title: Neuroanatomic connectivity of the human ascending arousal system critical to consciousness and its disorders.
abstract: The ascending reticular activating system (ARAS) mediates arousal, an essential component of human consciousness. Lesions of the ARAS cause coma, the most severe disorder of consciousness. Because of current methodological limitations, including of postmortem tissue analysis, the neuroanatomic connectivity of the human ARAS is poorly understood. We applied the advanced imaging technique of high angular resolution diffusion imaging (HARDI) to elucidate the structural connectivity of the ARAS in 3 adult human brains, 2 of which were imaged postmortem. High angular resolution diffusion imaging tractography identified the ARAS connectivity previously described in animals and also revealed novel human pathways connecting the brainstem to the thalamus, the hypothalamus, and the basal forebrain. Each pathway contained different distributions of fiber tracts from known neurotransmitter-specific ARAS nuclei in the brainstem. The histologically guided tractography findings reported here provide initial evidence for human-specific pathways of the ARAS. The unique composition of neurotransmitter-specific fiber tracts within each ARAS pathway suggests structural specializations that subserve the different functional characteristics of human arousal. This ARAS connectivity analysis provides proof of principle that HARDI tractography may affect the study of human consciousness and its disorders, including in neuropathologic studies of patients dying in coma and the persistent vegetative state.
authors.affiliation: Department of Neurology, Brigham and Women's Hospital, 75 Francis St, Boston, MA 02115, USA. bedlow@partners.org
authors.forename: Brian L
authors.initials: BL
authors.lastname: Edlow
authors.forename: Emi
authors.initials: E
authors.lastname: Takahashi
authors.forename: Ona
authors.initials: O
authors.lastname: Wu
authors.forename: Thomas
authors.initials: T
authors.lastname: Benner
authors.forename: Guangping
authors.initials: G
authors.lastname: Dai
authors.forename: Lihong
authors.initials: L
authors.lastname: Bu
authors.forename: Patricia Ellen
authors.initials: PE
authors.lastname: Grant
authors.forename: David M
authors.initials: DM
authors.lastname: Greer
authors.forename: Steven M
authors.initials: SM
authors.lastname: Greenberg
authors.forename: Hannah C
authors.initials: HC
authors.lastname: Kinney
authors.forename: Rebecca D
authors.initials: RD
authors.lastname: Folkerth
mesh_terms: D000328:Adult; D001143:Arousal / Q000502:physiology*; D001344:Autopsy; D001933:Brain Stem / Q000033:anatomy & histology / Q000473:pathology; D002102:Cadaver; D003243:Consciousness / Q000502:physiology*; D003244:Consciousness Disorders / Q000473:pathology*; D056324:Diffusion Tensor Imaging; D004210:Dissection; D005260:Female; D006801:Humans; D007031:Hypothalamus / Q000033:anatomy & histology / Q000473:pathology; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009434:Neural Pathways / Q000033:anatomy & histology* / Q000473:pathology*; D009445:Neuroanatomy; D018377:Neurotransmitter Agents / Q000502:physiology; D016548:Prosencephalon / Q000033:anatomy & histology / Q000473:pathology; D011712:Pyramidal Tracts / Q000033:anatomy & histology / Q000473:pathology / Q000502:physiology; D013788:Thalamus / Q000033:anatomy & histology / Q000473:pathology
chemical_list: D018377:Neurotransmitter Agents