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Rossi-Pool R, Salinas E, Zainos A, Alvarez M, Vergara J, Parga N, Romo R (2016) Emergence of an abstract categorical code enabling the discrimination of temporally structured tactile stimuli. Proceedings of the National Academy of Sciences USA, 113(49):E7966-7975    
What are the neural codes that allow the discrimination of two vibrotactile stimulus patterns of equal mean frequency? We recorded single-neuron activity in primary somatosensory (S1) and dorsal premotor (DPC) cortex while trained monkeys performed a challenging pattern discrimination task. We found a faithful representation of the stimuli in S1 and a heavily transformed, more abstract, and highly varied set of responses in DPC. Most notably, in addition to memory-related activity and responses encoding the monkeys’ choices, the DPC data included a large set of categorical neurons that code specific combinations of past and present stimuli and, at the same time, are strongly predictive of the monkeys’ behavior
The problem of neural coding in perceptual decision making revolves around two fundamental questions: (i) How are the neural representations of sensory stimuli related to perception, and (ii) what attributes of these neural responses are relevant for downstream networks, and how do they influence decision making? We studied these two questions by recording neurons in primary somatosensory (S1) and dorsal premotor (DPC) cortex while trained monkeys reported whether the temporal pattern structure of two sequential vibrotactile stimuli (of equal mean frequency) was the same or different. We found that S1 neurons coded the temporal patterns in a literal way and only during the stimulation periods and did not reflect the monkeys’ decisions. In contrast, DPC neurons coded the stimulus patterns as broader categories and signaled them during the working memory, comparison, and decision periods. These results show that the initial sensory representation is transformed into an intermediate, more abstract categorical code that combines past and present information to ultimately generate a perceptually informed choice