Evidence from studies exploring the effects of selective serotonergic drugs on cognitive processes in animals, healthy volunteers and clinical patients have suggested that they have cognitive enhancing properties. The primary aim of this thesis was to assess the effect of the selective serotonin reuptake inhibitor, paroxetine, on cognitive performance in young and elderly healthy volunteers and in depressed elderly patients who participated in a clinical trial comparing the effects of paroxetine with the tricyclic antidepressant, lofepramine. As there were no published memory tests with multiple versions available for repeated use in the proposed healthy volunteers studies, four memory tests were devised and assessed for equivalence and the effects of practice.
Paroxetine improved the delayed verbal recall performance of the young healthy volunteers and one elderly subject from a series of three single case studies. Performance on a range of other attention, verbal, visual and spatial memory tests was not impaired or enhanced by paroxetine. No significant differences were found on any of the cognitive measures between the elderly depressed subjects treated with paroxetine and those treated with lofepramine. A dissociation between clinical and cognitive recovery was identified in a group of patients who did not respond to treatment with paroxetine.
A secondary aim of the thesis was to assess the effects of depression on
cognitive function in unmedicated elderly depressed patients by comparing
baseline data from the clinical trial with data from non-depressed control
subjects. Cognitive deficits were identified in the depressed patients on measures that required effort and spontaneous organisation of materials for
recall, such as word list recall, and on the Speed of Comprehension test
(Baddeley, 1992). The results of this study were compared to previous studies, particularly those involving medicated depressed subjects.