DEFINING THE CONSTRUCTS OF COGNITION AND FUNCTIONAL PERFORMANCE
The scientific construct of cognition generally refers to a broad range of functions including perception; attention and concentration; learning; and various aspects of memory, reasoning, and problem solving; as well as crystalized knowledge and speed of processing (Harvey, 2012). Attempts to enhance or improve these different aspects or domains of cognition require very different intervention strategies, which in turn have different potential levels of benefit. For instance, certain pharmacological compounds have demonstrated benefits in transmitter systems with specific cognitive benefits (acetylcholine and episodic memory; Risacher et al., 2013). Other compounds, such as amphetamine, have wide-ranging cognitive benefits that are not specifically related to the primary pharmacological effects of the compound (see Sostek, Buchsbaum, & Rapoport, 1980 for a classic early study). Behavioral interventions can either be targeted toward a particular cognitive domain, multiple domains (e.g., Fisher, Holland, Merzenich, & Vinogradov, 2009), or global cognition (McGurk, Mueser, Feldman, Wolfe, & Pascaris, 2007), and the assessment strategy chosen must be commensurate with the goal of the intervention in terms of the domain or domains targeted by the treatment.
It is beyond the scope of this chapter to fully describe the ranges of functioning that can be considered cognitive in nature. However, we subscribe to the idea that cognition is a broad construct that can be conceptualized in terms of separable cognitive domains, which are then amenable to measurement with specialized assessments (Nuechterlein et al., 2004). Traditional domains of cognitive functioning (e.g., sensation, perception, sustained attention, selective attention, working memory, episodic memory, executive functioning, processing speed) are differentially affected in healthy aging and various neuropsychiatric conditions and have been the target of cognitive enhancement interventions.
More recent conceptualizations of cognitive performance are focused on networks, which can affect an array of cognitive abilities (Callicott et al., 1999). For instance, impairments in striatal regions, such as those induced by Huntington’s disease and related conditions, impact an array of cognitive functions. These include processing speed, concentration and attention, and learning and memory (Paulsen et al., 1995). The notion of separable versus highly related cognitive domains may influence strategies for selecting measures for interventions aimed at enhancing cognition. First of all, if measures of different cognitive domains are highly inter- correlated, it may be challenging to develop interventions that are selective in their measured cognitive benefits. Certain interventions can have specific effects on a limited set of cognitive domains (Fisher et al., 2009), but global functioning is also likely to improve. Second, research on the correlates of real-world functioning has consistently suggested that specific measures from individual cognitive domains are much less strongly related to real-world outcomes than composite measures that summarize global performance (Green, 1996; McClure et al., 2007). Thus, the typical distal goal of improving functional outcomes may be better facilitated by interventions that are effective across multiple cognitive domains (Bowie, McGurk, Mausbach, Patterson, & Harvey, 2012). As a result, treatments with broad cognitive benefits may be the best ways to improve everyday functioning.
In recent years, there has been an emphasis on performance of functional everyday skills, often referred to as “functional capacity.” This generally refers to skills involved in everyday living and important to independence and includes tasks such as managing finances and medications; preparing meals; scheduling; driving; and activities related to way-finding. Generally, the literature shows that standardized measures of cognition do not capture the complexity of these tasks and therefore are considered to have low “ecological validity” (see Chapter 14). As a result, prediction of the ability to perform complex everyday activities is improved when a combined strategy of cognitive and functional capacity assessment is employed.