Understanding the function of neural circuits in the cerebral cortex of the non-human primate (NHP), the model system closest to human, is crucial to understanding normal cortical function and the circuit-level basis of human brain disorders. Optogenetics has emerged as a powerful tool for studying neural circuit function, by using light to perturb the activity of specific cell types genetically modified to express light-activated microbial opsins, and assessing the consequences of this perturbation on network activity and behavior. While successful in mice, it has been challenging to apply optogenetics to NHPs, largely due to the lack of multifunction integrated probes for precision light delivery and electrophysiology across mm-to-cm volumes through the depth of the NHP cortex. Large volume manipulations are essential in the large NHP brain in order to observe measurable electrophysiological or behavioral effects. An interdisciplinary team of PIs proposes to develop and test in vivo integrated penetrating arrays that allow for large-volume, spatiotemporally patterned optogenetic modulation and electrical recording of neural circuits in the NHP brain. This project requires the coordinated effort of 4 teams, including experts in photonic devices and LED development for optogenetics, materials and packaging for biocompatible devices, primate neurophysiology, and pioneers in electrode array design and commercialization.
In Aim 1 we develop the technology, and in Aim 2 we test it in vivo in the NHP visual cortex. We will initially develop a 4x4 mm penetrating 10x10 optrode array in a format analogous to the well- established Utah Electrical Array (UEA), with each probe serving as a waveguide allowing visible light to reach tissue depths >1.5mm. Following initial optimization of the probe's shank diameter and tip angle to minimize tissue damage, we will perform proof-of-concept in vivo NHP optogenetic experiments in deep cortical tissue, using broad-area illumination of the entire array. In a second stage, we will develop light coupling via LEDs, which will be integrated into a single platform and tested in vivo, consisting of a LED located over each optical probe. Completion of stage 2 will deliver a functional multioptrode array for large-volume patterned optogenetic stimulation. Parallel engineering efforts will add electrical recording capability, by utilizing the engineering resources already in place for the UEA, and will generate two types of integrated arrays. The ?interleaved? array consists of an optrode array inserted through the back plane of a modified UEA into which a grid of through-backplane holes is made via laser ablation to accommodate the optrodes. For the ?hybrid? array, each optrode shank will be coated with an isolation layer followed by a conductive layer, in order to allow recording while preventing light attenuation and stimulation artifacts. In vivo testing will assess the recording capabilities of both devices and subsequently the ability to perform simultaneous optical stimulation and electrical recordings. This technology will allow for unprecedented optogenetic investigations of mm-to-cm scale neural circuit function and dysfunction in NHPs, and for a new generation of therapeutic interventions via cell type specific optical neural control prosthetics.
Normal brain function depends on the orderly development of circuits in the cerebral cortex and on their intact function. The novel technology that will result from the work proposed in this application will allow for unprecedented optogenetic investigations of the function of specific cortical circuits in the non-human primate brain. Understanding how cortical circuits operate in the normal brain will provide a foundation for understanding the consequences of their dysfunction in disorders of brain function such as autism and schizophrenia, which have been directly linked to abnormalities in inter- areal connectivity (Belmonte et al., 2004, Lynall et al., 2010)117,118. Our technology will also open the possibility for a new generation of precise neurological and psychiatric therapeutic interventions via cell type specific optical neural control prosthetics, to restore lost cortical function (Bradley et al., 2005, Schmidt et al., 1996, Torab et al., 2011)119,120,121, or for treatment of neurological disorders such as epilepsy (Tonnesen et al., 2009)122. One of the key factors impeding the development of medical applications of optogenetics in humans has been the difficulty of applying this method to non- genetically tractable species and to large brains such as those of primates. The present proposal specifically tackles these problems and, therefore, will have an important positive impact in the future development of optogenetics for medical applications in humans.
