Neuroplasticity: Thalamus as a regulator
Article by: Emil Koch, on 24 October 2023, at 12:25 CEST
Every time we learn something, the brain changes. This requires an unprecedented adaptability that is not fully understood. For a long time, scientists believed the brain would lose its ability to adapt in adulthood. However, just as the adult brain continues with hippocampal neurogenesis, as confirmed by Penn Medicine researchers, the adult brain remains capable of adaptation. Yet, where this neuroplasticity is located and regulated remained poorly understood until recently. New evidence suggests a pivotal role of the thalamus in neuroplasticity regulation.
In a new study by the Netherlands Institute for Neuroscience, Yi Qin and colleagues investigated the visual system of mice. They wanted to understand how the visual cortex in mice responds to prolonged covering of one eye by exhibiting reduced responsiveness to the covered eye and enhanced responsiveness to the uncovered eye. Only their discovery of the vital role of the thalamus during critical periods of the development of vision gave them a clue. To test their hypothesis, they removed the GABA-alpha 1 subunit, a specific receptor for the inhibitory neurotransmitter GABA, during a critical developmental period of the visual cortex in mice and found that visual cortex adaptations were no longer present. Yet, these findings didn't allow conclusions for adult mice.
Therefore, the team replicated the experiment in the same way, knocking out the GABA-alpha 1 subunit, and uncovered that visual cortex plasticity also occurs in adult mice with the subunit but no switch without. Thus, they reasoned the thalamus plays a fundamental role in cortex plasticity. Would a reverse relationship hold, they wondered. Given the cortico-thalamic loops, the researchers then investigated the influence of the visual cortex on thalamus plasticity by reversing the experiment and shutting down the visual cortex. In adult animals, the shift in thalamus responses remained unchanged, but during the critical period in young animals, shutting down the visual cortex caused the shift to revert back to the thalamus.
Levelt and Qin highlighted the potential role of the thalamus not only in sensory processes but also in memory and other functions such as eye control. Specifically, they propose that the condition of lazy eye, where poor vision happens only on one side, might have origins in the thalamus. In support, a review by Munivenkatappa and Agrawal (2016) provides evidence for thalamic involvement in recovery after brain injury. Another study by Kurzawski et al. (2022) substantiated short-term plasticity in the adult human thalamus. Taken together, studying the thalamus may inform insights into neuroplasticity for future research and treatment strategies for various neurological conditions.
References:
Discovery of Molecular Signatures of Immature Neurons in The Human Brain Throughout Life Provide New Insights into Brain Plasticity and Other Functions, According to Penn Medicine Researchers. (2022, July 18). Penn Medicine News. https://www.pennmedicine.org/news/news-releases/2022/july/discovery-of-molecular-signatures-of-immature-neurons-in-the-human-brain. Accessed on 10/07/2023.
Kurzawski, J. W., Lunghi, C., Biagi, L., Tosetti, M., Morrone, M. C., & Binda, P. (2022). Short-term plasticity in the human visual thalamus. eLife, 11. https://doi.org/10.7554/elife.74565.
Munivenkatappa, A., & Agrawal, A. (2016). Role of thalamus in recovery of traumatic brain injury. Journal of Neurosciences in Rural Practice, 07(S 01), S076–S079. https://doi.org/10.4103/0976-3147.196468.
Thalamus regulates adaptability of the adult brain. (2023, October 23). ScienceDaily. https://www.sciencedaily.com/releases/2023/10/231006104518.htm. Accessed on 10/07/2023.