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 (Ca
²⁺
). The ability to measure ACh and Ca
²⁺
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.