Integrated tapered fibertrode for simultaneous control and readout of neural activity over small brain volumes with reduced light-induced artefacts

Recognizing the neural patterns underlying different brain functions is essential to achieve a more comprehensive view on how small sets of neurons organize in complex 3D networks to determine different behaviours. In this framework, optogenetic techniques have been successfully proven as a powerful tool to control brain functions achieving millisecond temporal resolution and cell-type specificity, by combining the use of light-gated opsins and ad-hoc light delivery optoelectronic devices. However, targeting small brain volumes with simultaneous electrical recording results in the introduction of photoelectric artefacts, in particular when light emission and recoding sites are very close one to each other. In this work we take advantage of the photonic properties of tapered fibers to present a fully integrated fibertrode to target small brain volumes with abated photoelectric noise. The device hosts a light emitting window just below a recording pad, and exploits the angled light emission from the window to achieve simultaneous activation and electrical readout of small groups of cells with no photoelectric artifacts in vivo. Despite the highly non-planar surface of the fiber taper, windows size, shape and electrodes impedance can be modulated by controlling the fabrication parameters during focused ion beam milling and deposition, thus resulting in a versatile, integrated and customizable optogenetic tool for neurobiology studies in closed-loop configuration over small brain volumes.