DECIPHERING THE COMPLEXITY OF THE HUMAN BRAIN, WITH ITS BILLIONS OF NEURONS, IS ONE OF SCIENCE’S most tantalizing puzzles. In the last three decades, noninvasive advances in brain imaging have led to significant breakthroughs in how we understand the inner workings of the mind. We know, for instance, that language is primarily processed in the left hemisphere and that a particular occipital sulcus—or groove in the brain—first translates visual inputs. But while researchers have a rough sense of the brain’s functional neighborhoods, they still don’t have a clear street-level view.
Tyler Perrachione, an associate professor and director of the Communication Neuroscience Research Laboratory, is angling to get a sharper image. “The current atlases we have are very coarse,” he says. “Over its 30-year history, brain imaging has helped teach us what the average brain looks like. Human brains are organized basically the same, but the local organization is still pretty different.”
Perrachione is pursuing multiple studies to get a finer-scale understanding of neural organization and function. Having a more detailed picture of individual brain structure and tissue properties has promising medical applications. Physicians could target more effective rehabilitation strategies for stroke victims, and neurosurgeons would have clearer margins for avoiding brain tissue that might damage a patient’s cognition or speech. “It’s like a personalized medicine approach to brain mapping,” Perrachione says.
Using new methods developed by his lab, Perrachione is working to create individual maps of the temporal lobe that can shed light on the nuances of typical brains and those of people with developmental communication disorders. Such insights could reveal clues about the origins of dyslexia or autism and illuminate new avenues for research.
“Can we find meaningful organization in the structure of the brain that’s consistent across people but unique to each person?” he says. “We may find that the reasons some kids struggle to read or communicate are different from the reasons other kids struggle. Ultimately, it gives us an entry point to ask more precise questions than we’ve been able to ask before. And maybe we can begin to understand the etiology of these disorders.”
REVEALING SCANS
At the heart of Perrachione’s research is a bank of 1,200 high-resolution MRI brain scans collected from academic and medical centers across Boston. In 2019, colleagues from BU, Northeastern, MIT, Harvard, and Massachusetts General Hospital contributed brain scans from more than 1,200 anonymous patients and research subjects with and without developmental disorders, ranging in age from 4 to 40. Roughly half of the scans come from individuals with dyslexia and about five percent come from those with autism.
“Everyone was excited about it,” Perrachione says of the collection. Unlike donated brain tissue, which can only be studied once, MRI brain scans are an infinitely reusable resource that can be analyzed over and over again, limited only by the curiosity of the investigator. The scans provide an opportunity to test assumptions that scientists have about which areas of the brain are responsible for certain functions. The reality is that “human behaviors don’t always cleanly map onto the brain” in the ways scientists have categorized them, Perrachione concedes. “Sometimes the organization of the brain surprises us.”
In a study comparing the fMRI brain scans of subjects with and without dyslexia, Perrachione looked at whether reading disabilities may be the result of differences in neural organization or activity. His lab evaluated the activation of the frontal and temporal lobes during language-related tasks to discern if there was a difference in responsiveness. There wasn’t. “Our findings indicate people with dyslexia aren’t wired differently for language,” Perrachione says. Instead, they may have “trouble bringing their language system to bear on a visual task like reading. This helps us narrow down where the problem is and how we should target remediation.”
In a separate study on the brain scans of autistic subjects, Perrachione’s lab did discover a striking anatomical variation in children with autism. The auditory cortex—the part of the brain that is responsible for processing sound—was markedly larger in kids with autism. Because the original study from which the scans were taken also collected questionnaires from subjects, Perrachione was able to find a compelling correlation: children with larger auditory cortices in the right hemisphere had more severe autism symptomology, such as challenges with attention, social interaction, and repetitive behaviors.
Human brains are organized basically the same, but the local organization is still pretty different.
—Tyler Perrachione
Perrachione has a hunch that the larger auditory cortices may explain why some children with autism seem to get overwhelmed in busy environments. “Imagine you have a bigger pipe bringing sound information into your brain,” he says. “You can see how that might make it hard to filter out extra sounds and be distracting. Having more tissue that processes sound could dominate your attention or cause hypersensitivity to auditory stimuli.”
Perrachione’s dream is to collect long-term datasets of individual brains over decades to better understand neural plasticity. “The challenge in neuroscience is that when we look at a brain scan, we’re looking at a snapshot. But everything we are today is a consequence of everything that we’ve been through,” he says. “It would be tremendous if we could get longitudinal datasets about tissue organization and structural connectivity over time. To really understand an individual brain not as a fixed state, but as a transition across development—to have a four-dimensional view. It’s not so much about what the brain is, but where it’s come from and where it’s going.”
