Fig. 2. Reticular pathways of the human default ascending arousal network.

Deterministic tractography results from a seed region in the mesencephalic reticular formation (mRt), the brainstem region stimulated by Moruzzi and Magoun in their seminal investigations of the reticular activating system (13), are shown from a right ventro-lateral perspective in Specimen 1. Tracts are color-coded by the fractional anisotropy (FA) along each segment (inset color bar). Tracts are superimposed upon a non-diffusion-weighted (b=0) axial image at the level of the mid-pons. The fiber tracts emanating from mRt travel in the ponto-mesencephalic tegmentum and connect with the thalamus, hypothalamus, and basal forebrain via the following bundles: DTT_L = dorsal tegmental tract, lateral division; DTT_M = dorsal tegmental tract, medial division; VTT_C = ventral tegmental tract, caudal division; VTT_R = ventral tegmental tract, rostral division.