Long-term effects of vaccination on attentional performance

To investigate the possible influence of stimulation of the immune system on cognitive tasks, C healthy volunteers were vaccinated against hepatitis B and tested over a 6 month-period in a simple reaction times and the Stroop task. In general, the "Stroop effect" demonstrates that both the name and meaning of a word are automatically processed even when voluntary attention is trying hard not to process them. Unlike placebo group, vaccinated subjects showed a persistent lack of the classical Stroop effect. These findings may be explained by a constraint satisfaction model of the Stroop task, assuming a selective weakening of the connection matrix, and suggest that immune-cognitive effects may occur, besides the well known immune-cognitive influences like those elicited by emotional stress. (C) 2004 Elsevier Ltd. All rights reserved.