When subjects performed a working memory task, the functional connectivity between the frontal lobe and the hippocampus was disrupted in the AD patients and they recruited a different network that

included the amygdala, prefrontal regions, and anterior and posterior cingulated gyrus to perform the task. The activation in the frontal lobes of the healthy controls showed strong correlation with posterior cortical areas, while Inhibitors,research,lifescience,medical in the AD patients the frontal lobe activity was primarily correlated with other frontal regions. In a follow-up study with semantic and episodic memory task, it was shown that the different network in the AD patients represents a compensatory mechanism as the activity in the network was correlated with memory performance.42 Recent work also suggests that cognitive performance is not only a function of a single network, but that the interaction between networks plays a role in cognition.43 In an associative memory task performed by mild AD patients, MCI Inhibitors,research,lifescience,medical subjects, and healthy controls, it was shown that activation of the hippocampus and deactivation of medial and lateral parietal regions was reciprocal.35 The hippocampus was part of a network that included regions in the occipital-temporal lobes and frontal lobes while Inhibitors,research,lifescience,medical the deactivation in the parietal regions was part of the default network44 that includes the posterior cingulate and medial frontal lobe regions. The activation in the memory network and the

deactivation in the default network were linearly correlated, providing evidence that the activation dynamics in the two networks are directly connected. The level of deactivation of the default network during Inhibitors,research,lifescience,medical a cognitive task differed among healthy controls, MCI patients, and AD patients.45 Investigation of the default network measured during fixation (no task) has shown Inhibitors,research,lifescience,medical altered functional connectivity between the left and right hippocampus to the rest of the brain in AD patients compared with healthy controls.46 This

raises the possibility of utilizing the default network to quantify the functional impairment in the brain without using a cognitive task. In particular, Wang and colleagues found that the functional connectivity between the hippocampus and visual cortices was impaired, further supporting the results of impaired functional connectivity found during a visual matching task in MCI patients. In addition, the to functional connectivity between the hippocampus and posterior cingulate are strongly disrupted in AD patients.36 The network connectivity also can be investigated using diffusion tensor imaging (DTI), which provides a measure of the structural integrity of the white matter tracts connecting regions of the brain.47 Recent Talazoparib chemical structure application of DTI with AD patients has found decreases in the structural integrity of the white matter tracts in the corpus callosum, cingulum, and fornix, and frontal, temporal, and occipital lobe white matter areas.