Selective impairment of the conflict network in patients with frontal lesions

Many neuroimaging studies investigated the role of frontal brain areas in monitoring and resolving conflict, but until now there exist only few lesion studies. In order to reassess the necessity of frontal brain areas for accomplishing this executive function, we used a lesion study design to compare 11 neurological patients with frontal brain lesions with 11 patients with non-frontal brain lesions and 11 healthy controls with regard to their performance in the Attention Network Test (ANT), especially in the conflict effect. Besides a general slowing effect in both patient groups indicated by a slower overall mean reaction time as compared to the healthy controls, a significant difference between the three groups was given for the conflict effect and the relative conflict effect. In doing so medium effect sizes were found for the conflict effect and relative conflict effect between the frontal group and non-frontal group and great effect sizes between patients and healthy controls indicating greater difficulties of resolving conflict in the patients with frontal brain lesions. As no differences were found for other cognitive functions, these results indicate that patients with frontal lesions are selectively impaired in the conflict effect of the ANT. This dissociation complements the results of functional magnetic resonance imaging (fMRI) studies (Fan et al., 2002, 2005, 2007, 2008) proving the necessity of these brain areas for this executive function