The direct pathway from the brainstem reticular formation to the cerebral cortex in the ascending reticular activating system: A diffusion tensor imaging study

Precise evaluation of the ascending reticular activating system (ARAS) is important for diagnosis, prediction of prognosis, and management of patients with disorders of impaired consciousness. In the current study, we attempted to reconstruct the direct neural pathway between the brainstem reticular formation (RF) and the cerebral cortex in normal subjects, using diffusion tensor imaging (DTI). Forty-one healthy subjects were recruited for this study. DTIs were performed using a sensitivity-encoding head coil at 1.5Tesla with FMRIB Software Library. For connectivity of the brainstem RF, we used two regions of interest (ROIs) for the brainstem RF (seed ROI) and the thalamus and hypothalamus (exclusion ROI). Connectivity was defined as the incidence of connection between the brainstem RF and target brain regions at the threshold of 5 and 50 streamlines. Regarding the thresholds of 5 and 50, the brainstem RF showed high connectivity to the lateral prefrontal cortex (lPFC, 67.1% and 20.7%) and ventromedial prefrontal cortex (vmPFC, 50.0% and 18.3%), respectively. In contrast, the brainstem RF showed low connectivity to the primary motor cortex (31.7% and 3.7%), premotor cortex (24.4% and 3.7%), primary somatosensory cortex (23.2% and 2.4%), orbitofrontal cortex (17.1% and 7.3%), and posterior parietal cortex (12.2% and 0%), respectively. The brainstem RF was mainly connected to the prefrontal cortex, particularly lPFC and vmPFC. We believe that the methodology and results of this study would be useful to clinicians involved in the care of patients with impaired consciousness and researchers in studies of the ARAS.