@Article{ ValverdeSalzmannBLS2012,
title = {Color Blobs in Cortical Areas V1 and V2 of the New World Monkey Callithrix jacchus, Revealed by Non-Differential Optical Imaging},
journal = {Journal of Neuroscience},
year = {2012},
month = {6},
volume = {32},
number = {23},
pages = {7881-7894},
abstract = {Color vision is reserved to only few mammals, such as Old World monkeys and humans. Most Old World monkeys are trichromats. Among them, macaques were shown to exhibit functional domains of color-selectivity, in areas V1 and V2 of the visual cortex. Such color domains have not yet been shown in New World monkeys. In marmosets a sex-linked dichotomy results in dichromatic and trichromatic genotypes, rendering most male marmosets color-blind. Here we used trichromatic female marmosets to examine the intrinsic signal response in V1 and V2 to chromatic and achromatic stimuli, using optical imaging. To activate the subsystems individually, we used spatially homogeneous isoluminant color opponent (red/green, blue/yellow) and hue versus achromatic flicker (red/gray, green/gray, blue/gray, yellow/gray), as well as achromatic luminance flicker. In contrast to previous optical imaging studies in marmosets, we find clearly segregated color domains, similar to those seen in macaques. Red/green and red/gray flicker were found to be the appropriate stimulus for revealing color domains in single-condition maps. Blue/gray and blue/yellow flicker stimuli resulted in faint patch-patterns. A recently described multimodal vessel mapping approach allowed for an accurate alignment of the functional and anatomical datasets. Color domains were tightly colocalized with cytochrome oxidase blobs in V1 and with thin stripes in V2. Thus, our findings are in accord with 2-Deoxy-d-glucose studies performed in V1 of macaques and studies on color representation in V2. Our results suggest a similar organization of early cortical color processing in trichromats of both Old World and New World monkeys.},
web_url = {http://www.jneurosci.org/content/32/23/7881.full.pdf+html},
state = {published},
DOI = {10.1523/​JNEUROSCI.4832-11.2012},
author = {Valverde Salzmann MF{valverde}, Bartels A{abartels}{Department Physiology of Cognitive Processes}, Logothetis NK{nikos}{Department Physiology of Cognitive Processes} and Sch\"uz A{schuez}{Department Physiology of Cognitive Processes}}
}

@Article{ ValverdeSalzmannWLS2011,
title = {Multimodal vessel mapping for precise large area alignment of functional optical imaging data to neuroanatomical preparations in marmosets},
journal = {Journal of Neuroscience Methods},
year = {2011},
month = {9},
volume = {201},
number = {1},
pages = {159-172},
abstract = {Imaging technologies, such as intrinsic optical imaging (IOI), functional magnetic resonance imaging (fMRI) or multiphoton microscopy provide excellent opportunities to study the relationship between functional signals recorded from a cortical area and the underlying anatomical structure. This, in turn, requires accurate alignment of the recorded functional imaging data with histological datasets from the imaged tissue obtained after the functional experiment. This alignment is complicated by distortions of the tissue which naturally occur during histological treatment, and is particularly difficult to achieve over large cortical areas, such as primate visual areas. We present here a method that uses IOI vessel maps revealed in the time course of the intrinsic signal, in combination with vascular casts and vascular lumen labeling techniques together with a pseudo three dimensional (p3D) reconstruction of the tissue architecture in order to facilitate alignment of IOI data with posthoc histological datasets. We demonstrate that by such a multimodal vessel mapping approach, we are able to constitute a hook in anatomical-functional data alignment that enables the accurate assignment of functional signals over large cortical regions. As an example, we present precise alignments of IOI responses showing orientation selectivity of primate V1 with anatomical sections stained for cytochrome-oxidase-reactivity.},
web_url = {http://www.sciencedirect.com/science?_ob=MiamiImageURL&_cid=271055&_user=29041&_pii=S0165027011004584&_check=y&_origin=&_coverDate=30-Sep-2011&view=c&wchp=dGLzVlB-zSkWz&md5=02ccc2eea51f6889a3cd0629dfffe55a/1-s2.0-S0165027011004584-main.pdf},
state = {published},
DOI = {10.1016/j.jneumeth.2011.07.029},
author = {Valverde Salzmann MF{valverde}, Wallace DJ{dhw}{Research Group Neural Population Imaging}, Logothetis NK{nikos}{Department Physiology of Cognitive Processes} and Sch\"uz A{schuez}{Department Physiology of Cognitive Processes}}
}

@Poster{ ValverdeSalzmannBLS2012_2,
title = {Color blobs in visual areas V1 and V2 of the common marmoset},
year = {2012},
month = {10},
volume = {52},
number = {261.11},
abstract = {Color vision is reserved to only few mammals, such as Old World monkeys and humans. Most Old World monkeys are trichromats. Among them, macaques were shown to exhibit functional domains of color-selectivity, in areas V1 and V2 of the visual cortex. Such color domains have not yet been shown in New World monkeys. In marmosets a sex-linked dichotomy results in dichromatic and trichromatic genotypes, rendering most male marmosets color-blind. Here we used trichromatic female marmosets to examine the intrinsic signal response in V1 and V2 to chromatic and achromatic stimuli, using optical imaging. In order to activate the visual subsystems individually, we used spatially homogeneous isoluminant color opponent (red/green, blue/yellow) and hue versus achromatic flicker (red/gray, green/gray, blue/gray, yellow/gray), as well as achromatic luminance flicker. In contrast to previous optical imaging studies in marmosets, we find clearly segregated color domains, similar to those seen in macaques. Red/green and red/gray flicker were found to be the appropriate stimulus for revealing color domains in single condition maps (see figure). Blue/gray and blue/yellow flicker stimuli resulted in faint patch-patterns. A recently described multimodal vessel mapping approach allowed for an accurate alignment of the functional and anatomical datasets. Color domains were tightly colocalized with cytochrome oxidase blobs in V1 and with thin stripes in V2. Thus, our findings are in accord with 2-Deoxy-D-glucose studies performed in V1 of macaques and studies on color representation in V2. Our results suggest a similar organization of early cortical color processing in trichromats of both, Old World and New World monkeys.},
file_url = {fileadmin/user_upload/files/publications/2012/Neuroscience-2012-Valverde.pdf},
web_url = {http://www.sfn.org/am2012/},
event_name = {42nd Annual Meeting of the Society for Neuroscience (Neuroscience 2012)},
event_place = {New Orleans, LA, USA},
state = {published},
author = {Valverde Salzmann MF{valverde}{Department High-Field Magnetic Resonance}, Bartels A{abartels}{Department Physiology of Cognitive Processes}, Logothetis NK{nikos}{Department Physiology of Cognitive Processes} and Sch\"uz A{schuez}{Department Physiology of Cognitive Processes}}
}

@Poster{ ValverdeSalzmannLP2011,
title = {High-Resolution Imaging of Vessels in the Isolated Rat Brain},
year = {2011},
month = {5},
volume = {19},
number = {2382},
abstract = {While several atlases are available depicting the spatial distribution of various parameters either measured with MRI or from histological section, no comparable comprehensive data exists for the distribution of vessels in the rat brain. Angiography is able to use the blood flow in the brain of the living rat to display the largest arteries, while SWI can visualize veins down to medium size. The aim of this study was to obtain a full picture of vessels even down to relatively small size in the isolated rat brain perfused
with contrast agents at ultra-high field.},
file_url = {fileadmin/user_upload/files/publications/ISMRM-2011-2382.pdf},
web_url = {http://www.ismrm.org/11/},
event_name = {19th Annual Meeting and Exhibition of the International Society for Magnetic Resonance in Medicine (ISMRM 2011)},
event_place = {Montréal, Canada},
state = {published},
author = {Valverde Salzmann MF{valverde}{Department High-Field Magnetic Resonance}, Logothetis NK{nikos}{Department Physiology of Cognitive Processes} and Pohmann R{rolf}{Department High-Field Magnetic Resonance}}
}

@Poster{ 4912,
title = {Hypercolumns vs. pinwheels},
journal = {Neural Plasticity},
year = {2007},
month = {9},
volume = {2007},
pages = {36},
abstract = {“Optical imaging” maps of the visual cortex after systematic
application of variously oriented visual stimuli provide an
opportunity to test different hypotheses on the distribution
of orientation sensitive neurons over the surface of the cortex.
Rectilinear “slabs” of uniform orientation, as postulated
in some earlier models, are not supported by the evidence.
What is compatible with the optical imaging maps is the
arrangement of neurons with different orientation around
centers, regularly spaced at distances of about 0.5mm in a
hexagonal array. According to the model proposed by [3],
the orientations to which the neurons are sensitive should
be arranged either radially, or, more likely, like the tangents [1] of circles around said centers, whereby in either case twice the same orientation occurs in opposite positions of the “hypercolumn” thus defined. The centers of the hypercolumns very likely coincide with the so-called cytochrome oxidase “blobs” which are spaced at the same distance. The fact that within these “blobs” orientation tuning of cortical neurons becomes undefined [4], makes the array of orientations around these centers less spectacular, and indeed other interpretations of the coloured maps produced by optical recording were put forward. So-called “pinwheels” stole the show, that is centers around which neurons with different orientation sensitivity crowd with the colours representing their orientation clashing without interposed indifferent regions.
In these pinwheels each of the different orientations occurs only once as you go full circle around their center.
They most likely correspond to the corners between the hypercolumns in their hexagonal array, and the different orientations within one “pinwheel” most likely belong to three different hypercolumns that meet there [2].
The distinction between the two entities, orientation hypercolumns and pinwheels may sound academic but becomes
crucial when one endeavours to underpin orientation
specificity of cortical neurons with schemes of neuronal interactions at the elementary level. The accompanying illustration should help the reader to partake in this discussion.},
web_url = {http://www.hindawi.com/journals/np/2007/023250/abs/},
event_name = {39th Annual General Meeting of the European Brain and Behaviour Society},
event_place = {Trieste, Italy},
state = {published},
DOI = {doi:10.1155/2007/23250},
author = {Valverde M{valverde} and Braitenberg V{braitenb}}
}

@Poster{ 4859,
title = {Pinwheels vs. Bow Ties},
year = {2007},
month = {7},
volume = {10},
pages = {93},
abstract = {“Optical imaging” of the visual cortex after application of variously oriented visual stimuli
provides an opportunity to test different models of the distribution of orientation sensitive neurons
over the surface of the cortex. Rectilinear “slabs” of uniform orientation are not supported
by the evidence. What is compatible with the optical imaging is the arrangement of neurons
with different orientation around centers, regularly spaced at distances of about 0.5 mm in a
hexagonal array. According to a model proposed in 1979 [1], the orientations to which the
neurons are sensitive should be arranged either radially, or, more likely, like the tangents [2]
of circles around said centers, whereby in either case twice the same orientation occurs in opposite
positions of the “hypercolumn” thus defined. For this reason each colour, indicating a
certain orientation on the optical recording maps, should form a blotch the shape of two sectors
meeting at the center of the hypercolumn. We chose the term “bow tie” for this configuration,
to match the facetiousness of the competing term “pinwheel”. The centers of the hypercolumns
very likely coincide with the so-called cytochrome oxidase “blobs” which are spaced
at the same distance. The fact that within these “blobs” orientation tuning of cortical neurons
becomes rather undefined [3], makes the array of orientations around these centers less spectacular,
and indeed other interpretations of the coloured maps were put forward. “Pinwheels”
stole the show, i.e. centers around which neurons with different orientation sensitivity crowd
with the colours representing their orientation clashing without interposed indifferent regions.
In these pinwheels each of the different orientations occurs only once as you go full circle
around their center. They most likely correspond to the corners between the hypercolumns in
their hexagonal array, and the different orientations within one “pinwheel” most likely belong
to three different hypercolumns that meet there [4].
The distinction between the two entities, orientation hypercolumns and pinwheels may
sound academic but becomes crucial when one endeavours to underpin orientation specificity
of cortical neurons with schemes of neuronal interactions at the elementary level. This is fairly
easy in the case of the hypercolumns under the assumption that in their centers are housed
special inhibitory neurons [2], while a similar elementary scheme was never found as an explanation
of the pinwheels.
On the coloured maps obtained with “optical recording” it is possible to discern both “pinwheels”
and “bow ties” as an aid to the localization of the two types of centers.},
web_url = {http://www.twk.tuebingen.mpg.de/twk07/abstract.php?_load_id=valverde01},
event_name = {10th Tübinger Wahrnehmungskonferenz (TWK 2007)},
event_place = {Tübingen, Germany},
state = {published},
author = {Valverde M{valverde} and Braitenberg V{braitenb}}
}