Mapping striate and extrastriate visual areas in human cerebral cortex.

Abstract

Functional magnetic resonance imaging (fMRI) was used to identify and map the representation of the visual field in seven areas of human cerebral cortex and to identify at least two additional visually responsive regions.The cortical locations of neurons responding to stimulation along the vertical or horizontal visual field meridia were charted on three-dimensional models of the cortex and on unfolded maps of the cortical surface. These maps were used to identify the borders among areas that would be topographically homologous to areas Vl, V2, V3, VP, and parts of V3A and V4 of the macaque monkey. Visually responsive areas homologous to the middle temporal/medial superior temporal area complex and unidentified parietal visual areas were also observed. The topography of the visual areas identified thus far is consistent with the organization in macaque monkeys. However, these and other findings suggest that human and simian cortical organization may begin to differ in extrastriate cortex at, or beyond, V3A and V4.In contrast to our extensive knowledge of cortical organization in nonhuman primates, far less is known about the identity and topography of functional subdivisions in human cerebral cortex. In the macaque monkey cortex, 30 or more distinct visual areas have been tentatively identified (1). In the human brain, a strong case has been made for only two or three areas (Vi, V2, and middle temporal) (2, 4-6), though several additional areas have been proposed (6-11). Brain images produced by functional magnetic resonance imaging (fMRI) show signals that are thought to represent local changes in blood oxygenation. These changes can be elicited by sensory-evoked neural activity though other factors such as alterations in blood volume and proton movement may also contribute [for review, see DeYoe et al. (12)]. We have used this technology to chart several functionally distinct visual areas in the human. Preliminary reports of this work have appeared (13,14). MATERIALS AND METHODSTo map angular positions within the visual field, four male and two female subjects (ages 24-40 years old) viewed a flickering black-and-white-checkered hemifield that rotated slowly about a central fixation point during a fMRI scan. To map visual field eccentricity (distance from the center of gaze), subjects viewed an expanding checkered annulus. In this manner, neurons responding to stimulation at different locations in the visual field were activated at different times during the stimulus sequence. Corresponding differences in the temporal phase of the fMRI response thus identified the retinotopic locationThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 2382represented by each active site in the brain (12). A similar technique has been described by Engel et al. (15).To enhance activation of extrastriate cortex (12) and to help maintain attention and arousal, the subj...

Methods for quantifying intra- and inter-subject variability of evoked potential data applied to the multifocal visual evoked potential

“…One hypothesis that could explain the relatively great intra-subject variability of the I′ min across the visual field (relative to the intrasubject variability of the I′ max ) might be that the I′ min contain significant extrastriate contributions, perhaps associated with relatively weak, very small and/or deep regions of cortical activation (DeYoe et al, 1996). An alternative hypothesis/ possible contributing factor that might explain the variations in the I′ min across the visual field for any given subject could be varying M and P contributions across the visual field (Dacey, 1993, Baseler et al, 1997.…”

“…Reasons for the variability and noisiness at the I′ min rotations could be due to any combination of a number of factors. It's possible that the source or sources at the C′(t,θ min ) rotation consist of substantial extrastriate contributions that are relatively weak, small, and/or deep (DeYoe et al, 1996). Another possible explanation that could contribute to inter-subject differences in the I′ min (as well as the less extensive differences in I′ max ) could be individual differences in feedback and/or attention (Seiple et al, 2002;Slotnick et al, 2002).…”

“…The variability in the cortical folding patterns of human primary visual areas has been observed using functional magnetic resonance imaging (fMRI) in conjunction with structural MRI and retinotopic mapping techniques (DeYoe et al, 1996;Engel et al, 1997). The variability in the folding patterns of cortex in human visual areas has also been noted in VEP studies (Maier et al, 1987;Foxe and Simpson, 2002;Zhang and Hood 2004b).…”

Spatial maps in frontal and prefrontal cortex

“…Previous imaging studies of retinotopic areas in occipital cortex -especially in areas beyond V1 and V2 -have also revealed variability in the precise location of areal boundaries and the degree to which maps are represented in their entirety (i.e. including upper, middle, and lower visual fields) (DeYoe et al, 1996;Hadjikhani et al, 1998;Huk et al, 2002). There are several reasons why maps in higherlevel areas are more difficult to accurately and reliably measure.…”

Spatial resolution of EEG cortical source imaging revealed by localization of retinotopic organization in human primary visual cortex

“…motor/sensory-related tasks (Darvas et al, 2004) and tonotopic organization of human auditory cortex (Talavage et al, 2004). In particular, the retinotopic activity in the human visual cortex (Sereno et al, 1995;DeYoe et al, 1996;Engel et al, 1997;Warnking et al, 2002;Grill-Spector and Malach 2004) has been well studied. The retinotopic maps constructed using fMRI have been frequently applied to visual ERP studies in order to identify functional or anatomical locations of the localized ERP sources Di Russo et al, 2005).…”