What Can Developmental and Comparative Cognitive Neuroscience Tell Us About the Adult Human Brain? Michael L Platt and Elizabeth S Spelke
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Available online at www.sciencedirect.com What can developmental and comparative cognitive neuroscience tell us about the adult human brain? Michael L Platt and Elizabeth S Spelke Current Opinion in Neurobiology 2009, 19:1–5 0959-4388/$ – see front matter Published by Elsevier Ltd. DOI 10.1016/j.conb.2009.06.002 Michael L Platt Introduction Center for Cognitive Neuroscience, Duke An oft-repeated dictum in biology holds that ontogeny recapitulates phy- University, United States logeny. Despite failures of Haeckl’s principle to predict in strict form the e-mail: [email protected] morphological, behavioral, or cognitive stages an organism passes through Michael Platt is an associate during development, the underlying sentiment continues to inform con- temporary approaches to mind and brain. For example, studies of behavior professor of Neurobiology and and cognition in developing humans provide an anchor for understanding Evolutionary Anthropology at Duke both intellectual primitives and the nature of representation in animal University, and Director of the minds. Conversely, comparative studies of cognition in animals serve to Center for Cognitive Neuroscience. address seemingly intractable questions concerning the roles of innate His research focuses on the capacities, culture, and language in the development of mature human neuroethology and neuroeconomics cognition. And both comparative and developmental studies shed light on of human and nonhuman primate the neural mechanisms that subserve the most complex and distinctive behavior and cognition. Michael cognitive abilities of adult humans, such as the capacity for abstract thought. received his BA from Yale and his PhD from the University of Both developmental and comparative approaches to cognition provide Pennsylvania, both in biological uniquely powerful data that can inform the search for homologies in brain anthropology, and was a post- and mind. Homologous features of cognition are defined as those psycho- doctoral fellow in neuroscience at logical and neurobiological traits that evolved in the common ancestor of New York University. related phyletic groups that emerge from shared developmental pathways and serve closely related behavioral functions. Nothing in this definition Elizabeth S Spelke requires that such traits emerge early in development: the developmental Department of Psychology, Harvard pathways that produce homologous patterns of sexual or parental behavior, University, United States for example, may be long. Nevertheless, a central discovery of develop- e-mail: [email protected] mental and comparative research on cognitive neuroscience, over the past decades, is that the cognitive traits that humans share with other animals Elizabeth Spelke is The Marshall L. tend to emerge early in human development. This conclusion stems from Berkman Professor of Psychology research probing the behavioral and neurobiological signatures of specific at Harvard University. Her cognitive abilities in human children and nonhuman animals. laboratory focuses on the sources of uniquely human cognitive Consider, for example, the sense of number. Even in adults, sensitivity to capacities, including the capacity numerosity – a fuzzy sense of number – follows psychophysical principles for formal mathematics, the that characterize the number sense in preverbal infants and animals. Most capacity for constructing and using importantly, the number sense follows Weber’s Law in that sensitivity symbolic representations such as improves with numerical distance and declines with numerical magnitude, maps, the capacity for developing as if the underlying representation of numerosity (at least for collections of comprehensive taxonomies of objects or events greater than 2 or 3) were encoded on a ratio scale (i.e. objects, and the capacity for logarithmically). Moreover, nonhuman animals, human infants, and human reasoning about other humans and adults represent number abstractly, detecting the common cardinal values of their social groups. visuo-spatial arrays of objects and temporal sequences of sounds or actions [1–3,18]. And finally, numerical representations enter into arithmetic oper- ations of ordering, addition, and subtraction for animals, infants, and adults [4–6,19,20]. www.sciencedirect.com Current Opinion in Neurobiology 2009, 19:1–5 2 Signalling mechanisms These three behavioral signatures of number sense are that will be necessary to adjudicate current hypotheses joined by evidence of common brain mechanisms for regarding cognitive homologies and differences in these representing number in nonhuman animals, human chil- domains. dren, and adults. Brain imaging studies show activation of parietal cortex in both adult humans and children when The evidence they make numerical discriminations [17,21], and Our reviews begin with a paper by Passingham who neurons in the fundus of the intraparietal sulcus in evaluates the evidence for and against the macaque macaque monkeys show approximately logarithmic tun- monkey as a model for human brain function. The author ing functions for numerosity [7]. In both types of exper- notes that although macaques are often used in neuro- iments, responses to number are independent of sensory biological studies to understand the way the human brain modality and stimulus format, providing evidence for works, there are important differences in both cognition abstract numerical representations [8]. And these and brain structure between the two species. Although quantity representations are transformed by the oper- these differences might appear to limit the strong com- ations of numerical comparison and arithmetic. parisons that can be drawn, Passingham argues that a parallel approach using brain imaging in humans and The above studies also begin to shed light on the neural single neuron recordings in monkeys performing similar, mechanisms by which abstract concepts of number are if not identical, tasks provides an important means for formed and used. Studies of humans and monkeys impli- assessing functional homology in brain and cognition. cate the intraparietal sulcus as an important locus of numerical processing. Yet this cannot be the whole story, Our focus next turns to the cognitive and neural mech- since a wide array of animals, including birds, fish, and anisms underlying spatial cognition in adult humans, insects, without a cerebral cortex – let alone a parietal lobe children, and animals. Landau and Lakusta review evi- – can discriminate number and do so in a way that obeys dence that reorienting behavior in humans and animals Weber’s Law (e.g. [9–11]). Number is such a fundamental relies on geometric representations of spatial layout, and, aspect of the world that its core representation may moreover, that this information is encapsulated in a way depend on mechanisms that evolved early in the history consistent with a cognitive module (cf. [12]). The authors of animal life: mechanisms whose operation was amplified show that although infants as young as 18 months use by the higher brain systems that emerged later in evol- geometry to reorient, this capacity changes dramatically ution. Further studies of the underlying neurobiological over development by incorporating non-geometric infor- mechanisms of numerical representation will be instru- mation. The authors argue that the uniquely human mental in reconstructing this evolutionary history and faculty of language provides a tool that strengthens the enriching understanding of how the human brain integration of geometric and non-geometric information, represents number abstractly. thus enabling the uniquely human construction of maps of the environment. Complementing this review, Vallor- The goal of this issue is to evaluate critically the case for tigara reviews recent work on controlled rearing studies in cognitive homology in five domains considered funda- animals to study the role of experience in the use of mental to adult human cognition. Specifically, we have geometric information for navigation. He finds that, at invited reviews of the literature on cognitive develop- least in domestic chicks, experience with specific geo- ment, comparative cognition, and where these studies metries contributes little to the ability to learn and are sufficiently advanced, neural mechanism, by leading remember geometric information in other environments. experts in their respective fields. We focus on the prin- He concludes that basic features of natural geometry are ciples governing spatial cognition, tool use and physical largely innate, but in agreement with Landau and cognition, social cognition, economic decision making, Lakusta allows that language and other types of non- and numerical thinking as a precursor for symbolic geometric experience influence the development of representation. On balance, these reviews favor the hy- uniquely human forms of spatial knowledge. pothesis that both animals and preverbal children are endowed with biological primitives of adult human cog- These reviews exemplify how understanding of spatial nition in all these domains. Yet, uncertainties remain cognition has advanced through synergistic comparative regarding the specific mechanisms that mediate these and developmental studies. Studies of reorientation in processes. Further, some of these reviews begin to shed human adults and children were based directly on pioneer- light on unique features of cognition in humans and in ing studies of reorientation in rodents [13,14]. The system other species that have confronted