Organizational principles of human visual cortex revealed by receptor mapping - PubMed (original) (raw)

Organizational principles of human visual cortex revealed by receptor mapping

Simon B Eickhoff et al. Cereb Cortex. 2008 Nov.

Abstract

This receptorarchitectonic study of the human visual cortex investigated interareal differences in mean receptor concentrations and laminar distribution patterns of 16 neurotransmitter receptors in the dorsal and ventral parts of areas V1, V2, V3 as well as in adjoining areas V4 (ventrally) and V3A (dorsally). Both the functional hierarchy of these areas and a distinction between dorsal and ventral visual cortices were reflected by significant receptorarchitectonic differences. The observation that dorso-ventral differences existed in all extrastriate areas (including V2) is particularly important for the discussion about the relationship between dorsal and ventral V3 as it indicates that a receptorarchitectonic distinction between the ventral and dorsal visual cortices is present in but not specific to V3. This molecular specificity is mirrored by previously reported differences in retinal microstructure and functional differences as revealed in behavioral experiments demonstrating differential advantages for stimulus processing in the upper and lower visual fields. We argue that these anatomical and functional differences may be regarded as the result of an evolutionary optimization adapting to the processing of the most relevant stimuli occurring in the upper and lower visual fields.

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Figures

Figure 1.

Figure 1.

Contrast-enhanced, color-coded autoradiographs for the muscarinic M2 receptor (left) and the benzodiazepine binding sites (middle). Note that the calcarine section of V1 has not been included in the color coding and smoothing due to its obvious distortions caused by tangentional sectioning of a cortical folding. The location of cytoarchitectonic borders is shown for comparison in panel (right). Cortical areas were defined by receptorarchitectonic differences and cytoarchitectonic examination of adjacent cell body stained sections using quantitative methods (Schleicher et al. 2005) and established anatomical criteria (Amunts et al. 2000; Rottschy et al. 2007). White lines denote the borders between visual areas, whereas the boxes indicate the ROIs, from which receptor density profiles were extracted for all 16 analyzed receptors (Eickhoff, Schleicher, et al. 2007). For illustration, these profiles extracted from this particular section for the adrenergic α2 receptor are shown in the smaller inserts. Further details and additional examples for this approach are provided by Eickhoff et al. (2007) and Eickhoff, Rottschy, et al. (2007).

Figure 2.

Figure 2.

Significant (P < 0,05, family-wise error corrected) differences in mean receptor concentration (A) or laminar receptor distribution pattern (B) between visual areas, which are either adjacent or corresponding to each other in the retinotopic organization of early visual cortex.

Figure 3.

Figure 3.

Synopsis of the mean concentrations for those receptors, which showed consistent differences reflecting cortical hierarchy (A) or visual stream distinction (B). All bars represent grand mean concentrations obtained from averaging the mean (across ROIs) concentrations of the 4 individual cases. The lower rows give the mean difference between hierarchically adjacent (A, separately by visual stream), respectively, corresponding areas (B). Significant differences are shown by colored bars, nonsignificant ones in gray. Lines denote the minimum and maximum difference observed in individual cases. Because the statistical analysis was carried out as a conjunction requiring significant effects in each case, these lines do not implicate statistical significance. Confidence intervals, however, would contradict the logic of multisubject conjunction studies needed to analyze the small sample sizes available for autoradiographic data.

Figure 4.

Figure 4.

Laminar distribution patterns in ventral/dorsal V2 and V3 as well as V4/V3A for those receptors, showing consistent laminar differences between both visual streams (cf. Fig. 2). All displayed profiles are grand mean profiles obtained from averaging the mean (across ROIs) profiles of the 4 individual cases analyzed in this study.

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