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Edward Ester, John Serences, Edward Awh; Global mechanisms of sensory recruitment during working memory maintenance. Journal of Vision 2009;9(8):597. doi: 10.1167/9.8.597.
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© ARVO (1962-2015); The Authors (2016-present)
According to the sensory recruitment hypothesis, information is stored in working memory via sustained activity in the same sensory regions that encode memoranda. In a recent study, we reported that patterns of delay activity in primary visual cortex (V1) reliably indexed specific feature values (color, orientation) of remembered objects (Serences, Ester, Vogel, & Awh, in press, Psychological Science). Here, we asked whether stimulus-specific delay activity would also be observed in cortical regions that were not activated by bottom-up stimulation, as has been observed during sustained attention to motion stimuli (Serences & Boynton, 2007, Neuron). Observers were shown an oriented grating in either the right or left visual field, followed by a post-cue that instructed them to remember or forget this orientation across a 16s delay period. Our analysis was restricted to voxels that showed the strongest contralateral (relative to ipsilateral) responses during a separate set of functional localizer scans. Consistent with prior reports, the pattern of activation in both contralateral and ipsilateral regions of V1 enabled accurate classification of the to-be-remembered orientation during the encoding phase of each trial. Moreover, we found that a similar activation pattern was maintained throughout the delay period in both contralateral and ipsilateral regions of V1. Importantly, these delay period effects were absent in trials with the “no-memory” postcue, showing that positive results during “remember” trials were not a passive effect of encoding the sample stimulus. Thus, the sensory regions that are recruited during rehearsal in visual WM extend beyond the regions that respond in a bottom-up fashion to the memoranda. This type of spatially-global gain modulation may serve to enhance mnemonic acuity by increasing the number of neurons dedicated to representing the memoranda.
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