Bottom-Up Dependent Gating of Frontal Signals in Early Visual Cortex
Leeland B. Ekstrom,1,2,3
Pieter R. Roelfsema,4,5
John T. Arsenault,1,6
Giorgio Bonmassar,1
Wim Vanduffel1,6,7*
The frontal eye field (FEF) is one of several cortical regions thought to modulate sensory inputs. Moreover, several hypotheses suggest that the FEF can only modulate early visual areas in the presence of a visual stimulus. To test for bottom-up gating of frontal signals, we microstimulated subregions in the FEF of two monkeys and measured the effects throughout the brain with functional magnetic resonance imaging. The activity of higher-order visual areas was strongly modulated by FEF stimulation, independent of visual stimulation. In contrast, FEF stimulation induced a topographically specific pattern of enhancement and suppression in early visual areas, but only in the presence of a visual stimulus. Modulation strength depended on stimulus contrast and on the presence of distractors. We conclude that bottom-up activation is needed to enable top-down modulation of early visual cortex and that stimulus saliency determines the strength of this modulation.
1 Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, MA 02129, USA.
2 Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
3 Department of Nuclear Science and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
4 Department of Vision and Cognition, Netherlands Institute for Neuroscience, an institute of the Royal Netherlands Academy of Arts and Sciences, Meibergdreef 47, 1105 BA, Amsterdam, Netherlands.
5 Department of Experimental Neurophysiology, Center for Neurogenomics and Cognitive Research, Vrije Universiteit, de Boelelaan 1085, 1081 HV, Amsterdam, Netherlands.
6 Laboratorium voor Neuroen Psychofysiologie, K. U. Leuven Medical School, Campus Gasthuisberg, 3000 Leuven, Belgium.
7 Department of Radiology, Harvard Medical School, Charlestown, MA 02129, USA.
* To whom correspondence should be addressed. E-mail: wim{at}nmr.mgh.harvard.edu
