Locating the functional and anatomical boundaries of human primary visual cortex - PubMed (original) (raw)

Locating the functional and anatomical boundaries of human primary visual cortex

Oliver Hinds et al. Neuroimage. 2009.

Abstract

The primary visual cortex (V1) can be delineated both functionally by its topographic map of the visual field and anatomically by its distinct pattern of laminar myelination. Although it is commonly assumed that the specialized anatomy V1 exhibits corresponds in location with functionally defined V1, demonstrating this in human has not been possible thus far due to the difficulty of determining the location of V1 both functionally and anatomically in the same individual. In this study we use MRI to measure the anatomical and functional V1 boundaries in the same individual and demonstrate close agreement between them. Functional V1 location was measured by parcellating occipital cortex of 10 living humans into visual cortical areas based on the topographic map of the visual field measured using functional MRI. Anatomical V1 location was estimated for these same subjects using a surface-based probabilistic atlas derived from high-resolution structural MRI of the stria of Gennari in 10 intact ex vivo human hemispheres. To ensure that the atlas prediction was correct, it was validated against V1 location measured using an observer-independent cortical parcellation based on the laminar pattern of cell density in serial brain sections from 10 separate individuals. The close agreement between the independent anatomically and functionally derived V1 boundaries indicates that the whole extent of V1 can be accurately predicted based on cortical surface reconstructions computed from structural MRI scans, eliminating the need for functional localizers of V1. In addition, that the primary cortical folds predict the location of functional V1 suggests that the mechanism giving rise to V1 location is tied to the development of the cortical folds.

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Figures

Figure 1

Figure 1

Validation of the surface-based probabilistic atlas of V1 on an independent dataset. An inflated representation of both the left and right hemispheres of each subject are shown. Surfaces were reconstructed from data used by Amunts et al. (2000) to study the variability of V1 in stereotaxic space. The location of anatomical V1 determined from histology is shown in blue, the location of V1 predicted using the probabilistic atlas of Hinds et al. (2008) thresholded at p = 0.8 is shown in green, and the region they share is colored in yellow. Close agreement between the atlas prediction and measured location is apparent.

Figure 2

Figure 2

Computing the atlas probability threshold that yields the minimum-bias estimate of the V1 boundary. (A) The mean signed boundary distance between the measured (from histology) and atlas-predicted V1 boundary, measured at atlas probabilities ranging from 0.1 to 1.0. The signed distance treats distances as negative if the predicted boundary is within the measured boundary and positive if outside. The minimum at 0.8 indicates that thresholding the probabilistic atlas at this level yields the minimum-bias V1 boundary prediction. (B) the mean unsigned boundary distance, which represents the more standard root-mean-square error between the boundary estimates.

Figure 3

Figure 3

V1 boundary comparison on the inflated cortex for an example subject. The location of anatomical V1 predicted by the probabilistic atlas shown in green. Locations determined to lie on the functional V1 boundary via fMRI are colored based on the measured surface-based distance to the nearest location on the anatomical V1 boundary.

Figure 4

Figure 4

Alignment of the anatomical and functional V1 boundary. A portion of the flattened left and right occipital lobes is shown for each of the ten subjects with the location of anatomical V1 predicted by the probabilistic atlas shown in green. Locations determined to lie on the functional V1 boundary via fMRI are colored based on the measured surface-based distance to the nearest location on the anatomical V1 boundary. The color bar indicates the measured distance in mm. For each subject the occipital region of each hemisphere is shown with superior to the top and posterior to the left for left hemispheres and to the right for right hemispheres.

Figure 5

Figure 5

Agreement between independent measurements of V1 boundary location. (A) A histogram of the distance between the measured V1 boundary defined via analysis of histological data by Amunts et al. (2000) and the predicted V1 boundary based on the atlas of Hinds et al. (2008). The histogram represents the number of surface vertices on the atlas-predicted boundary that fall within a range of distances to the measured boundary. (B) A similar histogram where the distance computed is between each vertex of the functional boundary of V1 and the atlas-predicted boundary in the same subjects.

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