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Ralf A. W. Galuske, Wolf Singer, Matthias M. H. J. Munk; Cortical states determine the polarity of orientation plasticity in primary visual cortex. Journal of Vision 2006;6(6):403. doi: 10.1167/6.6.403.
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In the present study we examine in how far orientation maps in the visual cortex are susceptible to use-dependent modifications under conditions of enhanced synchronization of neuronal responses. To induce modifications, we paired visual stimulation with oriented gratings to electrical activation of the mesencephalic reticular formation (MRF). This structure plays a central role in regulating wakefulness and gating attention and is known to enhance stimulus-induced synchronization of cortical responses. Our results indicate that cortical responses to stimuli which were paired with reticular activation were enhanced as seen by optical imaging of intrinsic signals and extracellular recordings of cortical units. Orientation domains representing the repetitively presented stimuli were enhanced and enlarged into the neighboring regions. Simultaneously recorded cortical units likewise expressed a shift in orientation preference towards the paired orientation if their pre-pairing preference differed 10°–30° from the orientation of the conditioned stimulus. This effect was strongly dependent on the degree of cortical activation as determined by the amount EEG-power induced by MRF stimulation in the gamma-frequency range (25–65Hz). If no or very weak cortical activation was induced, cortical responses habituated upon repetitive stimulus presentation. This study shows that the representation of stimulus orientation in cat adult visual cortex is susceptible to use-dependent modification if the cortex is in a sufficiently activated functional state. The recruitment of additional cell populations by changing their response selectivity and synchronization pattern provides important constituents of the neuronal mechanisms for the modification of representations in neocortex.
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