Summary: New research identifies a cellular mechanism that links early sound exposure to sensory processing and cognitive development in the immature brain.
Source: University of Maryland
Early sound experience and the developing brain
Many expectant parents play music—often classical—during pregnancy with the hope of enhancing their child’s future cognitive abilities. Although prior studies have hinted that prenatal sound exposure can influence later brain function, the specific brain structures responsible for that influence remained unidentified. A new study from University of Maryland neuroscientists provides the first direct evidence of a neural mechanism that could underlie this early link between auditory input and cortical development, a phenomenon sometimes referred to as the “Mozart effect.”
Subplate neurons: more than scaffolding
The research, published in the online early edition of the Proceedings of the National Academy of Sciences, shows that subplate neurons—an early-formed cell type in the cerebral cortex—can respond to sound and transmit sensory information during a critical window of development. Subplate neurons form early in the cortex and have been widely viewed as a temporary structural scaffold that guides the formation of permanent cortical circuits. After those circuits are established, most subplate neurons typically disappear. Because of that transient role, scientists previously assumed subplate cells did not actively convey sensory signals.
Using young ferrets as an animal model, the research team led by Patrick Kanold, professor of biology at the University of Maryland, recorded sound-evoked electrical activity directly from subplate neurons for the first time. The recordings revealed that these neurons respond to auditory stimuli at very early ages—indeed, before the animals’ ear canals open and before the classical thalamocortical pathway to layer 4 of cortex is fully established.
Rewriting the timeline of sensory processing
Conventional understanding held that sound-driven cortical activity begins only after thalamic inputs reach cortical layer 4 and peripheral sensory organs (ears and eyes) start transmitting signals. However, the new data show that subplate neurons receive thalamic-like input and exhibit sound-evoked spikes earlier than layer 4 neurons. The team observed that auditory responses first emerge in the subplate and later appear in the future thalamocortical input layer. Spike latencies were longer in layer 4 than in subplate, consistent with subplate neurons relaying early thalamic information to the developing cortex.
Electrode array recordings also revealed an emerging topographic organization of early auditory responses, suggesting that rudimentary cortical maps begin to form before the conventional thalamocortical pathways are fully active. In other words, early sensory experience can activate and potentially shape subplate circuits ahead of permanent cortical wiring.
Implications for diagnosis and care
By pinpointing a source of very early sensory activity in the cortex, this work opens new avenues for understanding how environmental stimuli influence neural development and for detecting atypical development. If subplate function is disrupted, the resulting changes in early sensory processing might contribute to developmental disorders such as autism spectrum disorder or other cognitive deficits. Identifying such disruptions earlier could improve the timing and effectiveness of interventions.
The findings have also drawn attention from researchers studying human sensory development. Rhodri Cusack, professor of cognitive neuroscience, noted that these results underscore how sensory systems are influenced by the environment from a very early stage, including the third trimester in humans. That observation highlights the importance of optimizing sensory environments for premature infants in neonatal intensive care units—populations that are especially vulnerable during early cortical development.
The study, titled “Subplate neurons are the first cortical neurons to respond to sensory stimuli,” was led by Patrick O. Kanold with co-authors Jessica M. Wess, Amal Isaiah, and Paul V. Watkins. The paper appeared in the Proceedings of the National Academy of Sciences in November 2017 (doi:10.1073/pnas.1710793114).
Funding for the work was provided by the National Institutes of Health (Award No. R01DC009607) and the Alfred P. Sloan Foundation. The authors note that the content of the report does not necessarily reflect the views of the funding organizations.
Key takeaways
- Subplate neurons in the developing cortex respond to sound earlier than previously recognized, before ear opening and before permanent thalamocortical circuits to layer 4 are fully established.
- These early responses show an emerging topographic organization, suggesting that sensory maps begin forming prior to mature cortical wiring.
- Understanding subplate function could improve early diagnosis and intervention strategies for developmental disorders and guide care practices for premature infants.
Contact: University of Maryland, press office
Abstract (condensed)
In developing mammals, thalamic fibers initially target subplate neurons rather than layer 4. Electrophysiological recordings in young ferrets demonstrate that auditory cortex neurons respond to sound at very young ages, even before ear opening. Single-unit recordings show that auditory responses emerge first in subplate neurons and later in layer 4, with longer latencies in layer 4 consistent with relay via subplate. Array recordings reveal an early nascent topographic organization. These results indicate that sound-evoked activity and cortical topography emerge earlier and in a different layer than previously thought, suggesting that early sensory experience can shape subplate circuits before permanent thalamocortical connections form.
University of Maryland (2017). Source of Early Brain Activity Identified. NeuroscienceNews.