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Mitchell Riley, Xue-Lian Qi, Hua Tang, David Blake, Christos Constantinidis; Plasticity of prefrontal cortical responses during learning in a working memory task. Journal of Vision 2016;16(12):704. doi: https://doi.org/10.1167/16.12.704.
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© ARVO (1962-2015); The Authors (2016-present)
Training to improve working memory is associated with increased BOLD signal from the lateral prefrontal cortex and confers lasting cognitive benefits in humans. The neural substrate underlying these changes is poorly understood. In a previous series of experiments we identified increases in prefrontal activity after training monkeys in working memory tasks. However, these experiments provided only snapshots of changes at the start and end of training. To assess how brain changes are effected by different aspects of training, we recorded neuronal activity with a chronic 64-electrode array in the prefrontal cortex of 2 monkeys, as they learned to perform a visuo-spatial working memory task. We re-sampled the same cortical locations every day, which provided an unbiased cross-section of population activity. Training involved three stages. First, the monkey was presented with two stimuli in rapid succession and had to indicate if they appeared at the same or different location by selecting one of two saccade targets signifying match or non-match. Second, the monkey had to generalize the task to new stimuli, appearing at any location. Third, an increasing delay period was imposed, placing more demand on working memory. Visual stimuli were also presented passively in a fixation task. A total of 736 multi-unit activity (MUA) records were selective for the location of the stimuli (ANOVA, p< 0.05). MUAs obtained at each subsequent stage of training were characterized by increased firing rate during the stimulus presentation and the delay period. Interestingly, increased rate was also observed during the fixation task. The findings demonstrate that working memory training induces plastic formation of new visually responsive cell assemblies. Increases in the proportion of activated neurons and discharge rate may have been underestimated by single-electrode recordings. The results also demonstrate that activity changes induced by training transfer between stimuli and task conditions.
Meeting abstract presented at VSS 2016
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