Occlusion of LTP-Like Plasticity in Human Primary Motor Cortex by Action Observation

Passive observation of motor actions induces cortical activity in the primary motor cortex (M1) of the onlooker, which could potentially contribute to motor learning. While recent studies report modulation of motor performance following action observation, the neurophysiological mechanism supporting these behavioral changes remains to be specifically defined. Here, we assessed whether the observation of a repetitive thumb movement – similarly to active motor practice – would inhibit subsequent long-term potentiation-like (LTP) plasticity induced by paired-associative stimulation (PAS). Before undergoing PAS, participants were asked to either 1) perform abductions of the right thumb as fast as possible; 2) passively observe someone else perform thumb abductions; or 3) passively observe a moving dot mimicking thumb movements. Motor evoked potentials (MEP) were used to assess cortical excitability before and after motor practice (or observation) and at two time points following PAS. Results show that, similarly to participants in the motor practice group, individuals observing repeated motor actions showed marked inhibition of PAS-induced LTP, while the “moving dot” group displayed the expected increase in MEP amplitude, despite differences in baseline excitability. Interestingly, LTP occlusion in the action-observation group was present even if no increase in cortical excitability or movement speed was observed following observation. These results suggest that mere observation of repeated hand actions is sufficient to induce LTP, despite the absence of motor learning

The triple helix: 50 years later, the outcome

Triplex-forming oligonucleotides constitute an interesting DNA sequence-specific tool that can be used to target cleaving or cross-linking agents, transcription factors or nucleases to a chosen site on the DNA. They are not only used as biotechnological tools but also to induce modifications on DNA with the aim to control gene expression, such as by site-directed mutagenesis or DNA recombination. Here, we report the state of art of the triplex-based anti-gene strategy 50 years after the discovery of such a structure, and we show the importance of the actual applications and the main challenges that we still have ahead of us

Impact of galvanic vestibular stimulation electrode current density on brain current flow patterns: Does electrode size matter?

Background Galvanic vestibular stimulation (GVS) uses at least one electrode placed on the mastoid process with one or multiple placed over other head areas to stimulate the vestibular system. The exact electrode size used is not given much importance in the literature and has not been reported in several studies. In a previous study, we compared the clinical effects of using different electrode sizes (3 cm2 and 35 cm2) with placebo but with the same injected current, on postural control. We observed significant improvement using the smaller size electrode but not with the bigger size electrode. The goal of this study was to simulate the current flow patterns with the intent to shed light and potentially explain the experimental outcome. Methods We used an ultra-high-resolution structural dataset and developed a model to simulate the application of different electrode sizes. We considered current flow in the brain and in the vestibular labyrinth. Results Our simulation results verified the focality increase using smaller electrodes that we postulated as the main reason for our clinical effect. The use of smaller size electrodes in combination with the montage employed also result in higher induced electric field (E-field) in the brain. Conclusions Electrode size and related current density is a critical parameter to characterize any GVS administration as the choice impacts the induced E-field. It is evident that the higher induced E-field likely contributed to the clinical outcome reported in our prior study. </jats:sec

Maximum induced E-field (based on 99th percentile) in the brain and vestibular regions across the two models.

The percentage increase of E-field with respect to the larger electrode model is noted in the final column.</p

Electrode placements and model detail.

Two different electrode sizes were simulated to apply GVS: 35 cm2 (A-C) and ~3 cm2 (D-F). The electrodes were placed on the skin-tissue mask in a Bilateral-Bipolar configuration. (G): The two electrode sizes were overlaid on the same head model geometry to highlight final placement with respect to the anatomy. (H): To highlight the region of interest in the model geometry with respect to other tissues and the stimulation electrode, certain tissue masks were made semi-transparent. (I): The dashed section in (H) is expanded to further highlight model detail.</p

Comparison of GVS induced current flow using small- and large-size electrodes.

Columns A (A1, A2, A3) and B (B1, B2, B3) correspond to the 35 cm2 and 3 cm2 electrodes, respectively. The current streamlines from both models are overlaid in C1. C2 and C3 indicate the difference in induced E-field due to the two electrode sizes. The first row (A1, B1 and C1) shows the current streamline plots with the brain, SCC and otolith organs masks visible to provide enhanced visualization of current flow with respect to their anatomy. The second row (A2, B2, and C2) shows the induced brain surface E-field plots. Similarly, the third row (A3, B3, and C3) shows the induced E-field plots on the vestibular labyrinth.</p

S1 Data -

(ZIP)</p

Corticospinal excitability before (black) and after (white) observation of moving dots, observation of thumb movements, or execution of thumb movements.

<p>Bars indicate standard error of the mean.</p

Raw MEP values (mV). Data are presented as mean and SD.

<p>Raw MEP values (mV). Data are presented as mean and SD.</p