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Abstract: Non-human primates have served as an important model for understanding functional brain organization in humans. The ability to conduct functional magnetic resonance imaging (MRI) studies in monkeys promises to bridge the gap between human functional imaging studies and a large body of anatomical, electrophysiological, and functional optical imaging studies in non-human primates.
We used a high magnetic field 4.7 Tesla vertical scanner to perform anatomical and functional MRI in awake macaque monkeys. High-field scanners provide higher blood oxygen level dependent signal (BOLD) and a greater signal-to-noise ratio (SNR). With a dedicated vertical primate scanner, monkeys may perform better for long scans with a more natural upright position. We found that improvements in behavioral training were essential for obtaining greater data stability. After extensive training, the average translational movement decreased from over 500 um to less than 80 um in monkeys. We can reliably detect of sub-millimeter laminar structure, neural activation and permitted MR based mapping of sensory areas in awake non-human primates.
We also investigated pulsed infrared optical stimulation of cortex in monkeys and its potential for optical controls. In a high field (9.4 Tesla) scanner we recorded images of primary somatosensory cortex of squirrel monkeys during optical stimulation of a single digit location in area 1. Optical stimulation was introduced via a fiberoptic and a newly developed long-term MR-compatible, optical transparent window. We found that optical stimulation evokes significant changes in cerebral blood volume weighted MR signals. Furthermore, we observed that the light stimulation can not only directly drive the stimulated site, but also peripheral cortical activity. Stimulation of a single digit location in area 1 resulted in focal, digit-specific activation in areas 3b, 2, and possibly 3a. Such activations were confined primarily to the middle layers in these nearby areas. Our data demonstrate that pulse infrared laser excitation, used in conjunction with functional MRI, has the potential to play a key role in the future development of human brain-machine interfaces.
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