Development Of Multi-Modal Techniques For The Investigation Of Brain Energetics

University of Minnesota Ph.D. dissertation. October 2015. Major: Biomedical Engineering. Advisor: Wei Chen. 1 computer file (PDF); ix, 139 pages.The study of spontaneous and highly variable brain activity, or task-evoked activity and its quantitative relationship with neuroimaging signals, is severely restricted by the lack of techniques to investigate multiple measures of brain activity simultaneously. In order to study the coupling and interactions between metabolic, hemodynamic, and neuronal activity, we here develop the technology to acquire in vivo magnetic resonance (MR) spectroscopy (MRS) simultaneously from two or more nuclei, as well as develop MR-compatible electrodes for neuronal recording in the MR scanner with minimal susceptibility artifacts. We apply these techniques to investigate metabolic trends resulting from a whole brain occlusion in the rat and to study neuronal, hemodynamic, and network responses to changes in anesthesia depth. Lastly, we show the first steps in developing an MR-compatible optrode to allow simultaneous MR imaging (MRI), neuronal recording, and optogenetic stimulation. With these new techniques, a wide field of studies becomes feasible to investigate direct neuronal, metabolic, and hemodynamic correlations under resting and working conditions to advance our understanding of brain function and dysfunction

Doctor of Philosophy

dissertationPrecise optical neural stimulation is an essential element in the use of optogenetics to elicit predictable neural action potentials within the brain, but accessing specific neocortical layers, light scattering, columniation, and ease of tissue damage pose unique challenges to the device engineer. This dissertation presents the design, simulation, microfabrication, and characterization of the Utah Optrode Array (UOA) for precise neural tissue targeting through three main objectives: 1. Maskless wafer-level microfabrication of optical penetrating neural arrays out of soda- lime glass: Utah Optrode Array. 2. Utah Optrode Array customization using stereotactic brain atlases and 3D CAD modeling for optogenetic neocortical interrogation in small rodents and nonhuman primates. 3. Single optrode characterization of the UOA for neocortical illumination. Maskless microfabrication techniques were used to create 169 individual 9 × 9 arrays 3.85 mm × 3.85 mm with 1.1 mm long optrodes from a single two inch glass wafer. The 9 × 9 UOA was too large for precise targeting of the upper layers of the cortex in smaller animals such as mice, so an array customization method was developed using Solidworks and off-the-shelf brain atlases to create 8 × 6 arrays 3.45 mm × 2.45 mm with 400 μm long optrodes. Stereotactic atlases were imported into Solidworks, splined, and lofted together to create a single 3D CAD model of a specific region of interest in the brain. Chronic and acute brain trauma showed excellent results for the 8 × 6 arrays in C57BL/6 wild-type mice (Mus musculus) and macaque monkey (Macaca fascicularis). Simulation, characterization, and radiometric testing of a single optrode of the 9 × 9 array was necessary to prove the ability to transmit light directly to specific tissue. Zemax optical design software was used to predict the light transmission capabilities, and then these results were compared to actual bench-top results. Insertion loss was both predicted and measured to be 3.7 dB. Power budgeting showed 9% of the light was lost at the interfaces of the UOA's backplane and tip in air, and 48% was lost through back-scattering, leaving 43% transmitting through the optrode with no measurable taper loss. Scanning electron microscopy showed small amounts of devitrification of the glass, and atomic force microscopy showed average surface roughness to be 13.5 nm and a root mean square roughness of 20.6 nm. The output beam was profiled in fluorescein dye with a total divergence angle of 63◦ with a cross over distance to adjacent beams at 255 μm

Frequency-selective control of cortical and subcortical networks by central thalamus

Central thalamus plays a critical role in forebrain arousal and organized behavior. However, network-level mechanisms that link its activity to brain state remain enigmatic. Here, we combined optogenetics, fMRI, electrophysiology, and video-EEG monitoring to characterize the central thalamus-driven global brain networks responsible for switching brain state. 40 and 100 Hz stimulations of central thalamus caused widespread activation of forebrain, including frontal cortex, sensorimotor cortex, and striatum, and transitioned the brain to a state of arousal in asleep rats. In contrast, 10 Hz stimulation evoked significantly less activation of forebrain, inhibition of sensory cortex, and behavioral arrest. To investigate possible mechanisms underlying the frequency-dependent cortical inhibition, we performed recordings in zona incerta, where 10, but not 40, Hz stimulation evoked spindle-like oscillations. Importantly, suppressing incertal activity during 10 Hz central thalamus stimulation reduced the evoked cortical inhibition. These findings identify key brain-wide dynamics underlying central thalamus arousal regulation

Frequency-selective control of cortical and subcortical networks by central thalamus

Abstract Central thalamus plays a critical role in forebrain arousal and organized behavior. However, network-level mechanisms that link its activity to brain state remain enigmatic. Here, we combined optogenetics, fMRI, electrophysiology, and video-EEG monitoring to characterize the central thalamus-driven global brain networks responsible for switching brain state. 40 and 100 Hz stimulations of central thalamus caused widespread activation of forebrain, including frontal cortex, sensorimotor cortex, and striatum, and transitioned the brain to a state of arousal in asleep rats. In contrast, 10 Hz stimulation evoked significantly less activation of forebrain, inhibition of sensory cortex, and behavioral arrest. To investigate possible mechanisms underlying the frequencydependent cortical inhibition, we performed recordings in zona incerta, where 10, but not 40, Hz stimulation evoked spindle-like oscillations. Importantly, suppressing incertal activity during 10 Hz central thalamus stimulation reduced the evoked cortical inhibition. These findings identify key brain-wide dynamics underlying central thalamus arousal regulation