Echo, a female superhero in Marvel’s Daredevil and Avengers comic books, is one of the very few deaf characters of the genre. Because she is deaf, Echo pays attention to visual details and movements, allowing her to learn new abilities by watching others.
But what actually causes these ‘super senses’ to develop after profound hearing loss in non-superheroes?
“We know when you lose one sense, the remaining senses become heightened to help you navigate the world better,” explained Blake Butler, PhD, an adjunct research professor with Western’s Department of Psychology.
Many people believe, like Echo, this phenomenon occurs in the deaf by watching and learning new behaviours. However, Butler and Stephen Lomber, PhD, Professor with the Department of Physiology and Pharmacology, and Psychology, and Canada Research Chair in Brain Plasticity and Development, are looking at the anatomy underlying these sensory enhancements so they can understand better how the deaf brain transforms and reorganizes itself.
The team’s latest findings, published in the Journal of Neuroscience, reveal hearing loss dramatically changes how auditory regions of the brain send out information.
“What we found was the normal projection from the auditory cortex to the superior colliculus is all but gone in the deaf model, and is instead replaced by a more dispersed pattern,” said Butler. “It is a much different pattern of outputs than what we see in the case of normal hearing.”
This is the first study to look information the auditory cortex sends out, and also one of the first to identify a major anatomical difference between hearing and non-hearing models.
The research challenges conventional thinking that has said changes in the neural pathways into, and between, the sensory cortical brain regions account for enhancements in the deaf.
“It was previously thought inputs to the auditory cortex would be the location of this major structural reorganization,” explained Butler. “We were expecting to see much larger inputs from the visual cortex in these areas that become involved in visual processing, but we don’t see that at all. Those connections seem to be just maintained despite the onset of deafness.”
This study demonstrates sensory behaviour is changed by large-scale reorganization of outputs.
Using tract-tracing neuroanatomy, the researchers compared the ‘brain maps’ of normal hearing and deaf animal models and were able to uncover the differences between the two groups.
Butler and Lomber are part of Western’s Brain and Mind Institute, and were assisted in the research project by undergraduate thesis student Julia Sunstrum, now an MSc candidate with the Neuroscience program at the Schulich Medicine & Dentistry.
The research findings suggest the outputs from the auditory cortex play an important role in the deaf brain. “Now that we have this answer, there are recording and behavioural experiments to do as a follow-up,” said Lomber. “This is a big piece of the puzzle.”
The researchers’ long-term goal is to help design a device that restores hearing by re-engaging the brain.
“We need to know what deafness is doing, both structurally and functionally, to alter the way our brain is organized,” said Butler. “There is a lot we can do to manipulate how the brain works, but we need to know what has been done already in order to know what change to reverse.”