Long-Term Visual Impairment in V1 of Mice after TBI

Article: Injuries to primary visual cortex cause long-term dysfunction of neural circuits
Source: Institute of Physical Chemistry, Polish Academy of Sciences (Poland)
Published: January 10, 2022

Chronic neuron loss (top),
reduced neuron firing (middle), and
disrupted visual responses (bottom)
in V1 of mice after TBI

Neuroplasticity is the remarkable ability of neural tissue to form new connections to reorganize, adapt, and self-repair. Yet, neuroplasticity, too, has its limits, as even mild head injuries can have lasting consequences for brain function at the cellular level. Traumatic brain injury (TBI) can lead to long-term visual impairment, such as loss of visual acuity or cortical blindness. In the present study, scientists examined the effects of TBI on long-term visual circuit function of adult mice to see how the neurons respond to visual stimuli two weeks and three months after mild controlled cortical impact injury to the primary visual cortex (V1). The findings show that although the primary visual cortex remained largely intact in the brain-injured mice, there was a 35% reduction in the number of neurons, with most of the affected neurons being inhibitory (rather than excitatory) neurons, and restricted to superficial layers. The researchers further report that less than half of the isolated neurons were sensitive to visual stimuli (32% at two weeks after injury and 49% at three months after injury), compared with 90% of V1 cells in the control group. Finally, there was as much as a threefold decrease in neuronal activity after the brain injury, and the cells themselves had worse spatial orientation (demonstrating impaired responses to visual stimuli and weaker size selectivity and orientation tuning). These findings reveal that even a single, mild contusion injury can produce long-lasting impairment to the way neurons encode information in the primary visual cortex.

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Frankowski JC, Foik AT, Tierno A, et al. "Traumatic brain injury to primary visual cortex produces long-lasting circuit dysfunction." Communications Biology.  4:1297. 17 November 2021. https://doi.org/10.1038/s42003-021-02808-5