Functional Brain Imaging in Dementia: CCCD 2012

Introduction: Functional brain imaging involves the use of different imaging modalities that provide “on-line” information about the brain activity during the performance of task or at rest. There are several available imaging modalities such as quantitative electro-encephalogram (QEEG), which detects electrophysiological changes, Positron Emission Tomography (PET), which detects glucose and water metabolism and functional Magnetic Resonance Image (fMRI), which detects hemodynamic changes during activities and at rest. In this paper we will summarize the evidence for using fMRI in subjects with pre-clinical and clinical dementia. Functional MRI technique identifies brain activation/deactivation based on imaging of the endogenous blood-oxygen-level-dependent (BOLD) contrast signal. The BOLD signal is the product of the integrated synaptic activity of neurons via MRI signal changes due to hemodynamic changes, mainly change in oxyhemoglobin/deoxyhemoglobin ratio. There are mainly two types of studies using fMRI in pre-clinical and clinical dementia: 1Functional activation studies: Increased BOLD signal is usually interpreted as “activation” of the underlying brain areas during a task and negative BOLD response as “deactivation”, which is thought to represent decreases in neuronal activity below baseline levels of activity. Typically, fMRI experiments compare the MRI signal during one cognitive condition to a control condition like viewing familiar objects or to a passive baseline condition like visual fixation. (1-2-) 2Functional connectivity studies (fc-MRI). These techniques examine the correlation between the intrinsic oscillations or time courses of different brain regions (3-).