Experimental studies of the central nervous system related to anaesthesia. IV. Effects of pentobarbital placement in caudate nucleus.

THE STATE OF AWARENESS is known to have a functional relationship with the brain stem reticular formation. This follows the work of Moruzzi and Magoun. 1 The concept of the ascending (reticular activating) fibres arising from the reticular formation and influencing widespread central nervous system centres is illustrated in Figure 1. It is known that thalamocurtieal trafl~e is multidirectional. 1 The state of awareness is characterized in electroencephalographic recordings obtained from the cerebral cortex of man and experimental animals by the pattern of activation. 1 This consists of fast, low amplitude waves in the EEC tracing. Sleep, on the other hand, is associated with the EEC pattern of deactivation which is characterized by higher amplitude and slower electrical recordings. During the production and maintenance of anaesthesia, there is a graded pattern of fast activity progressing through slower activity to increasingly prolonged periods of suppression ( Fig. 2) 3 It has not proved possible to produce deep sedation, or marked cortical deactivation, by the local injection of pentobarbital into the brain stem reticular formation. Therefore, a search was instituted for other subcortical sites which might prove more sensitive to the action of this drug.