6 Abstraction of Mental Representations :

ion of Mental Representations: Theoretical Considerations and N eu roscientific Evidence Kalina Christoff and Kamyar Keramatian The ability to conceive of highly abstract concepts is a fundamental feature of human cognition. Using abstract mental representations, we can organize perceptions garnered from disparate experiences, develop novel solutions to problems we encounter, and predict future outcomes based on past experiences. All of these faculties have been shown to rely on the integrity of the lateral prefrontal cortex (e.g., Milner, 1964;Luria, 1966; Shallice, 1982; Duncan et al., 1995). Understanding abstract hought and the nature ofabstract mental representations, therefore, may provide a useful framework for understanding the functions and organization of lateral prefrontal cortex. In this chapter, we focus on the evidence and implications for an organization of prefrontal cortex according to different levels of abstraction in representational content. In the first section, we offer a historical review of some ofthe central concepts found in philosophical theories ofabstraction and discuss how they motivate contemporary investigation in the field of cognitive neuroscience. In the second section, we describe two recent functional neuroimaging experiments that examine the role of abstract representations in terms of lateral prefrontal cortex organization. The results of these experiments suggest a topographical organization oflateral prefrontal regions according to the level of abstraction in representational content (Fig. 6-1). This topography appears to follow an arcuatel posterior-to-anterior direction, with concrete working memory representations corresponding to posterior prefrontal regions and representations at increasing levels of abstraction corresponding to progressively anterior regions. HISTORICAL DEVELOPMENT IN THEORIES OF ABSTRACTION Discussions of abstraction are ubiquitous in cognitive neuroscience literature, with terms such as "abstract cognitive abilities," "abstract thought," and