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Cereb Cortex. 2018 Jul 1;28(7):2405-2421. doi: 10.1093/cercor/bhx142.

A Quadrantic Bias in Prefrontal Representation of Visual-Mnemonic Space.

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Department of Physiology, McGill University, Montreal, Quebec, Canada.
Department of Physiology and Pharmacology, University of Western Ontario, Ontario, Canada.
Department of Neuro- & Pathophysiology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany.
Division of Neurosurgery, Ottawa Hospital Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
Robarts Research Institute, University of Western Ontario, Ontario, Canada.
Brain and Mind Institute, University of Western Ontario, Ontario, Canada.
Department of Psychiatry, University of Western Ontario, Ontario, Canada.


Single neurons in primate dorsolateral prefrontal cortex (dLPFC) are known to encode working memory (WM) representations of visual space. Psychophysical studies have shown that the horizontal and vertical meridians of the visual field can bias spatial information maintained in WM. However, most studies and models have tacitly assumed that dLPFC neurons represent mnemonic space homogenously. The anatomical organization of these representations has also eluded clear parametric description. We investigated these issues by recording from neuronal ensembles in macaque dLPFC with microelectrode arrays while subjects performed an oculomotor delayed-response task. We found that spatial WM representations in macaque dLPFC are biased by the vertical and horizontal meridians of the visual field, dividing mnemonic space into quadrants. This bias is reflected in single neuron firing rates, neuronal ensemble representations, the spike count correlation structure, and eye movement patterns. We also found that dLPFC representations of mnemonic space cluster anatomically in a nonretinotopic manner that partially reflects the organization of visual space. These results provide an explanation for known WM biases, and reveal novel principles of WM representation in prefrontal neuronal ensembles and across the cortical surface, as well as the need to reconceptualize models of WM to accommodate the observed representational biases.

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