J. S. Kerr

Separate and combined effects of the social drugs on psychomotor performance

Ten female subjects (five smokers and five non-smokers) performed a choice reaction time task (CRT), a compensatory tracking task (CTT), a short-term memory task (STM) and were tested for their critical flicker fusion threshold (CFF) at set points over 4 h after the administration of each possible combination of nicotine (2 mg gum or placebo), caffeine (250 mg capsule or placebo) and alcohol (30 g or placebo). Memory and motor function were shown to be facilitated by nicotine or caffeine, and the debilitating effects of alcohol were frequently antagonised by either drug. In spite of the differences in their neuropharmacological actions, combinations of nicotine, caffeine and alcohol may be compared through their effects on common information processing mechanisms involved in psychomotor performance.

The effects of acute and repeated doses of zolpidem on subjective sleep, psychomotor performance and cognitive function in elderly volunteers

SummaryWe gave 24 healthy elderly volunteers with a perceived sleep onset of at least 30 minutes zolpidem 5 mg, zolpidem 10 mg, or placebo for 7 days in a double-blind, three-way, crossover study.The morning after nocturnal dosing, psychomotor performance and cognitive ability were measured using tests which are sensitive to the residual effects of hypnotics and to the effects of drugs on various indicators of sleep quality. The tests were: Choice Reaction Time; Tracking; Critical Flicker Fusion Threshold; Memory Scanning; Word Recognition; the Leeds Sleep Evaluation Questionnaire and Line Analogue Rating Scales.Zolpidem produced a subjective improvement in sleep but did not impair performance the following day. Furthermore, during repeated administration, there was no tolerance to the effects of sleep latency and quality of sleep, nor adverse effects on task performance.

Psychomotor performance in smokers following single and repeated doses of nicotine gum

The psychomotor effects of single and repeated doses of 2 mg nicotine gum were investigated in 13 regular smokers who had abstained from tobacco overnight. In comparison to baseline, a first dose of nicotine led to significantly raised critical flicker fusion thresholds, faster motor reaction times, improved compensatory tracking performance, and faster short-term memory reaction times. Performance after a second and third dose of nicotine remained significantly improved on all measures in comparison to baseline, and absolutely improved when comparing first and third nicotine doses on measures of sensorimotor performance. Throughout, comparisons with a placebo gum condition confirmed that these effects were genuine and not subject to the development of acute nicotine tolerance, suggesting that the enhancement of psychomotor performance experienced by smokers after a first cigarette may be maintained by repeated smoking.

Behavioural toxicity of antidepressants with particular reference to moclobemide

The clinical decision to use a particular antidepressant should be made with reference to the behavioural toxicity profiles of substances in current use. Antidepressants can be cardiotoxic, proconvulsant, able to cause weight gain and sleep disturbance, and also impair psychological functions necessary for everyday living. Behavioural toxicity (reduction in psychomotor activity or cognitive ability) tends to augment levels of psychomotor and cognitive retardation; meta-analysis of controlled studies of antidepressants shows that some tricyclics can disrupt these functions. In comparison with these, moclobemide is relatively free from significant behavioural toxicity within the dose-ranges used. No relevant differences were found between placebo and 200 mg moclobemide on a battery of psychomotor and cognitive tests: with 400 mg, there was a significant impairment of peripheral reaction time, but no other measure of the test battery was impaired. In comparison, amitriptyline 50 mg, produced a noticeable and significant impairment of psychomotor and cognitive skills on most test measures. On the whole moclobemide has been found to be free from any behavioural toxicity likely to interfere with the well-being of patients or their performance of the tasks of everyday living.

The psychomotor and cognitive effects of a new antihistamine, mizolastine, compared to terfenadine, triprolidine and placebo in healthy volunteers

Eighteen healthy volunteers received mizolastine 5 mg, 15 mg or 45 mg, terfenadine 60 mg, triprolidine 10 mg or placebo in a 6-way crossover, double blind study. Following each dose, subjects performed a series of tests of cognitive function and psychomotor performance at 1, 3, 5, 8 and 24 hours post-dose. The test battery included critical flicker fusion, choice reaction time, tracking, Stroop and Sternberg memory tests and assessment of subjective sedation.Sedative effects and a concomitant reduction in psychomotor and cognitive function were observed following triprolidine, terfenadine and the highest dose of mizolastine, 45 mg, e.g. triprolidine reduced CFF threshold by 1.5 Hz and increased reaction time by 50 ms, impairments comparable to those caused by blood alcohol concentrations of 50 mg%, the legal limit in many countries. Mizolastine 5 mg did not differ significantly from placebo and at 15 mg differed only at one test point at one time.It may be concluded that mizolastine (5 mg and 15 mg) is free from disruptive effects on cognitive function and psychomotor performance, in contrast to terfenadine 60 mg, triprolidine 10 mg and mizolastine 45 mg.

THE EFFECTS OF PRACTICE ON CHOICE REACTION TIME AND CRITICAL FLICKER FUSION THRESHOLD

The use of psychometrics in psychopharmacology assumes that subjects are trained to ‘plateau’ performance levels prior to experimental data being collected. Fourteen healthy, naive volunteers were tested on CFF and CRT over a 5‐day period. On days 1 and 5 subjects carried out the tests six times, with intervals of 10 min between the trials. On days 2, 3 and 4, the subjects were tested once on both CFF and CRT. CFF scores reached a ‘plateau’ after three trials. There was no effect of time on CFF on either day 1 or 5. There was a significant interaction between day, time and CFF thresholds (F = 3 · 71, p < 0·006) which was probably a result of the method of limits technique used in this CFF task, but there were no significant differences in CFF thresholds between test days. The CRT scores reached a ‘plateau’ after six trials on day 1 and this ‘plateau’ was maintained over the following days. The results show performance ‘plateaus’ on CFF and CRT tests are reached after three trials and four sessions of 20 trials respectively.

The effects of alcohol alone or in combination with other drugs on information processing, task performance and subjective responses

This paper reviews the effects of alcohol on human psychomotor performance and cognitive function. It concentrates particularly on effects on reaction time and on skills related to car driving. The effects of alcohol on performance are very variable at low doses (under 1 g per kg body weight). The variability is due to the different measures and methods employed by the researchers and to the large interindividual and interoccasional differences in the effects of alcohol. That is, alcohol affects different people in different ways and it affects the same person differently on separate occasions. Greater performance deficits are observed as the dose increases and as the tasks become more complex. Although results vary, both nicotine and caffeine appear to antagonize the detrimental effects of alcohol on performance. Many other drugs interact with alcohol, the most important of which are sedative agents that can combine synergistically with alcohol to produce profound psychomotor and cognitive impairment.

Two myths of addiction: the addictive personality and the issue of free choice

This short review paper examines two aspects of addiction controversies: whether there is such an entity as an addictive personality, and the question of whether free choice is involved in substance use. The former is part of an argument with a long history, with the case for the existence of an addictive personality being put more often, particularly in the USA. The latter is a more recent development in the debate that raises important issues in the research on substance use and addition. It is concluded that there is no evidence for the existence of a personality type that is prone to addiction, and that free choice can be seen to be a part of substance use, i.e. the compulsion element is lacking.

CITALOPRAM COMPARED TO DOTHIEPIN AND PLACEBO : EFFECTS ON COGNITIVE FUNCTION AND PSYCHOMOTOR PERFORMANCE

Three doses of citalopram (10, 20 and 40 mg), and placebo were administered to healthy volunteers for periods of 8 days each. Dothiepin 75 mg was given as an acute dose on days 1 and 8 only, with placebo dothiepin on days 2–7. Subjects were tested on days 1 and 8 of the dosing periods on a battery of psychometric tests. The results showed that citalopram at all doses had no detrimental effects on psychomotor performance. The effect of citalopram on critical flicker fusion (CFF) was to raise thresholds. This indicates an improvement in CNS function, i.e. an elevation of cognitive processing ability, with no evidence of an arousing or alerting effect. The effects were apparent after both acute and sub‐chronic dosing. These data are in contrast to those collected for dothiepin, which showed significant impairment of cognitive and psychomotor function on most of the measures employed. The most frequent adverse events reported for citalopram were drowsiness, nausea and headache, with the nausea appearing to be dose dependent. The main adverse events reported for dothiepin were drowsiness, sleepiness and dizziness. The rates of adverse events for all active treatments were not statistically significantly different to placebo. It is concluded that citalopram is relatively free from behavioural toxicity and so represents a significant improvement over the older antidepressant agents such as dothiepin.

Effects of Nicotine Gum on Short-Term Memory

To investigate the effects of nicotine on memory function, 20 subjects (10 non-smokers and 10 smokers who had been allowed to smoke normally until testing) attended the laboratory at their “preferred nicotine level” and completed a short-term memory task (memory scanning) at set points for 4 hours after the administration of 2mg or 0mg (placebo) nicotine polacrilex gum. The results suggest that nicotine enhanced memory reaction time performance (P>0.01) when subjects were probed for information already present in short-term memory (correct positive responses) but had no effect on reaction time when the information was absent from memory (correct negative responses). It is suggested that nicotine facilitates the processing of stimulus information in short-term memory.