Chronic multi-modal monitoring of neural activity in rodents and primates

We developed multi-modal systems comprising implantable carbon fiber (CF)-based electrodes to record synchronously chemical (e.g. dopamine) and electrical (e.g. local field potential, LFP) forms of activity in the brain. These systems were equipped with implantable micro-invasive probes and moveable silica-based CF probes capable of recording chronically from fixed locations, or from multiple depths along predetermined trajectories, respectively, spanning 48 spatially distinct sites in the caudate nucleus and the putamen. Electrochemical fast scan cyclic voltammetry (FSCV) was implemented in combination with standard electrophysiology to provide subsecond chemical and electrical recordings. The chronic stability of our micro-invasive probes, as tested previously in rodents and translated for use in nonhuman primate (NHP), was necessary to ensure functional recording from fixed locations in the brain without degradation in probe sensitivity over time. These systems were used to examine the relationship between dopamine and beta-band LFPs, prominent biomarkers of untreated Parkinson’s disease. We recorded dopamine and beta in rhesus monkeys performing oculomotor tasks in which reward valuation and movement control, key functions impaired in Parkinson’s disease, could be quantified. Highly stable measurements of dopamine and LFP neural signals were made over a period of months.