Wellesley’s Mark Goldman Asks, “How Do We Hold Onto a Memory?”
$45,000 Sloan Foundation Fellowship May Help Find the Answer

April 6, 2007
Arlie Corday

GoldmanWELLESLEY, Mass. -- Mark Goldman, an assistant professor of physics and member of the neuroscience program at Wellesley College, is among 21 New England researchers to be honored with a 2007 Alfred P. Sloan Foundation Fellowship. Each scientist is expected to receive a $45,000 two-year grant, and the fellowships begin Sept. 1.

Goldman, at right, joined the Wellesley faculty in the fall of 2003 following postdoctoral work in the Brain and Cognitive Sciences Department at MIT. He earned a Ph.D. in physics from Harvard University in 2000 and a B.S. in physics from Stanford University in 1993. His research is in the field of computational neuroscience, which uses computer and mathematical models to understand a variety of brain functions.

He is currently on a sabbatical at Stanford University, studying the eye movement system and its ability to adapt and learn. To support his work, he has also earned a grant from the National Institutes of Health, a Brachmann-Hoffman Fellowship from Wellesley College and a Research Corporation Cottrell College Science Award.

 “The Sloan is money to work on whatever questions I find interesting at the time,” Goldman said. “It’s a merit fellowship, as opposed to a grant for a specific topic of research.”

Established in 1955 to provide research grants to early-career scientists and scholars, the Sloan Research fellowships are awarded to investigators in fields including physics, chemistry, mathematics and molecular biology. Here are a couple of questions and answers about Goldman and his work:

Q. What kinds of research are you currently interested in?

neuronA. The main question I am interested in is: How does a group of neurons hold onto a short-term memory – memory that lasts for tens of seconds. This form of memory is thought to be maintained by neurons whose activity persists for tens of seconds following the disappearance of a stimulus. So, for example, when you look up a number in the phone book, close the book, and then remember the number for just long enough to dial it, it is thought that this memory is being held by a group of neurons whose activity repeatedly “recites” the number, "443-7899, 443-7899, 443-7899..."
And, as a theoretical neuroscientist, I ask the question, "How is such activity being produced? How does a group of cells produce elevated activity that represents a physical stimulus [in the above case, the sight of the phone number] when that stimulus is no longer present?"

For cognitive tasks like remembering a phone number, it is very difficult to tease apart the neural circuitry in enough detail to make a mathematical model. So I use a simpler system to try to get at this question. The circuit is located in the brain stem, the more primitive area of the brain, and is involved in controlling how we move our eyes and hold our gaze fixed on the objects we are looking at. It is called the oculomotor neural integrator circuit because it acts like an adding machine, or “integrator.” Activity in this circuit controls the tension of the eye muscles – the more activity there is in the circuit, the more tension is applied to the muscles and the further the eyes move away from center.  When we want to move our eyes by a given amount, say five units, we send a corresponding-sized pulse of input into the integrator and it adds five units of activity to its current level to move the eyes by the appropriate amount. The connection to short-term memory is that, as in the cognitive memory circuits, a pulse of input directly stimulates activity only briefly, but the circuit “remembers” to hold its new activity level for much longer.

Although I study this circuit in order to understand the neural basis of memory-related activity, this work also has more direct clinical implications for understanding disorders of the oculomotor system that controls movement of the eyes.

Q. How will you use the Sloan fellowship grant?

The fellowship does not have a specific topic. I expect to use it for this research, at least in part. I also plan to study how the oculomotor system can adapt to situations where, perhaps due to an injury, the oculomotor system isn’t working correctly and needs to relearn proper performance. Experiments have been done where animals in a virtual environment are tricked into thinking their eyes are drifting rather than being held fixed.

My collaborators have found that the animal learns to compensate for this drift so that, when the animal is placed back into a normal environment, its eyes continue to drift in a manner appropriate to perform correctly in the virtual environment it had been living in.

This research may have applications to clinical disorders in humans – people with problems keeping their eyes fixed on objects they are trying to look at. The deeper application is that hopefully we’re going to learn something about how short-term memories are stored. There are plenty of disorders, including schizophrenia, whose core symptoms involve short-term memory deficits. However, at this stage, my work is completely at the basic research level, trying to understand what is happening in the brain when we hold on to a short-term memory.