This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: A decades-long collaboration between two scientists at the Department of Energy's Oak Ridge National Laboratory is reshaping how we understand learning. Their findings suggest that cellular membranes play a direct role in how memory and learning form in the brain.
This work aims to advance materials science for neuromorphic, or low-power, brain-inspired computing technologies and research on neurological disorders. The discovery was made possible by ORNL's unique combination of expertise in soft matter science, world-leading neutron capabilities and co-located user facilities, which allowed researchers to investigate biological membranes in ways not previously possible. "Science is a conversation," said John Katsaras, neutron scattering scientist at ORNL's Spallation Neutron Source, a Department of Energy Office of Science user facility.
"Many years ago, Pat [Collier] and I wanted to see what would happen when we combined our scientific interests. He wanted to explore soft matter systems for neuromorphic computing [computing systems designed to mimic how the brain processes information], and I've studied the structure and dynamics of lipid membranes over the past 40 years. We are now applying decades of our soft matter experience to a problem neither one of us would have imagined pursuing five years ago." Soft matter includes materials that readily change shape, such as membranes, gels and polymers.
Although biological membranes vary in complexity, they all share a common foundation: a lipid bilayer, or double layer of molecules. Each lipid contains a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. To study membrane properties under electrical stimulation, Katsaras and Collier used water droplets suspended in oil, known as a droplet interface bilayer.
These early experiments showed unexpected electrical data, prompting them to shift their attention to membranes surrounding neurons, where many memory and learning processes occur. "Our early measurements revealed stable changes in the membrane's electrical behavior—patterns typically associated with neural activity," said Collier, a cleanroom process engineer at ORNL's Center for Nanophase Materials Sciences, also a DOE Office of Science user facility. "Working with a broad group of collaborators, we developed new experimental approaches and observed results consistent with biological memory and learning occurring in these bilayers." Scientists have long known that ion activity drives brain signaling.
Katsaras and Collier have shown that lipid bilayers play an active role in regulating how these ions flow through membrane proteins. "We've shown memristance and memcapacitance [electrical properties of devices with electrical resistance that depend on the history of applied voltage] taking place within the same membrane," Collier said. "In one region of a membrane, a lipid bilayer might rearrange to form a memory resistor, and in another region, it can behave as a memory capacitor.
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