Activity and functional connectivity of inferior frontal cortex associated with response conflict.

The traditional Stroop test of cognitive interference requires overt speech responses. One alternative, the counting Stroop, generates cognitive interference similar to the traditional Stroop test but allows button press responses. Previous counting Stroop studies have used concrete words in the control condition, which may have masked inferior frontal activation. We studied 7 healthy young adults using fMRI on a counting Stroop condition, with a nonlinguistic control condition (geometric shapes). As expected, we found activation in bilateral inferior frontal gyri, as well as in lateral and medial prefrontal, inferior parietal, and extrastriate cortices. Additional functional connectivity analyses using inferior frontal activation clusters (right area 44, left area 47) as seed volumes showed connectivity with superior frontal area 8 and anterior cingulate gyrus, suggesting that the role of inferior frontal cortex was related to response conflict and inhibition. Connectivity with left perisylvian language areas was not observed, which further underscores the nonlinguistic nature of inferior frontal activity. We conclude that bilateral inferior frontal cortex is involved in response suppression associated with interference in the counting Stroop task.