Overview of Cognitive Function in ALS, with Special Attention to the Temporal Lobe: Semantic Fluency and Rating the Approachability of Faces

Abstract

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that affects upper and lower motor neurons and is more recently known to be associated with declines in cognitive and behavioral functions for a subset of patients (Strong, et al., 1996; Strong et al., 2009). The cognitive changes associated with ALS can vary from mild impairments that may or may not affect the individual’s daily functioning to more severe cognitive and behavioral changes that meet criteria for a diagnosis of frontotemporal dementia (ALS-FTD). There are at least mild cognitive changes in 40 to 60% of sporadic and familial ALS patients (Massman et al., 1996; Phukan et al., 1996; Ringholz et al., 2005; Wheaton et al., 2007). The cognitive and behavioral changes associated with ALS follow a pattern consistent with involvement of the frontal and temporal lobes (Strong et al., 2009, Hodges et al., 2004), presenting as difficulties with attention, working memory, verbal fluency, and semantic abilities (Abe et al., 1997; Ringholz et al., 2005; Rippon et al., 2006, Schmolck et al., 2007; Strong et al, 1999; Strong et al., 2009). Furthermore, 15% of ALS patients demonstrate more severe cognitive and behavioral changes consistent with ALS-FTD (Lomen-Hoeth et al., 2002; Ringholz et al., 2005; Wheaton et al., 2007), presenting as declines in judgment, problem solving, and reasoning, which are more frontally mediated cognitive functions. In addition to cognitive changes, up to 25% of patients with ALS may also experience significant changes in their behavior, mood, and personality characteristics (Hodges et al., 2004; Kertesz et al., 2005), including a loss of empathy, problems with organization and planning, changes in social behavior and personality, difficulties with impulse control, and apathy. The temporal lobes are purported to be involved in auditory perception, language comprehension, naming, processing of semantic knowledge and long-term memory storage, high-level visual processing of complex stimuli such as faces and scenes, and episodic memory (Lezak, 1995). In addition, they contain the amygdala and associated limbic areas, which are key structures for processing emotional stimuli and detecting threat from the environment, and are of particular interest for ALS patients. ALS patients show a lack of