Neuronal modulation in the prefrontal cortex in a transitive inference task: evidence of neuronal correlates of mental schema management

When informed that A > B and B > C, humans and other animals can easily conclude that A > C. This remarkable trait of advanced animals, which allows them to manipulate knowledge flexibly to infer logical relations, has only recently garnered interest in mainstream neuroscience. How the brain controls these logical processes remains an unanswered question that has been merely superficially addressed in neuroimaging and lesion studies, which are unable to identify the underlying neuronal computations. We observed that the activation pattern of neurons in the prefrontal cortex (PFC) during pair comparisons in a highly demanding transitive inference task fully supports the behavioral performance of the two monkeys that we tested. Our results indicate that the PFC contributes to the construction and use of a mental schema to represent premises. This evidence provides a novel framework for understanding the function of various areas of brain in logic processes and impairments to them in degenerative, traumatic, and psychiatric pathologies. SIGNIFICANCE STATEMENT: In cognitive neuroscience, it is unknown how information that leads to inferential deductions are encoded and manipulated at the neuronal level. We addressed this question by recording single-unit activity from the dorsolateral prefrontal cortex of monkeys that were performing a transitive inference (TI) task. The TI required one to choose the higher ranked of two items, based on previous, indirect experience. Our results demonstrated that single-neuron activity supports the construction of an abstract, mental schema of ordered items in solving the task and that this representation is independent of the reward value that is experienced for the single items. These findings identify the neural substrates of abstract mental representations that support inferential thinking

Action selection uncertainty in the test phase of a transitive inference task: Neuronal correlates in monkey premotor cortex.

Cognitively advanced animals are able to dynamically interact with the environment. In this process, action selection could be strongly influenced by the confidence value assigned to single items in the stream of incoming sensory information. A form of dynamic representation of the environment is the organization of learned items in hierarchically ordered series. In a 6-items transitive inference task, when the list A > B > C > D > E > F is finally created, the probability of choosing B in the pair BC is lower than for the pair BE suggesting that the confidence for the value of B is variable and related to the mental representation of all other elements presented/experienced together. This relationship between performance and symbol separation is also know as symbolic distance effect. Previous work has focused on the contribution of sensory information to confidence. We explored how confidence on target value could influence action selection by measuring neuronal activity in the premotor cortex of 2 trained monkeys. We selected neurons with activity modulated by the direction of movement and we analyzed how directionality is influenced by the symbolic distance of items to compare. Our results show that directionality in premotor cortex increases with symbolic distance and uncertainty providing support to the idea that the motor system contributes to perceptual confidence