Top-down resolution of lexico-semantic competition in speech production and the role of the left inferior frontal gyrus: an fMRI study

Recent neurobiological speech production accounts propose the left inferior frontal gyrus (LIFG) resolves lexical competition using top-down control. The current fMRI experiment investigates whether response set membership influences LIFG involvement. In the picture-word interference paradigm target pictures were presented with distractor words that were, or were not, targets on other trials. Production models predict greater LIFG involvement in the high-coactivation trials with response set target-distractor pairs. Surprisingly, we found no effect of response set. Semantic interference elicited activation in the left posterior temporal cortex, similar to previous reports. Pooling data across response set conditions revealed additional significant activation in pars orbitalis of the LIFG, indicating detection benefited from the additional statistical power. Our findings challenge the co-activation assumption and indicate inconsistent LIFG results reported in the literature might reflect a combination of small effect size and low signal-to-noise, thus questioning the prominent role afforded to the LIFG.