An fMRI study of the Trail Making Test.

This study investigated the cerebral correlates of the Trail Making Test (TMT), used commonly as a measure of frontal lobe function. Such work sheds additional light on the known shortcomings of the TMT as a localizing instrument, as indicated, for example, by studies of patients with focal brain lesions. Functional magnetic resonance imaging (fMRI) was used to record brain activity while participants performed the TMT using a custom-built, fiber-optic fMRI-compatible writing device, the "virtual stylus". Unlike in a previous fMRI study that used a verbal adaptation of the TMT, the virtual stylus enabled a closer depiction of the brain regions engaged by the actual paper-and-pencil task. Twelve, right-handed healthy young adults participated. In Part A of the task, participants were required to link in ascending order numbers (1-2-3 ...) that were randomly distributed on a computer screen. In Part B, participants were required to link alternately between numbers and letters (1-A-2-B ...). Although behavioral performance was somewhat less than typically obtained with the TMT due to use of the virtual stylus, distinct left-sided dorsolateral and medial frontal activity was revealed when comparing Part B versus Part A. These findings agree with existing literature showing sensitivity of the TMT to frontal regions in the left hemisphere. However, other activity was also observed (left middle and superior temporal gyrus) reinforcing that the brain-behavior correlations for the TMT are multifaceted and not restricted to the frontal lobe.