When Sridevi (Sri) Sarma, ‘06, introduces herself, she might say, “I got my PhD at MIT in control theory.” She might add, “I studied in the Laboratory for Information and Decision Systems (LIDS) with Prof. Munther Dahleh, and now I apply what I learned to the brain.” This, the ‘brain’ part, is when you want to get to know her.
“Turning your career to the interface of neuroscience with control theory is not the typical route for EECS graduates,” Sri Sarma continues. Indeed, she leads a research lab that studies neurological disorders and deep brain stimulation therapy at Johns Hopkins University in the department of Biomedical Engineering. She is also a professor and mentor to students. Her description of what she gained in her graduate training and experiences in EECS at MIT are as insightful as her discussions of her work are compelling. She shares a bit of both.
Sri’s path to brain-implant controller design started during the time she was doing her doctoral studies in LIDS. While her graduate studies were focused on control theory, she was taking courses in neuroscience on the side. “We had to do a minor in something, but I really wasn’t looking to do anything interdisciplinary,” she explains. A class project led her to do a three-day case study on her aunt who had early-onset Parkinson’s disease—giving her a completely different perspective of what it’s like to live with this disease. Sri saw an opening to put her training to use in finding a better way to help people with neurological disorders. “I was motivated to better understand what’s happening in the brain, to use my training in systems modeling and control to better understand the brain, and how to design better therapy.”
At the Institute for Computational Medicine at Johns Hopkins University, one of Sri’s research areas involves optimizing deep brain stimulation (DBS) for Parkinson’s disease and Epilepsy patients. DBS is a procedure during which an electrode is surgically implanted in the brain. The electrode is connected to a wire, which sits under the skin and terminates at a neurostimulator (Figure 1). The neurostimulator contains a battery operated current source that injects current to the tip of the electrode. The current impulses can be targeted in such a way that they are able to alter the electrical activity in the diseased brain to alleviate some of the motor symptoms in Parkinson’s and to suppress seizures in Epilepsy patients.
Most doctors who work with DBS do their best to adjust the instrumentation, but it’s essentially a shot in the dark. “After a Parkinson’s patient recovers from surgery, the doctor can literally tweak the parameters of the stimulators,” she said, adding that while the pulse train of current that goes into the electrodes is constant, the intensity of the pulse can be tweaked. Typically doctors ask patients to walk around the room and perform certain tasks while the pulse’s parameters are changed. This process is laborious, expensive and lengthy – taking potentially up to a year to optimize the treatment.
Sri’s goal is to create a more intelligent system for both placing and controlling the electrodes. In current practice, once the parameters are correct, she says, the same high-power signal runs 24 hours a day, 7 days a week – until the batteries run out three to five years later. At this point another surgery and another round of tweaks are required. Plus, the electrical impulses can trigger other circuits in the brain, making patients impulsive, anxious and/or depressed. Sri thinks it’s possible to re-imagine the whole system. The normal brain operates in a low-power environment. “Why not a low-power alternative for DBS?” she reasons, adding that the electrical signal can be designed to work smarter. “We want to implant an intelligent chip that continuously measures neural activity, and responds with appropriate stimulation with the goal of getting the patient’s brain to look more like a healthy brain.”
She is now analyzing data from both primates and humans to build models of what exactly DBS is doing. The systems approach and computational framework she brought from LIDS can be both exciting and challenging to neuroscience colleagues who have a set way of doing things. She has found that designing experiments in current neuroscience practice can lead to data overload—whereas the desired outcome is to understand the dynamics of neural systems. In this case a systems engineer is most appropriate. It is hard for neuroscientists to understand and/or appreciate what a systems engineer is trying to accomplish and vice versa.
“LIDS gave me the systems perspective – the methodology and tools to apply to this field. I have not run across many with my training looking at these problems,” she said. Specifically, Sri has much to say about working with her PhD advisor, Munther Dahleh.
“I met Prof. Dahleh when I took his Introduction to Linear Systems (6.241) course my first semester at MIT. After some 15 courses in EECS, I graduated with the recollection that this was the most difficult class that I had ever taken in my life. Despite this, I still remember Dahleh being the most dynamic and effective teacher I have had. This is why I decided to join his lab for my PhD.”
Now ‘in the shoes’ of her master teacher and mentor, Sri defines just how keenly she has drawn on her work under Prof. Dahleh. “He taught me that clarity is key. You must be clear in your logic in how to go from one step to another when teaching new material. Every step must be justified and placed in the broad context and clearly motivated. You must be sensitive to the variability in students’ abilities and adjust to each individual to the extent possible.” Sri continues, “As a mentor, Dahleh has this amazing foresight in your work. With a grand vision from the outset that we students don’t see because we are focused on minute detail, Dahleh embarks with us on our journey—following our lead yet allowing us to get stuck so that we learn why a certain path leads to a dead end. Dahleh manages to stay with us until we realize that the finish line is ever so close to his grand vision—now clear to each of us as well. By his example, we learn how to communicate our work both orally and in written form to others in the community. Dahleh taught me that nothing changes when communicating with the neuroscience community except vocabulary and context. The thought process and logic remain the same—a point that is making me successful in my research. I stick to my control systems perspective and training and just place it in new contexts. This leads to very different and novel ways to learn about the brain. In short, Dahleh is incredible and remains a wonderful mentor and one of the most important people in my life.”
Having spent three years as a postdoc with Emery Brown in the Brain and Cognitive Science department, learning about neuroscience following her minor in that field while completing her PhD in control theory, Sridevi is now in a good position to build an effective new cadre of researchers who bridge the training and thinking gaps toward major advances in neuroscience research.
[We would like to acknowledge the article “A Novel Approach to Controlling the Brain” by Katherine Stoel Gammon in LIDS-All magazine about Sridevi Sarma.