Some expectant parents play
classical music for their unborn babies, hoping to boost their children’s
cognitive capacity. While some research supports a link between prenatal sound
exposure and improved brain function, scientists had not identified any structures
responsible for this link in the developing brain. A new study by University of
Maryland School of Medicine (UMSOM) scientists, along with colleagues from the
University of Maryland College Park, is the first to identify a mechanism that
could explain an early link between sound input and cognitive function, often
called the 'Mozart effect'. Working with an animal model, the researchers found
that a type of cell in the brain’s primary processing area during early
development, long thought to have no role in transmitting sensory information,
may conduct such signals after all. Working with young ferrets, researchers observed
sound-induced nerve impulses in subplate neurons, which help guide the
formation of neural circuits in the same way that a scaffolding helps a
construction crew erect a new building. This is the first time such impulses
have been seen in these neurons. During development, subplate neurons are among
the first neurons to form in the cerebral cortex–the outer part of the
mammalian brain that controls perception, memory and, in humans, higher
functions such as language and abstract reasoning.
The role of subplate neurons is
thought to be temporary. Once the brain’s permanent neural circuits form, most
subplate neurons disappear. Researchers assumed that subplate neurons had no
role in transmitting sensory information, given their transient nature. Scientists
had thought that mammalian brains transmit their first sensory signals in
response to sound after the thalamus, a large relay center, fully connects to
the cerebral cortex. Studies from some mammals demonstrate that the connection
of the thalamus and the cortex also coincides with the opening of the ear
canals, which allows sounds to activate the inner ear. This timing provided
support for the traditional model of when sound processing begins in the brain.
However, researchers had struggled to reconcile this conventional model with
observations of sound-induced brain activity much earlier in the developmental
process. Until they directly measured the response of subplate neurons to
sound, the phenomenon had largely been overlooked. By identifying a source of
early sensory nerve signals, the current study could lead to new ways to
diagnose autism and other cognitive deficits that emerge early in development.
Early diagnosis is an important first step toward early intervention and
treatment. The next step is to begin studying in more detail how subplate
neurons affect brain development.
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