title: Spike synchrony generated by modulatory common input through NMDA-type synapses.
abstract: Common excitatory input to neurons increases their firing rates and the strength of the spike correlation (synchrony) between them. Little is known, however, about the synchronizing effects of modulatory common input. Here, we show that modulatory common input with the slow synaptic kinetics of N-methyl-d-aspartate (NMDA) receptors enhances firing rates and also produces synchrony. Tight synchrony (correlations on the order of milliseconds) always increases with modulatory strength. Unexpectedly, the relationship between strength of modulation and strength of loose synchrony (tens of milliseconds) is not monotonic: The strongest loose synchrony is obtained for intermediate modulatory amplitudes. This finding explains recent neurophysiological results showing that in cortical areas V1 and V2, presumed modulatory top-down input due to contour grouping increases (loose and tight) synchrony but that additional modulatory input due to top-down attention does not change tight synchrony and actually decreases loose synchrony. These neurophysiological findings are understood from our model of integrate-and-fire neurons under the assumption that contour grouping as well as attention lead to additive modulatory common input through NMDA-type synapses. In contrast, circuits with common projections through model α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors did not exhibit the paradoxical decrease of synchrony with increased input. Our results suggest that NMDA receptors play a critical role in top-down response modulation in the visual cortex.
authors.affiliation: School of Science and Engineering, Tokyo Denki University, Saitama, Japan; and Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, Maryland nwagatsuma@rd.dendai.ac.jp.
authors.forename: Nobuhiko
authors.initials: N
authors.lastname: Wagatsuma
authors.affiliation: Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: von der Heydt
authors.affiliation: Zanvyl Krieger Mind/Brain Institute, Johns Hopkins University, Baltimore, Maryland.
authors.forename: Ernst
authors.initials: E
authors.lastname: Niebur
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001288:Attention / Q000502:physiology; D003344:Cortical Synchronization / Q000502:physiology*; D007700:Kinetics; D008251:Macaca; D008959:Models, Neurological; D016571:Neural Networks, Computer; D018091:Receptors, AMPA / Q000378:metabolism; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D013569:Synapses / Q000502:physiology*; D014793:Visual Cortex / Q000378:metabolism; D014796:Visual Perception / Q000502:physiology
chemical_list: D018091:Receptors, AMPA; D016194:Receptors, N-Methyl-D-Aspartate
keywords: N-methyl-d-aspartate-type synapse; border ownership; modulatory input; selective attention; synchrony