Linking retinotopic fMRI mapping and anatomical probability maps of human occipital areas V1 and V2 A.M. Wohlschl7ger, a,b,c, T K. Specht, a,b,d C. Lie, a H. Mohlberg, a A. Wohlschl7ger, e K. Bente, a,b U. Pietrzyk, a,b,f T. Stfcker, a,b K. Zilles, a,b,g K. Amunts, a,b and G.R. Fink a,b,d a Institut fu ¨r Medizin, Forschungszentrum Ju ¨lich, 52425 Ju ¨lich, Germany b Brain Imaging Centre West (BICW), Forschungszentrum Ju ¨lich, Germany c Neurologie, Nuklearmedizin und Radiologie, Technische Universita ¨t Mu ¨nchen, Germany d Neurologische Klinik, Universita ¨tsklinikum der RWTH Aachen, Germany e Arbeitsbereich Psychologie, Max Planck Institut fu ¨r Kognitions- und Neurowissenschaften, Mu ¨nchen, Germany f Medizinische Physik, Universita ¨t Wuppertal, Germany g C. & O. Vogt-Hirnforschungsinstitut, Heinrich-Heine-Universita ¨t Du ¨sseldorf, Germany Received 29 June 2004; revised 14 January 2005; accepted 18 January 2005 Available online 3 March 2005 Using functional MRI, we characterized field sign maps of the occipital cortex and created three-dimensional maps of these areas. By averaging the individual maps into group maps, probability maps of functionally defined V1 or V2 were determined and compared to anatomical probability maps of Brodmann areas BA17 and BA18 derived from cytoarchitectonic analysis (Amunts, K., Malikovic, A., Mohlberg, H., Schormann, T., Zilles, K., 2000. Brodmann’s areas 17 and 18 brought into stereotaxic space—where and how variable? NeuroImage 11, 66–84). Comparison of areas BA17/V1 and BA18/V2 revealed good agreement of the anatomical and functional probability maps. Taking into account that our functional stimulation (due to constraints of the visual angle of stimulation achievable in the MR scanner) only identified parts of V1 and V2, for statistical evaluation of the spatial correlation of V1 and BA17, or V2 and BA18, respectively, the a priori measure k was calculated testing the hypothesis that a region can only be part of functionally defined V1 or V2 if it is also in anatomically defined BA17 or BA18, respectively. k = 1 means the hypothesis is fully true, k =0 means functionally and anatomically defined visual areas are inde- pendent. When applying this measure to the probability maps, k was equal to 0.84 for both V1/BA17 and V2/BA18. The data thus show a good correspondence of functionally and anatomically derived segre- gations of early visual processing areas and serve as a basis for employing anatomical probability maps of V1 and V2 in group analyses to characterize functional activations of early visual processing areas. D 2005 Elsevier Inc. All rights reserved. Keywords: Retinotopy; Cytoarchitecture; Striate cortex Introduction It has been known for long that the cytoarchitectonic organi- zation of the human visual cortex is associated with its functional organization. Brodmann areas (BA) 17 and 18 of the visual cortex can be identified by differences in cytoarchitecture. They belong to the most frequently and intensely studied cortical regions. There is large agreement that BA17 and 18 correspond to areas V1 and V2, respectively. The retinotopic character of the early visual areas has rendered it possible to determine functionally the borders of V1 and V2 and to create maps of their positions relative to the landmarks of occipital cortex by non-invasive fMRI measurements (DeYoe et al., 1996; Engel et al., 1994; Sereno et al., 1995; Tootell et al., 1998). Yet, to date, no direct comparison of the localization of anatomi cally and functionally derived maps has been performed to show that comparable results can be obtained with the different methods in the human brain. For many functional imaging studies which employ visual paradigms, knowledge of the functional organization of occipital cortex is important as it may facilitate the interpretation of the functional activations observed. It is an implicit assumption that functionally defined visual areas can be equated to their cytoarchitectonic correlates classified as Brodmann areas. There- fore, it is an important question whether in humans clear spatial links can be established between maps of cytoarchitecture and function. Functional MRI studies in animals, such as monkeys (Fize et al., 2003) and cats (Olman et al., 2003), show a good agreement of retinotopic maps with electrophysiological data of the same species. Likewise, a study by Schuett et al. (2002) demonstrated good agreement of retinotopic maps derived from optical imaging to anatomical maps as well as electrophysiological data (all acquired within the same animal). 1053-8119/$ - see front matter D 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2005.01.021 T Corresponding author. Institut fqr Medizin, Forschungszentrum Jqlich, 52425 Jqlich, Germany. Fax: +49 89 4140 4867. E-mail address: wohlschlaeger@lrz.tu-muenchen.de (A.M. Wohlschl7ger). Available online on ScienceDirect (www.sciencedirect.com). www.elsevier.com/locate/ynimg NeuroImage 26 (2005) 73 – 82