An additive factor analysis of the effect of sub-anaesthetic doses of nitrous oxide on information processing: evidence for an impairment of the motor adjustment stage.
BACKGROUND
Nitrous oxide (N(2)O) inhalation, at subanaesthetic concentrations, impairs choice reaction time (RT). However, the functional locus of this effect remains to be ascertained. In the present study, this issue was investigated by applying the additive factor logic to the RTs of rats performing a visuo-motor task.


METHODS
The task consisted of either a left-side or a right-side body displacement to a visual stimulus displayed in either the left or right hemispace. The experimental design involved the manipulation of two task factors (stimulus luminance and foreperiod duration) the effects of which are additive on RT. Inhaled N(2)O (from 0% to 60%) was varied as the third factor of the design.


RESULTS
N(2)O prolonged RT in a dose-dependent manner and this effect was additive with that of stimulus luminance, whilst it interacted with that of foreperiod duration. Moreover, at low concentrations (10-20%), N(2)O abolished the effect of foreperiod, possibly through a disturbance of time estimation processes, whereas at higher concentrations (30-40%) N(2)O enhanced the effect of foreperiod, probably by slowing down motor processes. Movement time (MT) was decreased by N(2)O at 20-40%.


CONCLUSIONS
The present data provide evidence that N(2)O impairs information processing by altering at least the stage of motor adjustment. In addition, N(2)O spares the sensory processes implemented during the stimulus preprocessing stage. A subsidiary result is that at some concentrations, N(2)O displays opposite effects on reaction time and movement time. These results demonstrate that the additive factor method constitutes a powerful new tool for studying the pharmacology of information processing in animal models.
Courtière
Alain
A
Institut de Médecine Navale du Service de Santé des Armées, 83800 Toulon Naval, France. a.courtiere@imnssa.net
Hardouin
Jeannine
J
Vidal
Franck
F
Possamaï
Camille-Aimé
CA
Hasbroucq
Thierry
T
D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002755:Choice Behavior / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005163:Factor Analysis, Statistical; D007839:Functional Laterality; D009068:Movement / Q000187:drug effects; D009609:Nitrous Oxide / Q000494:pharmacology*; D010775:Photic Stimulation; D011597:Psychomotor Performance / Q000187:drug effects*; D051381:Rats; D020318:Rats, Long-Evans; D011930:Reaction Time / Q000187:drug effects
D018685:Anesthetics, Inhalation; D009609:Nitrous Oxide