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Member-Initiated Symposia2012 Symposia Distinguishing perceptual shifts from response biases Human visual cortex: from receptive fields to maps to clusters to perception Neuromodulation of Visual Perception Part-whole relationships in visual cortex Pulvinar and Vision: New insights into circuitry and function What does fMRI tell us about brain homologies?
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What does fMRI tell us about brain homologies?Friday, May 11, 1:00 - 3:00 pm Organizer: Reza Rajimehr, McGovern Institute for Brain Research, Massachusetts Institute of Technology
Symposium DescriptionOver the past 20 years, the functional magnetic resonance imaging
(fMRI) has provided a great deal of knowledge about the functional organization
of human visual cortex. In recent years, the development of the fMRI technique
in non-human primates has enabled neuroscientists to directly compare the
topographic organization and functional properties of visual cortical areas
across species. These comparative studies have shown striking similarities
('homologies') between human and monkey visual cortex. Many visual cortical
areas in human can be corresponded to homologous areas in monkey - though
detailed cross-species comparisons have also shown specific variations in
visual feature selectivity of cortical areas and spatial arrangement of visual
areas on the cortical sheet. Comparing cortical structures in human versus
monkey provides a framework for generalizing results from invasive
neurobiological studies in monkeys to humans. It also provides important clues
for understanding the evolution of cerebral cortex in primates. In this
symposium, we would like to highlight recent fMRI studies on the organization
of visual cortex in human versus monkey. We will have 5 speakers. Each speaker
will give a 25-minute talk (including 5 minutes of discussion time). Martin
Sereno will introduce the concept of brain homology, elaborate on its
importance, and evaluate technical limitations in addressing the homology
questions. He will then continue with some examples of cross-species comparison
for retinotopic cortical areas. David Van Essen will describe recent progress
in applying surface-based analysis and visualization methods that provide a
powerful approach for comparisons among primate species, including macaque,
chimpanzee, and human. Hauke Kolster will test the homology between visual
areas in occipital cortex of human and macaque in terms of topological
organization, functional characteristics, and population receptive field sizes.
Jonathan Winawer will review different organizational schemes for visual area
V4 in human, relative to those in macaque. Reza Rajimehr will compare
object-selective cortex (including face and scene areas) in human versus
macaque. The symposium will be of interest to visual neuroscientists (faculty
and students) and a general audience who will benefit from a series of
integrated talks on fundamental yet relatively ignored topic of brain homology. Presentations Evolution, taxonomy, homology, and primate visual areas
Martin Sereno, Department of Cognitive Science, UC San
Diego Evolution involves the repeated branching of lineages, some of which
become extinct. The problem of determining the relationship between
cortical areas within the brains of surviving branches (e.g., humans,
macaques, owl monkeys) is difficult because of: (1) missing evolutionary
intermediates, (2) different measurement techniques, (3) body size
differences, and (4) duplication, fusion, and reorganization of brain areas.
Routine invasive experiments are carried out in very few species (one
loris, several New and Old World monkeys). The closest to humans are
macaque monkeys. However, the last common ancestor of humans and macaques
dates to more than 30 million years ago. Since then, New and Old World
monkey brains have evolved independently from ape and human brains,
resulting in complex mixes of shared and unique features. Evolutionary
biologists are often interested in “shared derived” characters --
specializations from a basal condition that are peculiar to a species or
grouping of species. These are important for classification (e.g., a
brain feature unique to macaque-like monkeys). Evolutionary biologists
also distinguish similarities due to inheritance (homology -- e.g., MT), from
similarities due to parallel or convergent evolution (homoplasy -- e.g., layer
4A staining in humans and owl monkey. By contrast with taxonomists,
neuroscientists are usually interested in trying to determine which
features are conserved across species (whether by inheritance or parallel
evolution), indicating that those features may have a basic functional
and/or developmental role. The only way to obtain either of these kinds
of information is to examine data from multiple species. Surface-based analyses of human, macaque, and chimpanzee cortical
organization
David Van Essen, Department of Anatomy and Neurobiology,
Washington University School of Medicine Human and macaque cortex differ markedly in surface area (nine-fold),
in their pattern of convolutions, and in the relationship of cortical areas to
these convolutions. Nonetheless, there are numerous similarities and
putative homologies in cortical organization revealed by architectonic and
other anatomical methods and more recently by noninvasive functional imaging
methods. There are also differences in functional organization,
particularly in regions of rapid evolutionary expansion in the human lineage.
This presentation will highlight recent progress in applying surface-based
analysis and visualization methods that provide a powerful general approach for
comparisons among primate species, including the macaque, chimpanzee, and
human. One major facet involves surface-based atlases that are substrates for
increasingly accurate cortical parcellations in each species as well as maps of
functional organization revealed using resting-state and task-evoked fMRI.
Additional insights into cortical parcellations as well as evolutionary
relationships are provided by myelin maps that have been obtained noninvasively
in each species. Together, these multiple modalities provide new insights
regarding visual cortical organization in each species. Surface-based
registration provides a key method for making objective interspecies
comparisons, using explicit landmarks that represent known or candidate
homologies between areas. Recent algorithmic improvements in
landmark-based registration, coupled with refinements in the available set of
candidate homologies, provide a fresh perspective on primate cortical evolution
and species differences in the pattern of evolutionary expansion. Comparative mapping of visual areas in the human and macaque occipital
cortex
Hauke Kolster, Laboratorium voor Neurofysiologie en
Psychofysiologie, Katholieke Universiteit Leuven Medical School The introduction of functional magnetic resonance imaging (fMRI) as a
non-invasive imaging modality has enabled the study of human cortical processes
with high spatial specificity and allowed for a direct comparison of the human
and the macaque within the same modality. This presentation will focus on the
phase-encoded retinotopic mapping technique, which is used to establish
parcellations of cortex consisting of distinct visual areas. These
parcellations may then be used to test for similarities between the cortical
organizations of the two species. Results from ongoing work will be presented
with regard to retinotopic organization of the areas as well as their
characterizations by functional localizers and population receptive field (pRF)
sizes. Recent developments in fMRI methodology, such as improved resolution and
stimulus design as well as analytical pRF methods have resulted in higher
quality of the retinotopic field maps and revealed visual field-map clusters as
new organizational principles in the human and macaque occipital cortex. In
addition, measurements of population-average neuronal properties have the
potential to establish a direct link between fMRI studies in the human and
single cell studies in the monkey. An inter-subject registration algorithm will
be presented, which uses a spatial correlation of the retinotopic and the
functional test data to directly compare the functional characteristics of a
set of putative homologue areas across subjects and species. The results
indicate strong similarities between twelve visual areas in occipital cortex of
human and macaque in terms of topological organization, functional
characteristics and pRF sizes. The fourth visual area: A question of human and macaque homology
Jonathan Winawer, Psychology Department, Stanford
University The fourth visual area, V4, was identified in rhesus macaque and
described in a series of anatomical and functional studies (Zeki 1971, 1978).
Because of its critical role in seeing color and form, V4 has remained an area
of intense study. The identification of a color-sensitive region on the ventral
surface of human visual cortex, anterior to V3, suggested the possible homology
between this area, labeled 'Human V4' or 'hV4' (McKeefry, 1997; Wade, 2002) and
macaque V4 (mV4). Both areas are retinotopically organized. Homology is not
uniformly accepted because of substantial differences in spatial organization,
though these differences have been questioned (Hansen, 2007). MV4 is a split
hemifield map, with parts adjacent to the ventral and dorsal portions of the V3
map. In contrast, some groups have reported that hV4 falls wholly on ventral
occipital cortex. Over the last 20 years, several organizational schemes have
been proposed for hV4 and surrounding maps. In this presentation I review
evidence for the different schemes, with emphasis on recent findings showing
that an artifact of functional MRI caused by the transverse sinus afflicts
measurements of the hV4 map in many (but not all) hemispheres. By focusing on
subjects where the hV4 map is relatively remote from the sinus artifact, we
show that hV4 can be best described as a single, unbroken map on the ventral
surface representing the full contralateral visual hemifield. These results
support claims of substantial deviations from homology between human and
macaque in the organization of the 4th visual map. Spatial organization of face and scene areas in human and macaque visual
cortex
Reza Rajimehr, McGovern Institute for Brain Research,
Massachusetts Institute of Technology
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