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A measure of consciousness and memory during isoflurane administration: The coherent frequency.
Munglani, R., Andrade, J., Sapsford, D.J., Baddeley, A.D. & Jones, J.G.
British Journal of Anaesthesia, 71, 633-641.
Year of publication:
The effects of anaesthesia on brain function were investigated by assessing cognitive performance and auditory evoked responses (AERs) in seven volunteers anaesthetised with isoflurane. Cognitive performance was assessed at 0.0%, 0.2% and 0.4% isoflurane, using a semantic categorisation task and a within-list word recognition task. At 0.4% isoflurane, performance was assessed before and after electrical stimulation of the subject's hand, intended to mimic the arousing effects of surgery. Also, at 0.8% isoflurane, a word list was read repeatedly to the subject. AERs were recorded, using stimulatory frequencies of 5-47 Hz, at each of these levels. Both cognitive performance and the coherent frequency of the AER declined as the inhaled concentration of isoflurane increased, whereas electrical stimulation led to improved cognitive performance. No evidence was found for memory of words presented at the highest level of anaesthetic.