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The Journal of Neuroscience, November 4, 2009, 29(44):13962-13970; doi:10.1523/JNEUROSCI.1402-09.2009

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Behavioral/Systems/Cognitive
Stimulus-Induced and State-Dependent Sustained Gamma Activity Is Tightly Coupled to the Hemodynamic Response in Humans

Stefan P. Koch,¹ Peter Werner,¹ Jens Steinbrink,¹ Pascal Fries,² and Hellmuth Obrig^1,3

¹Berlin NeuroImaging Center, Charité–Universitätsmedizin Berlin, 10117 Berlin, Germany, ²Donders Institute for Brain, Cognition, and Behaviour, Radboud University Nijmegen, 6500 HB Nijmegen, The Netherlands, and ³Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, and Day Clinic of Cognitive Neurology, University of Leipzig, 04103 Leipzig, Germany

Correspondence should be addressed to Stefan P. Koch, Berlin NeuroImaging Center/Department of Neurology, Charité Campus Mitte, Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany. Email: stefan.koch{at}charite.de

A prompt behavioral response to a stimulus depends both on the salience of the stimulus as well as the subject's preparedness. Thus, both stimulus properties and cognitive factors, such as attention, may determine the strength of neuronal synchronization in the gamma range. For a comprehensive investigation of stimulus–response processing through noninvasive imaging, it is, however, a crucial issue whether both kinds of gamma modulation elicit a hemodynamic response. Here, we show that, in the human visual cortex, stimulus strength and internal state modulate sustained gamma activity and hemodynamic response in close correspondence. When participants reported velocity changes of gratings varying in contrast, gamma activity (35–70 Hz) increased systematically with contrast. For stimuli of constant contrast, the amplitude of gamma activity before the behaviorally relevant velocity change was inversely correlated to the behavioral response latency. This indicates that gamma activity also reflects an overall attentive state. For both sources of variance, gamma activity was tightly coupled to the hemodynamic response measured through optical topography. Because of the close relationship between high-frequency neuronal activity and the hemodynamic signal, we conclude that both stimulus-induced and state-dependent gamma activity trigger a metabolic demand and are amenable to vascular-based imaging.

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Received March 24, 2009; revised Aug. 20, 2009; accepted Aug. 24, 2009.

Correspondence should be addressed to Stefan P. Koch, Berlin NeuroImaging Center/Department of Neurology, Charité Campus Mitte, Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany. Email: stefan.koch{at}charite.de

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