Stroop Performance in Normal Control Subjects: An fMRI Study Staci A. Gruber,* , † Jadwiga Rogowska,* Philip Holcomb,† Salvatore Soraci,† and Deborah Yurgelun-Todd* *Cognitive Neuroimaging Laboratory, Brain Imaging Center, Harvard Medical School, McLean Hospital, 115 Mill Street, Belmont, Massachusetts 02478-9106; and †Department of Psychology, Tufts University, Medford, Massachusetts 02115 Received October 2, 2000 In an attempt to clarify regional signal intensity changes, which may accompany the performance of the Stroop Color–Word task, healthy subjects were im- aged using the fMRI BOLD technique while perform- ing a modified version of the task. Both the AAA and VOA subdivisions of the anterior cingulate cortex were significantly activated during the interference condition; however, only the signal intensity change within the VOA correlated with task performance. Ad- ditionally, signal intensity change was significantly increased in the VOA subdivision of the cingulate cor- tex when controlling for signal intensity change present during the performance of a color naming task. This study extends previous findings by demon- strating that in healthy adults, a subdivision of the cingulate cortex is specifically associated with the cog- nitive demands present in the interference condition. © 2002 Elsevier Science (USA) Key Words: stroop; fMRI; anterior cingulate subdivi- sions; cognitive challenge. INTRODUCTION The interference subtest of the Stroop Color–Word test has been shown to reliably produce interference effects on response latency; however, the identification of focal cortical brain regions associated with the net- work that underlies the interference process has been more difficult to characterize. Positron emission tomog- raphy (PET) investigations provided the first evidence for regional brain changes during the Stroop interfer- ence subtest, particularly within the anterior cingulate cortex. Many of these studies were limited in their spatial resolution, however, and generally considered the entire anterior cingulate as a single functional region. The application of functional magnetic reso- nance imaging (fMRI) methods in the current study allows for improved visualization of changes in cortical signal intensity during cognitive challenge paradigms enabling the further subdivision of the anterior cingu- late into discrete subregions. Considered one of the most reliable psychometric tests (Jensen et al., 1965; Uechi, 1972), and found to remain relatively unaffected by test–retest situations (MacLeod, 1991), the Stroop Color–Word task has been used both as a screening instrument and as part of a large battery of tests for the screening and detection of frontal/executive brain dysfunction. The original Stroop task is comprised of three subtests, designed to establish competing response tendencies within the study subject and assess the subject’s ability to sup- press interfering stimuli. In the Color Naming subtest, the subject is asked to report the color of randomly sequenced color rectangles, thus establishing the ten- dency to respond to color. In the Word Reading subtest, the subject is asked to read color words randomly printed in black ink, establishing a response set to reading color words. In the Interference condition, the subject is given color words which are printed in an incongruent ink color. The subject is asked to report the ink color, and therefore has to suppress the ten- dency to read the color word. All sections of the test are timed, and the time to complete each section is the dependent variable of interest. Difficulty with inhibi- tion is reflected by an increase in time in the interfer- ence section relative to the color naming or word read- ing sections. Slowed performance on the interference subtest has thusfar been interpreted to be reflective of difficulty with the ability to resist interference, a cog- nitive function associated with frontal cortical integ- rity (Mesulam, 1987). One advantage of the Stroop task is that it has been studied extensively by neuropsychologists and cogni- tive neuroscientists since it was introduced in 1935 (Stroop, 1935), and has gained prominence since the emergence of the automatic-controlled distinction in cognitive psychology (Posner and Snyder, 1975; Shif- frin and Schneider, 1977). This is largely due to the fact that the Stroop task appears to pit an automatic process (word reading) against a controlled, conscious process (color naming). It is widely used as an index of attention and executive control, as the task requires the ability to actively inhibit an overlearned response in favor of a more voluntary response. The interference effect or Stroop effect has been shown to be a robust phenomenon (Cohen et al., 1990; MacLeod, 1991), and NeuroImage 16, 349 –360 (2002) doi:10.1006/nimg.2002.1089, available online at http://www.idealibrary.com on 349 1053-8119/02 $35.00 © 2002 Elsevier Science (USA) All rights reserved.