User:Aria.fortier/Evolutionary neuroscience

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Evolutionary neuroscience is the scientific study of the evolution of nervous systems. Evolutionary neuroscientists investigate the evolution and natural history of nervous system structure, functions and emergent properties. The field draws on concepts and findings from both neuroscience and evolutionary biology. Historically, most empirical work has been in the area of comparative neuroanatomy, and modern studies often make use of phylogenetic comparative methods. Selective breeding and experimental evolution approaches are also being used more frequently.

Conceptually and theoretically, the field is related to fields as diverse as cognitive genomics, neurogenetics, developmental neuroscience, neuroethology, comparative psychology, evo-devo, behavioural neuroscience, cognitive neuroscience, behavioural ecology, biological anthropology and sociobiology. Evolutionary neuroscientists examine changes in genes, anatomy, physiology, and behaviour to study the evolution of changes in the brain. They study a multitude of processes including the evolution of vocal, visual, auditory, taste, and learning systems as well as language evolution and development. In addition, evolutionary neuroscientists study the evolution of specific areas or structures in the brain such as the amygdala, forebrain and cerebellum as well as the motor or visual cortex.

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History[edit] Studies of the brain began during ancient Egyptian times but studies in the field of evolutionary neuroscience began after the publication of Darwin's On the Origin of Species in 1859. At that time, brain evolution was largely viewed at the time in relation to the incorrect scala nature. Phylogeny and the evolution of the brain were still viewed as linear. During the early 20th century, there were several prevailing theories about evolution. Darwinism was based on the principles of natural selection and variation, Lamarckism was based on the passing down of acquired traits, Orthogenesis was based on the assumption that the tendency toward perfection steers evolution, and Saltationism argued that discontinuous variation creates new species. Darwin's became the most accepted and allowed people to start thinking about the way animals and their brains evolve.

The 1936 book The Comparative Anatomy of the Nervous System of Vertebrates Including Man by the Dutch neurologist C.U. Ariëns Kappers (first published in German in 1921) was a landmark publication in the field. Following the Evolutionary Synthesis, the study of comparative neuroanatomy was conducted with an evolutionary view, and modern studies incorporate developmental genetics. It is now accepted that phylogenetic changes occur independently between species over time and can not be linear. It is also believed that an increase in brain size correlates with an increase in neural centres and behaviour complexity.

Major Arguments[edit]
Over time, there are several arguments that would come to define the history of evolutionary neuroscience. The first is the argument between Etienne Geoffro St. Hilaire and George Cuvier over the topic of "common plan versus diversity". Geoffrey argued that all animals are built based on a single plan or archetype and he stressed the importance of homologies between organisms, while Cuvier believed that the structure of organs was determined by their function and that knowledge of the function of one organ could help discover the functions of other organs. He argued that there were at least four different archetypes. After Darwin, the idea of evolution was more accepted, and Geoffrey's idea of homologous structures was more accepted. The second major argument is that of the Scala Naturae (scale of nature) versus the phylogenetic bush. The Scala Naturae, later also called the phylogenetic scale, was based on the premise that phylogenies are linear or like a scale while the phylogenetic bush argument was based on the idea that phylogenies were nonlinear and resembled a bush more than a scale. Today it is accepted that phylogenies are nonlinear. A third major argument dealt with the size of the brain and whether relative size or absolute size was more relevant in determining function. In the late 18th century, it was determined that the brain-to-body ratio reduces as body size increases. However more recently, there is more focus on absolute brain size as this scales with internal structures and functions, with the degree of structural complexity, and with the amount of white matter in the brain, all suggesting that absolute size is a much better predictor of brain function. Finally, a fourth argument is that of natural selection (Darwinism) versus developmental constraints (concerted evolution). It is now accepted that the evolution of development is what causes adult species to show differences and evolutionary neuroscientists maintain that many aspects of brain function and structure are conserved across species.

Techniques
Throughout history, we see how evolutionary neuroscience has been dependent on developments in biological theory and techniques. The field of evolutionary neuroscience has been shaped by the development of new techniques that allow for the discovery and examination of parts of the nervous system. In 1873, Camillo Golgi devised the silver nitrate method which allowed for the description of the brain at the cellular level as opposed to simply the gross level. Santiago Ramon and Pedro Ramon used this method to analyze numerous parts of the brain, broadening the field of comparative neuroanatomy. In the second half of the 19th century, new techniques allowed scientists to identify neuronal cell groups and fibre bundles in brains. In 1885, Vittorio Marchi discovered a staining technique that let scientists see induced axonal degeneration in myelinated axons, in 1950, the “original Nauta procedure” allowed for more accurate identification of degenerating fibres, and in the 1970s, there were several discoveries of multiple molecular tracers which would be used for experiments even today. In the last 20 years, cladistics has also become a useful tool for looking at variation in the brain.

Evolution of the Human Brain
Darwin's theory allowed people to start thinking about the way animals and their brains evolve.

Amphioxi

The amphioxus was a small marine animal that looked like a worm. Something particular about them is that they didn’t have any brains. They only had a small nervous system that was actually a teeny clump of cells. Also, the amphioxus didn’t experience senses like humans. With no eyes, they only had a few cells that could detect changes in lights, and they couldn’t hear because they didn’t have any ears. To eat, they planted themselves in the seafloor and they would eat every minuscule creature who entered their mouth.

The amphioxus is the distant cousin of humans. All species had a common ancestor including humans that resembles very much today's amphioxus.

5500 million years ago, amphioxus and other simple creatures populated the oceans. During the Cambrian period, a new concept entered this world: hunting. Even though hunting doesn’t require a brain, the fact that some creatures could now sense the presence of another one was a big step in their evolution. More sophisticated sensory systems were developed. They could now see and sense their environment. They could detect objects through vibration in the water like sharks today. These new advances are really what set animals apart from amphioxi because these amphioxi didn't get the chance to develop as much. Next, the fact that animals were now able to hunt and get hunted, they needed more sophisticated movements. Because the amphioxus rather had a rudimentary diet, the amphioxus did not develop these new skills. Once these changes happened, evolution favoured those who performed their tasks best. This is called natural selection. This is where the body budget enters. Newer animals developed cardiovascular systems, respiratory systems, and adaptable immune systems. These new systems made body budgeting even more challenging than before. After this evolution, these animals needed a centre of command that would make their body run efficiently. They needed a brain. After this, animals evolved different brains according to their needs. Therefore, the most important job of the brain is to control the body.

Reptile Brain

The cerebral cortex of reptiles resembles that of mammals, although simplified. Although the evolution and function of the human cerebral cortex is still shrouded in mystery, we know that it is the most dramatically changed part of the brain during recent evolution. With the help of researchers, we know that reptiles have similar types of neurons as humans even though humans are not evolved from the reptile species.

Tunicate

The tunicate, also known as sea squirts, is a marine invertebrate. The organisms life begins in a mobile larva stage. Once fully developed, the larva finds a rock and bonds itself to it then begins its changeover. The larva is no longer in need of many of its appendages due to its new lifestyle. The species starts to absorb its unused or unwanted parts, such as the cerebral ganglion.

Visual perception
Research about how visual perception has developed in evolution is today best understood through studying present-day primates since the organisation of the brain cannot be ascertained only by analyzing fossilized skulls.

The brain interprets visual information in the occipital lobe, a region in the back of the brain. The occipital lobe contains the visual cortex and the thalamus, which are the two main actors in processing visual information. The process of interpreting information has proven to be more complex than "what you see is what you get". Misinterpreting visual information is more common than previously believed.

As knowledge of the human brain has evolved, researchers discover that our visual perception is much closer to a construction of the brain than a direct "photograph" of what is in front of us. This can lead to misperceiving certain situations or elements in the brain's attempt to keep us safe. For example, an on-edge soldier believes a young child with a stick is a grown man with a gun, as the brain's sympathetic system, or fight-or-flight mode, is activated.

The rabbit–duck illusion is a famous ambiguous image in which a rabbit or a duck can be seen. The earliest known version is an unattributed drawing from the 23 October 1892 issue of Blätter, a German humour magazine. Wikipedia

An example of this phenomenon can be observed in the Rabbit-Duck illusion. Depending on how the image is looked at, the brain can interpret the image of a rabbit, or a duck. There is no right or wrong answer, but it is proof that what is seen may not be the reality of the situation.

Auditory Perception
The organisation of the human auditory cortex is divided into core, belt and parable. This closely resembles that of present-day primates.

The concept of auditory perception resembles visual perception very similarly. Our brain is wired to act on what it expects to experience. The sense of hearing helps situate an individual, but it also gives them hints about what else is around them. If something moves, they know approximately where it is and by the tone of it, the brain can predict what moved. If someone were to hear leaves rustling in a forest, the brain might interpret that sound as being an animal which could be a dangerous factor, but it would simply be another person walking. The brain can predict many things based on what it is interpreting, however, those predictions may not all be true.

Language development
Evidence of a rich cognitive life in primate relatives of humans is extensive, and a wide range of specific behaviours in line with Darwinian theory is well documented. However, until recently, research has disregarded nonhuman primates in the context of evolutionary linguistics, primarily because unlike vocal learning birds, our closest relatives seem to lack imitative abilities. Evolutionary speaking, there is great evidence suggesting a genetic groundwork for the concept of languages has been in place for millions of years, as with many other capabilities and behaviours observed today.

While evolutionary linguists agree on the fact that volitional control over vocalising and expressing language is a pretty recent leap in the history of the human race, that is not to say auditory perception is a recent development as well. Research has shown substantial evidence of well-defined neural pathways linking cortices to organise auditory perception in the brain. Thus, the issue lies in our abilities to imitate sounds.

Beyond the fact that primates may be poorly equipped to learn sounds, studies have shown them to learn and use gestures far better. Visual cues and motoric pathways developed millions of years earlier in our evolution, which seems to be one reason for our earlier ability to understand and use gestures.

Body Budgeting

In scientific terms, body budgeting is also known as allostasis. Body budgeting is a way for our body to prepare and predict our body's needs before they arise and it's a way it budgets energy to keep you alive and moving. Your brain doesn't help you budget for your conscious, thoughtful decision nor weigh your pros and cons. Instead, its role is to regulate water, salt, glucose, fat, dopamine, oxygen and many more.

External links[edit]

 * Brain Behavior and Evolution - (Journal)
 * "Comparative Vertebrate Neuroanatomy: Evolution and Adaptation" - Ann B. Butler, William Hodos
 * Sinauer.com - Principles of Brain Evolution Georg F. Striedter, University of California, Irvine' (book review, 2004)