Inhibitory Mechanisms and Impairment in Domain-Specific Reasoning: Studies of Healthy Elderly Adults and Patients with Alzheimer's Disease

Inhibitory Mechanisms and Impairment in Domain-Specific Reasoning: Studies of Healthy Elderly Adults and Patients with Alzheimer’s Disease Deborah Zaitchik (dzaitchiksamet@partners.org) Department of Psychiatry, Massachusetts General Hospital Charlestown, MA 02129 USA Gregg Solomon (gesolomo@nsf.gov) Division of Research on Learning National Science Foundation Arlington, VA 22230 USA Keywords: Alzheimer’s disease; inhibition; aging; domain- specificity; conceptual impairment; naive theories. Failure to inhibit? We hypothesize that the responses that the early behavioral theory would generate (e.g., attend to autonomous motion) are typically inhibited by the mature concepts of the later biological theory. This suggests that old concepts and outgrown theories are never ‘overwritten’ but continually ‘overridden’. If this is right, then inhibitory mechanisms play a crucial role in reasoning, learning, and conceptual change. We conclude by discussing whether the failure in most AD patients of their mature biological concepts to inhibit the earlier behavioral concepts arises because of the degradation of specific concepts in the domain or because of impairment to more general inhibitory mechanisms. Domain-specific impairment Recent studies suggest that reasoning in the conceptual domain of living things is especially vulnerable to impairment due to Alzheimer’s disease (AD). It is broadly claimed that AD patients have a progressive, bottom-up impairment in the hierarchical organization of semantic knowledge (e.g., they might have trouble identifying a zebra as a zebra rather than as a horse, but not as an animal rather than as a vegetable). Our finding of the re-emergence of the phenomena of animism and the failure to conserve species supports the claim that the domain is particularly vulnerable to impairment, but undermines the claim that the degradation of higher order concepts is based on degradation in lower-order concepts. We discuss the likely role that general inhibitory mechanisms play in development. There is growing understanding that a conceptual domain specifies not only a taxonomy, but also a rich set of causal concepts (Solomon et al., 1996; Zaitchik & Solomon, 2001). Our everyday concepts of living things are organized into a coherent intuitive theory. Development in this domain appears to involve the acquisition of two theories – an early behavioral theory that focuses on action and movement– and a later biological theory proper that focuses on bodily processes and the life cycle (e.g., birth, growth, death). Acknowledgments The authors acknowledge support from NIH (NIH/NIA AG020548 to DZ) and NSF (IR/D to GS). References Lombrozo, T. , Kelemen, D. , & Zaitchik, D. (2007). Inferring design: Evidence of a preference for teleological explanations from patients with Alzheimer’s disease. Psychological Science, 18, 999-1006. Solomon, G. E. A. , Johnson, S. C. , Zaitchik, D. , & Carey, S. (1996). Like father, like son: Children's understanding of how and why offspring resemble their parents. Child Development, 67, 151 - 171. Zaitchik, D. , Koff, E. Winner, E. , Brownell, H. , & Albert, M. (2006). The inference of emotions and beliefs in patients with Alzheimer’s disease. Neuropsychology; 20, Zaitchik, D. , & Solomon, G. E. A. (2001). Putting semantics back into the semantic representation of living things. Behavioral and Brain Sciences, 24, 496-497. Zaitchik, D. , & Solomon, G. E. A. (2006). Conservation of species, liquid, and belief: Evidence for category-specific conceptual impairment in patients with Alzheimer’s disease. Manuscript under review. Zaitchik, D. , & Solomon, G. E. A. (2008). Animist thinking in the elderly and in patients with Alzheimer’s disease. Cognitive Neuropsychology. 25, 27-37. Empirical evidence Using well-established methods from developmental psychology, we discovered the re-emergence of two striking phenomena characteristic of preschoolers’ early behavioral theory: 1) animism – the attribution of life to inanimate but active entities such as the sun and cars (Zaitchik & Solomon, in press); and 2) the failure to conserve species – the judgment that an animal can change its species simply by changing its appearance (Zaitchik & Solomon, 2006). Control tasks from the domains of naive physics and naive psychology showed spared performance relative to performance on tasks in the domain of naive biology (Lombrozo et al., 2007; Zaitchik et al., 2006).