Simple and disjunctive reaction time under the influence of chlorpromazine hydrochloride
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Abstract
This study aimed to clarify some relationships between the drug chlorpromazine hydrochloride and reaction time. Chlorpromazine is a drug in widespread use in the treatment of mental illnesses, particularly schizophrenia. The mechanisms of its action are not clearly defined physically or psychologically. The author's curiosity in the drug was stimulated by observations of its effects in a hospital setting. This stimulated curiosity in the effects of the drug on normal subjects.
Major interest in the drug has centered about its effect in contributing to remissions in schizophrenia. Many authors have described "dramatic" improvements soon after introduction of the drug, ranging from amelioration of symptoms to a "cure" for the illness. A frequently reported observation was diminution in assaultiveness, hyperactivity and destructiveness. A number of studies reported inhibition of conditioned responses in animals. Neurologists found increased concentration of the drug in areas of the central nervous system involved in motor functioning.
Some studies report the effects of rather large dosages of chlorpromazine on some simple intellectual and motoric tasks, but the results were contradictory.
In the absence of known basic studies it was decided that the most fruitful area for investigation was the effect of chlorpromazine on psychomotor functioning. Reaction time was chosen as an experimental variable, partly because it lends itself to precise measurement and partly because it has been demonstrated to be relatively consistent, within individual age groups, throughout the normal population. In addition reaction time is an integral part of all responses. Working with normal subjects and established psychophysical procedures some basic information was gathered.
The general hypothesis was that under the influence of chlorpromazine reaction time would increase and that increase in reaction time would vary directly with amount of dosage. It was expected that low dosage levels of chlorpromazine would have less effect on disjunctive reaction time than on simple reaction time.
The method of investigation chosen involved repeated measurements on the same subject. Two normal adult males served as subjects. A standard reaction time apparatus which permitted measurements in units of .01 seconds was used. The stimuli were a bell and a buzzer; and response involved pressing a telegraph key. Controls for fatigue, set, temporal conditioning, practice and suggestion were introduced. The latter was controlled by placebos and by utilizing both single-blind and double-blind dosage series.
Subjects were tested on two different days with each dosage used. The dosages were 0, placebo, and 25, 50, 75, 100, 125 and 150 milligrams. There were three tasks: simple reaction time, left hand; simple reaction time, right hand; and disjunctive reaction time. On each day reaction times were taken prior to drug administration and at 1, 1 1/2, 2, 2 1/2, 3 and 3 1/2 hours after drug administration. A total of 3600 reaction times were taken for each subject.
The data were treated statistically by analysis of variance. Separate analyses of variance were computed for each experimental condition and each subject. The data were converted to logarithms to correct a mild positive skewness.
The effect of chlorpromazine was to increase reaction time. The increase occurred as a positive non-linear function of dosage, reaching its maximum in this study at 150 milligrams. The percent change in reaction time from pre-drug to post-drug measures was greater for simple reaction time than for disjunctive reaction time at dosages of 100 milligrams and less. At 125 and 150 milligrams both types of reaction time appeared to be equally impaired.
In general, peak effects were reached between two and two and one-half hours after drug administration. At lower dosage levels reaction time tended to return to its predrug levels after three and one-half hours, at which time the last reading was taken. At the higher dosage levels impairment in reaction time was greater and at three and one-half hours remained substantially above its pre-drug level.
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Thesis (Ph.D.)--Boston University
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