Comparison of functional and cytoarchitectonic maps of human visual areas V1, V2, V3d, V3v, and V4(v)
Introduction
Retinotopic mapping has become the current gold standard for the in vivo delineation of early visual cortical areas in the human brain using non-invasive functional imaging. The principle behind this approach is to delineate the borders of retinotopically organised areas by finding the visual field meridian representations on cortical surface representations of individual brains (Sereno et al., 1995, DeYoe et al., 1996, Engel et al., 1997). The collection of retinotopic functional imaging data together with high-resolution structural data needed for cortical surface reconstruction is, however, time consuming and may thus limit the applicability of this approach, e.g., when examining patients who do not tolerate being scanned for a long time. Moreover excentric visual field localisations are technically difficult to access by retinotopic mapping due to limitations in the visual angle covered by standard stimulation devices. In practice, this approach is hence often restricted to the delineation of cortical regions representing the more central visual field. Finally, it is hardly feasible to obtain functional localisers for all areas involved in complex cortical networks, even in the visual cortex where higher areas become more and more tuned to particular stimulus features.
Anatomical a priori information on the location and extent of cortical areas in the visual system may help to overcome such limitations by providing a complementary frame of reference. Such anatomical maps based on the probabilistic, observer-independent mapping of cortical areas (Schleicher et al., 2005) have already been applied as references for the localisation of functional activations in fMRI and MEG studies of visual processing (Larsson et al., 2002, Barnikol et al., 2006, Dammers et al., 2007, Wohlschläger et al., 2005). Given that the location and extent of visual areas can also be delineated in vivo by retinotopic mapping as described above, the question obviously arises, how closely the maps derived from in vivo functional imaging and post-mortem anatomical analysis correspond to each other.
This question is addressed here directly by correlating architectonic and functional delineations of the early visual areas V1, V2, V3d, V3v, and V4(v). Retinotopic visual areas were delineated on surface reconstructions of the cortical grey–white matter boundary, which has emerged as the method of choice as it allows a definition of the meridian representation in spite of the convoluted cortical surface. Using this approach, the anatomical correlates of areas V1 (BA17) and V2 (BA18) (Amunts et al., 2000), which have already been compared to functional data (Wohlschläger et al., 2005) using a volume-based delineation, were re-analysed. We then quantitatively compared functionally defined dorsal V3 (V3d), ventral V3 (V3v), as well as a quarter-field representation lateral to V3v, V4(v), with their cytoarchitectonically defined putative anatomical correlate areas hOc3d (human occipital area 3, dorsal; Kujovic et al., 2007), hOc3v (human occipital area 3, ventral; Rottschy et al., 2007), and hOc4v (human occipital area 4, ventral; Rottschy et al., 2007).
Section snippets
Subjects and experimental paradigm
Twenty-four healthy subjects aged 21–38 years (mean age 26.4 ± 4.5 years, 10 female) participated in the study. All subjects were healthy without any history of neurological or psychiatric diseases, and had normal visual acuity. Informed written consent was obtained from all subjects. The study was approved by the ethics committee of the University Hospital Aachen, Germany.
Stimuli were presented via fMRI compatible goggles (subjects S1–S10: Silent Vision™, Avotec, FL; S11–S24: VisuaStim™,
Results
Using retinotopic mapping of polar angle and subsequent delineation of visual areas based on the representation of the vertical meridians, the following areas were defined separately for the left and right hemispheres of all 24 subjects: The dorsal and ventral parts of visual areas V1, V2, and V3, as well as a quarter-field visual field representation lateral of ventral V3, i.e., area V4(v). Similar to previous descriptions of anatomical data, also the functional probability maps for these
Discussion
The cortical parcellation defined by quantitative cytoarchitectonic analysis and summarised by the maximum probability map is not only supported by other histological modalities such as receptor autoradiography (for a review see Zilles and Amunts, 2009) but also by in vivo approaches. Most of the work comparing histological borders and functional data has been performed by comparing the location of significant fMRI activations to cytoarchitectonic areas. Using such an approach, it has been
Conclusion
Our data's most important implication for fMRI studies will pertain to situations where retinotopic maps have not been acquired for the individual subject, but detailed information about the activated visual areas is nevertheless useful. While retinotopic mapping is now routinely possible, this situation may nevertheless arise in experiments where scanning time is very limited (for example in the investigation of patients) or where the main focus rested on other functional systems. In such
Acknowledgments
We are grateful to our colleagues from the MR group of the Institute for Neurosciences and Medicine for their assistance in acquiring the fMRI data. G.R.F. was supported by the Deutsche Forschungsgemeinschaft. S.B.E. was supported by the Human Brain Project (R01-MH074457-01A1) and the Helmholtz Initiative on Systems-Biology “The Human Brain Model.” This work was part of a Human Brain Project/Neuroinformatics Research Grant funded by the National Institute of Biomedical Imaging and
References (52)
- et al.
Brodmann's areas 17 and 18 brought into stereotaxic space—where and how variable?
NeuroImage
(2000) - et al.
Analysis of neural mechanisms underlying verbal fluency in cytoarchitectonically defined stereotaxic space—the roles of Brodmann areas 44 and 45
Neuroimage
(2004) - et al.
Pattern reversal visual evoked responses of V1/V2 and V5/MT as revealed by MEG combined with probabilistic cytoarchitectonic maps
NeuroImage
(2006) - et al.
A new toolbox for combining magnetoencephalographic source analysis and cytoarchitectonic probabilistic data for anatomical classification of dynamic brain activity
NeuroImage
(2007) - et al.
A new SPM toolbox for combining probabilistic cytoarchitectonic maps and functional imaging data
NeuroImage
(2005) - et al.
Testing anatomically specified hypotheses in functional imaging using cytoarchitectonic maps
NeuroImage
(2006) - et al.
Anatomical mapping of functional activation in stereotactic coordinate space
Neuroimage
(1992) - et al.
Locating the functional and anatomical boundaries of human primary visual cortex
Neuroimage
(2009) Topographic maps are fundamental to sensory processing
Brain Res. Bull.
(1997)- et al.
Connectivity-based parcellation of human cortex using diffusion MRI: establishing reproducibility, validity and observer independence in BA 44/45 and SMA/pre-SMA
Neuroimage
(2007)