Researchers identify first brain cells that respond to sound.

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 have not identified any structures responsible for this link in the developing brain.  Now, a study led by researchers at the University of Maryland School of Medicine identifies 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.  The team state that 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 that 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. Studies in mammals demonstrated 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, 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 that very early in brain development, 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 that early auditory responses demonstrate that topographic maps emerge before the onset of spiking responses in layer 4. Data findings show that sound-evoked activity and topographic organization of the cortex emerge earlier and in a different layer than previously thought.

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

The team surmise their study shows that auditory cortex neurons respond to sound at very young ages, even before the opening of the ears, earlier that previously thought; and identify the neurons which respond to sound first, helping to shape the brain during development.  For the future, the researchers state the next step is to begin studying in more detail how subplate neurons affect brain development.

Source: University of Maryland School of Medicine


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