Animals

Six adult Corriedale ewes weighing 60–70 kg were used in this study. Experiments were conducted at The Florey Institute of Neuroscience and Mental Health and were approved by the Florey Institute Animal Ethics Committee. Studies were in accordance with the NHMRC Principles of Laboratory Animal Care, Prevention of Cruelty to Animals Act, Australia, 2004, and the NHMRC Australian Code of Practice for the Care & Use of Animals for Scientific Purpose (seventh edition, 2004).

Six animals were implanted with ED, EV, and SD arrays, however two of the SD and ED arrays and one of the EV arrays developed faults at the connector. Therefore, we evaluated the quality of recordings obtained from the ED (4 arrays), EV (5 arrays), and SD (4 arrays) arrays from six animals. As illustrated in Fig. 1, the ED and SD arrays were placed on different hemispheres and were adjacent to the EV array. The SD and ED arrays were manufactured by Cortec GMBH, Germany and the EV arrays were made in-house^1,25. The SD and ED arrays comprised 24 electrodes, with eight electrodes each of 500 µm, 750 µm, and 1000 µm diameter. Inter-electrode distance between similar electrode sizes was 4 mm and adjacent dissimilar sizes was 1.5 mm. The EV array had two sizes of electrodes, 500 µm and 750 µm; inter-electrode distance varied between electrodes (~2–6 mm). All electrodes were made of platinum. In this study, we used three electrode sizes for the ED and SD arrays and two sizes for the EV array. The largest size on the ED and SD arrays of 1 mm diameter would not fit within the dimensions of the blood vessel to be implanted and so was not used on an EV array. The 1 mm diameter was used in the ED and SD arrays based on previous studies showing that this is the optimum size to improve noise susceptibility while maintaining acceptable spatial resolution for a brain-computer interface³⁶. Device positions were assessed immediately after deployment, and prior to termination of the experiment.