Novel electrode technologies for neural recordings

Abstract

Neural recording electrode technologies have contributed considerably to neuroscience by enabling the extracellular detection of low-frequency local field potential oscillations and high-frequency action potentials of single units. Nevertheless, several long-standing limitations exist, including low multiplexity, deleterious chronic immune responses and long-term recording instability. Driven by initiatives encouraging the generation of novel neurotechnologies and the maturation of technologies to fabricate high-density electronics, novel electrode technologies are emerging. Here, we provide an overview of recently developed neural recording electrode technologies with high spatial integration, long-term stability and multiple functionalities. We describe how these emergent neurotechnologies can approach the ultimate goal of illuminating chronic brain activity with minimal disruption of the neural environment, thereby providing unprecedented opportunities for neuroscience research in the future.

Fig. 1 |. Neural recording electrode technologies.

On the left, conventional electrode technologies for in-vivo neural recordings are shown above the timeline, whereas key neuroscience discoveries and breakthroughs enabled by these technologies are shown below the timeline with the same colour coding as each corresponding electrode technology. On the right, recent development of neural recording electrode technologies is summarized in three categories for neural probes with high spatial integration, long-term temporal stability and multifunctional integration. Electrode technologies belonging to more than one category are connected with multiple lines.

Fig. 2 |. Basic principles and physical constraints of electrode technologies.

a | Schematic depicting the basic physical principles of measuring bioelectrical signals by recording electrodes in neural tissue, with representative raw, low-pass-filtered and high-pass-filtered neural recording traces (middle) and sorted spikes (right) measured by an electrode. b | The essential physical constraints (in particular, the spatiotemporal dilemma) of various existing neurotechnologies (in particular, implantable electrical probes, the main focus of this Review) have encouraged advances in the field of neuroengineering. The horizontal and vertical solid lines represent resolution in temporal and spatial scale, respectively, whereas the extent of the rectangular shade represents the spatiotemporal span of each neurotechnology.

Fig. 3 |. Emerging neural recording electrode technologies.

Schematics of representative emergent neural recording electrodes in recent development, shown in three categories for high spatial integration (Neuropixels and NeuroGrid (a)), long-term temporal stability (mesh electronics (b)) and multifunctional integration (multifunctional fiber and silicon probes incorporating optical stimulation and fluidic delivery capabilities (c)). For each representative electrode technology, a schematic for the standalone probe showing the basic structure and that for the probe interface on a mouse head are both shown. A close-up view of the electrode region is also included for the red dashed box in a, I and b. The same colour coding is used for all schematics: red, electrodes; orange, interconnect wires and I/O bonding pads; grey, insulating layer.