Epub ahead of print: Hulst et al. Functional adaptive changes within the hippocampal memory system of patients with multiple sclerosis. Hum Brain Mapp. 2011 Sep 6. doi: 10.1002/hbm.21359.
Background: Memory deficits are common in MS’ers. The part of the brain responsible for important aspects of memory is called the the hippocampus.
Methods: In this study a functional magnetic resonance imaging (fMRI) task was used to investigate changes in hippocampal function in MS’ers with and without cognitive decline.
“fMRI is a method that is used to assess the function of specific areas of the brain; it works by calculating how much oxygen the brain uses. The more active an area the more oxygen it extracts from the blood passing through it. By comparing fMRI images before and after a brain task we can work out what area or areas of the brain are involved in that specific task.”
In this study 50 MS’ers (34 cognitively preserved and 16 cognitively impaired) and 30 healthy controls completed an memory task (encoding and retrieval) that was used to specifically activate the hippocampus.
“Encoding refers to laying down or storing of a new memory and retrieval the process of recalling or remembering the information that forms that memory.”
Results: This study showed that both cognitively preserved and cognitively impaired MS’ers had changes in brain activation with these tasks.
The following summary is for the neuroscientists amongst you:
During encoding of correctly remembered items, increased brain activation was seen in the parahippocampal areas bilaterally and in the left anterior cingulate gyrus in the cognitively preserved patients compared to the controls (unclustered, Z ≥ 3.1, P ≤ 0.001). No brain areas showed less activation.
In cognitively impaired MS’ers the right (para)hippocampal areas and the prefrontal cortex showed less brain activation compared to controls (cluster-corrected, P < 0.05). The posterior cingulate gyrus and the left precuneus showed increased activation in cognitively impaired patients when compared to controls (unclustered Z ≥ 3.1, P ≤ 0.001).
Conclusion: These results suggest the presence of functional adaptation in the memory network before cognitive decline becomes evident in MS, as displayed by the increased brain activation in the hippocampal-cingulate memory system in cognitively preserved MS’ers. Interestingly, cognitively impaired MS’ers showed less activation in the hippocampal network during correct encoding. These findings are important for future cognitive therapeutic studies, since cognitive intervention might be most effective before cognitive impairment is present and when adaptive changes of the brain are most prominent.
“What this study shows is that MS’ers adapt to the damage caused by MS and these adaptations allow MS’ers to cope cognitively. However, in MS’ers with cognitive impairment these mechanisms fail and this is associated with less brain activation in important areas compared to normal control subjects.”
“Another example of why we need to treat MS early and aggressively to prevent cognitive impairment or at least maintain the pathways that are responsible for the adaptations.”
Additional reading: fMRI