The main question refers to what is the position and extents of areas 44 and 45, traditionally associated with Broca’s area. They also want to study whether there is a correlation between cytoarchitectonic borders and sulcus contours. Finally, they are also interested in the gender differences and inter-subject variability in these areas.
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Why are they asking that question?
Because there is variability among the available cytoarchitectonic maps and having a reliable architectonic description of these areas will contribute to interpret functional imaging data.
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The laminar distributions of cell densities.
The found that the cytoarchitecture of areas of 44 and 45 closely fits with that of previous studies (Economo and Koskinas, 1925; Kononova, 1949). The also observed that the cytoarchitectonic borders do not coincide with sulcar contours. Finally, the results showed that there is intersubject variability in areas 44 and 45 and there was left-over-right hemispheric variability in area 44. Finally, male subjects had higher cell densities on the left hemisphere in contrast to the right.
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How many “subjects” do they test?
Ten subjects, five male and five female.
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What is “constrained variability”?
It refers to a kind of variability that is limited by certain factors. For example, intersubject variability of areas 44 and 45 can vary in terms of cytoarchitectonic characteristics or volume, but there are some stable features that will remain the same, such as the fact that both areas will be roughly located at pars opercularis and triangularis.
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How do we interpret the inter-hemispheric asymmetries observed?
The authors found asymmetry in the cytoarchitecture and volume of area 44 in the majority of brains. In particular, the GLI was higher on the left hemisphere, and this was consistently higher on the left in male brains. As for volume, the differences are greater and they are found in all subject. These differences are associated with speech lateralization in the left hemisphere. However, this observation is simply a correlation, there is no cause-effect relationship.
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How do these findings impact our understanding and use of traditional Brodamnn’s areas?
In some studies, the sulcal patterns are used to mark the borders of the speech region. If cytoarchitectonic areas 44 and 45 cannot be localized on the basis of sulcal contours, it is likely that other areas won´t be either. Thus Brodmann´s areas are a system that can be used for reference, but it is important to remember that there is no connection between cytoarchitectonic borders and circumvolutions.
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Why do we say that Amunt’s et al. are not interested in “speech”? What are they interested in? How do their findings connect with cognitive neuroscience of language?
The authors´ goal is not to study the functioning of the brain during language processing. In fact, they are not interested in any linguistic task, and that is why we say they are not interested in speech. Their main purpose is to improve the interpretation of functional imaging data. Since imaging data relies on cytoarchitectonic borders and Brodmann’s areas, it is important to have a clear understanding of the relation between Brodmann’s areas and cytoarthitectonic areas. This knowledge also contributes to the study of the cognitive neuroscience of language because functional imaging data is one of the main sources of information about the functioning of the brain during language processing.
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