Stimulation transcrânienne à courant direct

La stimulation transcrânienne à courant direct ou stimulation transcrânienne à courant continu (tDCS) est une technique d’électrostimulation du cerveau, ou stimulation électrique transcrânienne (tES). Elle permet de moduler l'excitabilité corticospinale : deux électrodes, une anode (excitatrice) et une cathode (inhibitrice), sont positionnées sur le crâne en fonction des régions dont on souhaite influencer le fonctionnement. La tDCS fonctionne par l'induction d'un courant électrique de un à deux milliampères d’amplitude pendant dix à trente minutes, passant de l'anode vers la cathode à travers les tissus. Les effets observés sont la conséquence de l’hyperexcitabilité des neurones causée par l’anode ou l’hypoexcitabilité par la cathode. La tDCS peut être utilisée avec des sujets sains comme méthode d'investigation du fonctionnement normal, ou avec différentes populations cliniques à fins thérapeutiques. Des sujets atteints de la maladie d'Alzheimer, de Parkinson, de Huntington, d’une

Does anodal cerebellar tDCS boost transfer of after-effects from throwing to pointing during prism adaptation?

Lisa Aïcha Mireille Julie Fleury

Prism Adaptation (PA) is a useful method to study the mechanisms of sensorimotor adaptation. After-effects following adaptation to the prismatic deviation constitute the probe that adaptive mechanisms occurred, and current evidence suggests an involvement of the cerebellum at this level. Whether after-effects are transferable to another task is of great interest both for understanding the nature of sensorimotor transformations and for clinical purposes. However, the processes of transfer and their underlying neural substrates remain poorly understood. Transfer from throwing to pointing is known to occur only in individuals who had previously reached a good level of expertise in throwing (e.g., dart players), not in novices. The aim of this study was to ascertain whether anodal stimulation of the cerebellum could boost after-effects transfer from throwing to pointing in novice participants. Healthy participants received anodal or sham transcranial direction current stimulation (tDCS) of the right cerebellum during a PA procedure involving a throwing task and were tested for transfer on a pointing task. Terminal errors and kinematic parameters were in the dependent variables for statistical analyses. Results showed that active stimulation had no significant beneficial effects on error reduction or throwing after-effects. Moreover, the overall magnitude of transfer to pointing did not change. Interestingly, we found a significant effect of the stimulation on the longitudinal evolution of pointing errors and on pointing kinematic parameters during transfer assessment. These results provide new insights on the implication of the cerebellum in transfer and on the possibility to use anodal tDCS to enhance cerebellar contribution during PA in further investigations. From a network approach, we suggest that cerebellum is part of a more complex circuitry responsible for the development of transfer which is likely embracing the primary motor cortex due to its role in motor memories consolidation. This paves the way for further work entailing multiple-sites stimulation to explore the role of M1-cerebellum dynamic interplay in transfer.

FRONTIERS MEDIA SA2022

The aging brain as a model to understand motor skill acquisition in humans and its restoration using non-invasive brain stimulation

Pablo Maceira Elvira

Motor skill acquisition is essential to our survival, as it enables an efficient interaction with the changing world around us. The acquisition of novel sequential tasks, of particular relevance due to their pervasiveness in everyday life activities, can become more challenging at an advanced age, with structural and functional changes in the brain often resulting in diminished learning abilities. During the pursuit of my doctoral degree, I studied some of the processes leading to the acquisition of a novel sequential motor task, and how some of the mechanisms underlying these processes differ between healthy young and older adults. Young adults acquired the sequential task effectively by prioritizing its accurate execution early in training and focusing on increasing their speed thereafter, resulting in the generation of mechanically efficient execution patterns in the replication of the sequence. In contrast, older adults improved both the accuracy and the speed simultaneously and gradually after more extensive practice, which resulted in an overall decreased performance of the task. However, anodal direct current stimulation applied over the motor cortex partially restored skill acquisition in older adults by facilitating the early improvement of the accuracy, enabling an accelerated generation of efficient execution patterns in the sequence, similar to those seen in young adults. Further investigations into the effects of stimulation to improve skill acquisition in healthy older adults showed age not to be a determinant factor for an individual's proneness to benefit from stimulation; rather, it is the state of the neural system of each individual what likely determines the potential benefits to be had from stimulation. Therefore, a better understanding of the mechanisms targeted by stimulation and the identification of parameters signaling an individual's likelihood to benefit from it are needed to use these techniques to their full potential. Leveraging this knowledge and taking advantage of the portability, robustness and accessibility of this technique could represent an attractive option for applications involving extensive motor training, such as rehabilitative training provided after stroke.

EPFL2022

Fabrication and validation of an intraneural interface tailored for optic nerve stimulation

Eleonora Borda

Technological progress in materials science and microengineering along with new discoveries in neuroscience have contributed to restore lost or impaired sensory functions by closely interfacing with the nervous system. Electronic devices have begun to be integrated within the body to artificially reproduce or record the electrical encoding of neural signals, the language of the nervous system. This has allowed us to restore the impaired communication between the missing or defective organ and the brain. As evidence of this, cochlear implants have returned hearing to millions of people world wide. On the other hand, there is no suitable solution yet for the 43 millions people who are currently blind. Nevertheless, several research groups and companies are trying to tackle this issue. So far, different devices have demonstrated the capability of restoring a certain degree of artificial vision, however, with limited success in delivering meaningful improvements in daily life activities. This is because, unlike hearing, vision is an extremely complex sense and requires higher stimulation resolution. Limitations of retinal prostheses have pushed further the investigation of other targets along the visual pathway, such as the optic nerve, the thalamus and the visual cortex. Among these, our group has started to explore the possibility of stimulating the optic nerve. The main advantages are the direct stimulation of the axon fibers and the access to the entire visual field with only one device. It is also interesting because it could work for those patients who are not eligible for retinal prostheses, due to severe eye trauma or retinal detachment, and it does not require optical transparency.In this thesis, we investigate stimulation strategies and materials to improve the outcome of optic nerve prostheses and make them one step closer to a viable option for blind patients. We first propose the use of machine learning algorithms to classify cortical activity upon electrical stimulation of the optic nerve. Secondly, we investigate a strategy to achieve higher spatial selectivity of the optic nerve stimulation. We design a three-dimensional (3D) multilayer concentric bipolar (CB) configuration and fabricate a modified version of the OpticSELINE. We validate the efficacy of the novel design during in-vivo experiments on rabbits and find that cortical activation is reduced when using the 3D multilayer CB electrodes compared to the classic monopolar configuration. In parallel, we explore the use of novel polymers, namely Off-Stoichiometry Thiol- Ene Epoxy (OSTE+), to design conformable neural interfaces. Their chemistry makes them a suitable candidate for easy integration in cleanroom processes and they show superior adhesion properties with respect to standard thin films currently in use. Hence, we characterise their usability as substrate and encapsulation for neural interfaces in-vitro and in-vivo. Lastly, we propose an alternative fabrication technique, ink-jet printing of platinum on flexible substrates, for neurophysiology applications. Altogether, the findings highlighted in this thesis will hopefully lead to a more in-depth investigation of the optic nerve prosthesis and can also be relevant for other applications in the field of neuroprosthetics.

EPFL2022

Fabrication and validation of an intraneural interface tailored for optic nerve stimulation

Eleonora Borda

EPFL2022

The aging brain as a model to understand motor skill acquisition in humans and its restoration using non-invasive brain stimulation

Pablo Maceira Elvira

EPFL2022

Does anodal cerebellar tDCS boost transfer of after-effects from throwing to pointing during prism adaptation?

Lisa Aïcha Mireille Julie Fleury

FRONTIERS MEDIA SA2022