A Closed-Loop Optogenetic Stimulation Device

A Miniaturized Closed-Loop Optogenetic Brain Stimulation Device

This paper presents a tetherless and miniaturized closed-loop optogenetic brain stimulation device, designed as a back mountable device for laboratory mice. The device has the ability to sense the biomarkers corresponding to major depressive disorder (MDD) from local field potential (LFP), and produces a feedback signal to control the closed-loop operation after on-device processing of the sensed signals. MDD is a chronic neurological disorder and there are still many unanswered questions about the underlying neurological mechanisms behind its occurrence. Along with other brain stimulation paradigms, optogenetics has recently proved effective in the study of MDD. Most of these experiments have used tethered and connected devices. However, the use of tethered devices in optogenetic brain stimulation experiments has the drawback of hindering the free movement of the laboratory animal subjects undergoing stimulation. To address this issue, the proposed device is small, light-weight, untethered, and back-mountable. The device consists of: (i) an optrode which houses an electrode for collecting neural signals, an optical source for delivering light stimulations, and a temperature sensor for monitoring the temperature increase at the stimulation site, (ii) a neural sensor for acquisition and pre-processing of the neural signals to obtain LFP signals in the frequency range of 4 to 200 Hz, as electrophysiological biomarkers of MDD (iii) a classifier for classification of the signal into four classes: normal, abnormal alpha, abnormal theta, and abnormal gamma oscillations, (iv) a control algorithm to select stimulation parameters based on the input class, and (v) a stimulator for generating light stimulations. The design, implementation, and evaluation of the device are presented, and the results are discussed. The neural sensor and the stimulator are circular in shape with a radius of 8 mm. Pre-recorded neural signals from the mouse hippocampus are used for the evaluation of the device.

Towards a Tri-Color Wireless Photometry System for the Monitoring of Neuronal Activity in the Basal Forebrain and Hippocampus

Healthy cholinergic function is important for brain function, and disruption of the system is thought to be the cause of dementia, including Alzheimer's disease. The 'Cholinergic Hypothesis' theorizes that cognitive decline is due disruption of the cholinergic system, defined by the low concentration of neurotransmitters such as acetylcholine (ACh) and neurotransmitter-releasing elements such as calcium ions (Ca²⁺). The ability to measure ACh and Ca²⁺ concentrations enables researchers to make inferences on the relationship between these indicators that play a role in the onset of neurological conditions. Current commercial devices have one or more of the following limitations: i) they are tethered making it difficult to verify in naturally behaving animal subjects, ii) they are capable of only measuring a single indicator at any given time, or iii) they have multiple shanks that penetrate the cortex. We propose a tri-color miniaturized photometry system capable of optically stimulating indicators in neurons located in the hippocampus and basal forebrain and optically reading the neurons' response. The resulting device has an average gain of 123 dB and a power consumption of 29 mW, comparable to other state-of-the-art devices.

Biodegradable Optical Fiber in a Soft Optoelectronic Device for Wireless Optogenetic Applications

Optogenetics is a new neuroscience technology that uses light-responsive proteins to stimulate neurons with light and control the emotions and/or behavior of animals. There are a few approaches to deliver light to neurons in vivo, including a using an optical fiber that can send light from an external source to a target neuron, directly inserting a light-emitting device, and shooting light to penetrate tissue from the outside. Among these methods, inserting a wireless light-emitting device that is capable of being used for an experiment while leaving an animal completely free is a method that has been studied in recent years. At the same time, the possibility of causing mechanical and thermal damage to neural tissues has been highlighted as an issue due to the stiffness of robust injection tools and the photoelectric efficiency of light-emitting diodes (LEDs). In this study, we developed a device that can send light from a wireless light-emitting device to a target neuron without mechanical and thermal effects and analyzed the optical and thermal characteristics of the device to be used for optogenetic studies.

Studies of Parylene/Silicone-Coated Soft Bio-Implantable Optoelectronic Device

Optogenetics is a new neuroscience technology, consisting of biological technology that activates a nerve by light and engineering technology that transmits light to the nerve. In order to transmit light to the target nerve, fiber optics or light-emitting devices have been inserted into the living body, while the motions or emotions of freely moving animals can be controlled using a wirelessly operated optoelectronic device. However, in order to keep optoelectronic devices small in size and operational for a long time in vivo, the need for a thin but robust protective layer has emerged. In this paper, we developed a protective layer, consisting of Parylene and silicone that can protect soft optoelectronic devices inside saline solution for a long time. A chemical vapor deposited Parylene C film between the polydimethylsiloxane layers showed promising optical, mechanical, and water-barrier properties. We expect that these protective layers can be used as an encapsulation film on bio-implantable devices, including wireless optogenetic applications.