Neurodegenerative Disorders of Frontal Lobe

Abstract

In this chapter, we review neurodegenerative diseases affecting the human frontal lobe or its associated striatal pathways. Almost all neurodegenerative diseases affect frontal function, but the group of frontotemporal dementias (FTD) has particularly serious and specific effects, thus providing interesting insights into the role of frontal circuits in human behavior. Traditionally, the study of neurodegenerative disorders affecting frontal lobes has relied on a conventional clinicopathological approach, defining particular clinical diagnoses and attempting to match this to a pattern of pathology in the brain. However, some limitations arise and new concepts such as neuronal network disintegration may arise trying to explain the overlap between the clinical presentation and the pathological phenotypes of frontal lobe neurodegenerative diseases. The last decade has endorsed a surge of new evidence proposing dysfunction within neural networks in relation to the clinical and pathological heterogeneity of neurodegenerative disorders.These networks relate to resting state and intrinsic connectivity functional MRI (fMRI), EEG and MEG studies that correlate with clinical presentations of abnormal behaviors in neurodegenerative diseases. Three major networks have been associated with aberrant behaviors in neurodegenerative diseasesdthe salience network (SN), the default mode network (DMN) and theexecutive-control network (ECN). This approach will be briefly discussed. Here, we introduce the main disorders involving frontal lobes or frontostriatal circuits? degeneration, such as the FTD spectrum, Alzheimer?s disease (AD), Parkinson?s disease (PD), Huntington?s disease (HD) and progressive lateral sclerosis (PLS). We focus our descriptions on structural and functional frontal and/or frontostriatal abnormalities observed in these disorders and their associations to clinical, behavioral and cognitive symptoms.