power supply. The outer boundary of the top plate is drilled with holes corresponding to 58 increments of hand piece (wrist joint) angle, from 2908 through to 1908. The hand piece is able to be constrained statically to any angle by placing steel pins through the top plate holes
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on either side of the hand piece while located at the appropriate position. An AC Servo motor (Baldor, Fort Smith, AR, USA) is mounted underneath the unit and is coupled to the shaft of the manipulandum. The motor is driven by a Baldor D3S Motor Drive and a PMAC motion control card (Delta Tau Data, Northridge, CA, USA). Specification of movement amplitude, frequency and duration of the hand piece and monitoring of potentiometer signals is achieved via a PC with custom-built LabVIEW (National Instruments, TX, USA) routines and a National Instruments 16 bit A / D converter (e.g. PCI-MIO-16XE-50). Potentiometer output is calibrated regularly to ensure accuracy of recorded displacement data. In the event of a system malfunction, adjustable magnetic switches and physical stops at the extreme ranges of joint angle prevent over-rotation of the wrist, and a footswitch device for the subjects and a hand button for the experimenters provide mechanisms to immediately disengage the motor during a trial. For protocols involving bimanual tasks, a second manipulandum is utilised. This unit is a replication of the first with the exception of the motor, i.e. the hand piece can only be actively moved by the subject. A potentiometer is attached to the shaft of the hand piece so that displacement data can also be collected from the second manipulandum.
3.5. Data processing and analysis Unix workstation for data processing, SuperANOVA
Fig. 1. Top view of the manipulandum set up for use with the left hand. The motor is located underneath the unit.
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software (Abacus Concepts, Berkeley, CA, USA) for statistical analysis of data.
4. Detailed procedure (i) Subjects complete the TMS safety checklist to ensure they have no contraindications to TMS. Handedness of the subjects is assessed using the Edinburgh Handedness Questionnaire [6]. (ii) The subject is seated in the chair with their shoulders in slight abduction (10–208), elbows at 90–1108 and forearms supported and in a neutral position. The hand is inserted and secured into the hand piece so that the wrist joint is aligned coaxially with the shaft of the manipulanda. A neck support is positioned at the base of the occipital lobe with the subject’s head resting lightly upon it. (iii) EMG electrodes are placed 2 cm apart on the belly of the flexor carpi radialis (FCR) muscle in the proximal forearm. For each stimulus, 100 ms of EMG data is collected, plus an additional 20 ms prior to stimulus onset. EMG signals are sampled at 4000 Hz, amplified (Grass P511) and bandpass filtered (30–2000 Hz). (iv) The stimulus cap is placed over the subject’s head and securely fastened using velcro straps. The cap has pre-marked grid locations (1-cm intervals) on the anterior two-thirds. The grid centre (0,0) is carefully aligned at the intersection of the subject’s inter-aural and inion-nasion lines (vertex). (v) Suprathreshold magnetic stimuli are delivered through a figure-of-eight coil over the cortex contralateral to the driven manipulandum. The coil is orientated at an angle 458 to the midline and tangential to the scalp, such that the induced current flow is in an anterior–posterior direction along the motor strip [10]. To determine the optimal site of stimulation the coil is systematically moved around the grid locations and eight stimuli delivered at each. Evoked responses are averaged on-line to determine the site eliciting motor evoked potentials (MEPs) of the largest amplitude. This site is defined as the ‘hot spot’. Once determined, the stimulating coil is clamped in position at this location with care taken to maintain coil orientation, and all further stimuli are delivered with the coil in this position. The position and orientation of the coil in relation to the subject’s head are checked repeatedly through the test session. (vi) The excitability threshold for the subject’s FCR muscle is determined by incrementing and decrementing stimulus intensity in 2–3% intervals until MEPs of the appropriate size are elicited. Rest threshold is defined as the minimum intensity at which four of eight consecutive stimuli yield a response of at least 50 mV [7]. Active threshold is defined as the minimum intensity at which four of eight consecutive stimuli yield a discernable MEP (|100 mV) while the FCR is activated at 10% maximum
voluntary contraction MVC [7]. A visual display of EMG activity at high gain is used to guide the subjects in obtaining the required level of activation. Test stimulus intensity for TMS is set to 110–120% of each individual’s rest threshold. For paired TMS, conditioning stimulus intensity is set as 90% of active threshold [1,4,9]. (vii) A static trial is completed by delivering eight stimuli at test stimulus intensity while the target limb is at rest and constrained at a specified angle on the top plate. This may be neutral (08) or any other angle within wrist joint range of motion (290 to 908). (viii) Motion of the driven hand piece is determined and initiated by running a custom built programme 1 (LabVIEW) which specifies trial duration (e.g. 60 s) and outputs a voltage to be interpreted by the A / D converter of the motion control card to specify movement amplitude (e.g. 908) and movement frequency (e.g. 1 Hz). TMS stimuli are delivered during the passive movement trial (Fig. 2). The timing of stimuli is determined by an interactive cursor-positioning function that enables stimuli to be added to the input file relevant to hand piece angle (6less than 18) and / or time (6less than 1 ms). Stimuli are programmed to be delivered in eight distinct phases of the movement cycle, the location of which is determined by dividing the flexion–extension cycle (peak flexion to peak flexion) into eight even intervals of time and establishing the centre of this time period. Eight stimuli are delivered per trial, one in each phase of the movement cycle. Several input files are created so that the order of cycle phases is randomised between trials. For each condition, eight passive movement trials are completed in order to collect eight MEPs per phase. Visual feedback is provided to assist the subjects in maintaining EMG silence in the target FCR muscle during movement. Static trials may be repeated during or after the passive movement trials. (ix) Procedures may be repeated with variations in protocol, such as: different frequencies of movement; different movement amplitudes; alternative target muscle / s; use of a paired pulse paradigm with subthreshold conditioning stimuli to investigate intracortical inhibition and facilitation; concurrent activation of the limb ipsilateral to stimulation, such as in a tracking task; stimulation of a static target limb while the contralateral limb undergoes passive movement. (x) Data are processed and analysed using custom built routines housed on a Unix workstation. For each response collected the root mean square (rms) amplitude of EMG activity 10 ms prior to the stimulus is determined and responses are removed from further analysis if EMG silence is not maintained in this period. All remaining responses in each of the cycle phases and conditions are averaged and MEP parameters such as amplitude, area and latency are measured. MEP parameters from the different
1
Programme available upon request (e-mail: [email protected]).
G.N. Lewis, W.D. Byblow / Brain Research Protocols 8 (2001) 82 – 87
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Fig. 2. (A) An input file specifying a 60-s passive movement trial with eight stimuli delivered. The top panel indicates the specified motion of the hand piece. Note the ramping periods at the beginning and end of the trial to slowly bring hand piece motion up to and down from the specified amplitude (908). The bottom panel indicates the timing of the TMS stimuli. Time (in seconds) is shown along the bottom of the figure. (B) One movement cycle showing the angle and position of the wrist joint at the eight cycle phases.
phases of passive movement are expressed as relative to static MEP values to provide an indication of modulations in MEP parameters during movement relative to resting conditions. (xi) Group data are statistically analysed using repeated measures ANOVAs with a Hunyh-Feldt correction factor. Main effects and interactions are investigated using Bonferroni adjusted t-tests.
5. Results The protocol has demonstrated distinct modulations in MEP amplitude and latency during different phases of the passive movement cycle [3,5] (Fig. 3). In general, response amplitude in the FCR muscle is inhibited or comparable to static values during the extension phase of the movement, and is markedly potentiated during the flexion phase. Modulations in response amplitude persist after accounting for the effects of changes in corticomotor excitability due to alterations in static position. These effects have been noted in movement frequencies from 0.2 to 1.0 Hz and movement amplitudes from 50 to 1008. Greater modulations in response amplitude are revealed when higher frequencies of movement are induced. Investigations of alternative musculature have demonstrated reciprocal, although less marked, modulatory effects in the extensor carpi radialis (ECR) muscle. Response amplitude in the ECR is greatest during the extension phase of the movement cycle and relatively inhibited
during the phases of wrist flexion. In contrast, examination of response amplitude in the abductor pollicis brevis (APB) muscle, which shares a common innervation to the FCR but is not manipulated during passive wrist movement, has revealed a lack of modulation in response amplitude during the different movement cycle phases. With the use of a paired pulse paradigm with subthreshold conditioning stimuli we have been able to show alterations in the extent of intracortical inhibition throughout the various phases of the movement cycle, whereas intracortical facilitation appears to remain relatively consistent across the cycle phases. In alternative paradigms, significant modulations in FCR and ECR response amplitude have also been demonstrated when the target limb is static and the contralateral limb is passively moved. In this condition, modulations in MEP amplitude are opposite to that obtained when the ipsilateral limb is stimulated, i.e. FCR and ECR response amplitude is relatively facilitated in the extension and flexion phases, respectively.
6. Discussion The use of a passive movement paradigm in conjunction with TMS allows us to assess how sensory information elicited during movement influences the excitability of the descending corticomotor pathway while the musculature is quiescent. The manipulanda and associated software utilised in the current protocol provide a means for accurately specifying and controlling the nature of the induced
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motoneuron excitability during passive movement are likely given the extensive pathways and interconnections with peripheral receptors and interneurons at this level, however the results obtained when using a paired-pulse paradigm have also suggested a contribution from cortical regions [5]. The use of alternative target musculature has also suggested that alterations in excitability are specific to the musculature receiving proprioceptive stimulation, and that the noted effects are more marked in musculature with greater cortical representation and corticospinal input. Further investigations in this area have the potential to elucidate more precisely the influence of sensory input on motor output, which has applications to a wide variety of areas in motor control. The use of two manipulanda also opens further areas of research on the transfer and influence of sensory information between hemispheres (at the spinal or cortical level), during both active and passive movement protocols.
6.1. Troubleshooting
Fig. 3. MEPs collected from the FCR muscle during the eight phases of passive wrist flexion–extension. One movement cycle is from peak flexion to peak flexion.
movement, and enables the delivery of magnetic stimuli to be precisely positioned and timed. The ability to accurately control the delivery of magnetic stimuli means that responses can be reliably evoked in comparable joint positions when required, reducing the total number of stimuli that are delivered, and permits a more detailed investigation of changes in pathway excitability during the movement cycle. The ability to specify various movement frequencies of the hand piece has enabled us to highlight the likely importance of Ia muscle afferent output to the changes in response amplitude evident [5]. This finding suggests that the protocol may be sensitive to alterations in afferent information and / or processing of sensory information, and future investigations are planned to use the experimental paradigm to examine proposed deficits in kinesthesia in Parkinson’s disease patients. Using the standard protocol, we are unable to determine the level of the neuroaxis at which receptor output may be influencing the excitability of the descending motor pathway. Substantial changes in
Although TMS is a non-invasive and relatively painless procedure, not all subjects are tolerant of stimulation for long periods, and appropriate responses can not be elicited from all subjects and musculature. The examination of upper limb musculature reduces the intensity of stimulation required and enhances the likelihood of evoking a suitable response [2,8]. Appropriate EMG electrodes and leads must be used to eliminate the occurrence of noise in the EMG signals related to activation of the motor, particularly when the target muscle is located in the hand undergoing motion. Not all subjects are able to maintain EMG silence in forearm musculature during movement, particularly at high movement frequencies. The provision of practice trials with visual or auditory feedback of EMG activity at a high gain generally enhances the subject’s ability to maintain quiescence. Longer recording sessions can become fatiguing for the subjects, leading to reductions in alertness. This may impact on MEP amplitude measures. Providing stimuli such as mathematical equations to solve can relieve this and also help to maintain a constant level of alertness throughout the test session.
7. Quick procedure (i) TMS safety checklist and subject handedness questionnaire completed. (ii) Subject is seated in front of the manipulanda and the limbs are positioned appropriately. A neck support is added to reduce subject head movement. (iii) EMG electrodes are applied to the subject’s target FCR muscle.
G.N. Lewis, W.D. Byblow / Brain Research Protocols 8 (2001) 82 – 87
(iv) The stimulus cap is securely placed on the subject’s head and aligned with the vertex. (v) Magnetic stimuli are delivered by a figure-of-eight coil at various grid sites to locate the hot spot for eliciting MEPs in the FCR muscle. (vi) The subject’s rest and active excitability thresholds are determined. Test stimulus intensity is set as 110–120% of rest threshold, conditioning stimulus intensity (for paired TMS) is set as 90% of active threshold. (vii) TMS stimuli are delivered with the hand at rest and stationary (static trials). (viii) TMS stimuli are delivered during eight phases of passive movement of the contralateral limb (passive movement trials). Eight trials for each condition are completed. Subjects receive visual feedback to help maintain EMG silence in the target muscle. (ix) Protocol is repeated with different trial variations, including the use of different movement parameters, alternative target muscles, conditioning stimuli, and active / passive movement of the limb ipsilateral to stimulation. (x) Data are processed and analysed using custom built routines housed on a Unix workstation. MEP parameters during passive movement are expressed as relative to static trials. (xi) Statistical analysis is performed on the group data.
8. Essential literature references The following are essential references: Refs. [5,7].
Acknowledgements We would like to acknowledge Cheuk (Sing) Chan and Paul Austin for their assistance in the development of the manipulanda. The materials used in this protocol were funded by grants obtained from the University of Auckland Research Committee. G.N. Lewis is supported by a
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scholarship from the Foundation for Research, Science and Technology.
References [1] G. Abbruzzese, A. Assini, A. Buccolieri, R. Marchese, C. Trompetto, Changes of intracortical inhibition during motor imagery in human subjects, Neurosci. Lett. 263 (1999) 113–116. [2] M.D. Caramia, A.M. Pardal, F. Zarola, P.M. Rossini, Electric versus magnetic transcranial stimulation of the brain in healthy humans: a comparative study of the central motor tracts conductivity and excitability, Brain Res. 479 (1989) 89–104. [3] R.G. Carson, W.D. Byblow, S. Riek, G.N. Lewis, J.W. Stinear, Passive movement alters the transmission of corticospinal input to upper limb motoneurons, in: Abstracts For 30th Annual Meeting of Society For Neuroscience, New Orleans, USA, 2000, p. 1231. [4] V. Di Lazzaro, D. Restuccia, A. Oliviero, P. Profice, L. Ferrara, A. Insola, P. Mazzone, P. Tonali, J.C. Rothwell, Magnetic transcranial stimulation at intensities below active motor threshold activates intracortical inhibitory circuits, Exp. Brain Res. 119 (1998) 265– 268. [5] G.N. Lewis, W.D. Byblow, R.G. Carson, Phasic modulation of corticomotor excitability during passive movement of the upper limb: effects of movement frequency and muscle specificity, Brain Res. 900 (2001) 282–294. [6] R.C. Oldfield, The assessment and analysis of handedness: the Edinburgh inventory, Neuropsychologia 9 (1971) 97–113. [7] P.M. Rossini, A.T. Barker, A. Berardelli, M.D. Caramia, G. Caruso, R.Q. Cracco, M.R. Dimitrijevic, M. Hallett, Y. Katayama, C.H. Lucking, C.D. Marsden, N.M.F. Murray, J.C. Rothwell, M. Swash, C. Tomberg, Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application. Report of an IFCN committee, Electroencephalogr. Clin. Neurophysiol. 91 (1994) 79–92. [8] E.M. Wassermann, L.M. McShane, M. Hallett, L.G. Cohen, Noninvasive mapping of muscle representations in human motor cortex, Electroencephalogr. Clin. Neurophysiol. 85 (1992) 1–8. [9] U. Ziemann, J.C. Rothwell, M.C. Ridding, Interaction between intracortical inhibition and facilitation in human motor cortex, J. Physiol. 496 (1996) 873–881. [10] U. Ziemann, F. Tergau, E.M. Wassermann, S. Wischer, J. Hildebrandt, W. Paulus, Demonstration of facilitatory I wave interaction in the human motor cortex by paired transcranial magnetic stimulation, J. Physiol. 511 (1998) 181–190.
Protocol
A method to monitor corticomotor excitability during passive rhythmic movement of the upper limb Gwyn N. Lewis*, Winston D. Byblow Human Motor Control Laboratory, Department of Sport and Exercise Science, University of Auckland, Private Bag 92019, Auckland, New Zealand Accepted 26 June 2001
Abstract A procedure is outlined in which the excitability of the corticomotor pathway is examined during rhythmic, passive upper limb movement. Using a custom built apparatus and software, wrist flexion–extension movements of a programmable frequency, amplitude and duration are induced while transcranial magnetic stimuli are delivered to the contralateral cortex over the area representing the flexor carpi radialis muscle. Stimuli are timed to occur during different phases of the movement cycle in order to examine the influence of ascending sensory input on the excitability of the corticospinal pathway. The protocol enables modulations in evoked responses to be analysed during movement of different frequencies and amplitudes, and permits alterations in cortical excitability to be examined by using paired pulse paradigms. The technique may also be utilised to examine hemispheric and segmental transfer if a stationary target limb is probed while the contralateral limb is passively moved. The protocol has potential use in examining corticomotor excitability in subjects with deficits in sensory and / or motor function, such as patients with Parkinson’s disease or individuals recovering from stroke. 2001 Elsevier Science B.V. All rights reserved. Theme: Motor systems and sensorimotor integration Topic: Control of posture and movement Keywords: Transcranial magnetic stimulation; Motor cortex; Passive movement; Ia Afferent
1. Type of research 1. Internationally codified basic principles and procedures for clinical applications on transcranial magnetic stimulation (TMS) in man [7]. 2. Investigation of corticomotor excitability during different phases of passive rhythmic movement of the upper limb [3,5]. 3. Investigation of corticomotor excitability during different phases of passive rhythmic movement of the contralateral upper limb [3].
2. Placement of electromyography (EMG) recording electrodes and reference cap: 15 min. 3. Determination of ‘hot spot’ and excitability thresholds: 15 min. 4. Test session of passive movement and static trials: 60–90 min depending on protocol. 5. Data processing and analysis: 50 min. 6. Total protocol: 150–180 min.
3. Materials
3.1. Subject information 2. Time required 1. Completion of handedness and TMS safety questionnaires: 10 min.
Edinburgh Handedness questionnaire [6] and TMS safety checklist.
3.2. Electromyography *Corresponding author. Tel.: 164-9-373-7599, ext. 3766; fax: 164-9373-7043. E-mail address: [email protected] (G.N. Lewis).
Ag /AgCl surface electrodes (Hydrospot, Physiometrix, MA, USA), amplifiers (Grass P511), MacLab 12 bit A / D
1385-299X / 01 / $ – see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S1385-299X( 01 )00093-9
G.N. Lewis, W.D. Byblow / Brain Research Protocols 8 (2001) 82 – 87
acquisition system (ADInstruments, NSW, Australia), PC with appropriate software (Scope, ADInstruments, NSW, Australia).
3.3. Magnetic stimulation Cotton cap with pre-marked grid for location of scalp stimulation sites, figure-of-eight stimulating coil (diameter 70 mm each), Magstim 200 stimulators and BiStim unit (Magstim, Whitland, Dyfed), subject chair with neck rest / head support and clamp system for holding stimulating coil.
3.4. Manipulanda Custom-built manipulandum consisting of a hand piece mounted on a steel framed table (61 cm wide344 cm deep373 cm high) and top plate (Fig. 1). The hand piece is a flat vertically-orientated plate with two adjustable posts on the dorsal side for securing the hand in position. The proximal end of the hand piece is mounted on a rotating shaft located coaxially with the wrist joint, enabling free rotation of the hand in the sagittal plane. The shaft of the hand piece is connected to a potentiometer with a 12-V power supply. The outer boundary of the top plate is drilled with holes corresponding to 58 increments of hand piece (wrist joint) angle, from 2908 through to 1908. The hand piece is able to be constrained statically to any angle by placing steel pins through the top plate holes
83
on either side of the hand piece while located at the appropriate position. An AC Servo motor (Baldor, Fort Smith, AR, USA) is mounted underneath the unit and is coupled to the shaft of the manipulandum. The motor is driven by a Baldor D3S Motor Drive and a PMAC motion control card (Delta Tau Data, Northridge, CA, USA). Specification of movement amplitude, frequency and duration of the hand piece and monitoring of potentiometer signals is achieved via a PC with custom-built LabVIEW (National Instruments, TX, USA) routines and a National Instruments 16 bit A / D converter (e.g. PCI-MIO-16XE-50). Potentiometer output is calibrated regularly to ensure accuracy of recorded displacement data. In the event of a system malfunction, adjustable magnetic switches and physical stops at the extreme ranges of joint angle prevent over-rotation of the wrist, and a footswitch device for the subjects and a hand button for the experimenters provide mechanisms to immediately disengage the motor during a trial. For protocols involving bimanual tasks, a second manipulandum is utilised. This unit is a replication of the first with the exception of the motor, i.e. the hand piece can only be actively moved by the subject. A potentiometer is attached to the shaft of the hand piece so that displacement data can also be collected from the second manipulandum.
3.5. Data processing and analysis Unix workstation for data processing, SuperANOVA
Fig. 1. Top view of the manipulandum set up for use with the left hand. The motor is located underneath the unit.
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G.N. Lewis, W.D. Byblow / Brain Research Protocols 8 (2001) 82 – 87
software (Abacus Concepts, Berkeley, CA, USA) for statistical analysis of data.
4. Detailed procedure (i) Subjects complete the TMS safety checklist to ensure they have no contraindications to TMS. Handedness of the subjects is assessed using the Edinburgh Handedness Questionnaire [6]. (ii) The subject is seated in the chair with their shoulders in slight abduction (10–208), elbows at 90–1108 and forearms supported and in a neutral position. The hand is inserted and secured into the hand piece so that the wrist joint is aligned coaxially with the shaft of the manipulanda. A neck support is positioned at the base of the occipital lobe with the subject’s head resting lightly upon it. (iii) EMG electrodes are placed 2 cm apart on the belly of the flexor carpi radialis (FCR) muscle in the proximal forearm. For each stimulus, 100 ms of EMG data is collected, plus an additional 20 ms prior to stimulus onset. EMG signals are sampled at 4000 Hz, amplified (Grass P511) and bandpass filtered (30–2000 Hz). (iv) The stimulus cap is placed over the subject’s head and securely fastened using velcro straps. The cap has pre-marked grid locations (1-cm intervals) on the anterior two-thirds. The grid centre (0,0) is carefully aligned at the intersection of the subject’s inter-aural and inion-nasion lines (vertex). (v) Suprathreshold magnetic stimuli are delivered through a figure-of-eight coil over the cortex contralateral to the driven manipulandum. The coil is orientated at an angle 458 to the midline and tangential to the scalp, such that the induced current flow is in an anterior–posterior direction along the motor strip [10]. To determine the optimal site of stimulation the coil is systematically moved around the grid locations and eight stimuli delivered at each. Evoked responses are averaged on-line to determine the site eliciting motor evoked potentials (MEPs) of the largest amplitude. This site is defined as the ‘hot spot’. Once determined, the stimulating coil is clamped in position at this location with care taken to maintain coil orientation, and all further stimuli are delivered with the coil in this position. The position and orientation of the coil in relation to the subject’s head are checked repeatedly through the test session. (vi) The excitability threshold for the subject’s FCR muscle is determined by incrementing and decrementing stimulus intensity in 2–3% intervals until MEPs of the appropriate size are elicited. Rest threshold is defined as the minimum intensity at which four of eight consecutive stimuli yield a response of at least 50 mV [7]. Active threshold is defined as the minimum intensity at which four of eight consecutive stimuli yield a discernable MEP (|100 mV) while the FCR is activated at 10% maximum
voluntary contraction MVC [7]. A visual display of EMG activity at high gain is used to guide the subjects in obtaining the required level of activation. Test stimulus intensity for TMS is set to 110–120% of each individual’s rest threshold. For paired TMS, conditioning stimulus intensity is set as 90% of active threshold [1,4,9]. (vii) A static trial is completed by delivering eight stimuli at test stimulus intensity while the target limb is at rest and constrained at a specified angle on the top plate. This may be neutral (08) or any other angle within wrist joint range of motion (290 to 908). (viii) Motion of the driven hand piece is determined and initiated by running a custom built programme 1 (LabVIEW) which specifies trial duration (e.g. 60 s) and outputs a voltage to be interpreted by the A / D converter of the motion control card to specify movement amplitude (e.g. 908) and movement frequency (e.g. 1 Hz). TMS stimuli are delivered during the passive movement trial (Fig. 2). The timing of stimuli is determined by an interactive cursor-positioning function that enables stimuli to be added to the input file relevant to hand piece angle (6less than 18) and / or time (6less than 1 ms). Stimuli are programmed to be delivered in eight distinct phases of the movement cycle, the location of which is determined by dividing the flexion–extension cycle (peak flexion to peak flexion) into eight even intervals of time and establishing the centre of this time period. Eight stimuli are delivered per trial, one in each phase of the movement cycle. Several input files are created so that the order of cycle phases is randomised between trials. For each condition, eight passive movement trials are completed in order to collect eight MEPs per phase. Visual feedback is provided to assist the subjects in maintaining EMG silence in the target FCR muscle during movement. Static trials may be repeated during or after the passive movement trials. (ix) Procedures may be repeated with variations in protocol, such as: different frequencies of movement; different movement amplitudes; alternative target muscle / s; use of a paired pulse paradigm with subthreshold conditioning stimuli to investigate intracortical inhibition and facilitation; concurrent activation of the limb ipsilateral to stimulation, such as in a tracking task; stimulation of a static target limb while the contralateral limb undergoes passive movement. (x) Data are processed and analysed using custom built routines housed on a Unix workstation. For each response collected the root mean square (rms) amplitude of EMG activity 10 ms prior to the stimulus is determined and responses are removed from further analysis if EMG silence is not maintained in this period. All remaining responses in each of the cycle phases and conditions are averaged and MEP parameters such as amplitude, area and latency are measured. MEP parameters from the different
1
Programme available upon request (e-mail: [email protected]).
G.N. Lewis, W.D. Byblow / Brain Research Protocols 8 (2001) 82 – 87
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Fig. 2. (A) An input file specifying a 60-s passive movement trial with eight stimuli delivered. The top panel indicates the specified motion of the hand piece. Note the ramping periods at the beginning and end of the trial to slowly bring hand piece motion up to and down from the specified amplitude (908). The bottom panel indicates the timing of the TMS stimuli. Time (in seconds) is shown along the bottom of the figure. (B) One movement cycle showing the angle and position of the wrist joint at the eight cycle phases.
phases of passive movement are expressed as relative to static MEP values to provide an indication of modulations in MEP parameters during movement relative to resting conditions. (xi) Group data are statistically analysed using repeated measures ANOVAs with a Hunyh-Feldt correction factor. Main effects and interactions are investigated using Bonferroni adjusted t-tests.
5. Results The protocol has demonstrated distinct modulations in MEP amplitude and latency during different phases of the passive movement cycle [3,5] (Fig. 3). In general, response amplitude in the FCR muscle is inhibited or comparable to static values during the extension phase of the movement, and is markedly potentiated during the flexion phase. Modulations in response amplitude persist after accounting for the effects of changes in corticomotor excitability due to alterations in static position. These effects have been noted in movement frequencies from 0.2 to 1.0 Hz and movement amplitudes from 50 to 1008. Greater modulations in response amplitude are revealed when higher frequencies of movement are induced. Investigations of alternative musculature have demonstrated reciprocal, although less marked, modulatory effects in the extensor carpi radialis (ECR) muscle. Response amplitude in the ECR is greatest during the extension phase of the movement cycle and relatively inhibited
during the phases of wrist flexion. In contrast, examination of response amplitude in the abductor pollicis brevis (APB) muscle, which shares a common innervation to the FCR but is not manipulated during passive wrist movement, has revealed a lack of modulation in response amplitude during the different movement cycle phases. With the use of a paired pulse paradigm with subthreshold conditioning stimuli we have been able to show alterations in the extent of intracortical inhibition throughout the various phases of the movement cycle, whereas intracortical facilitation appears to remain relatively consistent across the cycle phases. In alternative paradigms, significant modulations in FCR and ECR response amplitude have also been demonstrated when the target limb is static and the contralateral limb is passively moved. In this condition, modulations in MEP amplitude are opposite to that obtained when the ipsilateral limb is stimulated, i.e. FCR and ECR response amplitude is relatively facilitated in the extension and flexion phases, respectively.
6. Discussion The use of a passive movement paradigm in conjunction with TMS allows us to assess how sensory information elicited during movement influences the excitability of the descending corticomotor pathway while the musculature is quiescent. The manipulanda and associated software utilised in the current protocol provide a means for accurately specifying and controlling the nature of the induced
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motoneuron excitability during passive movement are likely given the extensive pathways and interconnections with peripheral receptors and interneurons at this level, however the results obtained when using a paired-pulse paradigm have also suggested a contribution from cortical regions [5]. The use of alternative target musculature has also suggested that alterations in excitability are specific to the musculature receiving proprioceptive stimulation, and that the noted effects are more marked in musculature with greater cortical representation and corticospinal input. Further investigations in this area have the potential to elucidate more precisely the influence of sensory input on motor output, which has applications to a wide variety of areas in motor control. The use of two manipulanda also opens further areas of research on the transfer and influence of sensory information between hemispheres (at the spinal or cortical level), during both active and passive movement protocols.
6.1. Troubleshooting
Fig. 3. MEPs collected from the FCR muscle during the eight phases of passive wrist flexion–extension. One movement cycle is from peak flexion to peak flexion.
movement, and enables the delivery of magnetic stimuli to be precisely positioned and timed. The ability to accurately control the delivery of magnetic stimuli means that responses can be reliably evoked in comparable joint positions when required, reducing the total number of stimuli that are delivered, and permits a more detailed investigation of changes in pathway excitability during the movement cycle. The ability to specify various movement frequencies of the hand piece has enabled us to highlight the likely importance of Ia muscle afferent output to the changes in response amplitude evident [5]. This finding suggests that the protocol may be sensitive to alterations in afferent information and / or processing of sensory information, and future investigations are planned to use the experimental paradigm to examine proposed deficits in kinesthesia in Parkinson’s disease patients. Using the standard protocol, we are unable to determine the level of the neuroaxis at which receptor output may be influencing the excitability of the descending motor pathway. Substantial changes in
Although TMS is a non-invasive and relatively painless procedure, not all subjects are tolerant of stimulation for long periods, and appropriate responses can not be elicited from all subjects and musculature. The examination of upper limb musculature reduces the intensity of stimulation required and enhances the likelihood of evoking a suitable response [2,8]. Appropriate EMG electrodes and leads must be used to eliminate the occurrence of noise in the EMG signals related to activation of the motor, particularly when the target muscle is located in the hand undergoing motion. Not all subjects are able to maintain EMG silence in forearm musculature during movement, particularly at high movement frequencies. The provision of practice trials with visual or auditory feedback of EMG activity at a high gain generally enhances the subject’s ability to maintain quiescence. Longer recording sessions can become fatiguing for the subjects, leading to reductions in alertness. This may impact on MEP amplitude measures. Providing stimuli such as mathematical equations to solve can relieve this and also help to maintain a constant level of alertness throughout the test session.
7. Quick procedure (i) TMS safety checklist and subject handedness questionnaire completed. (ii) Subject is seated in front of the manipulanda and the limbs are positioned appropriately. A neck support is added to reduce subject head movement. (iii) EMG electrodes are applied to the subject’s target FCR muscle.
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(iv) The stimulus cap is securely placed on the subject’s head and aligned with the vertex. (v) Magnetic stimuli are delivered by a figure-of-eight coil at various grid sites to locate the hot spot for eliciting MEPs in the FCR muscle. (vi) The subject’s rest and active excitability thresholds are determined. Test stimulus intensity is set as 110–120% of rest threshold, conditioning stimulus intensity (for paired TMS) is set as 90% of active threshold. (vii) TMS stimuli are delivered with the hand at rest and stationary (static trials). (viii) TMS stimuli are delivered during eight phases of passive movement of the contralateral limb (passive movement trials). Eight trials for each condition are completed. Subjects receive visual feedback to help maintain EMG silence in the target muscle. (ix) Protocol is repeated with different trial variations, including the use of different movement parameters, alternative target muscles, conditioning stimuli, and active / passive movement of the limb ipsilateral to stimulation. (x) Data are processed and analysed using custom built routines housed on a Unix workstation. MEP parameters during passive movement are expressed as relative to static trials. (xi) Statistical analysis is performed on the group data.
8. Essential literature references The following are essential references: Refs. [5,7].
Acknowledgements We would like to acknowledge Cheuk (Sing) Chan and Paul Austin for their assistance in the development of the manipulanda. The materials used in this protocol were funded by grants obtained from the University of Auckland Research Committee. G.N. Lewis is supported by a
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scholarship from the Foundation for Research, Science and Technology.
References [1] G. Abbruzzese, A. Assini, A. Buccolieri, R. Marchese, C. Trompetto, Changes of intracortical inhibition during motor imagery in human subjects, Neurosci. Lett. 263 (1999) 113–116. [2] M.D. Caramia, A.M. Pardal, F. Zarola, P.M. Rossini, Electric versus magnetic transcranial stimulation of the brain in healthy humans: a comparative study of the central motor tracts conductivity and excitability, Brain Res. 479 (1989) 89–104. [3] R.G. Carson, W.D. Byblow, S. Riek, G.N. Lewis, J.W. Stinear, Passive movement alters the transmission of corticospinal input to upper limb motoneurons, in: Abstracts For 30th Annual Meeting of Society For Neuroscience, New Orleans, USA, 2000, p. 1231. [4] V. Di Lazzaro, D. Restuccia, A. Oliviero, P. Profice, L. Ferrara, A. Insola, P. Mazzone, P. Tonali, J.C. Rothwell, Magnetic transcranial stimulation at intensities below active motor threshold activates intracortical inhibitory circuits, Exp. Brain Res. 119 (1998) 265– 268. [5] G.N. Lewis, W.D. Byblow, R.G. Carson, Phasic modulation of corticomotor excitability during passive movement of the upper limb: effects of movement frequency and muscle specificity, Brain Res. 900 (2001) 282–294. [6] R.C. Oldfield, The assessment and analysis of handedness: the Edinburgh inventory, Neuropsychologia 9 (1971) 97–113. [7] P.M. Rossini, A.T. Barker, A. Berardelli, M.D. Caramia, G. Caruso, R.Q. Cracco, M.R. Dimitrijevic, M. Hallett, Y. Katayama, C.H. Lucking, C.D. Marsden, N.M.F. Murray, J.C. Rothwell, M. Swash, C. Tomberg, Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles and procedures for routine clinical application. Report of an IFCN committee, Electroencephalogr. Clin. Neurophysiol. 91 (1994) 79–92. [8] E.M. Wassermann, L.M. McShane, M. Hallett, L.G. Cohen, Noninvasive mapping of muscle representations in human motor cortex, Electroencephalogr. Clin. Neurophysiol. 85 (1992) 1–8. [9] U. Ziemann, J.C. Rothwell, M.C. Ridding, Interaction between intracortical inhibition and facilitation in human motor cortex, J. Physiol. 496 (1996) 873–881. [10] U. Ziemann, F. Tergau, E.M. Wassermann, S. Wischer, J. Hildebrandt, W. Paulus, Demonstration of facilitatory I wave interaction in the human motor cortex by paired transcranial magnetic stimulation, J. Physiol. 511 (1998) 181–190.