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Reducing the TMS mapping acquisition time
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
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