Neurobiology of abstract magnitude rules
Final Report Abstract
Recent years have witnessed important progress in elucidating magnitude processing in the brain of primates. The semantic aspect of different types of magnitudes is represented by neurons in a fronto-parietal cortical network, with the intra-parietal sulcus (IPS) and the PFC as the key nodes. Important as it is as a first step, the mere representation of magnitude, however, does not on its own constitute a cognitive advantage to an organism. Although quantities are extracted from sensory input at the cortical level (specifically in the fundus of the IPS, area VIP), such quantities need to be further processed by integrating different sources of external and internal information before they can successfully influence behaviour. In other words, number need to be processed according to abstract principles, or rules. In this project, we explored how single neurons in the association cortices of rhesus monkeys can flexibly represent quantitative rules applied to multiple magnitudes, such as numerical quantity and line length. Our single-neuron recordings in behaviourally-trained macaques showed that the primate brain uses rule-selective neurons specialized in guiding decisions related to a specific magnitude type only, as well as generalizing neurons that respond abstractly to the overarching concept "magnitude rules." By recording local field potentials and manipulating dopamine receptors in prefrontal cortex while monkeys performed a ruleswitching task, we could decipher dopamine’s impact on rule representations. Our findings suggest that dopamine alters neural oscillations relevant for rule processing through dissociable actions at the receptor level. Because rule information contests with working memory representations, we also tested the working memory representation of competing relevant information in PFC networks as an interesting extension of the originally proposed research plan. We detected complementary roles for primate frontal and parietal cortex in guarding working memory from distractor stimuli. These data suggest that distracting stimuli can be bypassed by storing and retrieving target information, emphasizing active maintenance processes during working memory with complementary functions for frontal and parietal cortex in controlling memory content during rule-based tasks. Finally, we showed that behaviourally-relevant null quantity is dynamically and distinctly represented in working memory. In summary, we managed to advance our understanding of the neurobiology of abstract rule representations and rule-related working memory representations. Rule-selective neurons are important building blocks that give rise to goal-directed behaviour. Because neural networks in a given brain area need to deal with different types of cognitive information throughout an ongoing task, one of the key questions for future research is how a multitude of changing and competing information can be represented by the same neurons across time and task demands.
Publications
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(2013) Representation of abstract quantitative rules applied to spatial and numerical magnitudes in primate prefrontal cortex. J Neurosci. 33(17):7526-34
Eiselt AK, Nieder A
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(2014) Complementary roles for primate frontal and parietal cortex in guarding working memory from distractor stimuli. Neuron. 83(1):226-37
Jacob SN, Nieder A
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(2017) Evolution of cognitive and neural solutions enabling numerosity judgements: lessons from primates and corvids. Philos Trans R Soc Lond B Biol Sci. 19; 373(1740)
Nieder A
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(2018) Dopamine Receptors Influence Internally Generated Oscillations during Rule Processing in Primate Prefrontal Cortex. J Cogn Neurosci. 30(5):770-784
Ott T, Westendorff S, Nieder A
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(2019) Working memory representation of empty sets in the primate parietal and prefrontal cortices. Cortex. 114:102-114
Ramirez-Cardenas A, Nieder A
