A Developmental Fmri Study of the Effect of Context on Inhibition

Abstract:
This study examined the effects of parametrically manipulating the number of targets preceding a nontarget in a go nogo task using an event related fMRI design. Pokemon characters served as stimuli. Subjects were instructed to press to any Pokemon except "Meowth". A 75% target frequency was maintained across the study and stimuli were presented every 4 seconds. Echo planar images were acquired in 28 axial slice locations. Nontarget trials preceded by 1, 3 or 5 targets were analyzed with an ANOVA. Typically, nogo trials are compared to go trials introducing the confound of a motor response in one condition and not the other. This study compared nogo trials to one another that differed only in the preceding context (1, 3, or 5 preceding targets). Imaging results from 9 adults showed a monotonic increase in MR signal as a function of increasing number of preceding targets for right dorsolateral and inferior frontal cortex. Preliminary data from 7 year old children did not show this pattern, but showed reliable activity in the right anterior cingulate and orbitofrontal cortex for go versus nogo trials. Accuracy was 93% or greater for both age groups. The results will be discussed in terms of efficiency in representing context and parallel brain development and also with respect to equating task difficulty.