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The combination of in vivo extracellular recording and genetic-engineering-assisted optical stimulation is a powerful tool for the study of neuronal circuits. Precise analysis of complex neural circuits requires high-density integration of multiple cellular-size light sources and recording electrodes. However, high-density integration inevitably introduces stimulation artifact. We present minimal-stimulation-artifact (miniSTAR) μLED optoelectrodes that enable effective elimination of stimulation artifact. A multi-metal-layer structure with a shielding layer effectively suppresses capacitive coupling of stimulation signals. A heavily boron-doped silicon substrate silences the photovoltaic effect induced from LED illumination. With transient stimulation pulse shaping, we reduced stimulation artifact on miniSTAR μLED optoelectrodes to below 50 μV_pp, much smaller than a typical spike detection threshold, at optical stimulation of >50 mW mm^–2irradiance. We demonstrated high-temporal resolution (<1 ms) opto-electrophysiology without any artifact-induced signal quality degradation during in vivo experiments. MiniSTAR μLED optoelectrodes will facilitate functional mapping of local circuits and discoveries in the brain.

Dynamic interactions within and across brain areas underlie behavioral and cognitive functions. To understand the basis of these processes, the activities of distributed local circuits inside the brain of a behaving animal must be synchronously recorded while the inputs to these circuits are precisely manipulated. Even though recent technological advances have enabled such large‐scale recording capabilities, the development of the high‐spatiotemporal‐resolution and large‐scale modulation techniques to accompany those recordings has lagged. A novel neural probe is presented in this work that enables simultaneous electrical monitoring and optogenetic manipulation of deep neuronal circuits at large scales with a high spatiotemporal resolution. The “hectoSTAR” micro‐light‐emitting‐diode (μLED) optoelectrode features 256 recording electrodes and 128 stimulation μLEDs monolithically integrated on the surface of its four 30‐µm thick silicon micro‐needle shanks, covering a large volume with 1.3‐mm × 0.9‐mm cross‐sectional area located as deep as 6 mm inside the brain. The use of this device in behaving mice for dissecting long‐distance network interactions across cortical layers and hippocampal regions is demonstrated. The recording‐and‐stimulation capabilities hectoSTAR μLED optoelectrodes enables will open up new possibilities for the cellular and circuit‐based investigation of brain functions in behaving animals.