Towards miniaturized closed-loop optogenetic stimulation devices

OBJECTIVE

Electrical brain stimulation provides therapeutic benefits for patients with drug-resistant neurological disorders. It, however, has restricted access to cell-type selectivity which limits its treatment effectiveness. Optogenetics, in contrast, enables precise targeting of a specific cell type which can address the issue with electrical brain stimulation. It, nonetheless, disregards real-time brain responses in delivering optimized stimulation to target cells. Closed-loop optogenetics, on the other hand, senses the difference between normal and abnormal states of the brain, and modulates stimulation parameters to achieve the desired stimulation outcome. Current review articles on closed-loop optogenetics have focused on its theoretical aspects and potential benefits. A review of the recent progress in miniaturized closed-loop optogenetic stimulation devices is thus needed.

APPROACH

This paper presents a comprehensive study on the existing miniaturized closed-loop optogenetic stimulation devices and their internal components.

MAIN RESULTS

Hardware components of closed-loop optogenetic stimulation devices including electrode, light-guiding mechanism, optical source, neural recorder, and optical stimulator are discussed. Next, software modules of closed-loop optogenetic stimulation devices including feature extraction, classification, control, and stimulation parameter modulation are described. Then, the existing devices are categorized into open-loop and closed-loop groups, and the combined operation of their neural recorder, optical stimulator, and control approach is discussed. Finally, the challenges in the design and implementation of closed-loop optogenetic stimulation devices are presented, suggestions on how to tackle these challenges are given, and future directions for closed-loop optogenetics are stated.

SIGNIFICANCE

A generic architecture for closed-loop optogenetic stimulation devices involving both hardware and software perspectives is devised. A comprehensive investigation into the most current miniaturized and tetherless closed-loop optogenetic stimulation devices is given. A detailed comparison of the closed-loop optogenetic stimulation devices is presented.

In-vitro validation of a closed-loop optogenetic stimulation device

Closed-loop optogenetic stimulation (CLOS) involves real-time neural data collection and analysis, feedback control, and optical neuromodulation. Despite emergence of the CLOS devices, methods for validating such devices in-vitro are limited. This paper presents a CLOS device and introduces an in-vitro setup for validating CLOS devices. The CLOS device consists of an electrode, a neural detector, a control algorithm, and an optogenetic stimulator. The in-vitro setup consists of saline solution, a neural signal emitter, a photodiode and its amplifier, and a closed-loop simulation program. Synthetic neural signals are delivered to the CLOS device, and based on the sensed optical stimulations from the light source, the properties of the delivered neural signals are changed. Experiments are conducted to evaluate the closed-loop operation of the CLOS device, and verify the capability of the in-vitro setup to for validating the CLOS devices. The in-vitro setup enables refinement of CLOS devices before arduous in-vivo trials.

Portable closed-loop optogenetic stimulation device

This paper presents a closed-loop optogenetic stimulation device to achieve online modulation of neurons. The device is designed to be mountable on small rodents in pre-clinical settings. Considering the size of rodents and the need for portability, a single-piece self-contained device is developed which allows real-time photostimulation based on detected neuronal states. It consists of three components: a neural recorder, a control algorithm, and an optogenetic stimulator. The neural recorder which is realized by analogue circuitry measures the neural signal. The on-off control algorithm analyses the neural signal and controls the stimulation of the target neurons. The optogenetic stimulator performs sampling and digitization of the detected neural signal, runs the control algorithm, and manages the operation of the light source. The configurable neural recorder is capable of 64 dB amplification in the frequency range of 300 Hz to 6 KHz. The outcome of bench testing of the device is reported. The device is portable and headmountable which makes it suitable for use with small rodents in pre-clinical trials.