6 A Behavioral Approach to the Analysis of Reticular Formation Unit Activity

The brainstem reticular formation (RF) was one of the first structures to be investigated using single unit recording techniques. One procedure common to all the early studies was the attempt to eliminate spontaneous behavior prior to commencing unit studies. This was not done because investigators thought that behavior was unworthy of study. Rather, it was a direct result of the unit recording technology, which required the complete immobility of the animal. Immobility was most readily achieved with the use of barbiturate anesthesia. A major drawback of this anesthetic is that it almost completely eliminates spontaneous activity of cells in RF and many other regions. The subsequent use of chloralose anesthesia, which does not produce so severe a depression of spontaneous and elicited unit activity, was a great advance. More recently, techniques for recording from unanesthetized, head-restrained animals became available. These techniques allowed unit activity in the waking state to be observed for the first time. However, it is still necessary to eliminate most spontaneous behavior when using these procedures, since motor activity tends to produce small brain movements that cause the experimenter to "lose" the recorded cell. Thus, the behavioral expertise of researchers interested in unit activity in the RF and in many other areas has been largely devoted to teaching rats, cats, and monkeys to hold still during recording sessions. In many studies, this same goal was achieved by the use of curariform agents. The development of microwire and other recording techniques now allow unit recording in completely unrestrained, behaving animals. However, the adoption of this new methodology has been slow for several reasons. One is that many experimenters now have a considerable investment in the technology of recording from restrained animals. The apparent simplicity and lack of variability in the unit activity of the restrained preparation makes interpretation easier, although, as I will show below, this simplicity may be quite misleading. Perhaps the fundamental reason