On the neural mechanisms of reduced behavior in people with cognitive decline

How we generate our behavior does not often cross our minds. This seeming spontaneity is called into question when considering the inability of some patients with various disorders to produce voluntary behavior. The studies described in this thesis investigated brain mechanisms of impaired behavior generation, or apathy, in older individuals with memory deficits with two different measures of brain function. The first method probed biological markers of brain function in regions likely to be affected in these individuals. The results suggested that in the lateral part of the brain, namely the parietal lobe, lower levels of a marker of a neurotransmitter, important for learning and memory, were related to increased severity of apathy. The second method assessed the brain as a network, i.e. various regions functioning in a coordinated manner. We found that apathy was related to abnormalities in two specific networks that support the representations of goals and the execution of actions to fulfill the set goals. Together, these studies show two potentially complementary mechanisms that may underlie apathy in these individuals. Among the brain areas involved, current understanding of apathy does not ascribe a clear role for deficits in the lateral parietal region. We suggested that deficits in this region result in an inability to initiate intentional actions, leading to reduced behavior. In sum, this thesis integrates findings from neurobiology, brain function and cognitive science to understand the mechanisms underlying apathy.