Abstracts

Rationale: Current implantable brain devices for clinical and research applications require that each electrode is individually wired to a separate electronic system. Establishing a high-resolution interface over broad regions of the brain is infeasible under this constraint, as an electrode array with thousands of passive contacts would require thousands of wires to be individually connected. To overcome this limitation, we have developed new implantable electrode array technology that incorporates active, flexible electronics. This technology has enabled extremely flexible arrays of 720 and soon thousands of multiplexed and amplified sensors spaced as closely as 250 m apart, connected using just a few wires. Due to the prior technological limitation of wiring each electrode individually, it has not been possible to record high density, 2-dimensional (2-D) ECoG. In initial experiments using a 360-sensor array (10 mm x 9mm) we discovered recurring spatio-temporal (ST) patterns in a feline model of epilepsy, motivating new analytical methods for studying ECoG signals and continued electrode development towards higher density arrays with broader coverage.Methods: Using a 360 channel, high-density active electrode array with 500 m resolution, we explore ST patterns of local field potential spikes that occur within the surface area traditionally occupied by a single clinical electrode. We record subdural micro-electrocorticographic ( ECoG) signals in vivo from a feline model of acute neocortical epileptiform spikes and seizures induced with local administration of the GABA antagonist picrotoxin. To analyze the data, we employ a clustering algorithm to separate 2-D spike patterns and to isolate distinct classes of spikes unique to the ictal state. Our findings indicate that the 2-D patterns can be used to distinguish seizures from the non-seizure state.Results: We find two statistically significant ST patterns that uniquely characterize ictal epochs. Additionally, we present the most recent development of our array technology and examples of retinotopic and tonotopic maps produced from in vivo recordings.Conclusions: New high density micro-electrocorticographic ( ECoG) devices yield an unprecedented level of spatial and temporal resolution for recording distributed neural networks. Our characterization of 2-D spikes demonstrates that millimeter-scale ST spike dynamics contain useful information about ictal state. Further work will investigate whether patterns we identify can increase our understanding of seizure dynamics and their underlying mechanisms and inform new electrical stimulation protocols for seizure termination. ECoG is only one of the many possible applications of this technology, which also include cardiac, peripheral nerve and retinal prosthetic devices.