‘Weightless’ Micro-electrodes for recording Extracellular Unit Action Potentials from the Central Nervous System

IN order to record the activity of single nerve cells in the mammalian central nervous system it is necessary to maintain the tip of the recording electrode (a micropipette or metal needle) within some 30µ of the cell body1. The skeleton of the animal is usually rigidly clamped to a heavy metal base and in many experiments this base also carries the micro-electrode upon a rigid support. Unfortunately the exposed central nervous system expands with every beat of the heart and also with exhalation of air from the lungs. Because such movements can make records of unit activity difficult or impossible to obtain, a technique has been developed2,3 for recording from cells in the cerebral cortex in a rigidly enclosed cranial cavity. This system has proved so successful that lengthy records can be obtained from unanæsthetized, mobile animals. There are, however, limitations to this technique. It is not readily adaptable to exploration of a wide area of cortex; moreover, it cannot be applied to an examination of the spinal cord or brain-stem. For this reason we have developed the ‘weightless’ micro-electrode described below.