Fast and automatic activation of an abstract representation of money in the human ventral visual pathway

Abstract

Money, when used as an incentive, activates the same neural circuits as rewards associated with physiological needs. However, unlike physiological rewards, monetary stimuli are cultural artifacts: how are monetary stimuli identified in the first place? How and when does the brain identify a valid coin, i.e. a disc of metal that is, by social agreement, endowed with monetary properties? We took advantage of the changes in the Euro area in 2002 to compare neural responses to valid coins (Euros, Australian Dollars) with neural responses to invalid coins that have lost all monetary properties (French Francs, Finnish Marks). We show in magneto-encephalographic recordings, that the ventral visual pathway automatically distinguishes between valid and invalid coins, within only ∼150 ms. This automatic categorization operates as well on coins subjects were familiar with as on unfamiliar coins. No difference between neural responses to scrambled controls could be detected. These results could suggest the existence of a generic, all-purpose neural representation of money that is independent of experience. This finding is reminiscent of a central assumption in economics, money fungibility, or the fact that a unit of money is substitutable to another. From a neural point of view, our findings may indicate that the ventral visual pathway, a system previously thought to analyze visual features such as shape or color and to be influenced by daily experience, could also able to use conceptual attributes such as monetary validity to categorize familiar as well as unfamiliar visual objects. The symbolic abilities of the posterior fusiform region suggested here could constitute an efficient neural substrate to deal with culturally defined symbols, independently of experience, which probably fostered money's cultural emergence and success.

Figure 1. Paradigm.

A. Experimental design: each coin presented could be valid or invalid, familiar or unfamiliar for the French subjects who participated in the experiment. Note that French Francs and Finnish Marks were replaced by Euros in 2002 and are no longer in use. B. Stimuli: Unit of currency and 10 cent coins, for Euros, Australian Dollars, French Francs and Finnish Marks. C. Scrambled controls. D. 1-back task: subjects had to press a button whenever two identical stimuli were presented in a row.

Figure 2. Time-courses.

A. Superimposed evoked fields at the 151 channels (black) and root mean square across sensors (red), grand average across subjects and conditions. B. Statistical plots showing the F-value (color code) of the effect of monetary Validity (top), Object Type (middle) and their interaction (bottom), depending on time (x axis) and sensors (y axis). Both Validity, and the interaction Validity x Object Type, affect event-related fields between 150 and 175 ms (blue box).

Figure 3. Estimated neural sources of the mean 150–175 ms activity.

A. The 60% top-most responsive regions (yellow/red scale) are all located in the ventral visual pathway, in the posterior part of the right fusiform and lingual gyri. R: right, L: left. B. Mean 150–175 ms activity in the right posterior fusiform and lingual region, in response to scrambled controls (left) and coins (right), valid (red) or invalid (blue). Responses to controls are smaller than to coins, and responses to valid coins are smaller than responses to invalid coins. ***: p<0.001; **: p<0.01 C. Time-courses of neural responses in the posterior fusiform and lingual region. In this region the dissociation between coins (solid lines) and scrambled controls (dotted lines) is quickly followed by a dissociation between valid (red solid lines) and invalid (blue solid lines) coins, corresponding to the significant interaction between Object Type and Validity. Familiarity with the coins does not affect the responses (thin vs. thick lines). The yellow box indicates the 150–175 ms time range.