Optimizing the human brain
Dr. Deblina Sarkar’s breakthrough project on neurological biosensors
When she began studying nanoelectronics, Deblina Sarkar never thought she would one day apply her work to the human brain. A project on ultrasensitive biosensors led her to a position in MIT's Synthetic Neurobiology Group, where she found that she was able to integrate her experience in nanoengineering with her passion for neuroscience. After a prolific residence in the lab, which included developing a super-resolution microscope to look at nanoscale resolution of building blocks of brain, Sarkar is seeking out a new challenge. She wants to create the most efficient computational device. She is starting the Nano-Cybernetic Biotrek research group to do so, but there is no better computer than the human brain. “The brain is the lowest-power computer ever,” Sarkar says.
Sarkar and other neuroscientists hope to understand one of the many mysteries of the human brain: how a healthy brain differs from one with a neurological disease like Alzheimer’s, Parkinson’s, or Huntington’s. All of these neurodegenerative diseases affect the brain’s structure and function. To further characterize the differences between healthy and diseased brains, Sarkar’s new group will use new physics and materials to develop nanoelectronics for computing applications. These nanoelectronics will be adapted for biological use to create devices that Sarkar says “can be used to sense our biological information, and also to do some internal computation to detect if there’s something wrong in our bodies and either store that data internally or wirelessly transmit it outside the body.”
Sarkar’s goal is an ambitious one. Current innovations in bioelectronic interfaces only go to millimeter and centimeter scales, especially in an organ as sensitive as the brain. “What I want to build are extremely small and low-power devices which can give single-cell resolution and will be minimally invasive,” Sarkar says. She notes that if there is an issue with one cell, the avalanche effect due to the dependency of the human body on the interactions between its parts may cause greater issues. “Maybe a single cell in the circuit is affected, and that affects the functionality of the entire brain.”
Sarkar’s goal is to further neurobiological therapies in a minimally invasive way so that one can maximize treatment of the disease while minimizing side effects. Her approach — using nanoelectronics to treat neurological diseases — happens on the scale of cells, but why treat cells when it is much easier to treat tissues and organs?
The size of the nanoelectronics has posed a major obstacle for her research, since the physics of the nanodevices does not scale properly below certain lengths. For instance, below a scale of about five nanometers, voltage adjustment no longer controls electron movement. “You can think of it as a tap,” she explains. “The water is flowing, and you control the flow of water with a knob. If you make the knob too small, the control of the flow of electrons is affected. Basically, it will begin to leak, and you cannot turn it off.” This can have disastrous effects in the brain, whose operation relies upon carefully maintained voltages.
Voltage control is not the only issue Sarkar must navigate. Typically, bioelectronics comprise many small components, but the size adds up and results in an invasive device. Sarkar’s approach is to make the components smaller — around a few nanometers — so that the overall device is smaller — on the order of a few microns. She plans to incorporate methods such as using three-atom thick layers on her devices.
There are two primary dangers to implementing bioelectronics into the brain. Displacing biological tissue can disrupt the normal function of the brain. Sarkar notes that the size of the device must be less than 0.1 percent of the volume of a cell if it is to be considered truly non-invasive. Another potential danger is that the immune cells in the brain will recognize the device as foreign and attack it. However, if it is coated in a biological material that the immune cells see as their own, the device can be camouflaged. Another aspect Sarkar must consider is the power output of the device. “They must be low power so that the brain temperature doesn’t change too much. Power dissipation [within the brain] must be controlled so that the temperature does not increase by more than two degrees Celsius.”
How will she design these devices to work in the brain without disrupting its natural function? The answer lies in the organ itself. The brain serves as a model for computation because in traditional computers, while the error rate is very low, there is little space for automatic correction of the errors when they do happen. In the human body, the error rate is higher but it has its own correcting algorithms to account for defects. This works because there is redundancy in neuron function, and, as Sarkar explains, “That way the probability of committing an error is reduced, though a single neuron may commit more errors than a digital computational unit.” Moreover, components in computers can connect to a few other components, but in the brain, “One neuron connects to ten thousand other neurons [and then] to synapses, so the connectivity is really huge,” Sarkar says. “In brains, as a function of what kind of activity is going in the brain, the connections between the neurons can change.” This principle can be described simply by the phrase “use it or lose it”: if the brain does not use a pathway often, it will do away with those pathways altogether. Furthermore, neurons that fire together, wire together: the brain strengthens pathways that are used often. These communications between neurons can happen at any time and aren’t limited by switching as they are in computers.
But why change our biology at all? “It is very human to want to improve,” Sarkar says. She hopes that if humans make these changes, their neural function will improve, meaning humans could think faster and learn new skills quicker. In turn, humans would spend less time learning and performing basic tasks and could spend more time doing what they love, whether or not that be improving their own biology.
Sarkar’s career, both in its trajectory and in its day-to-day practice, requires a lot of flexibility. Sarkar has a message for students who, like her, may encounter a field that suddenly changes their career. “There is a saying in India that someone who can cook can also meditate.” In this, she explains that what matters in anything, whether it be science or sports or art, what matters are not the skills but rather the mindset — someone who shows promise and excitement in one field should see no obstacle in extending their passions to something unknown to them. “I would encourage students to go outside their comfort zone.”