Monocular activation of V1 and V2 in amblyopic adults measured with functional magnetic resonance imaging

Conner, Ian P.; Odom, J. Vernon; Schwartz, Terry L.; Mendola, Janine D.

doi:10.1016/j.jaapos.2007.01.119

Cited by 69 publications

(59 citation statements)

References 68 publications

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“…Initials enclosed by a dashed box indicates responses that are significantly reduced (t-test; P < 0.05) from that of the fellow fixing eye. There is variability across the population with not all amblyopes exhibit reduced magnitude responses for the phase-encoded stimulus, consistent with previous studies [Barnes et al, 2001;Conner et al, 2007a;Li et al, 2007a]. For the population as a whole, the amblyopic response is significantly reduced only in area V1 (T ¼ 2.1993, df ¼ 28; P < 0.05) and Vp (T ¼ 2.1141, df ¼ 28; P < 0.05); however, individual subjects display significant reductions (T > 1.965: P < 0.05, twotailed t-test) in response for the phase-encoded stimulus in all visual areas (e.g., in area V1, ML, HP, SB, YF, HQ, CQ, CW; area V2, WH, CQ, ML, HQ, CW, YF; area V3, ML, SB, ZF, CQ, YF, CW; area Vp, ZF, CQ, HQ, CW, YF; area V3a, WH, CW, CQ, HP, ZF, ML; area V4, HP, HQ; area MT, HQ, HP, CQ.…”

Section: Neural Modelingsupporting

confidence: 88%

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

Hess¹,

Li²,

Lu³

et al. 2010

Human Brain Mapping

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Although there is general agreement that the fMRI cortical response is reduced in humans with amblyopia, the deficit is subtle and has little correlation with threshold-based psychophysics. From a purely contrast sensitivity perspective, one would expect fMRI responses to be selectively reduced for stimuli of low contrasts. However, to date, all fMRI stimuli used in studies of amblyopia have been of high contrast. Furthermore, if the deficit is selective for low contrasts, one would expect it to reflect a selective M-cell loss, because M-cells have much higher contrast gain than P-cells and make a larger contribution to the threshold detection of stimuli of low spatial and medium temporal frequencies. To test these two predictions, we compared % BOLD response between the eyes of normals and amblyopes for low- and high-contrast stimuli using a phase-encoded design. The results suggest that the fMRI deficit in amblyopia depends upon stimulus contrast and that it is greater at high contrasts. This is consistent with a selective P-cell contrast deficit at a precortical or early cortical site.

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Section: Neural Modelingsupporting

confidence: 88%

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

Hess¹,

Li²,

Lu³

et al. 2010

Human Brain Mapping

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show abstract

“…Our results along with those of [Conner et al, 2007a] do not provide support for the suggestion that V1 and V2 are r Spatial Frequency Deficits in Amblyopia Using fMRI r r 4065 r spared in humans with amblyopia as proposed by [Muckli et al, 2006]. However, in agreement with the results of [Li et al, 2007a], we do find that some individuals exhibit less involvement of V1 and sometimes V2, though this is not a typical finding.…”

Section: Regional Involvementcontrasting

confidence: 76%

Selectivity as well as sensitivity loss characterizes the cortical spatial frequency deficit in amblyopia

Hess¹,

Li²,

Mansouri³

et al. 2009

Human Brain Mapping

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The processing deficit in amblyopia is not restricted to just high spatial frequencies but also involves low-medium spatial frequency processing, for suprathreshold stimuli with a broad orientational bandwidth. This is the case in all three forms of amblyopia; strabismic, anisometropic, and deprivation. Here we use both a random block design and a phase-encoded design to ascertain (1) the extent to which fMRI activation is reduced at low-mid spatial frequencies in different visual areas, (2) how accurately spatial frequency is mapped across the amblyopic cortex. We report a loss of function to suprathreshold low-medium spatial frequency stimuli that involves more than just area V1, suggesting a diffuse loss in spatial frequency processing in a number of different cortical areas. An analysis of the fidelity of the spatial frequency cortical map reveals that many voxels lose their spatial frequency preference when driven by the amblyopic eye, suggesting a broader tuning for spatial frequency for neurons driven by the amblyopic eye within this low-mid spatial frequency range.

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“…Others have argued that V1 activation is reduced (Demer et al, 1988;Kabasakal et al, 1995;Goodyear et al, 2000;Barnes et al, 2001;Choi et al, 2001;Algaze et al, 2002;Conner and Mendola, 2005). A number of studies have shown that the extrastriate visual cortex is also affected (Barnes et al, 2001;Conner et al, 2007;Li et al, 2007b). However, to date human brain imaging has not resolved whether the cortical deficit is due to fewer cells, reduced cortical magnification for the AME's input, a disordered projection, or loss of cells' spatial resolution for the AME's input.…”

Section: Introductionmentioning

confidence: 99%

Is the Cortical Deficit in Amblyopia Due to Reduced Cortical Magnification, Loss of Neural Resolution, or Neural Disorganization?

2015

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The neural basis of amblyopia is a matter of debate. The following possibilities have been suggested: loss of foveal cells, reduced cortical magnification, loss of spatial resolution of foveal cells, and topographical disarray in the cellular map. To resolve this we undertook a population receptive field (pRF) functional magnetic resonance imaging analysis in the central field in humans with moderate-to-severe amblyopia. We measured the relationship between averaged pRF size and retinal eccentricity in retinotopic visual areas. Results showed that cortical magnification is normal in the foveal field of strabismic amblyopes. However, the pRF sizes are enlarged for the amblyopic eye. We speculate that the pRF enlargement reflects loss of cellular resolution or an increased cellular positional disarray within the representation of the amblyopic eye.

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Monocular activation of V1 and V2 in amblyopic adults measured with functional magnetic resonance imaging

Abstract: Asymmetries in magnitude of monocular activation do occur in subjects with amblyopia, but these basic measures are limited in terms of sensitivity for mild to moderate amblyopia and for specificity between subtypes.

Cited by 69 publications

References 68 publications

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

The contrast dependence of the cortical fMRI deficit in amblyopia; a selective loss at higher contrasts

Selectivity as well as sensitivity loss characterizes the cortical spatial frequency deficit in amblyopia

Is the Cortical Deficit in Amblyopia Due to Reduced Cortical Magnification, Loss of Neural Resolution, or Neural Disorganization?

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