Researchers have created an implantable chip that detects and adjusts dopamine levels in mice brains by tracing the neurotransmitter itself rather than relying on electrical signals, as most brain implants do. When the levels drop below a defined point, the device automatically sends an electrical impulse to prod neurons to release more.
Pedram Mohseni, an electrical engineer at Case Western Reserve University who led the project, likens it to a home thermostat.
Ref: Neurochemostat: A Neural Interface SoC With Integrated Chemometrics for Closed-Loop Regulation of Brain Dopamine.. IEEE Transactions on Biomedical Circuits and Systems (June 2016) | DOI: 10.1109/TBCAS.2015.2453791
This paper presents a 3.3 x 3.2mm2 system-on-chip (SoC) fabricated in AMS 0.35 μm 2P/4M CMOS for closed-loop regulation of brain dopamine. The SoC uniquely integrates neurochemical sensing, on-the-fly chemometrics, and feedback-controlled electrical stimulation to realize a "neurochemostat" by maintaining brain levels of electrically evoked dopamine between two user-set thresholds. The SoC incorporates a 90 μW, custom-designed, digital signal processing (DSP) unit for real-time processing of neurochemical data obtained by 400 V/s fast-scan cyclic voltammetry (FSCV) with a carbon-fiber microelectrode (CFM). Specifically, the DSP unit executes a chemometrics algorithm based upon principal component regression (PCR) to resolve in real time electrically evoked brain dopamine levels from pH change and CFM background-current drift, two common interferents encountered using FSCV with a CFM in vivo. Further, the DSP unit directly links the chemically resolved dopamine levels to the activation of the electrical microstimulator in on-off-keying (OOK) fashion. Measured results from benchtop testing, flow injection analysis (FIA), and biological experiments with an anesthetized rat are presented.