- Email: [email protected]
The brain's intention to imitate: The neurobiology of intentional versus automatic imitation
314
Abstracts
muscles. Here, we investigated in 14 healthy volunteers the effect of parametric increases in isometric dorsi- and plantarflexion of the right foot on the size of tibialis anterior (TA) MEPs on the left side, which remained at rest. Transcranial magnetic stimulation (TMS) was used to test the TA MEPs on the left side at rest and during 10, 30, and 70% of a maximum voluntary dorsi- or plantarflexion of the right foot. EMG from the left resting TA muscle was comparable across conditions. The size of the left TA MEPs was significantly facilitated during 70% of dorsiflexion but not plantarflexion of the right foot. In order to investigate the possible mechanisms involved in this facilitation the left TA H-reflex and shortinterval intracortical inhibition (SICI) on the right hemisphere were tested during dorsiflexion of the right foot. SICI was reduced during 70% of dorsiflexion of the right foot. In three of the four subjects, in whom a TA H-reflex was elicited at rest, the TA reflex size was depressed. These results suggest that a unilateral voluntary contraction of a lower limb muscle influences the excitability of contralateral intracortical and spinal motoneurones, possibly through activation of interhemispheric connections at the cortical level and commissural interneurones at the spinal level. References: 1. Hortobagyi T, Taylor JL, Petersen NT, Russell G, Gandevia SC (2003) Changes in segmental and motor cortical output with contralateral muscle contractions and altered sensory inputs in humans. J Neurophysiology 90:2451-2459. 2. Perez MA and Cohen LG (2008) Mechanisms underlying functional changes in the primary motor cortex ipsilateral to an active hand. J Neurosci 28(22):5631-5640.
TMS Poster Only 234
Reducing the TMS mapping acquisition time
Grey M, Willerslev-Olsen M, University of Copenhagen (Copenhagen, DK) Objective: Transcranial Magnetic Stimulation (TMS) mapping of motor cortex excitability (Wassermann et al, 1992) is used to assess changes in corticospinal excitability in motor control and neurorehabilitation studies. The advent of real-time frameless stereotaxy improves accuracy and repeatability of coil placement/orientation. Here, we describe a modification of the traditional TMS mapping technique that reduces the number of stimuli required to produce a reliable map. Methods: Subjects were seated with the right arm supported and the wrist pronated. Surface electromyography was used to record motor evoked potentials (MEPs) in first dorsal interosseous (FDI) while the subjects held a small (w5% maximum) voluntary contraction. TMS was delivered at 0.8 Hz with a MagStim Rapid stimulator via a batwing design coil placed within an 8 3 8cm grid approximately centred over the hand area of the motor cortex. Stimulation intensity was set to 120% of the active FDI motor threshold when positioned at the hotspot. Coil position and orientation were monitored in real-time with frameless stereotaxy. For each stimulus, spatial coordinates and the MEP were recorded for offline analysis. In a conventional protocol, 3 MEPs were elicited at each of 64 points within the grid (192 stimuli). In a second protocol, 192 stimuli were elicited at randomly locations in the grid. The maps were compared with a correlation analysis using p , 0.05. Results: The maps produced with two protocols had a mean correlation coefficient of r 5 0.8 6 0.1. To determine the minimum number of stimuli needed to produce a reliable map, correlation coefficients were calculated between the conventional and random maps using successively fewer trials from the data acquired with the random protocol. Correlation coefficients began to exceed the 95% confidence interval when maps were limited to the first 35 6 25 stimuli from the random protocol. Conclusions: Frameless stereotaxy can be used to improve the accuracy TMS cortical excitability maps. We have shown that maps can be produced
with as few as 35 stimuli. At twice the standard deviation observed here (i.e. 85 stimuli), a reliable map can be recorded in as little as 68 seconds. Minimizing the acquisition time for this assessment will allow better timeresolution of excitability changes over time. Wassermann et al., 1992. Noninvasive mapping of muscle representations in human motor cortex. Electroencephalogr. Clin. Neurophysiol. 85,1–8.
TMS Poster Only 235
The brain’s intention to imitate: The neurobiology of intentional versus automatic imitation
Bien N, Roebroeck A, Goebel R, Sack AT, Maastricht University (Maastricht, NL) Objective: Imitation behavior is of utmost importance for human beings in their daily life. The mirror neuron system enabling us to imitate observed actions is considered to be involved in an array of processes including action recognition and action understanding. According to mirror neuron theory, action observation leads to an urge to imitate the observed action [1]. However, since such automatic imitation is not always appropriate, an inhibitive component keeping us from imitating everything we see seems equally crucial for an effective social behavior. The goal of the current study was to identify, functionally dissociate and specifically manipulate the neural correlates of this proposed inhibition of automatic imitation. Method: Time-resolved functional brain imaging was combined with effective brain connectivity analyses to reveal the cortical information flow during the execution of a stimulus-response-compatibility paradigm (fig. 1). FMRI-guided TMS (fig. 2) dentified the underlying functional dissociation by revealing the specific functional contribution of each involved brain area for successful imitation and the inhibition of imitation. Results: Within the identified connectivity network, right premotor cortex was functionally relevant for the process of automatic imitation. In contrast, right middle frontal gyrus was involved in general response inhibition, whereas left frontoparietal opercular cortex showed to be functionally relevant for the specific inhibition of automatic imitation, serving as a final gating mechanism for intentional imitation.
Conclusion: These findings suggest a functional dissociation between automatic and intentional imitation, as supported by some neuropsychological literature [2]. According to the neurobiological model presented in
Abstracts our study (fig. 3), patients suffering from echopraxia or obstinate imitation behavior may suffer from sustained defects at one or several levels of the revealed network, resulting in either increased imitation, or decreased inhibition, or combination of both. 1. Rizzolatti, G. and M.A. Arbib, Language within our grasp. Trends Neurosci, 998. 215: p. 188-94.
315 effects of vibration on projections to non-vibrated muscles were restored. This was associated with a significant improvement in motor control during piano playing as objectively shown in the MIDI data and the BMF and TCS scores. Patients perceived this improvement to last for up to 24hours. Conclusion: Proprioceptive training applied for only 15min significantly and immediately restored a differential pattern of SMO in musician’s dystonia and improved motor performance on the piano objectively and subjectively for up to 24 hours. This intervention might be a highly promising tool for rehabilitation of hand motor dysfunction.
tDCS Poster Only 237
Anodal tDCS over left M1 modulates corticomotor excitability bilaterally
Dundas JE, Thickbroom G, Mastaglia FL, Fox A, University of Western Australia (Perth, AU)
2. Lhermitte, F., B. Pillon, and M. Serdaru, Human autonomy and the frontal lobes. Part I: Imitation and utilization behavior: a neuropsychological study of 75 patients. Ann Neurol, 1986. 19(4): p. 326-34.
TMS Poster Only 236
Behavioural and neurophysiological effects of proprioceptive training in musician’s dystonia
Rosenkranz K1, Butler K2, Williamon A3, Rothwell J1, 1Institute of Neurology (London, UK); 2Princess Grace Hospital (London, UK); 3 Royal College of Music (London, UK) Objective: Sensorimotor organiation (SMO) is abnormal in musician’s dystonia but has been shown to be restored by a 15min intervention with proprioceptive stimulation. However, it is unclear whether this neurophysiological effect is associated with an improvement in motor control. This study assessed whether 15min of proprioceptive training improves SMO of the motorcortical hand area and the motor control in musician’s dystonia. Methods: Six musician’s dystonia patients who all showed a task-specific ring finger flexion while playing the piano, five healthy pianists and six healthy non-musicians were recruited. Proprioceptive training lasted 15min and consisted of attended muscle vibration applied discontinuously to one of three hand muscles at random. Before and after proprioceptive training, the SMO was explored by measuring changes in short-interval intracortical inhibition (SICI) during short periods of hand muscle vibration, the performance of a five-finger exercise was objectively evaluated by a MIDI piano, and subjects rated their performance subjectively on visual-analogue scales. The expression of dystonic symptoms were scored on the BMF and Tubiana-Chamagne scales (TCS). Results: At baseline, the SMO in healthy subjects was spatially differentiated: SICI is reduced in projections to the vibrated, but enhanced to the non-vibrated muscles. In musician´s dystonia this pattern was completely abolished. Proprioceptive training strengthened the spatial differentiation of SMO in all groups. Particularly in musician’s dystonia, the inhibitory
Objective: Transcranial direct current stimulation (tDCS) modulates excitability in the cortical area directly beneath the stimulating electrode, but recent studies suggest it might also induce effects in distant brain regions by modulating the activity of interconnected areas. As prolonged tDCS-effects on motor cortex (M1) excitability have been well established and anatomical connections are known to exist between both motor cortices, we aimed to study whether tDCS over the left M1 affected excitability in the homologous region of the unstimulated, contralateral motor cortex. Method: Eight participants received 10 min anodal tDCS (1mA) with the cathode positioned over the contralateral supraorbita. Motor evoked potentials (MEPs) from single pulse transcranial magnetic stimulation (TMS) were used to assess cortical excitability in left and right motor cortices every 5 mins for 30 min following stimulation. Results: During this period left motor cortex excitability increased (av. change in MEP amplitude: 12.6% 68.2; p , 0.05) and right motor cortex excitability decreased (av. change in MEP amplitude: 82.2% 66.4; p , 0.05). Conclusion: Our results demonstrate that anodal stimulation of the left M1 can modulate corticomotor excitability levels bilaterally - enhancing left M1 and suppressing right M1 excitability - presumably by modulating the activity in transcallosal and subcortical pathways interconnecting both motor cortices. These findings have implications for neurorehabilitation interventions assisting motor recovery after stroke.
TMS Poster Only 238
Silent period (SP) to transcranial magnetic stimulation: the EEG substrate
Kimiskidis VK1, Papagiannopoulos S1, Kazis DA1, Vasiliadis G1, Oikonomidi A1, Sotirakoglou K2, Pseftogianni D1, Anogianakis G1, Vlaikidis N1, 1Aristotle University of Thessaloniki (Thessaloniki, GR); 2 Agricultural University of Athens (Athens, GR) Background: It is now well established that the early part of SP (50-75 ms) is mainly of spinal origin while the later part is related to reduced motor cortex excitability. However, the EEG substrate of SP has not yet been identified. Recent experiments revealed that TMS of the motor cortex evokes a complex EEG response including a negative component peaking at 100 ms (N100) , which is thought to reflect cortical inhibitory processes. We hypothesized that N100 may underlie the later part of SP. Objective: To investigate whether SP duration correlates with N100 amplitude.
Abstracts
muscles. Here, we investigated in 14 healthy volunteers the effect of parametric increases in isometric dorsi- and plantarflexion of the right foot on the size of tibialis anterior (TA) MEPs on the left side, which remained at rest. Transcranial magnetic stimulation (TMS) was used to test the TA MEPs on the left side at rest and during 10, 30, and 70% of a maximum voluntary dorsi- or plantarflexion of the right foot. EMG from the left resting TA muscle was comparable across conditions. The size of the left TA MEPs was significantly facilitated during 70% of dorsiflexion but not plantarflexion of the right foot. In order to investigate the possible mechanisms involved in this facilitation the left TA H-reflex and shortinterval intracortical inhibition (SICI) on the right hemisphere were tested during dorsiflexion of the right foot. SICI was reduced during 70% of dorsiflexion of the right foot. In three of the four subjects, in whom a TA H-reflex was elicited at rest, the TA reflex size was depressed. These results suggest that a unilateral voluntary contraction of a lower limb muscle influences the excitability of contralateral intracortical and spinal motoneurones, possibly through activation of interhemispheric connections at the cortical level and commissural interneurones at the spinal level. References: 1. Hortobagyi T, Taylor JL, Petersen NT, Russell G, Gandevia SC (2003) Changes in segmental and motor cortical output with contralateral muscle contractions and altered sensory inputs in humans. J Neurophysiology 90:2451-2459. 2. Perez MA and Cohen LG (2008) Mechanisms underlying functional changes in the primary motor cortex ipsilateral to an active hand. J Neurosci 28(22):5631-5640.
TMS Poster Only 234
Reducing the TMS mapping acquisition time
Grey M, Willerslev-Olsen M, University of Copenhagen (Copenhagen, DK) Objective: Transcranial Magnetic Stimulation (TMS) mapping of motor cortex excitability (Wassermann et al, 1992) is used to assess changes in corticospinal excitability in motor control and neurorehabilitation studies. The advent of real-time frameless stereotaxy improves accuracy and repeatability of coil placement/orientation. Here, we describe a modification of the traditional TMS mapping technique that reduces the number of stimuli required to produce a reliable map. Methods: Subjects were seated with the right arm supported and the wrist pronated. Surface electromyography was used to record motor evoked potentials (MEPs) in first dorsal interosseous (FDI) while the subjects held a small (w5% maximum) voluntary contraction. TMS was delivered at 0.8 Hz with a MagStim Rapid stimulator via a batwing design coil placed within an 8 3 8cm grid approximately centred over the hand area of the motor cortex. Stimulation intensity was set to 120% of the active FDI motor threshold when positioned at the hotspot. Coil position and orientation were monitored in real-time with frameless stereotaxy. For each stimulus, spatial coordinates and the MEP were recorded for offline analysis. In a conventional protocol, 3 MEPs were elicited at each of 64 points within the grid (192 stimuli). In a second protocol, 192 stimuli were elicited at randomly locations in the grid. The maps were compared with a correlation analysis using p , 0.05. Results: The maps produced with two protocols had a mean correlation coefficient of r 5 0.8 6 0.1. To determine the minimum number of stimuli needed to produce a reliable map, correlation coefficients were calculated between the conventional and random maps using successively fewer trials from the data acquired with the random protocol. Correlation coefficients began to exceed the 95% confidence interval when maps were limited to the first 35 6 25 stimuli from the random protocol. Conclusions: Frameless stereotaxy can be used to improve the accuracy TMS cortical excitability maps. We have shown that maps can be produced
with as few as 35 stimuli. At twice the standard deviation observed here (i.e. 85 stimuli), a reliable map can be recorded in as little as 68 seconds. Minimizing the acquisition time for this assessment will allow better timeresolution of excitability changes over time. Wassermann et al., 1992. Noninvasive mapping of muscle representations in human motor cortex. Electroencephalogr. Clin. Neurophysiol. 85,1–8.
TMS Poster Only 235
The brain’s intention to imitate: The neurobiology of intentional versus automatic imitation
Bien N, Roebroeck A, Goebel R, Sack AT, Maastricht University (Maastricht, NL) Objective: Imitation behavior is of utmost importance for human beings in their daily life. The mirror neuron system enabling us to imitate observed actions is considered to be involved in an array of processes including action recognition and action understanding. According to mirror neuron theory, action observation leads to an urge to imitate the observed action [1]. However, since such automatic imitation is not always appropriate, an inhibitive component keeping us from imitating everything we see seems equally crucial for an effective social behavior. The goal of the current study was to identify, functionally dissociate and specifically manipulate the neural correlates of this proposed inhibition of automatic imitation. Method: Time-resolved functional brain imaging was combined with effective brain connectivity analyses to reveal the cortical information flow during the execution of a stimulus-response-compatibility paradigm (fig. 1). FMRI-guided TMS (fig. 2) dentified the underlying functional dissociation by revealing the specific functional contribution of each involved brain area for successful imitation and the inhibition of imitation. Results: Within the identified connectivity network, right premotor cortex was functionally relevant for the process of automatic imitation. In contrast, right middle frontal gyrus was involved in general response inhibition, whereas left frontoparietal opercular cortex showed to be functionally relevant for the specific inhibition of automatic imitation, serving as a final gating mechanism for intentional imitation.
Conclusion: These findings suggest a functional dissociation between automatic and intentional imitation, as supported by some neuropsychological literature [2]. According to the neurobiological model presented in
Abstracts our study (fig. 3), patients suffering from echopraxia or obstinate imitation behavior may suffer from sustained defects at one or several levels of the revealed network, resulting in either increased imitation, or decreased inhibition, or combination of both. 1. Rizzolatti, G. and M.A. Arbib, Language within our grasp. Trends Neurosci, 998. 215: p. 188-94.
315 effects of vibration on projections to non-vibrated muscles were restored. This was associated with a significant improvement in motor control during piano playing as objectively shown in the MIDI data and the BMF and TCS scores. Patients perceived this improvement to last for up to 24hours. Conclusion: Proprioceptive training applied for only 15min significantly and immediately restored a differential pattern of SMO in musician’s dystonia and improved motor performance on the piano objectively and subjectively for up to 24 hours. This intervention might be a highly promising tool for rehabilitation of hand motor dysfunction.
tDCS Poster Only 237
Anodal tDCS over left M1 modulates corticomotor excitability bilaterally
Dundas JE, Thickbroom G, Mastaglia FL, Fox A, University of Western Australia (Perth, AU)
2. Lhermitte, F., B. Pillon, and M. Serdaru, Human autonomy and the frontal lobes. Part I: Imitation and utilization behavior: a neuropsychological study of 75 patients. Ann Neurol, 1986. 19(4): p. 326-34.
TMS Poster Only 236
Behavioural and neurophysiological effects of proprioceptive training in musician’s dystonia
Rosenkranz K1, Butler K2, Williamon A3, Rothwell J1, 1Institute of Neurology (London, UK); 2Princess Grace Hospital (London, UK); 3 Royal College of Music (London, UK) Objective: Sensorimotor organiation (SMO) is abnormal in musician’s dystonia but has been shown to be restored by a 15min intervention with proprioceptive stimulation. However, it is unclear whether this neurophysiological effect is associated with an improvement in motor control. This study assessed whether 15min of proprioceptive training improves SMO of the motorcortical hand area and the motor control in musician’s dystonia. Methods: Six musician’s dystonia patients who all showed a task-specific ring finger flexion while playing the piano, five healthy pianists and six healthy non-musicians were recruited. Proprioceptive training lasted 15min and consisted of attended muscle vibration applied discontinuously to one of three hand muscles at random. Before and after proprioceptive training, the SMO was explored by measuring changes in short-interval intracortical inhibition (SICI) during short periods of hand muscle vibration, the performance of a five-finger exercise was objectively evaluated by a MIDI piano, and subjects rated their performance subjectively on visual-analogue scales. The expression of dystonic symptoms were scored on the BMF and Tubiana-Chamagne scales (TCS). Results: At baseline, the SMO in healthy subjects was spatially differentiated: SICI is reduced in projections to the vibrated, but enhanced to the non-vibrated muscles. In musician´s dystonia this pattern was completely abolished. Proprioceptive training strengthened the spatial differentiation of SMO in all groups. Particularly in musician’s dystonia, the inhibitory
Objective: Transcranial direct current stimulation (tDCS) modulates excitability in the cortical area directly beneath the stimulating electrode, but recent studies suggest it might also induce effects in distant brain regions by modulating the activity of interconnected areas. As prolonged tDCS-effects on motor cortex (M1) excitability have been well established and anatomical connections are known to exist between both motor cortices, we aimed to study whether tDCS over the left M1 affected excitability in the homologous region of the unstimulated, contralateral motor cortex. Method: Eight participants received 10 min anodal tDCS (1mA) with the cathode positioned over the contralateral supraorbita. Motor evoked potentials (MEPs) from single pulse transcranial magnetic stimulation (TMS) were used to assess cortical excitability in left and right motor cortices every 5 mins for 30 min following stimulation. Results: During this period left motor cortex excitability increased (av. change in MEP amplitude: 12.6% 68.2; p , 0.05) and right motor cortex excitability decreased (av. change in MEP amplitude: 82.2% 66.4; p , 0.05). Conclusion: Our results demonstrate that anodal stimulation of the left M1 can modulate corticomotor excitability levels bilaterally - enhancing left M1 and suppressing right M1 excitability - presumably by modulating the activity in transcallosal and subcortical pathways interconnecting both motor cortices. These findings have implications for neurorehabilitation interventions assisting motor recovery after stroke.
TMS Poster Only 238
Silent period (SP) to transcranial magnetic stimulation: the EEG substrate
Kimiskidis VK1, Papagiannopoulos S1, Kazis DA1, Vasiliadis G1, Oikonomidi A1, Sotirakoglou K2, Pseftogianni D1, Anogianakis G1, Vlaikidis N1, 1Aristotle University of Thessaloniki (Thessaloniki, GR); 2 Agricultural University of Athens (Athens, GR) Background: It is now well established that the early part of SP (50-75 ms) is mainly of spinal origin while the later part is related to reduced motor cortex excitability. However, the EEG substrate of SP has not yet been identified. Recent experiments revealed that TMS of the motor cortex evokes a complex EEG response including a negative component peaking at 100 ms (N100) , which is thought to reflect cortical inhibitory processes. We hypothesized that N100 may underlie the later part of SP. Objective: To investigate whether SP duration correlates with N100 amplitude.