Optic Flow Stimuli in and Near the Visual Field Centre: A Group fMRI Study of Motion Sensitive Regions Sabine Ohlendorf 1,3,6 , Andreas Sprenger 2 , Oliver Speck 3,4 , Sven Haller 5 , Hubert Kimmig 2,7 * 1 Neurologische Klinik, Universita ¨tsklinikum, Freiburg, Germany, 2 Klinik fu ¨ r Neurologie, Universita ¨tsklinikum Schleswig Holstein, Campus Lu ¨ beck, Lu ¨ beck, Germany, 3 Abteilung Ro ¨ ntgendiagnostik, Medizin Physik, Universita ¨tsklinikum, Freiburg, Germany, 4 Abteilung Biomedizinische Magnetresonanz, Institut fu ¨ r Experimentelle Physik, Universita ¨ t Magdeburg, Magdeburg, Germany, 5 Abteilung fu ¨ r Neuroradiologie, Universita ¨tsspital, Basel, Switzerland, 6 Fakulta ¨t fu ¨ r Biologie, Universita ¨t Freiburg, Freiburg, Germany, 7 Schwarzwald-Baar-Klinikum, Academic Teaching Hospital Universita ¨t Freiburg, Villingen-Schwenningen, Germany Abstract Motion stimuli in one visual hemifield activate human primary visual areas of the contralateral side, but suppress activity of the corresponding ipsilateral regions. While hemifield motion is rare in everyday life, motion in both hemifields occurs regularly whenever we move. Consequently, during motion primary visual regions should simultaneously receive excitatory and inhibitory inputs. A comparison of primary and higher visual cortex activations induced by bilateral and unilateral motion stimuli is missing up to now. Many motion studies focused on the MT+ complex in the parieto-occipito-temporal cortex. In single human subjects MT+ has been subdivided in area MT, which was activated by motion stimuli in the contralateral visual field, and area MST, which responded to motion in both the contra- and ipsilateral field. In this study we investigated the cortical activation when excitatory and inhibitory inputs interfere with each other in primary visual regions and we present for the first time group results of the MT+ subregions, allowing for comparisons with the group results of other motion processing studies. Using functional magnetic resonance imaging (fMRI), we investigated whole brain activations in a large group of healthy humans by applying optic flow stimuli in and near the visual field centre and performed a second level analysis. Primary visual areas were activated exclusively by motion in the contralateral field but to our surprise not by central flow fields. Inhibitory inputs to primary visual regions appear to cancel simultaneously occurring excitatory inputs during central flow field stimulation. Within MT+ we identified two subregions. Putative area MST (pMST) was activated by ipsi- and contralateral stimulation and located in the anterior part of MT+. The second subregion was located in the more posterior part of MT+ (putative area MT, pMT). Citation: Ohlendorf S, Sprenger A, Speck O, Haller S, Kimmig H (2008) Optic Flow Stimuli in and Near the Visual Field Centre: A Group fMRI Study of Motion Sensitive Regions. PLoS ONE 3(12): e4043. doi:10.1371/journal.pone.0004043 Editor: Naoum Issa, University of Chicago, United States of America Received May 24, 2008; Accepted November 9, 2008; Published December 29, 2008 Copyright: ß 2008 Ohlendorf et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was performed as part of the binational PhD project of author SO (Universities of Freiburg, Germany and Basel, Switzerland) within the Eltem program of Neurex, the 13 Neuroscience network in the upper Rhine Valley. Author HK is currently supported by a grant from DFG (SFB654-A4). Competing Interests: The authors have declared that no competing interests exist. * E-mail: hubert.kimmig@neuro.uni-luebeck.de Introduction In human imaging studies, the most significant activations related to motion processing have been found in the lingual region (ventral V3), in V3A, in the lateral occipital region (LOS), in the MT+ complex and in the intraparietal sulcus (IPS) of the posterior parietal cortex [cf. 1]. All these regions get direct or indirect input from the primary visual area (V1) [2,3]. In some fMRI studies investigating cortical processing of optic flow, V1 was activated [4], in others it was not activated [1] but its role in motion processing has never been discussed in that context. Visual motion (compared to stationary visual stimulation) in one hemifield seems to activate primary visual cortex of the contralateral side, but to suppress activation of the corresponding ipsilateral regions [5,6]. In everyday life, flow field motion occurs regularly in both visual hemifields, whenever we move. Therefore, during motion primary visual regions should receive both excitatory and inhibitory inputs, and fMRI activations in primary visual regions would be expected to be the result of such competing inputs. A comparison of bilateral motion stimuli (in both hemifields) with unilateral motion stimuli (in one hemifield) is however missing up to now. A well-known motion processing region, MT+ has been identified in humans by positron emission tomography [7,8], histological methods [9,10] and fMRI studies [11–14]. Human MT+ is located on the ascending limb of the inferior temporal sulcus. Until to date few fMRI studies investigated the human MT+ subdivision in MT and MST, their locations, size and functional properties. Subarea MT has been shown to be located in a more posterior part and subarea MST in a more anterior part of the MT+ complex. Morrone et al. [15] identified a ventral subarea of the MT+ complex which was especially sensitive to direction changing optic flow. Dukelow et al. [16] and Huk et al. [17] identified subarea MST which was activated by ipsilateral and contralateral flow field stimulation. MT was exclusively activated by contralateral stimulation and defined as the non-MST part of MT+. Furthermore, MT but not MST seemed to respond to retinotopic stimulation [17]. A subarea of MST was presumed to transform optic flow into head centric flow [4]; also MT has been shown to get spatial input [18]. To explain the effect that MST was activated by contralateral as well as ipsilateral stimulation while MT responded exclusively to contralateral stimulation, it is usually referred to the different receptive field PLoS ONE | www.plosone.org 1 December 2008 | Volume 3 | Issue 12 | e4043