Book T of C
Chap T of C
This is the 2007 version. Click here for the 2017 chapter 06 table of contents.
Weinberger, Sternberg and Gold (1984) reported that adrenaline acted as a switch for turning on memory-formation processes in rats even when they were anesthetized and unconscious. The researchers first gave rats enough anesthetic to eliminate any visible response to electric shock or electronically generated tones. Then they carried out a classical conditioning procedure, pairing the tone with the electric shock. One group of rats received an injection of adrenaline during the training procedure, the other did not. Only the group receiving the adrenaline showed evidence of conditioning later.
How did Weinberger and colleagues train an anesthetized rat?
What types of events are remembered after surgery?
The researchers emphasized that the adrenaline did not alter the rats' level of anesthesia. The rats remained "out cold" during the whole conditioning procedure. Adrenaline seemed to switch on areas of the brain where memories were formed, despite the anesthesia.
These findings may explain why patients who undergo surgery sometimes remember events that occur during deep anesthesia. Years ago doctors assumed these patients simply had overactive imaginations. However, evidence slowly accumulated that patients could indeed remember events that occurred during surgical operations if those events were sufficiently shocking.
Mostert (1975) reported an interesting study of this phenomenon during surgery that involved opening the chest wall.
I was one of the anesthetists who helped Levinson study 10 volunteer patients. At deep levels of di-ethyl ether anesthesia as judged from virtual electrical quiescence and only occasional spindles, Levinson presented the patients with a (feigned) alarming comment indicative of a life-threatening crisis. One month later the patients were hypnotized and regressed to the operation. Four were able to reproduce the words spoken, such as "the lung looks cancerous...it is black from living in the city." Four patients became anxious and awoke from the hypnosis, and two did not reproduce the suggestion. None of the patients had recall at the conscious level. (p.69)
What was Levinson's experiment?
How did Kihlstrom and colleagues show memory for non-shocking events heard during anesthesia?
Mostert maintained that earlier researchers failed to find evidence of memory during anesthesia because they presented patients with trivial stimuli such as word lists. Only arousing or shocking stimuli succeed in penetrating the anesthesia. Perhaps "shocking" remarks stimulate a small amount of adrenaline release
If sufficiently sensitive measures are used, researchers can demonstrate that regular, non-shocking stimuli also penetrate anesthesia to some extent. Kihlstrom, Schachter, Cork, Hurt and Behr (1990) were able to show memory for word lists, presented to anesthetized patients. They used the paired associates technique, reading pairs of words (the first a stimulus word, the second a response word) to the anesthetized patients.
After awakening, none of the patients could consciously recall any of the words, nor could they recognize them. Memory effects showed up only in a free association test. The free association test consisted of reading the stimulus words (the same ones used under anesthesia) one at a time. The patient was supposed to "report the first word that comes to mind" when hearing the stimulus word. Under these conditions, subjects who heard word-pairs during anesthesia were significantly more likely than control subjects to report the response words they heard under anesthesia.
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