The Enigmatic Reissner’s Fiber and the Origin of Chordates

Reissner’s fiber (RF) is a secreted filament that floats in the neural canal of chordates. Since its discovery in 1860, there has been no agreement on its primary function, and its strong conservation across chordate species has remained a mystery for comparative neuroanatomists. Several findings, including the chemical composition and the phylogenetic history of RF, clinical observations associating RF with the development of the neural canal, and more recent studies suggesting that RF is needed to develop a straight vertebral column, may shed light on the functions of this structure across chordates. In this article, we will briefly review the evidence mentioned above to suggest a role of RF in the origin of fundamental innovations of the chordate body plan, especially the elongation of the neural tube and maintenance of the body axis. We will also mention the relevance of RF for medical conditions like hydrocephalus, scoliosis of the vertebral spine and possibly regeneration of the spinal cord

Neuronal Density in Primary Visual Cortex (17 Visual Area), in Two Species of Octodon

Indexación: ScieloEstudios experimentales demuestran que modificaciones medioambientales pueden producir alteraciones en el desarrollo normal de la corteza cerebral visual y sus conexiones. Por otra parte, es posible que en condiciones naturales, las especies animales hayan desarrollado adaptaciones genéticas a las distintas condiciones de luminosidad en que realizan su actividad. Recientemente, se han observado variaciones significativas en la densidad neuronal cortical del área 17 (área visual primaria), en roedores silvestres con diferentes períodos diarios de actividad y relación filogenética distante (Abrothrix olivaceus y Phyllotis darwini), pero aún no se ha determinado la naturaleza genética o plástica de dichas diferencias. En este trabajo se compararon especies con una mayor cercanía filogenética, para disminuir al máximo la variable taxonómica. Se estudió la corteza visual primaria (área 17), de roedores silvestres nativos, de las especies Octodon degus (n=5) y Octodon bridgesi (n=3), pertenecientes a la Familia Octodontidae, con el propósito de evidenciar cambios a través de la medición de la densidad neuronal, mediante la técnica del disector óptico, en cortes de 40 µm, incluidos en celoidina y teñidos con Nissl. Complementariamente, se realizó una cuantificación de la densidad neuronal de la corteza motora de las especies en estudio. O. degus, que presenta un período de actividad diurna, evidenció una densidad neuronal menor en la corteza visual (34,32 ± 2,51 x 104 neuronas/mm3), que la observada en O. bridgesi (39,55 ± 0,64 x 104 neuronas/mm3), especie de período de actividad nocturna; lo cual fue estadísticamente significativo (t=3,44; p<0,05). Las diferencias encontradas se podrían relacionar con el tipo de condiciones de luminosidad en que se desenvuelven dichas especies, aunque no se puede descartar la influencia de otros factores. SUMMARY: Studies show that environmental modifications can produce profound alterations in the normal development of the visual cortex and its connectivity. For the other hand it is possible that in natural conditions, animal species have developed genetic adaptations to the different conditions of luminance in which they normally behave. Recently have observed significant changes in cortical neuronal density of area 17 (primary visual area), in two sympatric Chilean rodents with different daily activity (Phyllotis darwini and Abrothrix olivaceus), but have not yet determined the genetic nature or plastic such differences. In this paper we compared species with a closer phylogenetic relation so as to minimize the taxonomic variable. We studied the primary visual cortex (area 17) of wild rodents native of the species Octodon degus (n=5) and Octodon bridgesi (n=3), belonging to the Octodontidae family, in order to show changes in the neuronal density, using celloidin-embedded, 40µm-thickness Nissl sections, with the aid of an optical dissector. In addition, we performed a quantification of the neuronal density of the motor cortex of the species under study. O. degus, bearing a crepuscular-diurnal activity pattern, showed a lower neuronal density in the visual cortex (34.32 ± 2.51 x104 neuron/mm3) than that observed in O. bridgesi (39.55 ± 0.64 x104 neuron/mm3), a species that exhibits a nocturnal phase preference, which was statistically significant (t=3.44; p<0.05). These differences might be related to differences in daily activity in two species, but we cannot discount the influence of other factors

Evolutionary and classical concepts of homology: A reply to Aboitiz

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41688/1/10441_2004_Article_BF00154139.pd

From component reduced models to reduced modelling of multi-component systems

The present work focuses on the reduced modelling of multi-component systems, in particular on a two stages stamping chain process. Starting from snapshots collected by using the commercial software PAM-STAMP, the non-intrusive sparse-PGD constructor is used in order to build a parametric transfer function of each operation in a separated representation, circumventing the problem of the curse of dimensionality. Moreover, in order to fill the gap between this deterministic solution and the measured fields and safely applied control strategies, data driven-modeling can be employed according to the new “hybrid twin” methodology

Culture and Evolution

This chapter captures extensive discussions between people with different forms of expertise and viewpoints. It explores the relationships between language and music in evolutionary and cultural context. Rather than trying to essentialize either, they are characterized pragmatically in terms of features that appear to distinguish them (such as language’s compositional propositionality as opposed to music’s foregrounding of isochronicity), and those that they evidently share. Factors are considered that consti- tute proximate motivations for humans to communicate through language and music, ranging from language’s practical value in the organization of collective behavior to music’s significant role in eliciting and managing prosocial attitudes. Possible distal motivations are reviewed for music and language, in terms of the potentially adap- tive functions of human communication systems, and an assessment is made of the advantages which might accrue to flexible communicators in the light of ethological and archaeological evidence concerning the landscape of selection. Subsequently, the possible evolutionary relationships between music and language are explored, within a framework supplied by six possible models of their emergence. Issues of the roles of culture and of biology in the evolution of communication systems are then addressed within the framework of triadic niche construction, and the chapter concludes by sur- veying available comparative and phylogenetic issues that might inform the debate