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| |  DG DISPATCH - ECNP: Some SSRIs May Impair Vigilance And Long-Term Memory By Olwen Glynn Owen Special to DG News LONDON, UK -- September 27, 1999 -- Some antidepressants may have adverse effects on cognitive skills such as memory and vigilance according to researchers at the Experimental Psychopharmacology Unit, Maastricht University, The Netherlands.
In a study presented at the 12th congress of the European College of Neuropsychopharmacology, held in London September 21-25, Jeroen Schmitt and colleagues compared the effects of the selective serotonin reuptake inhibitors (SSRIs), paroxetine and sertraline. The researchers compared against placebo the effects of the drugs on vigilance, memory, learning tasks and sleep quality in 21 healthy non-depressed volunteers aged 30-50. The study was a randomised, double-blind, three-way cross-over study with three treatment periods of 14 days separated by 14-day washout periods. The daily starting doses of paroxetine and sertraline - 20 milligrams (mg) and 50 mg respectively - were doubled from day 8-14 of each treatment period. Assessments were carried out during the afternoon on days 7 and 14 of each regimen. Vigilance was assessed using the Mackworth Clock test where subjects have to spot deviations in a clockwise succession of briefly illuminated dots. When a dot was skipped, subjects pressed a button registering scores for reaction time and the number of correct responses. Other tests assessed short- and long-term memory storage and retrieval. Focussed and divided attention was studied with reading and listening tests and sleep quality was assessed by a subjective sleep questionnaire. Results showed both drugs were associated with a small reduction in subjective sleep quality. Neither drug affected focussed or divided attention or short-term memory skills. But paroxetine at both 20-mg and 40-mg doses significantly impaired vigilance and long-term memory function. The authors comment that other SSRIs as well as paroxetine impair vigilance, suggesting that serotonin inhibits other neurotransmitters that maintain arousal, especially where monotonous tasks are concerned. "Sertraline’s ability to block dopamine re-uptake sites and increase dopamine transmission probably attenuate the arousal-lowering effects of serotonergic inhibition of the dopaminergic system," according to the authors. Paroxetine’s anticholinergic properties, due to a relatively high affinity for muscarinic acetylcholine receptors, probably explain the impairment of long-term memory retrieval, they added.
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