F A C U LTY SPO TLIGH T
Assistant Professor of Engineering, Thayer School of Engineering ANNIE CHEN
Tell us about your lab and research. I call my workspace the multimodal neuroimaging lab—multimodal in that we use multiple modalities of studying human brain function. One example is EEG; in this lab specifically we use EEG caps, with which electrons are placed directly on the scalp to measure the difference in potential from one location to another and over time. We have a standard cap and one that we have built ourselves. Each of the caps has an elastic web where we attach optodes, which carry near-infrared light to the head. That light is then delivered into the head through the scalp, and we collect the light that comes back out again. Based on changes in the absorption at one wavelength versus another, we can calculate the oxygenation level of the brain. This method also allows us to track the oxygenation changes at the same time as the neurological changes. These measurements are important in certain diseases and the study of brain function. For example, ischemic blockage of blood flow or a bleed in the brain from hemorrhagic stroke causes the loss of neurons and brain function in specific regions. In this case, disrupted blood circulation is closely tied to disrupted neuron function. We are currently looking at stroke subjects in an attempt to understand the relationship between neuron function and vascular function in the brain during the recovery process. Another machine that is useful in this pursuit is the near-infrared spectroscopy machine, or NIRS for short. It has a bank of 32 lasers—all in the near infrared part of the spectrum. On our machine, they are specifically calibrated to 690, 785, 808, and 830 nm. There are repeating rows of four lasers in each color paired with Avalanche Photo Diodes (APDs), which count the photons that come back out. Right now, we’re interested in looking at traumatic brain injury, Alzheimer’s, and stroke. Alzheimer’s disease is typically thought to involve beta-amyloid plaques and neurofibrillary tangles in the brain that lead to cell death There’s strong SPRING 2012
Photo by John Sherman, courtesy of Thayer School of Engineering at Dartmouth
Solomon Diamond, Assistant Professor of Engineering at the Thayer School of Engineering.
evidence that the plaques are also causing inflammation of the local arterioles and small blood vessels in the brain that impair the reactivity of these vessels. Normally when the neurons are active, the blood vessels respond in a coordinated way called neuro-vascular coupling. But with inflammation this coupling is disrupted. This is thought to be one of the factors that accelerates the disease process. An accumulation of plaques leads to impaired function, and hypoxic stress in the microenvironment, both of which lead to an enhanced progression of cell death and greater cognitive decline. By measuring the neuron activity and the blood dynamics at the same time, we hope to identify the decoupling, and therefore the breakdown of the physiological relationship between neural and hemo factors early in the disease. We also hope to track the disease progress over time to help evaluate which therapeutics affect the physiology of the brain.
What was your path to becoming an engineer? How did you become interested in engineering? I spent a lot of my childhood wanting to be an inventor. As a child, I designed and built things for fun. I also grew up with a family business. I used to help out in our woodshop a lot, and I became skilled with the tools there, which helped me to come up with ideas to build things. At the time, I liked to make dart guns. I went through a whole series of design durations on different triggering mechanisms and propulsion mechanisms. I liked doing that sort of design work from a young age. I also just loved computers and technology. My family business also ran a small computer store, and I used to assemble the PC clones. That was “the thing” at the time. IBM had the market cornered and other producers started making separate motherboards, hard drives, and control cards. When I was in junior high, my dad and I would buy all the pieces, put them together and sell them 9
The Spring 2012 edition of the Dartmouth Undergraduate Journal of Science