Limitations of the Trail Making Test Part-B in Assessing Frontal Executive Dysfunction

Part B of the Trail Making Test (TMT-B) is one of the most widely used neuropsychological tests of "executive" function. A commonly held assumption is that the TMT-B can be used to detect frontal executive dysfunction. However, so far, research evidence has been limited and somewhat inconclusive. In this retrospective study, performance on the TMT-B of 55 patients with known focal frontal lesions, 27 patients with focal non-frontal lesions and 70 healthy controls was compared. Completion time and the number of errors made were examined. Patients with frontal and non-frontal lesions performed significantly worse than healthy controls for both completion time and the number of errors. However, there was no significant difference for both completion time and the number of errors when patients with frontal and non-frontal lesions were compared. Performance was also not significantly different between patients with focal lesions within different regions of the frontal lobe (orbital, left lateral, right lateral, medial). Our findings suggest that the TMT-B is a robust test for detection of brain dysfunction. However, its capacity for detecting frontal executive dysfunction appears rather limited. Clinicians should be cautious when drawing conclusions from performance on the TMT-B alone.