Head-mounted microendoscopic calcium imaging in dorsal premotor cortex of behaving rhesus macaque

Abstract

HighlightsFirst demonstration of head-mounted microendoscopic calcium imaging in behaving macaque.Surgical protocols developed for preparing the animal for calcium imaging, including virus injections to express GCaMP and chronic implantation of a GRIN lens to enable optical access to gyral cortex.Proof of concept plug-and-play calcium imaging in behaving macaques with months long stable recording capability allowing populations of individual neurons to be tracked longitudinally.Bilateral calcium imaging from dorsal premotor cortex exhibited dynamics selective to the animal's direction of reach and allowed decoding of the animal's motor behavior Summary A major effort is now underway across the brain sciences to identify, characterize and manipulate mesoscale neural circuits in order to elucidate the mechanisms underlying sensory perception, cognition and behavior. Optical imaging technologies, in conjunction with genetically encoded sensors and actuators, serve as important tools toward these goals, allowing access to large-scale genetically defined neuronal populations. In particular, one-photon miniature microscopes, coupled with genetically encoded calcium indicators and microendoscopic gradient-refractive index (GRIN) lenses, enable unprecedented readout of neural circuit dynamics in cortical and deep subcortical brain regions during active behavior in rodents. This has already led to breakthrough discoveries across a wide array of rodent brain regions and behaviors. However, in order to study the neural circuit mechanisms underlying more complex and clinically relevant human behaviors and cognitive functions, it is crucial to translate this technology to non-human primates. Here, we describe the first successful application of this technology in the rhesus macaque. We identified a viral strategy for robust expression of GCaMP, optimized a surgical protocol for microendoscope GRIN lens insertion, and created a chronic cranial chamber and lens mounting system for imaging in gyral cortex. Using these methods, we demonstrate the ability to perform plug-and-play, head-mounted recordings of cellular-resolution calcium dynamics from over 100 genetically-targeted neurons simultaneously in dorsal premotor cortex while the macaque performs a naturalistic motor reach task with the head unrestrained and freely moving. The recorded population of neurons exhibited calcium dynamics selective to the direction of reach, which we show can be used to decode the animal's trial-by-trial motor behavior. Recordings were stable over several months, allowing us to longitudinally track large populations of individual neurons and monitor their relationship to motor behavior over time. Finally, we demonstrate the ability to conduct simultaneous, multi-site imaging in bilateral dorsal premotor cortices, offering an opportunity to study distributed networks underlying complex behavior and cognition. Together, this work establishes headmounted microendoscopic calcium imaging in macaque as a powerful new approach for studying the neural ci...

Windows and periscopes into primate behavior

“…Imaging from the surface, Trautmann et al found similarly heterogeneous tuning among neuronal somata and processes. Together, this pair of studies provides complementary insights into the organization of movement representation across the cortical sheet (Trautmann et al, 2021) and across layers (Bollimunta et al, 2021). These data contribute to continued debate about the spatial organization of motor cortex (Omrani et al, 2017), which calcium imaging can resolve more decisively than electrophysiology.…”

“…Nevertheless, these studies mark an exciting foray into the use of calcium imaging in behaving macaques, and they chart a course to new discoveries into the neural mechanisms of movement and cognition. B) The miniscope system of Bollimunta et al (2021) consists of a miniature endoscope (black and gray), silicone elastomer (blue), aluminum cylinder (black), and cement/acrylic (green).…”

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Calcium imaging of neurons in monkeys making reaches is complicated by brain movements and limited by shallow imaging depth. In a pair of recent studies, Trautmann et al, 2021 andBollimunta et al (2021) present complementary solutions to these problems.

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“…This innovative approach broadens the utility of calcium imaging for studying deep-layer neurons and sets the stage to study dendritic computations in behaving monkeys. Bollimunta et al (2021) imaged neurons in the dorsal premotor cortex (PMd) with a surgically implanted, miniature endoscope (Figure 1B). One end of the endoscope interfaced with a camera that could be attached and removed in a matter of minutes.…”

“…Schematic cranial implants for calcium imagingA) The recording chamber of Trautmann et al, 2021 consists of a titanium cylinder (black), silicone artificial dura (blue), and tissue stabilizer (magenta). B) The miniscope system ofBollimunta et al (2021) consists of a miniature endoscope (black and gray), silicone elastomer (blue), aluminum cylinder (black), and cement/acrylic (green). In both panels, dashed outlines enclose components that are not permanently attached to the skull.…”