Development of tube tetrodes and a multi-tetrode drive for deep structure electrophysiological recordings in the...

Understanding the principles that underlie information processing by neuronal networks requires simultaneous recordings from large populations of well isolated single units. Twisted wire tetrodes (TWTs), typically made by winding together four ultrathin wires (diameter: 12-25 μm), are ideally suited for such population recordings. They are advantageous over single electrodes; both with respect to quality of isolation as well as the number of single units isolated and have therefore been used extensively for superficial cortical recordings. However, their limited tensile strength poses a difficulty to their use for recordings in deep brain areas. We therefore developed a method to overcome this limitation and utilize tetrodes for electrophysiological recordings in the inferotemporal cortex of rhesus macaque. We fabricated a novel, stiff tetrode called the tube tetrode (TuTe) and developed a multi-tetrode driving system for advancing up to 5 TuTes through a ball and socket chamber to precise locations in the temporal lobe of a rhesus macaque. The signal quality acquired with TuTes was comparable to conventional TWTs and allowed excellent isolation of multiple single units. We describe here a simple method for constructing TuTes, which requires only standard laboratory equipment. Further, our TuTes can be easily adapted to work with other microdrives commonly used for electrophysiological investigation in the macaque brain and produce minimal damage to the cortex along its path because of their ultrathin diameter. The tetrode development described here could allow studying neuronal populations in deep lying brain structures previously difficult to reach with the current technology.