A research group led by Prof. CAI Xinxia from the Aerospace Information Research Institute (AIR) of the Chinese Academy of Sciences developed a new method for fabricating high-precision, low-curvature microelectrode arrays (MEAs) which are designed for recording neuronal activities in the brain's deep, small volume region. The study was published in Microsystems & Nanoengineering.

Animals have a natural navigation system that directs them to destinations crucial for their survival. John O'Keefe, along with the couple May-Britt Moser and Edvard Moser who won the Nobel Prize in Physiology or Medicine 2014, has used microfilament electrodes to discover special cells in the brain—place cells and grid cells—located in the hippocampus and entorhinal cortex which help with spatial navigation. Accurately implanting electrodes in the deeper brain regions such as the ventral tegmental area (VTA) has been challenging. 

In this study, researchers introduced an innovative backside dry etching method to release residual stress of MEAs, allowing for precise control of electrode bend direction from positive to negative. They can create low-curvature MEAs by precisely adjusting certain parameters. 

To confirm the effectiveness of this method, researchers used simulation and histological methods, and found significant improvement in stress distribution and implantation accuracy of the low-curvature MEAs. This method shows a better performance in terms of curvature than the advanced neural probe Neuropixels.

In the goal-directed navigation task, researchers implanted the low-curvature MEAs into the VTA of rats, and recorded the movement trajectory of rats alongside the electrophysiological activity of VTA neurons. By analyzing both time and position data, they found specific discharge patterns and adaptive changes in the VTA neurons regarding rewards and spatial information. Notably, the disappearance and reconstruction of the place fields were linked to shifts in the relationship between path taken and outcomes achieved. 

The study develops low-curvature MEAs with improved temporal and spatial resolution, which enhances implantation accuracy and signal quality for deep brain neuron information detection. It also provides insights into the role of VTA in goal-directed navigation.