Functional-anatomical investigations on the visual system in New World Monkeys.

M.F. Valverde Salzmann, A. Schüz

Introduction

Functional studies on the visual cortex of primates has revealed a striking topology of domains for orientation selectivity as well as domains for color processing [1,2,3]. Anatomical studies indicate that this functional segregation is fundamentally based on the cytoarchitecture of the visual system. Many studies investigated the relationship between functional domains and architectonical structures such as cytochrome oxidase (CO) blobs. However, diverging results led to an ongoing controversy about the spatial relations of functional columns and thalamic input zones especially with respect to their tripartite subdivision into konio, parvo, and magno streams, associated with the perception of color, form, and motion [4,5].

Goals

The aim of our study is to investigate the arrangement of orientation columns on functional maps of orientation selectivity, with respect to the location of functional color domains and thalamic input zones such as CO blobs in V1 and V2 of the primates visual cortex.

Methods

We use intrinsic optical imaging, laminar microelectrode arrays and a variety of visual stimuli as achromatic gratings and color flicker to map the organization of functional domains in V1 and V2 of the common marmoset. Marmosets like other New World Monkeys show a well investigated genetic dichotomy that affects the expression of retinal photoreceptors sensitive for middle to long (M,L) wavelengths as well as the cellular basis of the parvo stream. Thus most male and some female marmosets are colorblind. However, few females show full trichromatic color vision [6,7]. This makes the marmoset an important model for investigations on the functional segregation of the three visual pathways.

Initial results

We developed a histological protocol for making 3D-reconstructions of the histologically processed cortex that facilitates the alignment of functional and anatomical data (also in Magnetic Resonance Imaging studies [8]) and increases accuracy. Thus, dislocation errors in alignments are reduced by more than 50% in comparison to those reported in previous studies [9]. We further developed a stimulus protocol that allows us to map color domains by using optical imaging in trichromatic marmosets. Our results show that color domains are most effectively activated by using red-green (L-M) flicker stimuli. We also showed that color domains in marmosets are colocalized with CO blobs in V1 and thin stripes in V2 [10].

Initial conclusion

We conclude that the observed color domain activation is primarily triggered by a modulation of the parvo stream ((L-M)-cone axis), thus supporting the notion that CO blobs in New World as well as in Old World trichromatic primates are segregated domains of color processing.

References

[1] Livingstone, M., D. Hubel: Anatomy and physiology of a color system in the primate visual cortex. The Journal of Neuroscience 4, 309-356 (1984).

[2] Landisman, C.E., D.Y. Ts’O: Color Processing in Macaque Striate Cortex: Relationship to Ocular Dominance, Cytochrome Oxidase, and Orientation. Journal of Neurophysiology 87, 3126-3167 (2002).

[3] Lu, H.D., A.W. Roe: Functional Organization of Color Domains in V1 and V2 of Macaque Monkey Revealed by Optical Imaging. Cerebral Cortex 18, 516-533 (2008).

[4] Livingstone, M., D. Hubel: Segregation of form color, movement, and depth: anatomy, physiology, and perception. Science 240, 740-9 (1988).

[5] Sincich, L.C., J.C. Horton: The Circuitry of V1 and V2: Integration of Color, Form, and Motion. Annual Review of Neuroscience 28, 303-26 (2005).

[6] Blessing, E.M., S.G. Solomon, M. Hashemi-Nezhad, B.J. Morris, P.R. Martin: Chromatic and spatial properties of parvocellular cells in the lateral geniculate nucleus of the marmoset (Callithrix jacchus). The Journal of Physiology 557, 229-245 (2004).

[7] Conway, B.R.: Color Vision, Cones, and Color-Coding in the Cortex. The Neuroscientist 15, 274-290 (2009).

[8] Valverde Salzmann, M.F., N.K. Logothetis, R. Pohmann: High-resolution imaging of vessels in the isolated rat brain. ISMRM: Montreal, Quebec, Canada (2011).

[9] Valverde Salzmann, M.F., D.J. Wallace, N.K. Logothetis, A. Schüz: Multimodal vessel mapping for precise large area alignment of functional optical imaging data to neuroanatomical preparations in marmosets. Journal of Neuroscience Methods 201, 159-172 (2011).

[10] Valverde Salzmann, M.F., A. Bartels, N.K. Logothetis, A. Schüz: Color blobs in cortical areas V1 and V2 of the new world monkey Callithrix jacchus, revealed by non-differential optical imaging. Journal of Neuroscience (2012) (in press).

Functional-anatomical investigations on the primary visual cortex in marmosets. (A) Intrinsic optical imaging (IOI) orientation map superimposed onto the 3D reconstruction of histological sections stained for cytochrome oxidase. (B) The pattern of the superficial cortical vasculature (from the same cortical region) labeled with FITC. Scale bar = 500 µm.