Abstracts

Cortical physiology has been studied in animals for more than 40 years using single electrodes to record action potentials under different stimulus or behavioral conditions. Microwires or microelectrode arrays have now made it possible to record the activity of dozens to hundreds of individual neurons and local field potentials (LFPs) simultaneously. An array of 96 silicon/platinum microelectrodes has been used to record chronically (months to years) from macaque primary motor cortex (M1). This technology, BrainGate, forms the basis for a human neuromotor prosthesis for persons with tetraparesis, now in pilot clinical trial. If the array also provides useful neural signals acutely [ndash] minutes to hours after placement in human cortex [ndash] it could prove valuable for applications in seizure detection, intraoperative monitoring, and neurocritical care. 4x4 mm arrays of 96 microelectrodes (Cyberkinetics, Inc.) were implanted into macaque M1 or visual cortex (V1, data courtesy of D.L. Ringach). In the M1 experiments, recordings were first attempted in the awake animal the following day. In V1, recordings were obtained beginning 10-20 minutes after array insertion while the animal was sedated with propofol/sufentanil. Single units, multi-unit waveforms, and LFPs were collected while the animal was sitting in a primate chair (M1) or while retinotopic mapping was performed (V1). Neural signals were transferred to a connector; amplified signals from each electrode were manually separated into data streams and stored digitally. In both animals receiving a M1 array, action potentials, multi-unit waveforms, and LFPs were recorded simultaneously on post-operative day 1. 62 and 29 discriminated units with [ldquo]fair[rdquo] (signal:noise ratio approx. 2 to 4) or better waveforms were recorded in each animal, respectively. LFPs were also observed from an additional 32 and 31 electrodes, respectively. In the 10 V1 animals, LFPs were seen consistently on all electrodes as soon as recording was initiated. Multi-unit waveforms were seen on most electrodes, and a range of 15-70 single units was isolated in each experiment. Microelectrode arrays can record from cortical neuronal ensembles as soon as 10-20 minutes after insertion. It thus may be possible to record human cortical neuronal activity in a variety of acute and subacute settings. Potential studies include high spatial resolution recording of epileptigenic tissue in patients undergoing subdural grid placement (including further investigation of interictal spike physiology and seizure prediction paradigms) and neuronal/LFP activity patterns in tissue at risk for ischemia secondary to subarachnoid hemorrhage-related vasospasm. (Supported by NINDS, VA, DARPA, ONR, Cyberkinetics.)