FUNCTIONAL MRI IN BEHAVING RHESUS MONKEY

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The long-term goal of this project is to apply Functional Magnetic Resonance imaging (fMRI) techniques to the awake behaving monkey so that powerful single unit recording techniques can be combined with more global views of brain function from MRI. The ability to correlate changes with direct electrical recordings will help to further clarify and extend the usefulness of fMRI. fMRI will have the potential to compensate for the two major limits of single-neuron recording in behaving monkeys - inability to survey the whole brain and inability to resolve detail at the level of cortical columns and patches. We have equipped a rhesus monkey with a cranial implant identical to those used for rigid head restraint during single-neuron recording. Activities during the preceding grant year have involved building basic apparatus and piloting fundamental methodology for the study of monkeys in the 4.7-T Bruker AVANCE-DRX. We constructed a cradle by which to support an anesthetized monkey in the 4.7-T scanner, with the head rigidly fixed inside the RF coil. In order to allow the monkey to hold the arms in a forward position during functional, we have designed and built a hemicylindrical RF coil with excellent RF homogeneity and sensitivity, which leaves free the space beneath the head. As a first step towards obtaining functional MR images of the monkey, using BOLD, we have detected a hemodynamic change in rhesus monkey cortex induced by a direct intervention (hypercapnia). We chose to manipulate blood flow with hypercapnia, rather than with brain activity, so as to circumvent the possible disruption, by anesthesia, of the functional linkage between brain activity and blood flow. This project will achieve a formal status of a TRD project begining next grant year, and experiments will continue towards carrying out fMRI in the awake monkey.