By Matt Wood
In the pre-dawn winter darkness of a cold January morning, workers at the University of Chicago used a forklift to unload several large wooden crates from the back of a flatbed semi-truck trailer. The largest of these crates, weighing over one-and-a-half tons, contained a photoemission electron microscope (PEEM) that had just cleared customs on its journey from a manufacturer in Germany.
The new microscope is the biggest piece of equipment needed in the quest by a team of UChicago researchers to build a complete wiring diagram of the brain. This diagram – known as the connectome – will help researchers reverse engineer the brain and unlock secrets of how it works by mapping every single connection between brain cells.
In 2024, Gregg Wildenberg, PhD, a Research Assistant Professor in the Department of Neurobiology at UChicago, Narayanan “Bobby” Kasthuri, PhD, Associate Professor of Neurobiology at UChicago and neuroscience researcher at Argonne National Laboratory, and Sarah King, PhD, Assistant Professor of Chemistry at UChicago, received a $4.8 million, three-year grant from the Brain Research Through Advancing Innovative Neurotechnologies (BRAIN) Initiative, part of the National Institutes of Health (NIH), to purchase the microscope and customize it for connectome imaging.
The project is a collaboration with researchers at Chicago State University and the University of Illinois at Chicago to drastically increase the speed of capturing brain images and build a pipeline of students who are trained to work with such powerful microscopes and analyze the imaging data.
Adapting old technology for higher volume
PEEM is an older imaging technology first developed in the 1980s, mostly used to scan two-dimensional hard surfaces and materials. Until now, connectome researchers used two other kinds of microscopes: scanning electron microscopy (SEM) and transmission electron microscopy (TEM), each with their own advantages and disadvantages. SEM can accommodate a wide variety of samples, but capturing images can be very slow. TEM captures images much more quickly, but the samples must be extremely thin and mounted on fragile grids, which are difficult to work with in large volumes.
Wildenberg and Kasthuri believe that PEEM can overcome these bottlenecks because it combines elements of SEM and TEM, using photons to capture a large field of view quickly like TEM but with sturdier equipment for mounting the samples like SEM. They have perfected preparation techniques that essentially turn ultra-thin slices of brains into hard 2D materials by fixing them in resin, more appropriate for PEEM’s usual applications.