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Field of Research
Numbers are an integral part of our everyday life: we use them to quantify, rank and identify virtually everything that is imaginable. The use of verbal symbols as a ‘mental tool’ enables humans to develop a unified concept of number, a concept that encompasses cardinal (numerical quantity), ordinal (numerical rank) and nominal (numerical label) aspects alike. While true counting and mathematics are cultural achievements that are bound up with language, it has become evident over the last decades that numerical competence does not emerge de novo in linguistic humans, but is built up from a biological precursor system.
Research in our lab is directed at understanding how abstract information, such as numbers and quantities, is represented and processed in the primate brain. To that end, we focus on parietal and frontal association cortices that operate at the apex of the cortical hierarchy. Our overall goal is to understand how higher brain centers enable intelligent, goal-directed behaviours, thus paving the way for a better understanding during its dysfunction in diseases.
Studies with behaviorally trained non-human primates that were carried out in the group characterized single neurons coding numerical quantity irrespective of specific sensory stimulus attributes, and identifed a parieto-frontal network of such neurons. This work complemented the emerging picture of the foundations of numerical competence in humans based on functional imaging and lesion studies, showing that the response properties of neurons can explain basic psychophysical findings. Neurons in the parietal and frontal lobe extract different forms of abstract quantity, ranging from number to spatial size and proportions. Moreover, prefrontal cortex (PFC) cells in the macaque encode semantic associations between set size and arbitrary visual signs.
Important as it is as a first step, the mere representation of magnitude does not however constitute a cognitive advantage to an organism in and of itself. Although quantities are extracted from sensory input at the cortical level, such quantities need to be further processed by integrating different sources of external and internal information before they can successfully influence behaviour.
Thus we have recently started to study single-neuron mechanisms of cognitive control functions and decisions based on numerical rules. These data showed that single PFC neurons have the capacity to represent flexible operations on the most abstract numerical quantities. Our findings support PFC network models implementing specific ‘rule-coding’ units that control the flow of information between segregated input, memory and output layers.
We speculate that these neuronal circuits in the monkey PFC could have been readily adopted in the course of primate evolution for the syntactic processing of numbers in formalized mathematical systems. We will now investigate how cognitive control via rules applied to multiple magnitudes and multiple magnitude rules applied to numerical quantity can emerge.