Sharpening Understanding of How the Deaf Brain Sees

Q&A with Stephen Lomber

We often see it in superhero movies: When people are deprived of one sense, they develop superhuman powers in another sense. While those depictions may be exaggerated, the underlying premise has a real scientific basis. When the brain is deprived of input from one sense, such as hearing, it often compensates with above-normal performance in another sensory system, such as vision. Over the past decade, various neuroimaging, physiological, and other neuroscience studies have converged to create a more complete picture of the brains of the deaf, and, in particular, how visual abilities are enhanced.

In a new review paper published in the Journal of Cognitive Neuroscience, a team of scientists led by lead author Caroline Alencar and senior author Stephen Lomber at the University of Western Ontario sought to synthesize what researchers know from both human and animal studies on the deaf. “We wanted to identify common themes,” Lomber says.  “Ultimately, our paper highlights similarities in the human and animal studies of the deaf. It also draws attention to how plastic the cortex is following any form of sensory deprivation, in this case – deafness.”

CNS spoke with Lomber about this research review paper, past work on the topic, and future directions.

CNS: How did you become interested in this research area?

Lomber: I became interested in this research area when I considered how cochlear implants activate a naïve sensory system, or how does a dormant sensory pathway deal with activation?  However, to really consider this question, it is necessary to understand what “deaf” auditory cortex is doing in the absence of visual input.  Another way to think about it is to ask the question of “what is auditory cortex doing just prior to the activation of a cochlear implant?”

CNS: In brief, what have we known previously about visual function in the brains of deaf people?

Lomber: In 2006, Bavelier and colleagues published a wonderful review paper on all the human visual psychophysical studies performed to date.  It identified that visual enhancements in the deaf are not a general condition, but that specific visual functions are improved.

CNS: Can you give an example of a study you looked at in your review that was particularly novel in its design or approach?

Lomber: A paper in 2010 by my team really helped move the field forward.  It established the causal link between crossmodal plasticity in cortex and enhanced visual functions in the deaf.  It also buttressed the idea that the cortex is organized more by specific behaviors, or tasks, and not by sensory modality.  We found that regions of auditory cortex mediate particular behaviors regardless of the type of sensory input.

CNS: In your review, what were your most excited to find?

Lomber: How far the field has come in the past decade.  Significant progress has been made in studies of human subjects, particularly with functional imaging, and animal models using reversible deactivation methods.

CNS: What’s next for this line of work? 

Lomber: Functional investigations will continue to guide the field, both psychophysical and functional imaging.  Electrophysiological studies of changes at the neuronal level are going to be key to understanding the psychophysical changes following hearing loss.

CNS: Is there anything I didn’t ask you about that you’d like to add?

Lomber: There is a remarkable similarity between the findings identified in deaf subjects and those identified in blind subjects.  Both types of studies demonstrate that the cortex is organized more by particular behaviors, or tasks, and not by sensory modality.

-Lisa M.P. Munoz