Plasticity of cerebral activation after training of episodic memory in cognitively impaired and healthy subjects

Aims: In patients with mild cognitive impairment (MCI) mnestic deficits occur long before the onset of dementia. While cognitive training programs have shown to improve performance the neural mechanisms remain less certain. In order to investigate cognitive training-related cerebral changes in MCI and controls a functional magnetic resonance imaging (fMRI) paradigm of episodic memory before and after cognitive training was applied.

Methods: 11 MCI patients and 11 controls underwent before and after one week of cognitive training fMRI scanning during an incidental episodic verbal memory task. Image preprocessing and statistical analysis was done using statistical parametric mapping (SPM8) routines.

Results: The MCI patients remembered significantly less stimuli than the controls as indicated by target errors. After training the number of target errors decreased significantly in both groups. Specific training-related changes of cerebral activation were found during the episodic retrieval task. In the controls, before training an activation of significant clusters (p<0.05, corrected, family-wise error) in the bilateral frontal, and right parietal and cerebellar cortices occurred, but decreased after training in the frontal cortices and the cerebellum. In contrast, in the MCI patients before training an activation of significant clusters comprised bilateral frontal and cerebellar cortices, and extended to anterior frontal and limbic cortices after the training.

Conclusions: In conclusion, the results of the study demonstrate after training an economisation of cerebral activity during an episodic verbal memory task in cognitively unimpaired older subjects whereas in MCI a compensation of pre-training activation deficits can be assumed.