Brain plasticity compensates for lost function after injury

Researchers from UCLA and Sydney’s Garvan Institute for Medical Research found that regions of the prefrontal cortex compensate for lost abilities after damage to the hippocampus – an area involved in learning and memory. It is a widely held view that centres of the brain are specialised for different functions. The present study shows that other areas can take on an new function if necessary – a phenomenon known as neural plasticity. This discovery could be of great importance to the development of new treatments for Alzheimer’s or stroke.

To investigate neural plasticity, the research group, led by Michael Fanselow, compared rats with hippocampal lesions to rats with intact brains on their respective learning abilities. Additionally, they monitored brain function prior to the damage, after damage, and after learning tasks. The rats with hippocampal lesions were still able to acquire new memories, although slower than their healthy counterparts. When comparing brain function before the lesion with brain function after learning in the lesioned animals, there were significant changes in regions known as the infralimbic cortex and the prelimbic cortex, both located in the prefrontal cortex. The infralimbic cortex became silenced after hippocampal lesion and the prelimbic cortex showed increased activity. 

In order to test whether both sites were necessary for the almost intact learning function, rats were lesioned in the infralimbic or prelimbic cortex in addition to the hippocampus. None of these rats maintained their learning abilities following damage. This suggests that both regions are needed to compensate for lost learning abilities in rats. In humans, these exact regions show changes following brain damage from Alzheimer’s or stroke. It seems neural plasticity compensates for lost function in humans as well. Depending on the extent of injury, the compensatory effects may not be sufficient. However, knowing the sites responsible for compensatory effects, new treatments may trigger plasticity by silencing or activating appropriate brain regions to make up for lost abilities in Alzheimer’s or stroke patients.  

Reference: Zelikowski, M. et al. (2013). Prefrontal microcircuit underlies contextual learning after hippocampal loss. Proceedings of the National Academy of Sciences, doi:10.1073/pnas.1301691110