Beyond common resources: the cortical basis for resolving task interference.

Recent studies have suggested that declining inhibitory control observed during simultaneous increases in working memory (WM) demands may be due to sharing common neural resources, although it is relatively unclear how these processes are successfully combined at a neural level. Event-related functional MRI was used to examine task performance that required inhibition of varying numbers of items held in WM. Common activation regions for WM and inhibition were observed and this functional overlap may constitute the cortical basis for task interference. However, maintaining successful inhibitory control under increasing WM demands tended not to increase activation in these overlapping regions as might be expected if these common areas reflect common resources essential for task performance. Instead, increased activation was observed predominantly in unique, inhibition-specific regions including dorsolateral prefrontal cortex. The finding that successfully maintaining weaker stimulus--response relationships in the face of competition from stronger, prepotent responses requires greater activity in these regions reveals the means by which the brain resolves task interference and supports theories of how top-down attentional control is implemented.