Dorsal Ventricular Ridge

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The Kolb and Whishaw
book (K&W) doesn't mention the dorsal ventricular ridge (DVR).  This isn't surprising since K&W is focused on humans, and humans don't have a DVR. 

Similarly, Wikipedia does not have a page for the DVR.   However, it does mention the DVR in reptiles and birds at:

Pallium (neuroanatomy) (Wiki)  
 

The evolutionary origin of the mammalian isocortex: insights from molecular developmental biology (Goog)   
    Full text available online for free. 
Abstract   

    "The isocortex is a distinctive feature of the mammalian brain, which has no clear counterpart in the cerebral hemispheres of other amniotes. Historically, there have been long-standing controversies regarding possible homologues of this structure in reptiles and birds.
    In these vertebrate classes, a structure denominated dorsal ventricular ridge develops in the lateral aspect of the hemisphere and, like the mammalian isocortex, receives ascending auditory and visual tectofugal projections. On these grounds, it has been postulated that part of the dorsal ventricular ridge is homologue to part of the mammalian isocortex (i.e. the auditory and the extrastriate visual cortices).
    Dissenting views have claimed that the dorsal ventricular ridge originates from a topographically different part of the hemisphere than the isocortex, and therefore there is no embryonic similarity between these two structures. Furthermore, recent evidence on the expression patterns of regulatory genes strongly suggests that a large part of the dorsal ventricular ridge arises from a region denominated the intermediate territory or ventral pallium, which in mammals gives rise to parts of the amygdalar complex among other structures.
    Considering that embryological criteria are in some cases more reliable to determine homology than comparisons of adult states, we are inclined for the developmental approach, which prescribes non-homology between the isocortex and the dorsal ventricular ridge. Additionally, we suggest a scenario for the origin of the isocortex as an expansion of the reptilian dorsal cortex, which is consistent with current evidence.
"   
My comment
    If the mammalian isocortex evolved "
as an expansion of the reptilian dorsal cortex", why don't mammals have a dorsal ventricular ridge?     

HTML:     

http://cogprints.org/132/1/BBS12.html   
My comment:
Unfortunately, the HTML doesn't provide the figures.     


Comparative development of the mammalian isocortex and the reptilian dorsal ventricular ridge.  Evolutionary considerations.  (Goog to PubMed)
    Full length article available online for free. 
Abstract: 
    "There has been a long debate about a possible homology between parts of the dorsal ventricular ridge (DVR) of reptiles and birds, and parts of the mammalian isocortex. Correspondence between these structures was originally proposed on the basis of connectional similarities between the DVR of birds and the mammalian auditory and extrastriate visual isocortical areas. Furthermore, the proposal of homology includes the possible embryological similarity of cells that give rise to the DVR and cells that give rise to the isocortex.
    Against this concept it has been claimed that the DVR and the isocortex originate in topographically different pallial compartments, an interpretation that is supported by recent developmental and molecular data. Other studies indicate that migrating cells can cross the borders between adjacent developmental compartments: cells that originate in subcortical components contribute a number of interneurons to the developing isocortex via tangential migration. This mechanism might reconcile the proposed homology with the developmental evidence, since cells originating in one compartment (the one corresponding to DVR) may become included in structures generated in a different compartment (the one corresponding to isocortex).
    However, there is no evidence in mammals of a structure homologous to the embryonic DVR that can produce isocortical neurons. In order to fully clarify the problem of isocortical origins, further comparative studies are needed of the embryonic development of the lateral and dorsal aspects of the cerebral hemispheres in amphibians, reptiles and mammals.
"     

HTML   


  Figure 1.

     "Diagram of the cerebral hemisphere of a reptile (Gekko gecko).
    The lateral cortex (L) receives projections from the olfactory bulb and is comparable to the mammalian olfactory cortex.
    The dorsal cortex (D) – its lateral aspect, and the pallial thickening which is particularly prominent in turtles and is not shown here – receive visual projections from the dorsal lateral geniculate nucleus (Ulinski, 1990), and have been proposed to be comparable to the primary visual cortex or striate cortex of mammals (Nauta and Karten, 1970).
    The medial (M) and the dorsomedial (DM) cortices (and also the medial aspect of the dorsal cortex) (Guirado et al., 1998) are considered to be homologues to the mammalian hippocampal formation (Nieuwenhuys et al., 1998).
    The anterior dorsal ventricular ridge (ADVR) has been compared to several mammalian telencephalic structures, among them the corpus striatum (Ariëns Kappers et al., 1936), the extrastriate isocortex (Karten, 1969), the basolateral amygdala (Bruce and Neary, 1995; Smith-Fernández et al., 1998), and the endopiriform nucleus (Striedter, 1997).  
    Medial is to the left. S, striatum; Se, septum; V, lateral ventricle. Redrawn from Butler (Butler, 1976).
"   
My comment
    The 'L' label for the lateral cortex has been cut off.  It belongs to the line extending down and to the right. 


Evolutionary divergence of the reptilian and mammalian brains: considerations on connectivity and development.  (PubMed)   
Only abstract available online. 
    "
The isocortex is a distinctive feature of the mammalian brain, with no clear counterpart in other amniotes. There have been long controversies regarding possible homologues of this structure in reptiles and birds.
    The brains of the latter are characterized by the presence of a structure termed dorsal ventricular ridge (DVR), which receives ascending auditory and visual projections, and has been postulated to be homologous to parts of the mammalian isocortex (i.e., the auditory and the extrastriate visual cortices).
    Dissenting views, now supported by molecular evidence, claim that the DVR originates from a region termed ventral pallium, while the isocortex may arise mostly from the dorsal pallium (in mammals, the ventral pallium relates to the claustroamygdaloid complex). Although it is possible that in mammals the embryonic ventral pallium contributes cells to the developing isocortex, there is no evidence yet supporting this alternative.
    The possibility is raised that the expansion of the cerebral cortex in the origin of mammals was product of a generalized dorsalizing influence in pallial development, at the expense of growth in ventral pallial regions. Importantly, the evidence suggests that organization of sensory projections is significantly different between mammals and sauropsids.
    In reptiles and birds, some sensory pathways project to the ventral pallium and others project to the dorsal pallium, while in mammals sensory projections end mainly in the dorsal pallium. We suggest a scenario for the origin of the mammalian isocortex which relies on the development of associative circuits between the olfactory, the dorsal and the hippocampal cortices in the earliest mammals.
"   


Homology in the evolution of the cerebral hemispheres.  The case of the reptilian dorsal ventricular ridge and its possible homology with the mammalian neocortex.  (PubMed)   
Only abstract available online. 
    "
The present paper reviews some issues related to the evolutionary origin of distinct components of the cerebral hemispheres in vertebrates, which entails the problem of biological homology between anatomical structures. Considering that the term homology is essentially a comparative concept, making emphasis on structural correspondences between organs or body parts, I use the term evolutionary, or phylogenetic homology to denote a common evolutionary origin of two characters. In particular, the controversy of a possible phylogenetic homology between reptilian dorsal ventricular ridge (DVR) and parts of mammalian neocortex is analyzed in some detail.
    Although it is likely that DVR is a derived character of reptiles while neocortex is a derived character of mammals, the two structures might still originate from the same primordial anlage in the common ancestor. One main problem in the comparison of telencephalic components between reptiles and mammals is that the protrusion of reptilian DVR into the lateral ventricle causes a distortion of the topographic relations in the hemisphere. In order to determine possible homologues of DVR, it is necessary to establish clear-cut telencephalic landmarks. Since lateral cortex is similarly localized in reptiles and mammals, it is suggested that the embryonic position and timing of development of reptilian DVR in relation to lateral cortex may give special insight on the phylogenetic origins of the former.
    If, as implied by the work of early authors, DVR arose in evolution through an extension of the embryonic period of neuronal proliferation and migration, it may be considered as a genuine novelty in brain evolution. It is also proposed that, regardless of whether DVR and extrastriate neocortex can or cannot be considered phylogenetic homologues, some of the integrative functions performed by them might have a common evolutionary origin, that became localized in reptilian DVR and in mammalian extrastriate neocortex.
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