Neuroscience Seminar Looks at Brain Plasticity
Our brains are incredibly complex. They process multiple kinds of sensory input and dictate the motion of our bodies. But what happens when some of that sensory input is lost?
Dr. Ella Striem-Amit of Georgetown University is investigating this question in her SAMP (sensory and motor plasticity) Lab. She studies neural processing in three categories of people with early-onset sensory and motor deprivation: people born without hands, and people who are born blind or deaf.
Does a handless person still use the “hand” area of their brain (in the sensorimotor cortex) when performing tasks with their feet? If an individual is born blind, how will that influence the way their visual cortex develops? Striem-Amit discussed these questions in a recent NIH Neuroscience Seminar Series lecture, “Plasticity, Abstraction and Variability: Lessons from Studying People Born Blind or Without Hands.”
Studying these conditions, Striem-Amit said, allows us to “uniquely target the causal role of environmental factors” in brain development.
Plasticity is the brain’s ability to change and adapt through growth and reorganization. To study the effects of congenital handlessness on brain organization, Striem-Amit used fMRI (functional MRI) to view the sensorimotor cortex as people born without hands completed tasks. The sensorimotor cortex, located in the parietal and frontal lobes, plays an influential role in executing body movements. Researchers have learned how to isolate motions of certain body parts to specific regions of the sensorimotor cortex.
The individuals in her study could use their feet to execute the same tasks the average person would use their hands for—everything from texting and writing to carving pumpkins and playing the drums.
What happens to the hand region of the sensorimotor cortex in individuals who use their feet as effectors? Striem-Amit evaluated two groups (handless individuals and a control group, i.e., those with hands) as they reached for and grasped an object. The control group used their feet for some trials and their hands for others.
Interestingly, Striem-Amit found that there are some areas in the sensorimotor cortex that seem to prefer certain kinds of actions (or movements) regardless of what body part is performing the action, and regardless of whether the individual has experience using a specific body part for a task.
However, looking specifically at the hand area of the primary sensorimotor cortex as handless individuals completed tasks, Striem-Amit found that participants did activate the hand area (in addition to the foot area), but the hand area “was not the primary driver of foot movement.” Some of the hand area also seemed to be “taken over” by other nearby body parts, such as the shoulder and abdomen.
“Compensatory use and plasticity don’t [entirely] overcome anatomical…constraints,” Striem-Amit found. In the future, she said she would like to find out what areas in the sensorimotor cortex also have the ability to reorganize to nearby regions, and which areas reorganize based on effector/body part use.
Photo: Yuqi Liu
Such a determination also might help in developing prosthetics (which might be able to read out which tasks people want to perform), she added, but that would require more research.
Researchers also still have a lot to learn about how the visual cortex develops in congenitally blind individuals. The visual cortex is located in the occipital lobe, in the rearmost portion of the brain. Interestingly, MRI scans of these individuals showed that some parts of the visual cortex still “know” how to organize themselves, even in the absence of sight. However, that didn’t tell Striem-Amit much about the function of other regions in the earlier stages of visual processing.
Researchers already knew that the primary visual cortex responds to more than just visual stimuli; Braille, sound, smell and other sensory input can also activate the primary visual cortex in blind individuals. These responses are far more varied in blind individuals than in sighted ones.
“Is brain plasticity variable?” Striem-Amit asked. “Are there different plastic patterns of visual use in blind people, and what does that tell us about the role of experience in generating consistency of brain organization and function?”
To answer those questions, she decided to look at functional connectivity from the visual cortex of blind people. She found that “blind people had 3-10 times as much variable functional connectivity compared to sighted people, from their visual cortex to multiple and meaningful other areas of the brain.”
Plasticity in the visual cortex must be inherently variable, she concluded, because it generates far more variable outcomes in the blind.
To demonstrate, she displayed a diagram that grouped blind individuals with similar kinds of functional connectivity. Some people have a strong connection between the visual and auditory cortices, for example, while others do not. Striem-Amit pointed out a pair of sisters with the same genetic blindness whose functional connectivity was so different they ended up in different parts of the diagram.
These observations may come in handy when determining which assistive technologies and treatments to offer each person, she revealed.
One example is Project Prakash, a nonprofit organization, led by Dr. Pawan Sinha of MIT, that treats curably blind youth in rural India. Young people are treated (the most common procedure is cataract removal) and then researchers track their sight restoration by studying behavioral and neural measurements. There is a lot of variability in outcomes, and not all of it is easily explained.
Striem-Amit proposed that brain connectivity plays a role in determining sight restoration. By examining data shared by the Project Prakash team, she found that “studying brain connectivity before surgery can help inform how sight will improve following surgery.”
Although this was a very small study, it has exciting implications.
“Could it tell us what networks are involved in improved sight recovery?” she asked. “Could we boost those networks in people who otherwise wouldn’t gain that much sight back?”
Striem-Amit considers plasticity in the early visual cortex in blindness to be unresolved at this point, but summarized that functional plasticity from congenital blindness and handlessness are variable and may even provide new opportunities for predictive treatment outcomes and individually tailored assistive treatments.