The instrument described enables acute electrical recording from single cells in the human cerebral cortex with minimal tissue trauma. In spite of the great long-term interest that has been manifest in this type of measurement, until now, such recordings have been extremely limited due to difficulties caused by cortical motions of several mm occurring when part of the cranium is removed during surgery. The new mechanism uses gas journal and thrust bearings to enable a recording microelectrode to continuously remain near a single cell while exerting extremely small contact force on the cortex. The recording microelectrode is mounted on a miniature lead screw attached to a rider tube which is supported in gas journal bearings so it can freely follow the pulsatile motion of the brain surface. The microelectrode, protruding up to 5 mm beyond the rider tube into the cortex, moves with the surface and thereby retains its relative position in the tissue throughout the motion. The rider tube weight is offset by an internally generated variable pressure force that automatically maintains the contact force less than 11.7 × 10−4 N (0.004 oz) for electrode insertion angles up to 1 rad from vertical. The resultant contact pressure is approximately 1.1 × 102 Pa (0.9 mm Hg), a value considerably less than the tissue capillary perfusion pressure. Recording depth is varied without disturbance to the cortex by actuating the lead screw with an assembly of gas thrust bearings which do not influence the axial motion of the rider tube. During checkout on rhesus monkeys, a single cell was “held” for 50 min in the presence of 3/4-mm peak-to-peak cortical motions. Recordings were obtained from a single cell in a human cerebral cortex undergoing 1-1/2-mm pulsations over a period of 17-1/2 min at which point the protocol was terminated in order to proceed with the surgery.

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