Many of us have thought that if we could only see inside someone's head, mysteries would be solved.
Erin Schuman is seeing. And solving.
Her aim is to figure out how the brain changes in response to learning and memory. As one of its projects, her lab analyzes data from electrodes implanted in the brains of epilepsy patients. The patients need surgery because their disease is not responding to drugs, and because physicians can't pinpoint the seizures' origin in the brain.
The electrodes, implanted in the brain's hippocampus, record seizure activity. Later, Schuman's group does simple memory tests with the patients and eavesdrops on the activity of the neurons. In 2006, the group found that the activity of single neurons in the hippocampus appeared to discriminate between new and old (familiar) images presented to the patient. They also found that when people failed to recognize a familiar object, the "familiar object" neurons still fired, indicating some sort of disconnect: the brain was getting it right, but the person still got it wrong.
The epilepsy studies are a small part of what goes on in Schuman's lab, but an important one. "If you want to understand how the brain changes with learning and memory, you'd like rapid behavioral feedback. In most nonhuman animal studies, even in monkeys, it takes a gazillion trials for the animal to show you it has learned something. With humans, you can show them something and 20 minutes later you ask if they remember it, and they say yes or no."
This research is allowing the lab to piece together the chain of neuronal firings that represents learning. Schuman's overarching goal: to understand how neurons store information.
Neurons don't touch one another; instead, they communicate by sending messages across the minuscule spaces, called synapses, between them. The strength of communication across synapses changes over time. Schuman's group is studying how these changes occur, and how they relate to learning.
Synapses need new proteins in order to change. Schuman's lab discovered that the new proteins appeared on the scene very rapidly—usually within 20 minutes—after a stimulus. The group thought that instead of being made in a neuron's cell body (where its DNA is), perhaps the proteins were being made in the dendrites: the branched processes that extend from the cell body and provide a home for synapses. Though ribosomes (the machinery for protein synthesis) had been observed in dendrites, dendritic protein synthesis was considered to be "kind of a wacky idea."
But in 2001, the group published time-lapse images showing that, in response to stimuli that change synaptic strength, neurons synthesized these proteins in dendrites.
"We still don't know the logic of cell-body versus dendritically synthesized proteins, but this system allows synapses to use proteins that are made locally. That's important. One cell might have 1,000 synapses, so it could be processing 1,000 bits of information. If all of the proteins were made in the cell body, how would you then target a specific protein to synapse number 507, for example?"
In 2006, Schuman showed that when it comes to changes in synapses, degrading proteins can be just as important as making them. She also showed that this degradation is also probably local. In response to synaptic activity, the proteasome—a cell biological machine that degrades proteins—moves into synapses and stays there. Currently, Schuman and her colleagues are trying to figure out how specific patterns of neural activity get translated into different profiles of protein synthesis and degradation.
Always interested in learning and memory, Schuman earned an undergraduate degree in physiologic psychology. ("It's now called neuroscience.") Her honors thesis was a twin study on what fraction of memory could be attributed to genes versus the environment. For her Ph.D., Schuman studied learning in mollusks. She completed a postdoc with Daniel Madison at Stanford University, where she became interested in synaptic transmission in the hippocampus.
Schuman lives in Southern California with her husband, also a scientist, and three daughters (Emma, Charlotte, and Camille). Even if she does unlock the secrets of the brain, Schuman says that having children is the most rewarding thing she's ever done.
