Reliability of a cranial window for chronic epidural recordings from the pig primary somatosensory cortex

Chronically implanted microelectrodes face adverse biological responses and various kinds of device failure. To overcome these challenges, a cranial window was developed allowing repeated access to the primary somatosensory cortex (S1) of the pig. This study evaluated the reliability of the signals recorded using repeated temporary placement of a micro-electrocorticography (µECoG) array via a cranial window. Seven pigs were implanted with a cranial window, which was accessed twice after implantation at 2-3 week intervals. Brain responses were evoked by electrical stimulation to the ulnar nerve. At each session, three trials were recorded, consisting of a hundred stimulations. Averaged responses of P1 amplitude, latency, and variance between channels were obtained. Signal characteristics were stable within and between sessions. No systematic errors were found for the P1 amplitude and channel variability. For the P1 latency, a systematic decrease in latency was found between session 1 (25±2 ms) and sessions 2 and 3 (24±2 ms). These results show that the temporary placement of microelectrodes to record brain signals is a good alternative to permanent implantation.