For studying neural networks in the brain, it is useful to record neuronal activities with neural probe array having 3-dimensionally-distributed high-density multi-electrodes. In this study, a vertically-stacked multi-shank Si neural probe array with sharpened tip has been proposed and developed for neuronal recording of 3-dimensionally-distributed neurons. This Si neural probe array has vertically-stacked 4x3 shanks with 156 recording sites. The probe shanks were decreased and the probe tips were sharpened with anisotropic etching after stacking process to suppress damages to neurons. The insertion characteristics of the stacked probe array were carefully evaluated, and it is indicated that the vertically-stacked multi-shank Si neural probe array with sharpened tips needs smaller insertion forces compared to those of normal tip probes for all the insertion conditions. As a result, the vertically-stacked multi-shank Si neural probe array with sharpened tips will realize the 3-dimensional neuronal recording and becomes versatile tools for advanced neurophysiology.

Background: Intraoperative neuromonitoring has been introduced to such surgery as head and neck, however, it is insufficient to predict the nerve function. In this study, we evaluate the nerve function by measuring the action potential directory in the operational field. Methods: Sciatic nerves of the rabbits were pulse stimulated electrically. The amplitude of the action potential of the nerve was evaluated on the nerve or surrounding tissue using by a custom-designed bio-amplifier. Results: Two different waveforms of electrotonic spread and the saltatory conduction were recorded. The conduction velocity was 60 m/s. The amplitude of saltatory conduction on the nerve and surrounding tissue 5 and 10 mm vertically away from the nerve was 2043, 891 and 562 mV. Discussion: The saltatory conduction in the neighboring tissue was evaluated. It makes possible to detect the action potential derived from the nerve within 10 mm away from the nerve in the operative field.

Recently, optogenetics using a combination of techniques developed in the fields of optics and genetics has attracted much attention. Si neural probes with an optical stimulation function have been recently used for optogenetics. Although the Si neural probe with an optical fiber placed on the probe shank has been developed, severe damages to brain tissues were caused during probe insertion because of the protruding optical fiber.We have proposed and fabricated a less-invasive Si opto neural probe with embedded optical fiber enabling layer-by-layer optical stimulation in the brain. The optical fiber was embedded in a trench formed inside the probe shank, which causes less damages to tissues and enables the layer-by-layer light stimulation with mirror structure inside the trench. This Si opto neural probe with embedded optical fiber can be used as a versatile tool for optogenetics and brain science.