Researchers identify first responders to sound in the brain.

Some expectant parents play classical music for their unborn babies hoping to boost their children’s cognitive capacity, and while some research supports a relationship between prenatal sound exposure and improved brain function, scientists have not yet identified any structures responsible for this link in the developing brain.  Now, a study led by researchers at the University of Maryland identifies a type of cell in the brain’s primary processing area during early development has a role in transmitting this prenatal sensory information.  The team states the mechanism they have identified could explain an early link between sound input and cognitive function known as the ‘Mozart effect.’  The study is published in the journal Proceedings of the National Academy of Sciences.

Previous studies show the role of subplate neurons is thought to be temporary with most subplate neurons disappearing once the brain’s permanent neural circuits form. Researchers assumed subplate neurons had no role in transmitting sensory information, given their transient nature. Studies in mammals demonstrated the connection of the thalamus and the cortex also coincides with the opening of the ear canals, that allow sounds to activate the inner ear, a timing providing support for the traditional model for sound processing beginning in the brain.  However, the global medical community had struggled to reconcile this conventional model with observations of sound-induced brain activity much earlier in the developmental process. The current study directly measures the response of subplate neurons to sound and suggests very early in brain development, the sound becomes an important sense.

The current study observes sound-induced nerve impulses in subplate neurons in young ferrets via electrophysiological recordings.  Results using electrode array recordings show early auditory responses demonstrate topographic maps emerge before the onset of spiking responses in the cortical layer four. Data findings show sound-evoked activity and topographic organization of the cortex emerge earlier and in a different layer of the brain than previously thought.

The group explains this means the early sound experience can activate and potentially sculpt subplate circuits before permanent thalamocortical circuits linking to layer 4 are present, with the potential for disruption of this early sensory activity to be utilized for early diagnosis of developmental disorders.

The team surmises their study shows auditory cortex neurons respond to sound at very young ages and identifies the neurons that respond to sound first, helping to shape the brain during development.  For the future, the researchers state the next step is to begin studying how subplate neurons affect brain development in more detail.

Source: University of Maryland School of Medicine

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