Opto-Array: an implantable array of LEDs built for behavioral optogenetic experiments in nonhuman primates

Abstract

Optogenetic methods revolutionized the landscape of systems neuroscience by allowing perturbation of neuronal activity with precise spatial and temporal resolution and cell-type specificity. However, optogenetic studies often struggle to obtain large behavioral effects in monkeys. We developed a new chronically implantable LED array, the Opto-Array, that can reliably deliver light to the cortical surface in large brains, specifically non-human primates. The Opto-Array includes 24 LEDs and one thermal sensor on a 5 by 5 grid of PCB encapsulated with a transparent parylene and a layer of silicone coating on the surface. The 2D configuration of this LED array allows perturbation of a large range of cortical surface areas from 1 by 1 mm for only one active LED up to 5 by 5 mm when the entire array is turned on. The thermal sensor is important to monitor the temperature of cortical tissue to avoid overheating and potential damage. The chronic characteristic of Opto-Array allows highly stable perturbation of neural activities in behavioral experiments, in which data can be collected and pooled over months. Another advantage is that Opto-Array is a safer alternative to acute methods such as using optical fiber and direct illumination that minimizes the tissue damage as well as the risk of infection from open cranial windows and chambers. Here we explain the physical properties and characteristics of the Opto-Array as well as the surgical techniques and procedures for the implantation in macaque monkeys.