Identification of the medial lemniscus in the human brain: Combined study of functional MRI and diffusion tensor tractography

The medial lemniscus (ML) plays a critical role in sensory function and skillful movement. Using combined functional MRI (fMRI) and diffusion tensor tractography (DTT), we attempted to identify the ML pathway and quantify the characteristics of the ML compared to the corticospinal tract (CST). Eleven young healthy subjects without any history of neurological disorder were recruited for this study. For tracking of the ML, a seed region of interest (ROI) was determined using the fMRI activation in the primary sensorimotor cortex (SM1) following proprioceptive input, and a target ROI was given in the ML area of the pons. We were able to locate the ML in 9 out of 11 subjects. All ML started from the ML area just posterior to the transpontine fiber in the pons, and ascended to the SM1 posterolaterally to the cerebral peduncle of the midbrain, the posterior limb of the internal capsule (PLIC), and the corona radiata along with the CST. The fractional anisotropy (FA) value of the ML was similar to that of the CST. We could identify the ML pathway in the human brain using the combined fMRI/DTT method. These results and technique will be helpful for research about the ML in the human brain.