Duke researchers develop new form of brain analysis

Scientists at Duke University’s Brain Stimulation Research Center have identified a new method of transcranial magnetic stimulation (TMS), a non-invasive treatment that is used in patients with obsessive-compulsive disorder and major depression and which may soon be used therapeutically for memory disorders like dementia and Alzheimer’s.

The researchers used functional MRI (fMRI) to measure controllability in the brain, i.e., how much change TMS induced while participants were working on a memory task.

The task involved working memory, i.e., keeping bits of information in the memory and manipulating the information in the mind before answering questions. Working memory is essential to perform everyday tasks like categorizing your shopping list in your mind before walking through various aisles in a grocery store. Working memory is severely impacted in patients with dementia and Alzheimer’s.

“Essentially, we look at the brain not as a set of discrete islands, but as a dense web of connections that have lots of mutual influence,” said lead researcher Dr. Simon Davis, PhD, Assistant Professor of Neurology at Duke. “Controllability allows us a framework for identifying which nodes in this web are most likely to be influenced by brain stimulation, and for that reason likely to show plasticity and improvement after TMS treatments.”

The scientists took a static image of the brain and used the controllability measure to predict dynamic activity.

“Brain activity is like the spatial pattern of traffic in a city. Although the traffic pattern is ever-changing, it is always confined by the topology of the road network,” said Lifu Deng, a Duke graduate student in the Department of Psychology and Neuroscience, and co-lead on the paper. “Controllability links the stimulation at one location to the global pattern of brain activity. In our study, for instance, this is the activation patterns signifying better working memory.”

Prior to this, scientists had no way of knowing which areas of the brain exert maximum influence and are likely to produce whole-brain changes because most studies focus on one area of the brain. This is the first instance where researchers have advanced the method and considered the brain as a whole. The study enrolled healthy adults but the findings have implications for people with memory deficits.

“Memory dysfunction is a network phenomenon that relies on multiple brain regions operating under coordinated dynamics. The typical focus on the TMS response at a single site represents a fundamental limitation in the approach of neurostimulation therapies because it neglects global impairments in the whole network that underlies memory dysfunction,” said Lysianne Beynel, PhD, a postdoctoral associate in the BSRC and first author on the study.

The authors hope that ultimately whole-brain non-invasive transcranial magnetic stimulation (TMS) can be used to promote healthy activity patterns in the brain and enhance memory function, which could potentially benefit patients with a range of cognitive disorders.