Evaluation of μECoG electrode arrays in the minipig: experimental procedure and neurosurgical approach

Emerging research on brain-machine interfaces (BMIs) requires the development of animal models for testing implantable BMI electrodes. New models are necessary in order to characterize and test newly constructed electrodes in an acute environment, and their properties and performance need to be evaluated in long-term, chronic implantations. Owing to their availability, small size and neuroanatomical similarity to the human brain, minipigs are frequently used for neurological studies. Despite this fact, there are still no standardized experimental and neurosurgical procedures available for recording of cortical potentials using implantable BMI electrodes in minipigs, and, until now, it was unclear whether these animals could also be used for long-term subdural electrode implantations. We have therefore evaluated the potential use of minipigs for acute and chronic implantation of micro-electrocorticogram (μECoG) electrodes we newly developed for BMI applications and we present a standardized neurosurgical approach to the minipig's cerebral cortex. A neurophysiological setup is described which is suitable to perform recordings of somatosensory evoked potentials (SEPs) with high spatial resolution - down to approx. 1-mm inter-electrode distance. Perioperative management, anesthesia and anatomical landmarks for electrode placement are discussed and common surgical pitfalls are described. While, due to their specific cranial anatomy, minipigs appear not optimally suited for chronic subdural implantations, the findings of the present study indicate that μECoG recording from the minipig cortex is a valuable new approach for acute in vivo characterization of subdural BMI electrode function.