Visual motion activates V5 in dyslexics

Vanni, Simo; Uusitalo, Mikko A.; Kiesilä, P.; Hari, Riitta

doi:10.1097/00001756-199705260-00029

Cited by 57 publications

(39 citation statements)

References 11 publications

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“…This area has been shown to be active in monkeys almost immediately after V1 (2) and suggested to be active even before V1 in humans (33). However, the 170-to 220-ms latencies in our study are in line with earlier magnetoencephalographic data showing V5 activation at 160 ms for motion stimuli (32,34). It is possible that our stimuli did not activate V5͞MT, but the signals with longer latencies at the ROI c come from other functional areas.…”

Section: Resultssupporting

confidence: 87%

See 1 more Smart Citation

Coinciding early activation of the human primary visual cortex and anteromedial cuneus

Vanni¹,

Tanskanen²,

Seppä³

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

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Proper understanding of processes underlying visual perception requires information on the activation order of distinct brain areas. We measured dynamics of cortical signals with magnetoencephalography while human subjects viewed stimuli at four visual quadrants. The signals were analyzed with minimum current estimates at the individual and group level. Activation emerged 55-70 ms after stimulus onset both in the primary posterior visual areas and in the anteromedial part of the cuneus. Other cortical areas were active after this initial dual activation. Comparison of data between species suggests that the anteromedial cuneus either comprises a homologue of the monkey area V6 or is an area unique to humans. Our results show that visual stimuli activate two cortical areas right from the beginning of the cortical response. The anteromedial cuneus has the temporal position needed to interact with the primary visual cortex V1 and thereby to modify information transferred via V1 to extrastriate cortices.A natomy of connections between primate visual cortices suggests a hierarchical organization of signal processing (1). However, the order of processes at different functional areas cannot be directly deduced from the anatomical hierarchy without relevant timing information. In monkeys, several areas become active immediately after the primary visual cortex (V1), while another set of areas is active at clearly longer latencies (2, 3). The areas showing early responses, such as V5͞middle temporal area (MT), medial superior temporal area, and frontal eye field, are specialized in analyzing dynamical visual information and in visuomotor transformation (for reviews, see refs. 4 and 5). The areas with longer latencies, such as V4, are sensitive to object form and color and participate in object recognition (6, 7). The dissimilarities in activation latencies and functional properties of these areas suggest diversity in the type and amount of necessary input and preprocessing before activation. Given the differences between monkey and human visual cortices (for a review, see ref. 8), we aimed to explore the dynamics and distribution of early cortical activation in humans. Neuromagnetic signals were recorded while the subjects viewed pattern reversal or luminance stimuli at the four visual quadrants. The signals were analyzed with minimum current estimates (MCEs), which require minimal human intervention for determining the location and orientation of the cortical currents (9). The individual three-dimensional estimates were aligned with a nonlinear transformation according to individual brain shapes (10, 11), and both the individual and group average MCEs were compared with the existing maps of human visual cortices (12-16). Materials and MethodsSubjects and Stimuli. We studied five female and five male subjects (mean age 27 years, range 20-42 years). The stimuli were generated with a Macintosh computer and presented with a dataprojector (VistaPro, Electrohome Ltd., Ontario, Canada) on a back projection screen, with viewing d...

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Section: Resultssupporting

confidence: 87%

“…The temporo-occipital source region was about 1 cm anterior and inferior to human MT͞V5 (x, y, and z Talairach coordinates for the ROI c are 42, Ϫ67, and Ϫ4 mm, respectively; data have been compared with a summary of V5 coordinates in ref. 32). However, because of its size, the ROI c should include activation of the human V5͞MT.…”

Section: Resultsmentioning

confidence: 99%

Coinciding early activation of the human primary visual cortex and anteromedial cuneus

Vanni¹,

Tanskanen²,

Seppä³

et al. 2001

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

201

125

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“…The average Talairach and Tournoux (1988) coordinates of our LOV5 source (Vanni et al, 2004) are very close to the coordinates of V5 reported in earlier studies (Eden et al, 1996;Tootell et al, 1995;Vanni et al, 1997;Watson et al, 1993). Also, in monkeys, this region is known to react to onset of a stimulus as well as to visual motion (Felleman and Kaas, 1984;Schmolesky et al, 1998).…”

Section: Discussionsupporting

confidence: 87%

Timing of interactions across the visual field in the human cortex

et al. 2004

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“…Some of these physiological and psychophysical findings have not been replicated (Victor et al, 1993;Walther-Muller, 1995;Hayduk et al, 1996;Johannes et al, 1996;Vanni et al, 1997). Consequently, the hypothesis for an M pathway deficit in dyslexia remains controversial.…”

Section: Abstract: Mt; V1; Neuroimaging; Fmri; Speed Discrimination;mentioning

confidence: 99%

“…First, visual evoked potentials (VEP) in dyslexics were reduced or delayed for stimuli with low spatial and high temporal frequencies (Livingstone et al, 1991;May et al, 1991;Lehmkuhle et al, 1993;Kubova et al, 1996). Second, in a functional magnetic resonance imaging (fMRI) study, Eden et al (1996) failed to find significant activity in MTϩ during the perception of moving dots in dyslexic subjects, suggesting a possible developmental lesion in MTϩ.Some of these physiological and psychophysical findings have not been replicated (Victor et al, 1993;Walther-Muller, 1995;Hayduk et al, 1996;Johannes et al, 1996;Vanni et al, 1997). Consequently, the hypothesis for an M pathway deficit in dyslexia remains controversial.…”

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confidence: 99%

Functional Magnetic Resonance Imaging of Early Visual Pathways in Dyslexia

1998

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We measured brain activity, perceptual thresholds, and reading performance in a group of dyslexic and normal readers to test the hypothesis that dyslexia is associated with an abnormality in the magnocellular (M) pathway of the early visual system. Functional magnetic resonance imaging (fMRI) was used to measure brain activity in conditions designed to preferentially stimulate the M pathway. Speed discrimination thresholds, which measure the minimal increase in stimulus speed that is just noticeable, were acquired in a paradigm modeled after a previous study of M pathway-lesioned monkeys. Dyslexics showed reduced brain activity compared with controls both in primary visual cortex (V1) and in several extrastriate areas, including area MT and adjacent motion-sensitive areas (MTϩ) that are believed to receive a predominant M pathway input. There was a strong three-way correlation between brain activity, speed discrimination thresholds, and reading speed. Subjects with higher V1 and MTϩ responses had lower perceptual thresholds (better performance) and were faster readers. These results support the hypothesis for an M pathway abnormality in dyslexia and imply strong relationships between the integrity of the M pathway, visual motion perception, and reading ability. Key words: MT; V1; neuroimaging; fMRI; speed discrimination; psychophysics; readingDevelopmental dyslexia can be defined as an unexpectedly low reading ability relative to IQ. The reduced reading performance cannot be explained by a lack of motivation, inadequate learning opportunity, abnormal sensory acuity, or an acquired brain lesion. Estimates of its prevalence range from 3 to 9% (Rutter and Yule, 1975;Shay witz et al., 1990).Several cognitive, sensory, and motor deficits have been correlated with dyslexia (Tallal et al., 1993;Shay witz et al., 1995Shay witz et al., , 1998Heilman et al., 1996;Stein and Walsh, 1997). The goal of the present study was to test whether dyslexia is correlated specifically with a deficit in one of the major visual pathways between the retina and cortex: the magnocellular (M) pathway (Livingstone et al., 1991).To test this hypothesis, we have relied on several of the main anatomical and f unctional features of the M pathway. Anatomically, the M pathway includes the retinal ganglion cells that project to the M layers of the lateral geniculate nucleus (LGN) of the thalamus, the M-layer LGN cells that project to primary visual cortex (V1), and the V1 cells that project to the extrastriate area MT and adjacent motion-sensitive areas (MTϩ) (Merigan and Maunsell, 1993). Hence, M pathway deficits should be evident in several sites within the visual pathways. In support of this hypothesis, Livingstone et al. (1991) conducted an anatomical postmortem study of LGN cell size in five dyslexic brains and found that cell bodies in the M layers of the LGN, but not other layers, were 27% smaller than matched controls.Functionally, lesions to the M layers of monkey LGN reduce behavioral sensitivity to lower spatial and higher temporal freque...

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Visual motion activates V5 in dyslexics

Cited by 57 publications

References 11 publications

Coinciding early activation of the human primary visual cortex and anteromedial cuneus

Coinciding early activation of the human primary visual cortex and anteromedial cuneus

Timing of interactions across the visual field in the human cortex

Functional Magnetic Resonance Imaging of Early Visual Pathways in Dyslexia

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