PITTSBURGH – An unprecedented study of brain plasticity and visual perception found that people who, as children, had undergone surgery removing half of their brain correctly recognized differences between pairs of words or faces more than 80% of the time. Considering the volume of removed brain tissue, the surprising accuracy highlights the brain’s capacity – and its limitations –to rewire itself and adapt to dramatic surgery or traumatic injury.
The findings, published by University of Pittsburgh researchers in the Proceedings of the National Academy of Sciences (PNAS), is the first-ever attempt to characterize neuroplasticity in humans and understand whether a single brain hemisphere can perform functions typically split between the two sides of the brain.
“The question of whether the brain is prewired with its functional capabilities from birth or if it dynamically organizes its function as it matures and experiences the environment drives much of vision science and neurobiology,” said senior author Marlene Behrmann, Ph.D., professor of ophthalmology and psychology at the University of Pittsburgh and Carnegie Mellon University. “Working with hemispherectomy patients allowed us to study the upper bounds of functional capacity of a single brain hemisphere. With the results from this study, we now have a foot in the door of human neuroplasticity and can finally begin examining the capabilities of brain reorganization.”
Neuroplasticity is a process that allows the brain to change its activity and rewire itself, either structurally or functionally, in response to changes in the environment. And even though brain plasticity peaks early in development, our brains continue to change well into adulthood.
As humans age, the two halves of our brains, called hemispheres, become increasingly specialized. Even though this division of labor is not absolute, the two hemispheres adopt distinct chief responsibilities: The left hemisphere matures into the primary place for reading printed words, and the right hemisphere matures into the primary place for recognizing faces.
But neuroplasticity has limitations, and this hemispheric preference becomes more rigid over time. In some cases, adults who develop a brain lesion because of stroke or a tumor might experience a reading impairment or become face blind, depending on whether the left or right hemisphere of the brain is affected.
But what happens when the brain is forced to change and adapt while it is still highly plastic? To answer this question, researchers looked at a special group of patients who had undergone a complete hemispherectomy – or a surgical removal of one hemisphere to control epileptic seizures –during childhood.
Because hemispherectomies are relatively rare, scientists seldom have access to more than a handful of patients at a time. But the Pitt team found an unexpected silver lining of the COVID-19 pandemic: the normalization of telemedicine services, which made it possible to enroll 40 hemispherectomy patients, an unprecedented number for studies of this kind.
To assess word recognition capacity, researchers presented their participants pairs of words, each differing by only one letter, such as “soap” and “soup” or “tank” and “tack.” To test how well the children recognized different faces, scientists showed them pairs of photos of people. Either stimulus appeared on the screen for only a fraction of a second, and the participants had to decide whether the pair of words or the pair of faces were the same or different.
Astoundingly, the single remaining hemisphere supported both of those functions. The capacity for word and face recognition between control subjects and people with hemispherectomies differed, but the differences were less than 10%, and the average accuracy exceeded 80%. In direct comparisons between matching hemispheres in patients and controls, patients’ accuracy on both face and word recognition was comparable regardless of the hemisphere removed.
“Reassuringly, losing half of the brain does not equate to losing half of its functionality,” said first author Michael Granovetter, Ph.D., a student in the Medical Scientist Training Program at Pitt’s School of Medicine. “While we can’t definitively predict how any given child might be affected by a hemispherectomy, the performance that we see in these patients is encouraging. The more we can understand plasticity after surgery, the more information, and perhaps added comfort, we can provide to parents who are making difficult decisions about their child’s treatment plan.”
Additional authors of this paper are Sophia Robert, B.S., and Leah Ettensohn, B.S., both of Carnegie Mellon University.
This research was supported by the National Eye Institute (R01EY027018), the National Institute of General Medical Sciences (T32GM081760) and the American Epilepsy Society (847556). This research was also supported by a National Eye Institute P30 CORE award EY08098 and unrestricted supporting funds from Research to Prevent Blindness and the Eye & Ear Foundation of Pittsburgh.
Top photo:
PHOTO DETAILS: (click images for high-res versions)
CREDIT: Marlene Behrmann
CAPTION: Marlene Behrmann, Ph.D.
Second photo:
PHOTO DETAILS: (click images for high-res versions)
CREDIT: Sophia Robert
CAPTION: Brain scans image. Examples of a single hemisphere in four children after surgery to manage drug-resistant epilepsy. Top row: Removal of the left hemisphere. Bottom row: Removal of the right hemisphere.
Third photo:
PHOTO DETAILS: (click images for high-res versions)
CREDIT: Michael Granovetter
CAPTION: Michael Granovetter, Ph.D.
FAQs
An unprecedented study of brain plasticity and visual perception found that people who, as children, had undergone surgery removing half of their brain correctly recognized differences between pairs of words or faces more than 80% of the time.
How much of the brain is devoted to facial recognition? ›
The ability to recognize faces is so important in humans that the brain appears to have an area solely devoted to the task: the fusiform gyrus. Brain imaging studies consistently find that this region of the temporal lobe becomes active when people look at faces.
Which half of the brain recognizes faces? ›
In the present study, comparable patterns of orientation-sensitive involvement of the right hemisphere are found for the recognition of faces and houses.
What part of the brain controls facial recognition? ›
The fusiform face area (FFA, meaning spindle-shaped face area) is a part of the human visual system (while also activated in people blind from birth) that is specialized for facial recognition. It is located in the inferior temporal cortex (IT), in the fusiform gyrus (Brodmann area 37).
Can facial recognition work with half a face? ›
Facial recognition technology works even when only half a face is visible, researchers from the University of Bradford have found. Using artificial intelligence techniques, the team achieved 100 percent recognition rates for both three-quarter and half faces.
How well can you function with half a brain? ›
You may wonder what your child's life will be like after a hemispherectomy. They may need this support after surgery, but the side of their brain that works well has already taken over for the affected side. Outcomes are good for walking, reading and behavioral issues, but some vision loss will happen.
Is facial recognition 100% accurate? ›
In ideal conditions, facial recognition systems can have near-perfect accuracy. Verification algorithms used to match subjects to clear reference images (like a passport photo or mugshot) can achieve accuracy scores as high as 99.97% on standard assessments like NIST's Facial Recognition Vendor Test (FRVT).
What percent of facial recognition is accurate? ›
Facial Recognition Accuracy. So how accurate is facial recognition, anyway? Broadly speaking, facial recognition technology is 99 percent accurate. But our industry as a whole has more work to do to secure that extra percentage point.
What is the face recognition theory? ›
One of the most widely accepted theories of face perception argues that understanding faces involves several stages: from basic perceptual manipulations on the sensory information to derive details about the person (such as age, gender or attractiveness), to being able to recall meaningful details such as their name ...
What side of the brain recognizes words? ›
Behrmann: We know that in adults, the left hemisphere is better than the right hemisphere of the brain in recognizing words. This is probably because in the majority of the population, language systems are more left- than right-sided.
"Super recogniser" is a term coined in 2009 by Harvard and University College London researchers for people with significantly better-than-average face recognition ability. Super recognisers are able to memorise and recall thousands of faces, often having seen them only once.
How many faces can the human brain recognize? ›
To qualify as "knowing" a face, the participants had to recognize two different photos of each person. By combining these two numbers and canceling out faces that appeared in both sets, the researchers determined the average person knows about 5000 faces, they report today in the Proceedings of the Royal Society B .
What causes poor facial recognition? ›
Causes of prosopagnosia (face blindness)
It can happen: if you do not develop the ability to recognise faces – this is the most common type and may run in families. from brain damage, such as following a stroke, head injury, inflammation of the brain (encephalitis), or Alzheimer's disease. if you're autistic.
What is lack of facial recognition called? ›
Prosopagnosia is a condition where you struggle to recognize faces or can't interpret facial expressions and cues. It usually happens because of brain damage, but some people have it at birth.
Why are humans so good at recognizing faces? ›
Scientists who study face perception have long argued that faces are “special” to us. There is a region in the brain, after all — the fusiform face area — that is, some neuroscientists argue, specifically dedicated to face recognition.
What portion of the brain is affected when you can t recognize faces? ›
Studies using positron-emission tomography scan and functional magnetic resonance imaging show that facial recognition networks are located in multiple brain regions, including the anterior temporal lobe, prefrontal cortex, inferior and middle temporal cortex, the hippocampus, the amygdala, and most importantly, and ...
What does the study of split-brain patients reveal about language? ›
For example, when they showed words and pictures to V.J.'s left hemisphere (by flashing them in her right visual field), she could read and name them aloud, but she couldn't write the corresponding words. The researchers concluded that her left hemisphere controls speech and reading, but not writing.
What is true about split-brain studies? ›
Research over the next twenty years showed that the disconnected right hemisphere is superior to the disconnected left hemisphere in allowing people to understand spatial information (such as maps), music, and emotions, whereas the disconnected left hemisphere is superior in allowing analytical thinking, talking, ...
Which area of the brain is involved in word recognition? ›
Left occipito-temporal cortex (OTC), also known as the Visual Word Form Area, responsible for visual recognition of letters and words. Left Temporo-parietal cortex (TPC), is responsible for storing and retrieving sounds (phonemes), and integrates phoneme/sound to grapheme/letter correspondence.
