Low-Curvature Microelectrode Arrays Offer Insights into Spatial Cognitive Information Coding of Ventral Tegmental Area

Th "Micro-Nano Sensing Technology" creative research group of NSFC from the Aerospace Information Research Institute (AIR) of the Chinese Academy of Sciences, led by Professor CAI Xinxia, has developed a new method for fabricating high-precision, low-curvature microelectrode arrays (MEAs). The MEAs are designed for recording neuronal activities in brain's deep, small volume region. Published in the Microsystems & Nanoengineering on October 14, the study implanted the low-curvature MEAs into the ventral tegmental area (VTA) of rats, employing a modified T-maze to highlight the VTA's important role in reward processing and spatial information coding during goal-directed navigation.

Much like GPS helps humans find their way, animals have a natural navigation system that directs them to goal locations including food sources, and habitats, crucial for their survival. Notably, John O’Keefe, along with the couple May-Britt and Edvard Moser, who won the Nobel Prize in Physiology or Medicine 2014,  previously used microfilament electrodes to discover special cells in the brain—place cells and grid cells—located in the hippocampus and entorhinal cortex, which helped with spatial navigation. However, accurately implanting electrodes in deeper brain regions, such as the VTA has been challenging, limiting the research in this important region.

The current study introduces an innovative backside dry etching method to release residual stress of microelectrode arrays, allowing for precise control of electrode bend direction from positive to negative. By precisely adjusting certain parameters, researchers can create low-curvature MEAs.

To confirm the effectiveness of this method, researchers used simulation and histological methods, which demonstrated significant improvement in stress distribution and implantation accuracy of the low-curvature microelectrode arrays. Compared with the advanced neural probe Neuropixels, this approach shows a better performance in terms of curvature.

In the goal-directed navigation task, researchers recorded the movement trajectory of rats alongside the electrophysiological activity of VTA neurons. By analyzing both time and position data, researchers 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 offers low-curvature microelectrode arrays with improved temporal and spatial resolution, enhancing implantation accuracy and signal quality for deep brain neuron information detection. It also provides new insights into the role of VTA in goal-directed navigation.

Graphical rendering of the research findings. (Image by AIR)