title: fMRI in the awake marmoset: somatosensory-evoked responses, functional connectivity, and comparison with propofol anesthesia.
abstract: Functional neuroimaging in animal models is essential for understanding the principles of neurovascular coupling and the physiological basis of fMRI signals that are widely used to study sensory and cognitive processing in the human brain. While hemodynamic responses to sensory stimuli have been characterized in humans, animal studies are able to combine very high resolution imaging with invasive measurements and pharmacological manipulation. To date, most high-resolution studies of neurovascular coupling in small animals have been carried out in anesthetized rodents. Here we report fMRI experiments in conscious, awake common marmosets (Callithrix jacchus), and compare responses to animals anesthetized with propofol. In conscious marmosets, robust BOLD fMRI responses to somatosensory stimulation of the forearm were found in contralateral and ipsilateral regions of the thalamus, primary (SI) and secondary (SII) somatosensory cortex, and the caudate nucleus. These responses were markedly stronger than those in anesthetized marmosets and showed a monotonic increase in the amplitude of the BOLD response with stimulus frequency. On the other hand, anesthesia significantly attenuated responses in thalamus, SI and SII, and abolished responses in caudate and ipsilateral SI. Moreover, anesthesia influenced several other aspects of the fMRI responses, including the shape of the hemodynamic response function and the interareal (SI-SII) spontaneous functional connectivity. Together, these findings demonstrate the value of the conscious, awake marmoset model for studying physiological responses in the somatosensory pathway, in the absence of anesthesia, so that the data can be compared most directly to fMRI in conscious humans.
authors.affiliation: Cerebral Microcirculation Unit, Laboratory of Functional and Molecular Imaging, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive, Building 10, Room B1D106, Bethesda, MD 20892, USA. liu@junjie.com
authors.forename: Junjie V
authors.initials: JV
authors.lastname: Liu
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Hirano
authors.forename: George C
authors.initials: GC
authors.lastname: Nascimento
authors.forename: Bojana
authors.initials: B
authors.lastname: Stefanovic
authors.forename: David A
authors.initials: DA
authors.lastname: Leopold
authors.forename: Afonso C
authors.initials: AC
authors.lastname: Silva
mesh_terms: D018686:Anesthetics, Intravenous / Q000494:pharmacology; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D002144:Callithrix; D005073:Evoked Potentials, Somatosensory / Q000187:drug effects / Q000502:physiology; D008279:Magnetic Resonance Imaging; D023421:Models, Animal; D009434:Neural Pathways / Q000187:drug effects / Q000502:physiology*; D015742:Propofol / Q000494:pharmacology; D014851:Wakefulness / Q000187:drug effects / Q000502:physiology*
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol