Conceptual mappings and neural reuse

TOO MUCH NEURAL REUSE, EVEN FOR A METAPHORICAL BRAIN Conceptual mappings are correspondances between conceptual domains (SPACE, TIME, FORCE, EMOTION, etc.) or between entities within the same conceptual domain. Through mapping, we project inferences, elements, and relations from one mental configuration to another. Sets of mappings can become entrenched, creating powerful cognitive habits. For example, across many cultures around the world, temporal relations are conceived by means of spatial relations, in language (“Saturday is almost here”), artifacts (timelines, calendars, sundials), or gesture (Núñez and Sweetser, 2006). Some of the mappings for this template are: duration is spatial extent, events are landmarks, or time is motion along a path. From over 30 years of conceptual mappings research emerges a picture of the conceptual system as a set of mapping habits. Instead of a static repository of concepts, we have a dynamic network connecting mental structures. Mapping is not exceptional: it is the norm. It is through mapping that concepts are formed, learned, and developed creatively. These ideas have boosted the interest in the most remarkable manifestations of mapping in language and thought: metaphor, metonymy, analogy, counterfactuals, etc. Metaphor has received far more attention than all the other phenomena combined. Researchers in Conceptual Metaphor Theory (CMT) (Lakoff and Johnson, 1980; Lakoff, 1993), have identified many sets of cross-domain mappings underlying conventional metaphorical expressions: TIME IS SPACE, LIFE IS A JOURNEY, ANGER IS HEAT, EVENTS ARE ACTIONS, etc. According to CMT, conceptual metaphors are static, ontological, fixed sets of partial correspondances between two conceptual domains. Metaphor transfers inferences from the source domain, more concrete or better structured, to the target domain, which is more abstract or less delineated. A system of thousands of metaphorical mappings constitutes the main mechanism for abstract thought in the human mind. From the nineties, the semantic postulates of CMT have been used to develop the Neural Theory of Language (NTL) (Gallese and Lakoff, 2005; Feldman, 2008; Lakoff, 2008). In NTL, conceptual metaphors are replaced by neural mappings, combinations of simple neural circuits that carry out conceptual mappings. The major function of all this neural binding is the reuse of sensorimotor brain mechanisms for new roles in language and reasoning. This is congenial with the grounding of abstract concepts in perceptual experience (Barsalou, 1999, 2008), called embodiment in conceptual mappings research (Johnson, 1987, 2008; Lakoff, 1987; Lakoff and Johnson, 1999). The overarching idea of CMT-NTL is a “metaphorical mind-brain,” based on direct, binary transfer across domains. The transfer is carried out through static cognitive habits, which are implemented by neural circuitry connecting pairs of brain areas. For the brain, metaphor is once more privileged over all other manifestations of mapping, just like it was for the mind. A good example of the rapidly growing interest in the neuroscience of metaphor is the Frontiers issue about the topic, currently being edited by Vicky T. Lai and Seana Coulson. But the metaphorical brain seems quite insufficient to account for the pervasiveness and complexity of neural reuse. In a recent BBS target article, Michael Anderson (2010) shows that what is going on in the brain dwarfs the predictions of embodiment or CMT-NTL. Statistics run on thousands of fMRI studies indicate that even fairly small brain regions are typically reused in multiple tasks, with even higher reuse probabilities if a region is involved in perception or action (Anderson et al., 2010). Neural reuse is ubiquitous and dynamic, and many of its results cannot be explained as domain-structuring inheritance. Anderson examines, among others, the following examples: the SNARC effect (a mental number line with magnitudes increasing from left to right), the correlation between finger representation and numerical cognition, the interaction of word and gesture, or the phonological loop in working memory. These cases present no metaphorical projection, and some of them involve more than two components. Rather than direct transfer of information, a given system seems to be reused for a non-primary purpose because it happens to have a function or structure that are appropriate for the particular cognitive task at hand. As Anderson claims, we need a broader theoretical framework, able to account for those individual phenomena as well as for the general prevalence of neural reuse.