Fig. 1. Schematics of neural interfaces with different modes and their spatial/temporal resolutions. (a) Schematic of different kinds of neural interfaces; (b) spatial and temporal resolutions of different neural interface technologies

Fig. 2. Principles of optical and electrical methods for neural recording. (a) Schematic of multimodal neural recording system combining two-photon fluorescence scanning microscopy imaging and synchronous electrophysiological recording; (b) fluorescence image analysis and extracted calcium signals^[37]; (c) schematics of extracellular electrophysiological recording in mice based on neural probe^[35]

Fig. 3. Schematics of optical neural recording methods and optogenetic manipulation methods based on genetically encoding. (a) Genetically encoded Ca²⁺ imaging; (b) principle of first genetically encoded voltage indicator; (c) excitatory pump and channel based on rhodopsin; (d) inhibitory opsin composed of chloride-conducting channel rhodopsin, protons, and chloride pumps; (e) G-protein-coupled receptors coupled to inhibitory Gi/o pathway

Fig. 4. Major optical imaging methods for hemodynamics. (a) Photograph of human cortex captured by surgical microscope (left) and corresponding speckle contrast image (right)^[106]; (b) three-dimensional reconstruction of cerebral vessels in rats by two-photon scanning imaging^[109]; (c) projection of mouse cerebral vascular depth imaged through cranial windows using phase-based OCT angiography^[113]; (d) acousto-optic microimaging of oxygen saturation in whole cerebral cortex of mice^[114]; (e) multi-channel mixing and (f) separation imaging of hemodynamic signals by optical endogenous imaging^[115]; (g) schematic of non-invasive NIR spectroscopic functional imaging of human brain^[116]

Fig. 5. Schematics and photographs of various approaches for in vivo optical imaging (or recording) and optogenetic neuroregulation in mice. (a) Method of standard benchtop microscopic imaging and optogenetic manipulation; (b) implantable GRIN lens for imaging brain area at depth or implantable microprism for imaging internal brain area; (c) miniaturized head-mounted microscope system and (d) fiberscope and fiber photometry system for in vivo imaging of free-behaving animals; (e) mesoscopic imaging system^[35] and (f) benchtop microscopic imaging system^[128] for in vivo imaging of head-fixed mouse; (g) head-mounted microscope^[129] and (h) fiberscope^[130] for in vivo imaging of free-behaving mouse

Fig. 6. Implantable neural electrodes for electrophysiology. (a) Scanning electron microscope (SEM) image of wire electrode^[162]; (b) illustration of glass microwire electrode^[163]; (c) illustration of Michigan electrode^[164]; (d) illustration of Utah electrode array^[165]; (e) illustration of neuropixels electrode^[166]; (f) 256-channel NeuroGrid flexible electrode^[167]; (g) e-Dura neural electrodes for stimulation of spinal cord^[168]; (h) injectable nanoelectronic mesh electrodes^[169]; (i) fluorescent staining image indicating integration of neuron-like electrodes with neurons in mouse brain^[170]; (j) micrograph (left) and SEM image (right) of NET neural electrode^[171]; (k) illustration of neurotassel electrodes^[172]; (l) Neuralink neural electrode implanted in mouse brain^[173]; (m) 3D distribution of 1024-channel flexible electrodes implanted in mouse brain shown by micro-CT scan^[174]

Fig. 7. Implanted optical waveguides and optical electrodes. (a) Schematics of tapered fibers for neural interfaces^[184]; (b) schematic of fluorescence collection of flat-ended and tapered fibers implanted in brain tissue^[197]; (c) SEM micrograph of tapered fiber with seven-window multipoint emission^[195]; (d) schematic of photonic neural probe array^[195]; (e) SEM image of phased array E-pixel of photonic neural probe^[195]; (f) D-pixels based on visible spectrum angle-selective single-photon avalanche diode (SPAD) detectors^[198]; (g) color SEM image of GaN-μLED (top) and fluorescence image of μLEDs in cultured cells(bottom)^[199]; (h) microscopic image and SEM image of μLED probe^[200]; (i) integrated wireless powered μLED neural probe^[201]; (j) SEM image of tip on prepared optrode^[202]; (k) fabrication of multifunctional fiber by fiber tapering method^[203]; (l) design drawing (top) and SEM image (bottom) of fabricated metal electrode on side of tapered fiber^[204]

Fig. 8. Schematics and applications of optoelectronic multimodal neural interface. (a) Cranial window setup in mouse for simultaneous in vivo optical imaging and electrical recording using rigid neural probe; calcium imaging results of transgenic mice using electrodes (b) before and (c) after electrical stimulation^[214]; (d) cranial window setup in mouse for simultaneous in vivo optical imaging and electrical recording using flexible neural probe; (e) 3D reconstruction of in vivo two-photon image of cellular and vascular structures at probe-tissue interface and probe after implantation for two months in mouse cortex^[171]; (f) 3D reconstruction of in vivo two-photon neuron image in Thy1-YFP mouse surrounding NET-e probe after implantation for two months^[215]; (g) simultaneous two-photon scanning blood flow imaging and flexible electrode recording of mouse cortex^[128], and (h) simultaneous laser speckle contrast blood flow imaging and flexible electrode recording^[35]; (i) neural signal recording by simultaneous wide-field calcium imaging and electrophysiology in mouse cortex and hippocampus^[216]; (j) schematic (left) and application (right) of simultaneous imaging and electrical stimulation in mouse by combination of head-mounted miniature microscope and rigid neural electrodes^[143]; (k) schematic (left) and application (right) of multimodal neural interface constructed by head-mounted microscope combined with flexible neural electrodes^[217]

Fig. 9. Schematics and applications of multimodal neural interface based on transparent neural electrode. (a) Comparison between transparent neural electrodes and opaque neural electrodes^[225]; OCT with (b) opaque platinum electrode array and (c) transparent graphene electrode array in mouse cortex^[225]; (d) electrical recording and stimulation with transparent graphene electrode array and simultaneously recorded fluorescence microscope image of FITC-Dextran green fluorescent dye labeled blood vessels^[225]; (e) bright-field microscope imaging exposed with graphene microelectrode array^[226]; (f) schematic of simultaneous electrophysiological recording and optical imaging^[227]; (g) image of graphene electrode array implanted in mouse cortex^[227]; (h) relative positions of graphene electrode array in mouse cortex and location of 4-AP drug injection^[227]; (i) normalized fluorescence intensity^[227]; (j) μECoG recording signals^[227]

Fig. 10. Schematics of neuroimaging and neural recording data analysis process. (a) Schematic of optical imaging data of neurons^[37]; (b) analysis process for optical imaging data of neurons; (c) schematic of electrical signal data of neurons^[128]; (d) analysis process for electrical signal data of neurons

Fig. 11. Increasing trend of neural signal recording scale^{[21,43,145,174,180,257-273]}