Effect of a subanesthetic dose of ketamine on memory and conscious awareness in healthy volunteers.
BACKGROUND
Ketamine is an NMDA receptor antagonist with psychotogenic and cognitive effects in healthy volunteers and schizophrenic patients which has been proposed to be a useful tool to investigate neurobiological basis of schizophrenia.


OBJECTIVE
The present study characterized the effects of a subanesthetic dose of ketamine on memory and related subjective states of awareness in healthy volunteers.


METHODS
Twenty-six subjects were given either a 60-min ketamine (0.5 mg/kg per hour) or a placebo infusion. To obtain constant plasma ketamine throughout the experiment, ketamine was administered using a computer-controlled infusion system. Subjects carried out episodic memory tasks involving words presented before and during infusion. Memory performance was assessed with recognition and free recall tasks. Subjective states of awareness were assessed using an experiential approach. Levels of psychopathology were evaluated with BPRS.


RESULTS
Ketamine impaired performance in free recall and recognition of words presented during, but not before, infusion. There were no differences between groups concerning states of awareness associated with recognition memory. Subjects under ketamine had higher BPRS total scores as well as BPRS negative and positive cluster scores than control subjects.


CONCLUSIONS
Ketamine decreases episodic memory performance by impairing encoding, but not retrieval processes. It does not selectively impair subjective states of awareness associated with recognition memory as it has been seen in patients with schizophrenia. Ketamine might mimic the memory impairment associated with acute, but not chronic, forms of schizophrenia.
Hetem
L A
LA
Departamento de Neurologia, Psiquiatria e Psicologia Médica, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, Brazil.
Danion
J M
JM
Diemunsch
P
P
Brandt
C
C
D000328:Adult; D001288:Attention / Q000187:drug effects; D001364:Awareness / Q000187:drug effects*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D005260:Female; D006801:Humans; D007649:Ketamine / Q000097:blood / Q000494:pharmacology*; D008297:Male; D008568:Memory / Q000187:drug effects*; D011939:Mental Recall / Q000187:drug effects; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors*
D018691:Excitatory Amino Acid Antagonists; D016194:Receptors, N-Methyl-D-Aspartate; D007649:Ketamine