Unconscious perception and general anaesthesia

Abstract

For ethical, quite apart from theoretical, reasons it is important to know whether or not general anaesthesia prevents the brain from registering the effects of external stimuli. Are apparently unconscious patients 'blind' and 'deaf' to happenings around them or could they be affected by, for example, what a surgeon says during the course of an operation? Does the absence of any overt response to an external stimulus indicate that the surgeon's conversation has no or lasting effect upon a patient's well-being, or could it be that, although apparently unconscious, the patient is by no means psychologically immune to what is going on in the vicinity? If an anaesthetized patient is not insulated from external stimuli, as demonstrated by the recent research of Evans and Richardson (1988) (see also review by Jones, 1988), then it is theoretically possible that the information they convey could be even more damaging than it would if consciously received (i.e. in the normal waking state). There are three reasons for this supposition. First, doctors may be less guarded in how they express themselves when patients are unconscious. Second, anaesthetized patients would be less able to defend themselves against the implications of what they had 'heard', i.e. because of anaesthesia they would be denied the opportunity of using normal, conscious, cognitive processes to rationalize or cope with 'bad news'. Third, and perhaps most serious of all, it is theoretically possible that information which bypasses consciousness may activate complexes (repressed systems of emotionally charged ideas), with unfortunate psychological consequences (e.g. postoperative depression). As we shall see later, anxiety generated by unconsciously received information could also have psychosomatic effe~cts postoperatively. It is in the light of these considerations that this chapter surveys a body of evidence from diverse sources which suggests that since unconscious perception occurs in many other contexts, there is every reason to assume that it may well occur during general anaesthesia.