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978-3-8439-4937-8, Reihe Mikrosystemtechnik
Maria Francisca Porto Cruz
Conformable epicortical implants for brain mapping: A technological perspective on neural recordings
189 Seiten, Dissertation Albert-Ludwigs-Universität Freiburg im Breisgau (2021), Softcover, B5
Electrocorticography has been for long one of the main pillars of brain mapping and, in recent years, miniaturization has paved the way for breakthrough applications targeting fine brain-computer communication. For this to become a reality, the gap between proof-of-concept and long-term reliability of new microelectrocorticography technologies must be narrowed down.
In this work, a state-of-the-art epicortical polyimide-based implant for the purpose of speech brain-computer interfaces is developed, validated in rat models and tested on a human patient. Having conformability to the brain’s morphology as a pre-requisite, neural metrics of the acquired signals are analysed from a technical standpoint, according to electrode material and size, routing layout and referencing configurations.
Electrode’s thermal noise is shown to correlate to the baseline signal from acute to chronic implantation stages, although an anticorrelation to active neural metrics is only seen for the acute scenario. On the other hand, crosstalk between neighbouring channels is observed as the path impedance from signal source to electrode’s phase boundary increases, which is typical of chronic phases. Depending on the boundary conditions, on-site referencing in bipolar configurations can either result in distortion of activity maps, leading to the wrong assignment of signal power to localization, or effective lowering of baseline activity and boosting of spatial selectivity.
Understanding the direct impact of technical design choices on the quality of recorded neural data is key. One thing is to have a functional implant and one other entirely is to have an optimized technology that transfers signals from brain to computer with minimal information loss in between. In summary, the present work points out the crucial technical aspects that play an actual role in vivo.