title: Correlated variability modifies working memory fidelity in primate prefrontal neuronal ensembles.
abstract: Neurons in the primate lateral prefrontal cortex (LPFC) encode working memory (WM) representations via sustained firing, a phenomenon hypothesized to arise from recurrent dynamics within ensembles of interconnected neurons. Here, we tested this hypothesis by using microelectrode arrays to examine spike count correlations (rsc) in LPFC neuronal ensembles during a spatial WM task. We found a pattern of pairwiserscduring WM maintenance indicative of stronger coupling between similarly tuned neurons and increased inhibition between dissimilarly tuned neurons. We then used a linear decoder to quantify the effects of the high-dimensionalrscstructure on information coding in the neuronal ensembles. We found that therscstructure could facilitate or impair coding, depending on the size of the ensemble and tuning properties of its constituent neurons. A simple optimization procedure demonstrated that near-maximum decoding performance could be achieved using a relatively small number of neurons. These WM-optimized subensembles were more signal correlation (rsignal)-diverse and anatomically dispersed than predicted by the statistics of the full recorded population of neurons, and they often contained neurons that were poorly WM-selective, yet enhanced coding fidelity by shaping the ensemble'srscstructure. We observed a pattern ofrscbetween LPFC neurons indicative of recurrent dynamics as a mechanism for WM-related activity and that therscstructure can increase the fidelity of WM representations. Thus, WM coding in LPFC neuronal ensembles arises from a complex synergy between single neuron coding properties and multidimensional, ensemble-level phenomena.
authors.affiliation: Department of Physiology, McGill University, Montreal, QC, H3G 1Y6, Canada; julio.martinez@robarts.ca matthew.leavitt@mail.mcgill.ca.|Department of Physiology and Pharmacology, University of Western Ontario, London, ON, N6A 5B7, Canada.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Leavitt
authors.affiliation: Department of Neurophysiology and Pathophysiology, University Medical Center Hamburg-Eppendorf, 20246 Hamburg, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Pieper
authors.affiliation: Division of Neurosurgery, Ottawa Hospital Research Institute, University of Ottawa, Ottawa, ON, K19 4E9, Canada.
authors.forename: Adam J
authors.initials: AJ
authors.lastname: Sachs
authors.affiliation: Department of Physiology, McGill University, Montreal, QC, H3G 1Y6, Canada; julio.martinez@robarts.ca matthew.leavitt@mail.mcgill.ca.|Department of Physiology and Pharmacology, University of Western Ontario, London, ON, N6A 5B7, Canada.|Robarts Research Institute, University of Western Ontario, London, ON, N6A 5B7, Canada.|Department of Psychiatry, University of Western Ontario, London, ON, N6A 5B7, Canada.|Brain and Mind Institute, University of Western Ontario, London, ON, N6A 5B7, Canada.
authors.forename: Julio C
authors.initials: JC
authors.lastname: Martinez-Trujillo
mesh_terms: D000200:Action Potentials; D000818:Animals; D008251:Macaca / Q000502:physiology*; D008297:Male; D008570:Memory, Short-Term; D009474:Neurons / Q000502:physiology*; D017397:Prefrontal Cortex / Q000166:cytology / Q000502:physiology*
keywords: decoding; macaque; noise correlations; prefrontal cortex; working memory