Which Are the Most Important Aspects of Microelectrode Implantation?

Chronically implanted intracranial electrodes containing microwire bundles capable of recording extracellular single unit action potentials provide significant insights into the ways neurons and neural networks regulate cognition, movement, and many aspects of human behavior, as well as insights into the neuronal basis of seizures. The most used electrode for these recordings is the commercially available Behnke-Fried hybrid electrode. In this design, a bundle of microwires protrude from the distal end of a macroelectrode. Adhering to a few simple techniques during insertion of these electrodes can maximize the number of neurons recorded and also achieve stable, high quality, and long-lasting recordings. Techniques include: (1) pre-loading the microwires into the macroelectrode bundle and cutting them to a 4–5 mm length with sharp scissors prior to use; (2) targeting the distal end of the macroelectrode to ensure that the microwires protrude into grey matter; (3) using orthogonal insertion trajectories whenever possible; (4) avoid kinking of the microwires; and (5) ensuring that the distal macroelectrode does not penetrate the grey matter where the microwires will be placed. This chapter will review the technical nuances for electrode insertion that lead to high quality recordings, a key first step to successful recording, sorting, and analysis of human single units.