A case study of functional MRI in dementia: Methods to assess functions of the frontal cortex and the medial temporal lobe

Functional magnetic resonance imaging (fMRI) was used to study brain activation during a memory task associated with the medial temporal lobe (MIL) (i.e. visual encoding) and a task associated with the frontal lobe (i.e. working memory) in a patient with dementia who was referred for a second opinion on Alzheimer's disease (AD). Frontal lobe and MIL activation were compared within this patient. MTL activation in the patient was also compared with a group of healthy elderly subjects and a group of mild to moderate patients with AD who also performed the visual encoding task. The patient showed a quite normal brain activation pattern during visual encoding, including activation in the right parahippocampal gyrus. With working memory, there was a small activated area in the precuneus, but no frontal lobe activation. This pattern deviated strongly from that of normal subjects. Voxelwise comparison of wholebrain activation during visual encoding showed that no regions were activated more widely in the healthy elderly group than in the patient. However, the mild to moderate AD group showed significantly decreased brain activation during memory encoding. Our data provide a functional-anatomical basis for the respective dysfunction (working memory) and functioning (encoding) of different memory systems, suggesting that in this case the frontal cortex does not function properly, while the medial temporal lobe does. These findings support the clinical diagnosis of non-Alzheimer type dementia and suggest a frontal lobe-type dementia, which was confirmed by follow up. We conclude that it is possible to measure brain activation during multiple tasks in single patients with fMRI. Comparing the activation patterns within the patient, and between the patient and populations of demented patients and controls, may improve our understanding of brain function in dementia.