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High-density cortical implants for cognitive neuroscience and rehabilitation of speech using brain-computer interfaces.

Periodic Reporting for period 2 - BrainCom (High-density cortical implants for cognitive neuroscience and rehabilitation of speech using brain-computer interfaces.)

Reporting period: 2017-12-01 to 2019-05-31

Over 5 million people suffer from aphasia worldwide, most often following a brain stroke, but also from neurodegenerative disorders affecting the motor production and articulation of speech, locked-in syndrome, or coma. While motor rehabilitation training can help people recover some of their speech ability in case of partial aphasia, new approaches remain to be explored to restore communication and, ultimately, speech in severe aphasic patients.

The goal of BrainCom is to develop a new generation of neuroprosthetic devices suitable to explore and repair high-level cognitive functions, with a primary focus on the restoration of speech and communication in aphasic patients.

An important limitation to this goal is the lack of animal models to detail the cortical dynamics of the speech network. Taking advantage of lesion cases and non-invasive neuroimaging studies, this network has been extensively characterized at a macroscopic level in humans. However, very few data are available at the cellular and multicellular level, which is the required resolution to obtain sufficient decoding precision to predict continuous speech. One of the reasons is the lack of an available technology capable of recording neural signals with a high spatial and temporal resolutions over large cortical areas. With this technology at hand, we will eventually identify the areas to extract the most relevant signals and properly understand the meaning of cortical signals to optimize decoding protocols.

The overarching goal of BrainCom is to nurture a technology paradigm shift by developing a new generation of very large-scale neuroprosthetic cortical devices based on novel materials and technologies that can provide a unique leap forward towards a new level of basic understanding of cortical speech networks and the advancement of rehabilitation solutions to restore speech and communication capabilities in disabled patients using innovative brain-computer paradigms. Ultimately, BrainCom will foster a novel line of knowledge and technologies that will seed the future generation of speech neural prostheses. To target the broadly distributed neural system of the language network, BrainCom will use novel electronic technologies based on nanomaterials in order to fabricate ultra-flexible cortical and intracortical implants enabling high density recording over large cortical areas with unprecedented spatial and temporal resolution.
The work has been focused towards the following objectives:
i) Develop electronic technologies for brain mapping to record from large number of active sites over large areas of the cortex. We have been developing the technology roadmap. The g-SGFET technology has reached high maturity, reaching very yields over 80% and high homogeneity, and reducing the 1/f electronic noise; we have validated in vitro and in vivo the recording capabilities of g-SGFETs; we have performed an in vitro assessment of g-SGFETs devices (8x8 arrays) for multiplexing strategies. We have successfully validated: (i) 2 different multiplexing strategies with arrays of 8x8 g-SGFET in acute in vivo experiments using discrete electronics, and (ii) the g-SGFETs in an in vivo chronic setting using a wireless headstage.
A first ASIC has been full-custom designed for a novel switch-less multiplexing strategy of g-SGFET arrays. The design of a 1024-channel ASIC with digital output for the switch-less multiplexing of 32x32-arrays of GFET sensors has been completed and is currently being fabricated.
ii) Advance the fundamental understanding of the link between surface and intracortical signals and dynamics in cortical circuits. We have developed flexible cranial interface and performed first of a kind distributed recordings together with 3D behaviour, and a Green-function-based frequency domain procedure for LFP decomposition, and we have identified sparse and distributed anatomical basis for decoding of spatial representation from hippocampal LFP in theta frequency band. We have established joined depth and ECoG recordings in motor cortex combined with 3D limb analysis in locomoting head-fixed mice and identified contribution of theta dynamics to motor cortex activity; we have performed first recordings in minipigs with 256 channel wireless recording system combined with vocalization analysis.
iii) Gain new fundamental understanding of the distributed brain circuits of speech and their plastic flexibility before and after lesions. We have started to characterize the brain dynamics underlying overt and inner speech production in humans, both at the whole brain level using non-invasive, and more locally using invasive large-scale electrophysiology. We have collected several datasets in patients with ECoG electrodes for word level speech production, characterizing the covert speech network. We have also developed original decoding methods, and characterization of best neural signals to be decoded (high and low frequency signals, inter-site correlations).
iv) Development of speech BCI proof of concept. We have developed a versatile software framework to allow customizable real-time processing of any type of data streams (including neural recordings from different recording systems), incorporating real-time DNN-based speech synthesis for closed-loop BCI applications. A first closed-loop speech BCI paradigm was tested in a new epileptic patient. We developed a neuromorphic approach to perform online spike sorting that anticipates the advent of very large scale neural recordings with BrainCom implants that will need to be processed at very low-power for a wireless usage.
v) Develop a solid ethics framework to identify and explore issues linked to the use of brain implants. Collaborative research has continued on questions generated by neural decoding techniques, including the prospect for involuntary speech and inadvertent ‘mind reading’. Further work has addressed questions concerning user responsibility, control of devices, and the status of brain data.
Building up on BrainCom technology, we expect to lay foundation for breakthroughs in both fundamental neuroscience and clinical rehabilitation. The BrainCom unique high-density implant technology will shed new light on the fundamental understanding of surface cortical activity with respect to intracortical signals in small and large animal models, which will naturally lead to identifying key neural activity features to be used in BCI decoders. Further, the brain dynamics underlying overt and inner speech production will be characterized in humans which will provide further insights into speech production. BrainCom novel technologies will advance two clinical applications. First, very high-density surface recordings will improve detailed per-operative mapping of functional areas to guide tissue removal during awake surgery. The goal is to provide an alternative to the classical delineation of functional areas made using electrical stimulation of the cortical surface. Second, BrainCom technology aims at developing BCI solutions to restore continuous speech in patients unable to speak. If successful, this will open a brand new area in the field of functional rehabilitation. Ultimately, the outcome of BrainCom is expected to open up new research directions towards a better fundamental understanding of the brain activity and towards a new generation of brain-machine interfaces for neurorehabilitation.
Figure 1: BrainCom main Research and Innovation activities