Investigating the Neural Substrates of Response Inhibition in the Stroop Test - A Voxel-Based Lesion-Symptom Mapping Study

Inhibition can be defined as our ability to resist interference and suppress automatic responses. It is a central part of cognitive control, which is crucial to selecting and prioritizing important information. Deficits in inhibition ability are thought to be at the core of many psychiatric disorders such as ADHD and OCD. Previous studies have identified a set of neural networks commonly engaged in inhibition tasks. These areas are sometimes collectively referred to as the fronto-parietal network, and include the anterior cingulate cortex (ACC), the lateral prefrontal cortex (LPFC), and certain parietal areas. However, the research results are conflicting, and there is still no absolute consensus about which brain regions are implicated in inhibition and how the brain organizes and executes cognitive control. Identifying the neural substrates of inhibition could potentially lead to increased understanding of brain-behavior relationships including the neurobiological underpinnings of many of the mental disorders. The primary aim of this study was to investigate the neuroanatomical basis of inhibition using a neuroimaging analysis technique called voxel-based lesion-symptom mapping (VLSM). VLSM is conducted by analyzing the relationship between tissue damage and behavioral performance on a voxel-by-voxel basis. We used behavioral data from the Color-Word Interference Test (a.k.a. the Stroop test) in combination with MRI-derived information on lesion characteristics obtained from patients with focal injury to different subsectors of the prefrontal cortex. The participants were recruited from the Dept. of Neurosurgery at Oslo University Hospital. The project used already-existing data collected in the project Mechanisms of Cognitive Control in the Human Brain led by Anne-Kristin Solbakk and Tor Endestad at Front Neurolab. Our main hypothesis was that damage to voxels in the left dorsolateral prefrontal cortex (DLPFC) or the left ventrolateral prefrontal cortex (VLPFC) would be associated with impaired Stroop performance. Our results showed no statistically significant associations between impaired Stroop performance and lesioned voxels in any parts of the prefrontal cortex. Factors that may have contributed to the null findings are discussed. Notably, the lack of significant findings was most likely related to methodological issues, specifically a lack of power in the regions where we expected to find an association between damaged tissue and impaired performance. Recommendations for future studies are outlined