Engineers record neurons to pinpoint synaptic links: Rice lab’s 3D electrode array reveals millisecond evolution of synaptic activity

It’s a mystery how human thoughts and dreams emerge from electrical pulses in the brain’s estimated 100 trillion synapses, and Rice University neuroengineer Chong Xie dreams of changing that by creating a system that can record all the electrical activity in a living brain.

In a recently published study in Nature Biomedical Engineering, Xie and colleagues described their latest achievement toward that goal, a 3D electrode array that allows them to map the locations and activity of up to 1 million potential synaptic links in a living brain based on recordings of the millisecond-scale evolution of electrical pulses in tens of thousands of neurons in a cubic millimeter of brain tissue.

“The thing that is novel about this work is the recording density,” said Xie, an associate professor of electrical and computer engineering at Rice and a core member of the Rice Neuroengineering Initiative. “Microcircuits in the brain are very mysterious. We don’t have many ways to map their activity, especially volumetrically. We want to deliver very dense recordings of the cortex because those are important, scientifically, for understanding how brain circuits work.”

Xie collaborated on the study with colleagues from Rice and the University of California, San Francisco, including Loren Frank of UCSF and co-corresponding author Lan Luan of Rice.

Neurons are small. Each cubic millimeter of brain tissue contains about 100,000. That density is roughly the same for humans and other mammals, including the rodents that are the subject of experiments in Xie’s lab. The processing power of the brain arises from synaptic connections between neurons. Synaptically linked neuron pairs are connected by narrow bridges of tissue called axons, which are just a few millionths of a meter in diameter.

Xie’s team has spent years developing a material called nanoelectronic thread (NET) that is thin, ultraflexible and biocompatible, a trifecta of properties for making minimally invasive electrode implants. In previous studies, Xie’s team has demonstrated techniques for emplanting tightly packed NET arrays of up to 128 electrodes. The researchers also showed their arrays could stay in place for up to 10 months, recording the pulsed spikes of electricity, or action potentials, in nearby neurons.

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