Microendoscopic Calcium Imaging In Supplementary Motor Area And Primary Motor Cortex Of Rhesus Macaques At Rest And During Arm Movement

Abstract

ABSTRACTThe motor cortical regions have undergone evolutionary expansion and specialization from rodents to primates. Therefore, the study of these regions in non-human primates (NHPs) is relevant to understand motor control in healthy conditions or in NHP models of movement disorders. The use of calcium imaging and miniature microscopes allows the study of multiple individual neurons in cortical regions. We used this method to examine the activities of supplementary motor area (SMA) and primary motor region (M1) in four rhesus macaques. We implanted gradient index (GRIN) lenses and expressed GCaMP6f in cortical projection neurons in these regions and imaged calcium transients for weeks to months while the animals were at rest (spontaneous or idle condition) or engaged in a simple arm reaching task. We found that in a proportion of cells, in both cortical regions, the calcium activity was directionally tuned during the arm reaching task, in agreement with previous electrophysiological findings. We identified pairs of cells, scattered across the imaging fields in SMA and M1, with synchronous activity. Finally, we found that neurons in SMA and M1 have calcium transients that occur in precisely timed sequences, and that the sequences and neuronal ensembles participating in the sequences are dynamic. The microendoscopic calcium imaging technique can be used to examine calcium dynamics in groups of corticofugal neurons in SMA and M1 and compare patterns of activity among cells.HIGHLIGHTSWe used one-photon miniature microscopes and microendoscopic calcium imaging to study the activity of cortical projection neurons in supplementary motor area (SMA) and primary motor region (M1) of rhesus macaques at rest and during a simple arm reaching task.In a proportion of cells in SMA and M1, the calcium transients were related to arm reaches and showed directional tuning.Coactivity between subsets of cell pairs in SMA and M1 were found during both rest and the reaching task. The strength of coactivity was not related to the distance between cells.Single cell calcium transients in SMA and M1 occur in precise time sequences. The neuronal ensembles participating in the sequences (and the sequences themselves) are dynamic.