Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Attenuation of N2 amplitude of laser-evoked potentials by theta burst stimulation of primary somatosensory cortex.
Theta burst stimulation (TBS) is a special repetitive transcranial magnetic stimulation (rTMS) paradigm, where bursts of low-intensity stimuli are applied in the theta frequency. The aim of this study was to investigate the effect of neuronavigated TBS over primary somatosensory cortex (SI) on laser-evoked potentials (LEPs) and acute pain perception induced with Tm : YAG laser stimulation. The amplitude changes of the N1, N2, and P2 components of LEPs and related subjective pain rating scores of 12 healthy subjects were analyzed prior to and following continuous TBS (cTBS), intermittent TBS (iTBS), intermediate TBS (imTBS), and sham stimulation. ⋯ The subjective pain perception also decreased during the experimental sessions, but did not differ significantly from the sham stimulation condition. The main finding of our study is that TBS over SI diminished the amplitude of the N2 component evoked from the contralateral side without any significant analgesic effects. Furthermore, imTBS produced responses similar to those observed by other forms of TBS induced excitability changes in the SI.
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Comparative Study
Contralesional paired associative stimulation increases paretic lower limb motor excitability post-stroke.
Following stroke, an abnormally high interhemispheric inhibitory drive from the contralesional to the ipsilesional primary motor cortex (M1) is evident during voluntary movement. Down-regulating motor excitability of the contralesional M1 using inhibitory neuromodulatory protocols has demonstrated a correlation between balanced interhemispheric interactions and increased motor recovery. In 2005, our laboratory first reported bidirectional modulation of healthy subjects' tibialis anterior (TA) motor excitability during walking, using a stimulation paradigm known as paired associative stimulation (PAS). ⋯ In healthy subjects, MEPs in response to TMS revealed that mean MEP amplitude from the stimulated TA decreased to 87% and the mean MEP amplitude from the non-stimulated TA increased to 126%. This is the first study to demonstrate that inhibitory PAS applied to the contralesional lower limb motor system of stroke survivors increases motor excitability of the paretic lower limb assessed during walking. This finding suggests that inhibitory PAS may be a useful tool to study how the human lower limb motor cortex recovers after neural injury, and that PAS may be a candidate adjuvant therapy for patients with neurological walking impairments.
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Comparative Study
Audiovisual temporal adaptation of speech: temporal order versus simultaneity judgments.
The temporal perception of simple auditory and visual stimuli can be modulated by exposure to asynchronous audiovisual speech. For instance, research using the temporal order judgment (TOJ) task has shown that exposure to temporally misaligned audiovisual speech signals can induce temporal adaptation that will influence the TOJs of other (simpler) audiovisual events (Navarra et al. (2005) Cognit Brain Res 25:499-507). Given that TOJ and simultaneity judgment (SJ) tasks appear to reflect different underlying mechanisms, we investigated whether adaptation to asynchronous speech inputs would also influence SJ task performance. ⋯ While performing these tasks, participants monitored a continuous speech stream for target words that were either presented in synchrony, or with the audio channel lagging 300 ms behind the video channel. We found that the sensitivity of participant's TOJ and SJ responses was reduced when the background speech stream was desynchronized. A significant modulation of the point of subjective simultaneity (PSS) was also observed in the SJ task but, interestingly, not in the TOJ task, thus supporting previous claims that TOJ and SJ tasks may tap somewhat different aspects of temporal perception.
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Comparative Study
Human stance control beyond steady state response and inverted pendulum simplification.
Systems theory analyses have suggested that human upright stance can be modelled in terms of continuous multi-sensory feedback control. So far, these analyses have considered mainly steady-state responses to periodic stimuli and relied on a simplifying model of the body's mechanics in the form of an inverted pendulum. Therefore, they may have ignored relevant aspects of the postural behaviour. ⋯ We also conclude that the 'inverted pendulum' simplification is a legitimate simplification. We demonstrate the utility of the model by implementing it into a humanoid robot that then mimics closely the human experimental data. Finally, we present a hypothetical concept on sensory reweighting mechanisms in human stance control, which is meant to serve as a framework for future research.
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The multidimensional experience of pain is thought to be partially influenced by the pain modulation system as well as by individual psychological components. Recent studies demonstrated possible common neural network mediating both domains. The present study examined the relationships between pain perception, pain modulation, and catastrophizing in healthy subjects. ⋯ In addition, significant negative correlations were found between PCS and DNIC effect (r = -0.34, p = 0.02). Moreover, once catastrophizing was entered into the regression analysis, the previously significant effect of gender was no longer found. In conclusion, individuals with high catastrophizing levels demonstrated higher pain intensities and lower effects of DNIC indicating that catastrophizing might have a significant impact on pain perception via an association with pain modulation.