Dendritic calcium signals in rhesus macaque motor cortex drive an optical brain-computer interface

Abstract

Calcium imaging is a powerful tool for recording from large populations of neurons in vivo. Imaging in rhesus macaque motor cortex can enable the discovery of fundamental principles of motor cortical function and can inform the design of next generation brain-computer interfaces (BCIs). Surface two-photon imaging, however, cannot presently access somatic calcium signals of neurons from all layers of macaque motor cortex due to photon scattering. Here, we demonstrate an implant and imaging system capable of chronic, motion-stabilized two-photon imaging of neuronal calcium signals from macaques engaged in a motor task. By imaging apical dendrites, we achieved optical access to large populations of deep and superficial cortical neurons across dorsal premotor (PMd) and gyral primary motor (M1) cortices. Dendritic signals from individual neurons displayed tuning for different directions of arm movement. Combining several technical advances, we developed an optical BCI (oBCI) driven by these dendritic signalswhich successfully decoded movement direction online. By fusing two-photon functional imaging with CLARITY volumetric imaging, we verified that many imaged dendrites which contributed to oBCI decoding originated from layer 5 output neurons, including a putative Betz cell. This approach establishes new opportunities for studying motor control and designing BCIs via two photon imaging.

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

“…It was striking to learn that high decoding performance could be maintained even when randomly subsampling just a single neuron from the population (Figure S7), providing strong evidence for the encoding of motor reach behavior among the imaged ensemble. Importantly, the withinsession selectivity preference distributions and decoding performances we observed are consistent with recent results obtained in motor cortex with two-photon microscopy (Trautmann et al, 2021) and previously reported results obtained electrophysiologically (Riehle and Requin, 1989;Kurata, 1993;Cisek and Kalaska, 2005). The ability to relate the functional properties of neuronal populations to their precise location and spatial organization within the brain is an additional major advantage of the optical imaging approach used in the present study.…”

“…This study also confirmed several advantages of one-photon microendoscopic calcium imaging with head-mounted miniscopes in comparison to traditional two-photon microscopy, especially as applied to NHP models. Most two-photon calcium imaging studies to date have relied on transparent cranial windows to optically access the superficial layers of cortex (Sadakane et al, 2015b;Li et al, 2017;Trautmann et al, 2021). In NHPs, these cranial window implants can be challenging to maintain and are associated with a high risk of infection, typically exhibiting a degradation in optical clarity (a ''clouding'' of the implant) over time due to the proliferation of pia and arachnoid cells and, in some cases, the re-growth of native dura (Arieli et al, 2002;Chen et al, 2002).…”

“…Successful application of calcium imaging in NHPs, however, has been slow to develop for a number of reasons. In particular, difficulties using conventional viruses to express genetically encoded calcium indicators in the NHP brain (Sadakane et al, 2015a) and imaging artifacts caused by movements of the larger volume NHP brain (Trautmann et al, 2021;Choi et al, 2018) have proven most challenging. Additionally, NHPs have a more mature immune system, as compared to that of rodents, that requires sophisticated surgical strategies and neural implant hardware, and limitations exist on the overall number of animals that can be used for trial-and-error technology development (Phillips et al, 2014).…”

“…Recent efforts applying two-photon microscopy and GCaMPbased calcium imaging in NHPs have overcome some of these challenges by refining aspects of the surgical and viral preparation and imaging system (Sadakane et al, 2015a;Seidemann et al, 2016;Yamada et al, 2016;Santisakultarm et al, 2016;Ebina et al, 2018;Zeng et al, 2019;Li et al, 2017;Ju et al, 2018;Garg et al, 2019;Trautmann et al, 2021). These efforts have so far relied on transparent glass or silicone windows implanted over the brain to enable imaging of cortex to depths less than approximately 500 mm (e.g., cortical layers 2 and 3).…”

“…The substantial motion artifacts inherent in this approach can be partially mitigated via mechanical pressure applied to the brain via the imaging window. While conventional adeno-associated viruses (AAVs) encoding GCaMP have in some cases proven sufficient for in vivo imaging (Li et al, 2017;Ju et al, 2018;Trautmann et al, 2021), novel viral strategies such as AAVs utilizing tetracycline-controlled transcriptional activation (e.g., Tet-Off) have proven more effective at driving adequate levels of GCaMP expression (Sadakane et al, 2015a;Garg et al, 2019). While two-photon calcium imaging through cranial windows has many merits, it also has several limitations, including (1) the infection risk of using glass or silicone surface windows, which also have limited functional lifetimes (e.g., degradation of optical clarity over time) and require daily maintenance; (2) cumbersome daily alignment between the microscope and the brain in order to maintain a consistent field of view (FOV) and track neurons across sessions; (3) an inability to image gyral cortex deeper than approximately 500 mm, sulcal cortical areas, or subcortical structures residing even deeper in the brain; (4) an inability to measure from multiple brain areas in true simultaneity with a single scanning laser beam; and (5) the necessity for head restraint, thereby limiting natural behavior.…”