Wireless Photometry Prototype for Tri-Color Excitation and Multi-Region Recording.

Visualizing neuronal activation and neurotransmitter release by using fluorescent sensors is increasingly popular. The main drawback of contemporary multi-color or multi-region fiber photometry systems is the tethered structure that prevents the free movement of the animals. Although wireless photometry devices exist, a review of literature has shown that these devices can only optically stimulate or excite with a single wavelength simultaneously, and the lifetime of the battery is short. To tackle this limitation, we present a prototype for implementing a fully wireless photometry system with multi-color and multi-region functions. This paper introduces an integrated circuit (IC) prototype fabricated in TSMC 180 nm CMOS process technology. The prototype includes 3-channel optical excitation, 2-channel optical recording, wireless power transfer, and wireless data telemetry blocks. The recording front end has an average gain of 107 dB and consumes 620 µW of power. The light-emitting diode (LED) driver block provides a peak current of 20 mA for optical excitation. The rectifier, the core of the wireless power transmission, operates with 63% power conversion efficiency at 13.56 MHz and a maximum of 87% at 2 MHz. The system is validated in a laboratory bench test environment and compared with state-of-the-art technologies. The optical excitation and recording front end and the wireless power transfer circuit evaluated in this paper will form the basis for a future miniaturized final device with a shank that can be used in in vivo experiments.

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.