30â IEEE CIRCUITS AND SYSTEMS MAGAZINE FOURTH QUARTER 2020 (a) Stimulation of Another Neural Circuit Closed-Loop Brain Stimulations Optical Stimulator Closed-Loop Controller Neural Signal Processor AI in Cloud (b) Optrode Headstage Neural Signal Processor * Neural Recording Interface (1) * Optical Stimulator (6) - Firing Rate Pattern Recognition (5) - Data Sorting (4) - Data Compression (3) - Signal Detection (2) Networks and Data Centers Figure 1. (a) CL optogenetic concept: The electrodes sense the low-voltage electrical activity of the targeted neurons, whose voltage is further conditioned and digitized by a neural recording interface. Then, the digitized neural signal is analyzed by a processor and a CL controller issue stimulation triggers when specific neural patterns occur. (b) Overview of a wireless CL optogenetic system: The neural signal is conditioned and digitized by an embedded neural recording interface. Then, the APs are processed digitally, e.g. detection and further compression to reduce the amount of data to be wirelessly transmitted, stored (e.g. in the cloud) and to be handled. After, each AP is sorted in situ according to its waveform, allowing to approximate when each individual neuron is active. Then, the firing rate (or " bursting " activity) of each neuron is estimated and the stimulation pulses are triggered when the firing rate reach a preconfigured value. Optical Fiber Blue Light Activated Neuron Electrode Neural Recording Interface