Introduction

Abstract

The functional aspects of the brain can be studied in many ways. It is possible to monitor its uptake of metabolites by imaging techniques displaying the course of radioactive labeled air, salts, or sugars with gamma cameras or positron emission tomography. However, to date these methods lack sufficient resolution in the temporal as well as spatial domain. More traditional techniques use the electrical activity produced by the myriad of nerve cells in the brain. Pasting gross electrodes to the human scalp allows us to monitor the ongoing activity of the more superficial cortical layers via the electroencephalogram as well as stimulated or voluntary activity through the various evoked potentials. The results thus obtained always reflect the activity of a relatively large group of nerve cells occupying some cm³ of brain tissue. Evoked potentials with better spatial resolution, originating from a few mm³ of brain tissue can be recorded by using microelectrodes with relatively large exposed tips that are pushed into the brain. Reducing the electrode tip to exposed lengths of only a few µm allows one to register the activity of only a few nerve cells; very small tips of around 0.1 µm even make it possible to penetrate a single nerve cell: the classical (intracellular) single-unit recording.