title: Methylphenidate does not enhance visual working memory but benefits motivation in macaque monkeys.
abstract: Working memory is a limited-capacity cognitive process that retains relevant information temporarily to guide thoughts and behavior. A large body of work has suggested that catecholamines exert a major modulatory influence on cognition, but there is only equivocal evidence of a direct influence on working memory ability, which would be reflected in a dependence on working memory load. Here we tested the contribution of catecholamines to working memory by administering a wide range of acute oral doses of the dopamine and norepinephrine reuptake inhibitor methylphenidate (MPH, 0.1-9 mg/kg) to three female macaque monkeys (Macaca mulatta), whose working memory ability was measured from their performance in a visual sequential comparison task. This task allows the systematic manipulation of working memory load, and we therefore tested the specific hypothesis that MPH modulates performance in a manner that depends on both dose and memory load. We found no evidence of a dose- or memory load-dependent effect of MPH on performance. In contrast, significant effects on measures of motivation were observed. These findings suggest that an acute increase in catecholamines does not seem to affect the retention of visual information per se. As such, these results help delimit the effects of MPH on cognition.
authors.affiliation: Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada.
authors.forename: Mariann
authors.initials: M
authors.lastname: Oemisch
authors.affiliation: Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada.
authors.forename: Kevin
authors.initials: K
authors.lastname: Johnston
authors.affiliation: Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada; Departments of Biomedical & Molecular Sciences and Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada. Electronic address: martin.pare@queensu.ca.
authors.forename: Martin
authors.initials: M
authors.lastname: Paré
mesh_terms: D000284:Administration, Oral; D000818:Animals; D018765:Dopamine Uptake Inhibitors / Q000008:administration & dosage*; D004305:Dose-Response Relationship, Drug; D005260:Female; D008253:Macaca mulatta; D008570:Memory, Short-Term / Q000187:drug effects* / Q000502:physiology; D008774:Methylphenidate / Q000008:administration & dosage*; D009042:Motivation / Q000187:drug effects* / Q000502:physiology; D011597:Psychomotor Performance / Q000187:drug effects / Q000502:physiology; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D014796:Visual Perception / Q000187:drug effects* / Q000502:physiology
chemical_list: D018765:Dopamine Uptake Inhibitors; D008774:Methylphenidate
keywords: Catecholamine; Change detection; Methylphenidate; Monkey; Motivation; Visual working memory capacity