Single and paired-pulse transcranial magnetic stimulation (TMS) were applied to the motor cortex of 12 healthy volunteers, who were instructed to relax under eyes-open and eyes-closed conditions with room lights on and after 30 min of blindfolding. Compared to the eyes-open condition, significantly larger motor-evoked potentials and less intracortical inhibition were observed during blindfolding. Visual deafferentation changes resting human motor cortex excitability and might be a novel way to promote brain plasticity. These results raise the issue of how widespread the effects of temporary deafferentation may be and whether they are mediated by discrete or diffuse systems. These findings also illustrate an important potential confound in TMS studies of the motor cortex.
"For example, stimulation of the dorso-lateral prefrontal cortex is associated with blood flow changes in the anterior cingulate cortex (Paus et al., 2001; Esslinger et al., 2014) and dopamine release in the caudate nucleus (Strafella et al., 2001). Such cross-modal plasticity-like effects may be transferred via direct cortico-cortical connections, indirectly via multi-sensory association areas, or via subcortical interplay at the thalamic level as indicated by findings in synaesthesia and sensory deprivation (Bavelier and Neville, 2002; Leon-Sarmiento et al., 2005; Dovern et al., 2012; Rothen and Terhune, 2012). Based on these crossmodal interactions, measurements of motor cortex excitability have also been investigated as a potential neural marker for the effect of rTMS of non-motor areas, e.g., the dorsolateral prefrontal cortex or the temporal cortex. "
[Show abstract][Hide abstract] ABSTRACT: Motor cortex excitability can be measured by single-and paired-pulse transcranial magnetic stimulation (TMS). Repetitive transcranial magnetic stimulation (rTMS) can induce neuroplastic effects in stimulated and in functionally connected cortical regions. Due to its ability to non-invasively modulate cortical activity, rTMS has been investigated for the treatment of various neurological and psychiatric disorders. However, such studies revealed a high variability of both clinical and neuronal effects induced by rTMS. In order to better elucidate this meta-plasticity, rTMS-induced changes in motor cortex excitability have been monitored in various studies in a pre-post stimulation design. Here, we give a literature review of studies investigating motor cortex excitability changes as a neuronal marker for rTMS effects over non-motor cortical areas. A systematic literature review in April 2014 resulted in 29 articles in which motor cortex excitability was assessed before and after rTMS over non-motor areas. The majority of the studies focused on the stimulation of one of three separate cortical areas: the prefrontal area (17 studies), the cerebellum (8 studies), or the temporal cortex (3 studies). One study assessed the effects of multi-site rTMS. Most studies investigated healthy controls but some also stimulated patients with neuropsychiatric conditions (e.g., affective disorders, tinnitus). Methods and findings of the identified studies were highly variable showing no clear systematic pattern of interaction of non-motor rTMS with measures of motor cortex excitability. Based on the available literature, the measurement of motor cortex excitability changes before and after non-motor rTMS has only limited value in the investigation of rTMS related meta-plasticity as a neuronal state or as a trait marker for neuropsychiatric diseases. Our results do not suggest that there are systematic alterations of cortical excitability changes during rTMS treatment, which calls into question the practice of readjusting the stimulation intensity according to the motor threshold over the course of the treatment.
Frontiers in Human Neuroscience 07/2015; 9. DOI:10.3389/fnhum.2015.00416 · 2.99 Impact Factor
"For example, the STS region, which is assumed to provide the main visual input to the mirror neuron system, responds to a large variety of different visual stimuli . It was shown previously that the presence or absence of visual input has an effect on M1 excitability , however, currently there is no evidence that differences in colour would have a similar effect . Moreover, it has to be noted that the TMS pulse was always applied in the short pause between the two series of changing colours, such that the rim colour was black in all conditions. "
[Show abstract][Hide abstract] ABSTRACT: Movement observation (MO) has been shown to activate the motor cortex of the observer as indicated by an increase of corticomotor excitability for muscles involved in the observed actions. Moreover, behavioral work has strongly suggested that this process occurs in a near-automatic manner. Here we further tested this proposal by applying transcranial magnetic stimulation (TMS) when subjects observed how an actor lifted objects of different weights as a single or a dual task. The secondary task was either an auditory discrimination task (experiment 1) or a visual discrimination task (experiment 2). In experiment 1, we found that corticomotor excitability reflected the force requirements indicated in the observed movies (i.e. higher responses when the actor had to apply higher forces). Interestingly, this effect was found irrespective of whether MO was performed as a single or a dual task. By contrast, no such systematic modulations of corticomotor excitability were observed in experiment 2 when visual distracters were present. We conclude that interference effects might arise when MO is performed while competing visual stimuli are present. However, when a secondary task is situated in a different modality, neural responses are in line with the notion that the observers motor system responds in a near-automatic manner. This suggests that MO is a task with very low cognitive demands which might be a valuable supplement for rehabilitation training, particularly, in the acute phase after the incident or in patients suffering from attention deficits. However, it is important to keep in mind that visual distracters might interfere with the neural response in M1.
PLoS ONE 11/2011; 6(11):e27292. DOI:10.1371/journal.pone.0027292 · 3.23 Impact Factor
"Therefore, LD was the specific intervention and EL, the control condition. In both sessions, subjects listened to standard songs during the 30 min of LD or EL and were instructed to remain awake during TMS measurements with their eyes open [12, 19]. These instructions were important to avoid sleepiness as the subjects remained with eyes closed, in a relatively resting condition for the 30-min period of LD or EL experiments. "
[Show abstract][Hide abstract] ABSTRACT: Increased, decreased or normal excitability to transcranial magnetic stimulation (TMS) has been reported in the motor (M1) and visual cortices of patients with migraine. Light deprivation (LD) has been reported to modulate M1 excitability in control subjects (CS). Still, effects of LD on M1 excitability compared to exposure to environmental light exposure (EL) had not been previously described in patients with migraine (MP). To further our knowledge about differences between CS and MP, regarding M1 excitability and effects of LD on M1 excitability, we opted for a novel approach by extending measurement conditions. We measured motor thresholds (MTs) to TMS, short-interval intracortical inhibition, and ratios between motor-evoked potential amplitudes and supramaximal M responses in MP and CS on two different days, before and after LD or EL. Motor thresholds significantly increased in MP in LD and EL sessions, and remained stable in CS. There were no significant between-group differences in other measures of TMS. Short-term variation of MTs was greater in MP compared to CS. Fluctuation in excitability over hours or days in MP is an issue that, until now, has been relatively neglected. The results presented here will help to reconcile conflicting observations.
Electronic supplementary material
The online version of this article (doi:10.1007/s10194-011-0379-4) contains supplementary material, which is available to authorized users.
The Journal of Headache and Pain 09/2011; 13(1):29-37. DOI:10.1007/s10194-011-0379-4 · 2.80 Impact Factor
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