Surgical Procedure for Implantation of Opto-Array in Nonhuman Primates

Abstract

Optogenetics allows precise temporal control of neuronal activity in the brain. Engineered viral vectors are routinely used to transduce neurons with light-sensitive opsins. However, reliable virus injection and light delivery in animals with large brains, such as nonhuman primates, has proven challenging. The Opto-Array is a novel yet simple device that is used to deliver light to extended regions of the cortex surface for high-throughput behavioral optogenetics in large brains. Here we present protocols for surgical delivery of virus (Basic Protocol 1) and implantation of the Opto-Array (Basic Protocol 2) in two separate surgeries in a rhesus monkey's inferior temporal cortex. As a proof of concept, we measured the behavioral performance of an animal detecting cortical optogenetic stimulations (Basic Protocol 3) with different illumination power and duration using the Opto-Array. The animal was able to detect the optogenetic stimulation for all tested illumination powers and durations. Regression analysis also showed both power and duration of illumination significantly modulate the detectability of the optogenetic stimulation. The outcome of this approach is superior to the standard practice of injecting and recording through a chamber for large areas of the cortex surface. Moreover, the chronic nature of the Opto-Array allows perturbation of neuronal activity of the same site across multiple sessions because it is highly stable; thus, data can be pooled over months. The detailed surgical method presented here makes it possible to use optogenetics to modulate neuronal activity across large regions of the cortex surface in the nonhuman primate brain. This method also lays the groundwork for future attempts to use optogenetics to restore vision in humans. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Virus injection surgery Basic Protocol 2: Opto-Array implantation surgery Basic Protocol 3: Cortical Perturbation Detection (CPD) task behavioral training.

Keywords: brain; cortex; inferior temporal cortex; monkey; optogenetics; surgery.

Figure 1:

head placement in low-profile head holder.

Figure 2:

coronal incision

Figure 3:

removing the zygomatic arch

Figure 4:

craniotomy with circular cutting wheel

Figure 5:

expanding the craniotomy

Figure 6:

dural opening

Figure 7:

virus injection

Figure 8:

dural closure after virus injection

Figure 9:

verification of virus expression

Figure 10:

Opto-Array implantation

Figure 11:

dural closure after Opto-Array implantation

Figure 12:

implantation of the pedestal connector and securing the wire

Figure 13:

Behavioral detectability of Opto-Array cortical stimulation at different illumination duration and powers. A. Schematic illustration of the behavioral task. The monkey’s task was to report whether a given trial did or did not include cortical stimulation. After 500 ms of initial central fixation an image appeared on the screen. The animal was required to keep fixation for 1000 ms until the fixation point and the image disappeared. In “stimulation” trials (randomly selected 50% of trials) we stimulated the cortex by activating the Opto-Array. The activations varied in duration (100, 200, and 400 ms) and light power 0.4, 1.2, and 2.5 mW). The stimulation (when present) began 1000ms after the animal started fixation (500ms after image appearance) After the disappearance of the image from the screen, two response targets appeared (each corresponding to a trial-type; “stimulation” and “no stimulation”), and the monkey reported a choice by fixating on one response target. A liquid reward was delivered if the choice was correct. B. Behavioral performance as a function of duration -and power of optogenetic stimulation in the detection task. The y-axis is the monkey’s stimulation report rate, and the x-axis is illumination power. The blue, red and yellow colors, respectively, represent stimulation trials with 100, 200 and 400 ms of illumination duration (hit rates). The black line represents data from no stimulation trials (false alarm rate). The error bars and the shaded gray area represent bootstrapped 95% confidence intervals (with 10,000 resamples).