Electrophysiological and neuroimaging studies have shown that attention to visual motion can increase the responsiveness of the motion-selective cortical area V5 and the posterior parietal cortex (PP). Increased or decreased activation in a cortical area is often attributed to attentional modulation of the cortical projections to that area. This leads to the notion that attention is associated with changes in connectivity. We have addressed attentional modulation of effective connectivity using functional magnetic resonance imaging (fMRI). Three subjects were scanned under identical stimulus conditions (visual motion) while varying only the attentional component of the task. Haemodynamic responses defined an occipito-parieto-frontal network, including the, primary visual cortex (V1), V5 and PP. A structural equation model of the interactions among these dorsal visual pathway areas revealed increased connectivity between V5 and PP related to attention. On the basis of our analysis and the neuroanatomical pattern of projections from the prefrontal cortex to PP, we attributed the source of modulatory influences, on the posterior visual pathway, to the prefrontal cortex (PFC). To test this hypothesis we included the PFC in our model as a ‘modulator ’ of the pathway between V5 and PP, using interaction terms in the structural equation model. This analysis revealed a significant modulatory effect of prefrontal regions on V5 afferents to posterior parietal cortex.

Highly accurate surface models of the cerebral cortex are becoming increasingly important as tools in the investigation of the functional organization of the human brain. The construction of such models is difficult using current neuroimaging technology due to the high degree of cortical folding. Even single voxel misclassifications can result in erroneous connections being created between adjacent banks of a sulcus, resulting in a topologically inaccurate model. These topological defects cause the cortical model to no longer be homeomorphic to a sheet, preventing the accurate inflation, flattening, or spherical morphing of the reconstructed cortex. Surface deformation techniques can guarantee the topological correctness of a model, but are time-consuming and may result in geometrically inaccurate models. In order to address this need we have developed a technique for taking a model of the cortex, detecting and fixing the topological defects while leaving that majority of the model intact, resulting in a surface that is both geometrically accurate and topologically correct.

Using noninvasive functional magnetic resonance imaging (fMRI) techniques, we analyzed the responses in human area MT with regard to visual motion, color, and luminance contrast sensitivity, and retinotopy. As in previous PET studies, we found that area MT responded selectively to moving (compared to stationary) stimuli. The location of human MT in the present fMRl results is consistent with that of MT in earlier PET and anatomical studies. In addition we found that area MT has a much higher contrast sensitivity than that in several other areas, includ-ing primary visual cortex (Vl). Functional MRI half-ampli-tudes in Vl and MT occurred at approximately 15 % and 1% luminance contrast, respectively. High sensitivity to con-trast and motion in MT have been closely associated with magnocellular stream specialization in nonhuman pri-mates. Human psychophysics indicates that visual motion ap-pears to diminish when moving color-varying stimuli are equated in luminance. Electrophysiological results from macaque MT suggest that the human percept could be due to decreases in firing of area MT cells at equiluminance. We show here that fMRl activity in human MT does in fact decrease at and near individually measured equilumi-nance. Tests with visuotopically restricted stimuli in each hem-ifield produced spatial variations in fMRl activity consistent with retinotopy in human homologs of macaque areas Vl, V2, V3, and VP. Such activity in area MT appeared much less retinotopic, as in macaque. However, it was possible to measure the interhemispheric spread of fMRl activity in human MT (half amplitude activation across the vertical meridian =-15’).

Using functional magnetic resonance imaging (fMRI) and cortical unfolding techniques, we analyzed the retinotopy, motion sensitivity, and functional organization of human area V3A. These data were compared with data from additional human cortical visual areas, including V1, V2, V3/VP, V4v, and MT (V5). Human V3A has a retinotopy that is similar to that reported previously in macaque: (1) it has a distinctive, continuous map of the contralateral hemifield immediately anterior to area V3, including a unique retinotopic representation of the upper visual field in superior occipital cortex; (2) in some cases the V3A foveal representation is displaced from and superior to the confluent foveal representations of V1, V2, V3, and VP; and (3) inferred receptive fields are significantly larger in human V3A, compared with those in more posterior areas such as V1. However, in other aspects human V3A appears quite different from its macaque counterpart: human V3A is relatively motionselective, whereas human V3 is less so. In macaque, the situation is qualitatively reversed: V3 is reported to be prominently motion-selective, whereas V3A is less so. As in human and macaque MT, the contrast sensitivity appears quite high in human areas V3 and V3A. Key words: fMRI; V3A; retinotopy; motion selectivity; visual cortex; MT/V5; human; primate After cortical visual areas V3 and V4 were identified and named in macaque monkeys, another region was discovered between them and named “V3 accessory ” (V3A) (Van Essen and Zeki, 1978; Zeki, 1978a,b). V3A is now regarded as a cortical area that is entirely independent and distinct from its similarly named neighbor, V3, in terms of its retinotopy (Van Essen and Zeki, 1978; Zeki, 1978a,b; Gattass et al., 1988), its histology (Burkhalter et al., 1986; Felleman and Van Essen, 1987; DeYoe et al.,

Here we review recent findings that reveal the functional properties of extra-striate regions in the human visual cortex that are involved in the representation and perception of objects. We characterize both the invariant and non-invariant properties of these regions and we discuss the correlation between activation of these regions and recognition. Overall, these results indicate that the lateral occipital complex plays an important role in human object recognition.

& A still photograph of an object in motion may convey dynamic information about the position of the object immediately before and after the photograph was taken (implied motion). Medial temporal/medial superior temporal cortex (MT/MST) is one of the main brain regions engaged in the perceptual analysis of visual motion. In two experiments we examined whether MT/MST is also involved in representing implied motion from static images. We found stronger functional magnetic resonance imaging (fMRI) activation within MT/MST during viewing of static photographs with implied motion compared to viewing of photographs without implied motion. These results suggest that brain regions involved in the visual analysis of motion are also engaged in processing implied dynamic information from static images. & The perception of motion is critical for our ability to interact with a dynamic environment. Neurophysiological studies in monkeys (for example, Britten, Newsome,

& These experiments use functional magnetic resonance imaging (fMRI) to reveal neural activity uniquely associated with perception of biological motion. We isolated brain areas activated during the viewing of point-light figures, then compared those areas to regions known to be involved in coherent-motion perception and kinetic-boundary perception. Coherent motion activated a region matching previous reports of human MT/MST complex located on the temporo-parietooccipital junction. Kinetic boundaries activated a region posterior and adjacent to human MT previously identified as the kinetic-occipital (KO) region or the lateral-occipital (LO) complex. The pattern of activation during viewing of biological

ion; visual motion perception; motion opponency; vision; visual cortex Computational theories of visual motion perception typically include a motion opponent stage in which, for example, the response of a hypothetical leftward-selective neuron is subtracted from that of a rightward-selective neuron to yield a neuronal signal for net rightward motion (van Santen and Sperling, 1984, 1985; Qian et al., 1994b; Adelson and Bergen, 1985; Simoncelli and Heeger, 1998). The importance of opponent mechanisms for motion perception is supported by a number of perceptual studies (Levinson and Sekuler, 1975a; Mather and Moulden, 1983; van Santen and Sperling, 1984; Stromeyer et al., 1984; Lubin, 1992; Qian et al., 1994a; Zemany et al., 1998). For example, superimposing two identical sinusoidal grating patterns moving in opposite directions produces what is called a counterphase grating. The counterphase grating appears to flicker in place with no net motion, as if the motions of the two com

distances can detect a possible genetic encoding. When applied to real data, this study highlighted genetic constraints on the shape of the central sulcus. We found from 10 pairs of monozygotic twins that the intrapair modal distance of the central sulcus was significantly smaller than the interpair modal distance, for both the left central sulcus (Z ##2.66; P < 0.005) and the right central sulcus (Z ##2.26; P < 0.05). Genetic constraints on the definition of the central sulcus shape were confirmed by applying the same experiment to 10 pairs of normal young individuals (Z ##1.39; Z ##0.63, i.e., values not significant at the P < 0.05 level) and 10 pairs of dizygotic twins (Z # 0.47; Z # 0.03, i.e., values not significant at the P < 0.05 level). 2000 Academic Press Key Words: cerebral cortex; central sulcus; Principal Component Analysis; genetic encoding. INTRODUCTION Cortical sulci of the human brain (and their counterpart gyri) form macroscopic anatomical landmarks on the surfac

Positron emission tomography (PET) was used to locate an area in human extrastriate cortex that subserves a specific component process of visual object recognition. Regional blood flow increased in a bilateral extrastriate area on the inferolateral surface of the brain near the border between the occipital and temporal lobes (and a smaller area in the right fusiform gyms) when subjects viewed line drawings of 3dimensional objects compared to viewing scrambled drawings with no clear shape interpretation. Responses were Seen for both novel and familiar objects, implicating this area in the bottom-up (i.e., memory-independent) analysis of visual shape.