To
build a representation of the external world, and give it a coherent
sense, our brain needs to process and integrate information coming from
all our senses, including vision and hearing. But whether this
“multisensory processing” is innate and present from birth in the human
brain, or rather depends on experience remains an open debate.
Now, a novel study shows that the ability of the brain to represent
coherent information across senses primarily relies on an innate
functional architecture of specific regions in the brain cortex that
work independently from any sensory experience acquired after birth.
The study, published in the current issue of Nature Human Behaviour,
adds to the old ‘nature versus nurture’ debate, and brings further
weight to the evidence that brain architecture can develop independently
from sensory experience.
“We hypothesized that some areas of the cortex, known to process more
than just one sensory input, may possess a predetermined structure that
aids perception of sensory events by matching coherent inputs across
sensory modalities,” explains the research lead. “Since this idea can
hardly be tested at birth, we purposely determined the consistent
responses across adults deprived since birth of either sight or hearing:
any shared brain response across these individuals, whose post-natal
experiences inevitably differ, would be indicative of an innate
computation”.
To conduct the study, the researchers compared the brain activity in
three different groups of individuals: people with typical development,
congenitally blind and congenitally deaf people. The specific brain
response was assessed with Magnetic Resonance Imaging (fMRI) while the
subjects were watching or listening to the same edited version of the
Walt Disney’s movie “101 Dalmatians”. Specifically, blind individuals
listened to the auditory version of the movie, while deaf people watched
the visual version. The same experimental conditions were adopted with
typically developed sighted and hearing individuals. Brain responses
were then compared.
“By measuring brain synchronization between individuals who were
watching the movie and those who were listening to the narrative, we
identified the regions in the brain which coupled information across
sensory modalities,” explains the first author of the
paper. “We found that a specific patch of cortex, the superior temporal
cortex, endorses a representation of the external world that is shared
across modalities and is independent from any visual or acoustic
experience since birth, as the same representation is present in blind
and deaf participants as well”.
In their work, the researchers provided evidence that this area of the
brain cortex encodes various basic properties of stimuli, and couples
information from the two different senses, the visual and the acoustic
channel.
“In simple words, this is the area where the visual image of a ‘dog’ is
coupled with the acoustic signal of the dog barking, making clear to our
brain that the two stimuli coming through two different senses refer to
the same ‘object’ in the world”, says the author. “Overall, these data
show that basic visual and auditory features are responsible for the
neural synchronization between blind and deaf individuals”, adds the
lead author.
“This research extends results from previous studies by several labs
including ours that consistently indicate that most of the large-scale
morphological and functional architecture in the human brain can develop
and function independently from any sensory experience” comments a
coauthor of the study. “The wider implications are that we should
promote more inclusive educational strategies and social policies for
individuals with sensory disabilities, as their brains are the same”
concludes the lead author.
https://www.nature.com/articles/s41562-022-01507-3
http://sciencemission.com/site/index.php?page=news&type=view&id=publications%2Fa-modality-independent&filter=22