Abstract
Neurons in the dorsolateral prefrontal (dlPFC) and posterior parietal cortex (PPC) are activated by different cognitive tasks and respond differently to the same stimuli depending on task. The conjunctive representations of multiple tasks in nonlinear fashion in single neuron activity, is known as nonlinear mixed selectivity (NMS). Here we compared nonlinear mixed selectivity in a working memory task in areas 8a and 46 of the dlPFC and 7a and lateral intraparietal cortex (LIP) of the PPC in macaque monkeys. NMS neurons were more frequent in dlPFC than in PPC and this was attributed to more cells gaining selectivity in the course of a trial. Additionally, in our task, the subjects’ behavioral performance improved within a behavioral session as they learned the session-specific statistics of the task. The magnitude of NMS in the dlPFC also increased as a function of time within a single session. On the other hand, we observed minimal rotation of population responses and no appreciable differences in NMS between correct and error trials in either area. Our results provide direct evidence demonstrating a specialization in NMS between dlPFC and PPC and reveal mechanisms of neural selectivity in areas recruited in working memory tasks.
SIGNIFICANCE STATEMENT
How the activity of neurons mediates performance of multiple cognitive tasks and where this is implemented in the brain remain unclear. One popular theory suggests that nonlinear mixed selectivity, altered tuning for the same stimuli depending on task or rule, allows neurons to represent multiple tasks contexts. We wished to test whether nonlinear mixed selectivity differed systematically between two areas that have been implicated in cognitive tasks, the dorsolateral prefrontal and posterior parietal cortex. Our results reveal only limited nonlinear selectivity in the two areas, though more prominent in the dorsolateral prefrontal cortex. Our results constrain theories of the neural basis of cognitive function.
Footnotes
The authors declare no competing financial interests.
Research reported in this paper was supported by the National Eye Institute and National Institute of Mental Health of the National Institutes of Health under award number R01 EY017077, R01 EY016773 and R01 MH116675.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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