A simple system for the recording of single unit activity in unrestrained cats.

For recording the activity of single neurons in unanesthetized animals two techniques can be used: permanently implanted microwires (7) or movable microelectrodes (1, 2, 4-6, 8). The latter method permits to make a selection of cells in the course of the experiment. However, cells cannot be kept for a long time and are easily lost during violent head movements. Besides, successive penetrations cause some demage to the brain tissue and increase the risk of infection. Several requirements should be met by any system to be really effective during behavioral experiments. The system should be precise, solid and easy to operate. Obviously the device should be small and light so that it does not cause too much discomfort to the animal. This is especially important when we try to relate some forms of spontaneous or acquired behavior to altered patterns of neuronal activity. Probably no single technique will solve all the problems involved in that type of research on unrestrained animals. Some systems successfully used are very complicated and expensive (1, 3, 4). Evart's hydraulic microelectrode positioner requires many specially machined parts. Other systems also required many small precise details, which need sophisticated shaping (4). The system described here is simple and easy to manufacture, yet enables a precise localization of the recording electrode. The micro-manipulator consists of a U-shaped, light-metal frame and of a fine-thread screw, rotating between its arms (Fig. 1). The microelectrode can be advanced to the target by turning the knob A. The depth of penetra