Abstract
Data from clinical and cross-sectional studies suggest that inflammation contributes to psychomotor slowing and attentional deficits found in depressive disorder. However, experimental evidence is still lacking. The aim of this study was to clarify the effect of inflammation on psychomotor slowing using an experimental and acute model of inflammation, in which twenty-two healthy volunteers received an intravenous injection of lipopolysaccharide (LPS, dose: 0.8 ng/kg body weight) and of placebo, in a randomized order following a double-blind within-subject crossover design. A reaction time test and a go/no-go test were conducted 3 h after the LPS/placebo injection and interleukin (IL)-6 and tumor necrosis factor (TNF)-α concentrations were assessed. No effect of experimental inflammation on reaction times or errors for either test was found. However, inflammation was related to worse self-rated performance and lower effort put in the tasks. Exploratory analyses indicated that reaction time fluctuated more over time during acute inflammation. These data indicate that acute inflammation has only modest effects on psychomotor speed and attention in healthy subjects objectively, but alters the subjective evaluation of test performance. Increased variability in reaction time might be the first objective sign of altered psychomotor ability and would merit further investigation.
Highlights
Psychomotor retardation is characterized by a slowing-down of physical movements, emotions, and thoughts (Caligiuri et al, 2003)
Reaction time tests outcomes after LPS versus placebo administration Reaction time was significantly slower in the go/no-go test compared to the simple reaction time test (b(SD) 1⁄4 159.07(13.01), p < .001), with no significant main effect of treatment (b(SD) 1⁄4 9.38(13.48), p 1⁄4 .490) and no significant interaction effect (b(SD) 1⁄4 6.51(18.66), p 1⁄4 .729), indicating no significant difference in reaction time after LPS administration compared to placebo administration in both tests (Fig. 1A)
A significant interaction was found for reaction time variability (go/no-go: b(SD) 1⁄4 -0.02(0.06), p 1⁄4 .737; LPS: b(SD) 1⁄4 -0.09(0.06), p 1⁄4 .132; interaction: b(SD) 1⁄4 0.20(0.08), p 1⁄4 .021), indicating that reaction time fluctuated more after LPS administration compared to placebo administration in the go/no-go test (Fig. S2)
Summary
Psychomotor retardation is characterized by a slowing-down of physical movements, emotions, and thoughts (Caligiuri et al, 2003). The model of LPS administration in healthy humans has been extensively used over the past 30 years to understand the mechanisms underlying cytokine-induced behavioral changes, because of its relevance for inflammation-associated depression (DellaGioia and Hannestad, 2010; Lasselin et al, 2020b, in press; Schedlowski et al, 2014). This model allows assessing the behavioral effects of inflammation in a safe and highly standardized manner, but the characterization of its effects on psychomotor slowing is lacking
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