User:Jinhl/Paleoneurology

Wikipedia Proposal: Paleoneurology

Presented by: Michael Derobertis, Lauren Okada, Ryan Scully, Hope Jin

Paleoneurology is the study of brain evolution by examining anatomical and morphological endocranial traits and volumes of endocranial casts (or endocasts).

Endocast of australopithecus sediba

Endocasts are formed either naturally, when a skull is filled with sediment that solidifies and fossilizes, or artificially; endocasts may also be created in the laboratory by casting the interior of the skull with a casting medium such as latex or silicone. A well-preserved endocast may reveal even specific anatomical traits, such as vascular patterns or cerebral asymmetries.

General definition

Paleoneurology focuses primarily on the models of endocasts to study the evolution of the brain. Mostly considered a subdivision of neuroscience, paleoneurology combines techniques from other fields of study including paleontology and archaeology.

Hominid Paleoneurology

Hominid paleoneurology is the study of brain evolution by directly examining the fossil record of humans and their closest hominid relatives (defined as species more closely related to humans than chimpanzees). Paleoneurologists analyze endocasts that reproduce details of the external morphology of brains that have been imprinted on the internal surfaces of skulls.

History

Humans have had a long interest in the brain and its functions. The first recorded study of the brain and its functions was from a papyrus text written by the ancient Egyptians during the 17th century BCE. The document details 48 medical ailments and makes references to how to deal with head wounds. Much later in the 6th century BCE the ancient Greeks began to focus on studies of the brain and the relationship between the optic nerve and the brain. Studies of brain evolution, however, did not come about until much later in human history.

In the late part of the 18th century and the early part of the 19th century thought of brain evolution was beginning. Two main views of life sprung forth; rationalism and transcendentalism. These formed the basis for the thought of scientists in this period. Georges Cuvier and Étienne Geoffroy St. Hilaire sprung forth as leaders in the new field of comparative anatomy. Curvier believed in the ability to create a functional morphology based simply on empirical evidence. He stressed function of the organ must coincide with its form. Geoffroy put a heavy emphasis on intuition as a method of understanding. His thought was based on two principles: the principle of connections and the principle of unity of plan. He was one of the first to look for homologies in organs across species, though he believed that this was evidence of a universal plan, not decent with modification.

The late part of the 19th century in comparative anatomy was heavily influenced by the work of Charles Darwin in the Origin of Species in 1859. This work completely changed the views of comparative anatomists. Within 8 years of Darwin's release of the origin of species, his views on decent from a common ancestor were widely accepted. This lead to a movement of trying to understand how different parts of the brain evolved.

The next major innovation which helped bring about paleoneurology was the microscope. The microscope was invented in the 17th century, but it was only used in biology in the late 19th century. The techniques on how to look at brain cells under a microscope took a long time to perfect. In 1873, with this tool in hand Camillo Golgi began to cellularly detail the brain and look at techniques to perfect axonal microscoping. Ludwig Edinger took advantage of this and came up with a new branch of anatomy called comparative neuroanatomy. Edinger held that vertebrates evolved in a linear progressive series. He also thought that changes in the brain were based on a series of additions and differentiations and that the most highly, complex brains were those that were the most encephalized.

The period of 1885-1935 was an explosion of ideas in comparative neuroanatomy. This era culminated in the publication of "The Comparative Anatomy of the Nervous System" by Arienns, Kappers, Huber, and Cosby. This explosion in ideas lead to Tilly Edinger founding the branch of paleoneurology int the time period of 1935-1960. Her paper, Die Fossilem Gehime, lead to the basis of the new branch. She was the first to study fossil records of brains of vertebrates in order to understand the evolutionary mechanisms that occurred.

Importance of Paleoneurolgy

The study of paleoneurology allows researchers to examine the evolutionary nature of human encephalization. Traditionally, paleoneurologists have focused on determining the volume of the ancient brain and the patterns that emerged among related species. By finding these measurements, researchers have been able to predict the average body weight of species. Endocasts also reveal traits of the ancient brain including relative lobe size, blood supply, and other general insight into the anatomy of evolving species.

Limitations

While paleoneurology is useful in the study of brain evolution, certain limitations to the information this study provides do exist. First, fossil preservation is a necessary aspect to ensure accuracy of the endocasts studied. Weathering, erosion, and overall gradual disfiguration may alter the naturally recovered endocasts or endocasts created from existing fossils. The morphology of the brain can also be difficult to both quanitfy and describe, further complicating the observations made from the study of endocasts. Additionally, paleoneurology provides very little insight into the actual anatomy within the brains of species studied; the study of endocasts is limited to the external anatomy only. The relationship among endocranial traits remains elusive. Comparative paleoeneurology reveals mostly only differences in endocranial size among related species, such as Gorilla gorilla. Since there is no proven direct relationship between brain size and intelligence, only inferences can be made regarding the developing behavior of ancient relatives of the Homo genus.

These limitations of paleoneurology are currently being dealt with by the development of more advanced tools to refine the study of endocasts.

Methods of Research

General

Paleoneurology revolves around the analysis of endocasts. Much of this analysis is focused on interpreting sulcal patterns, which is difficult because traces are often hardly recognizable, and there are not clear landmarks to use as reference points. Furthermore, the only clear reference plane is the midsagittal one, which is marked by distinct cerebral asymmetries. Since the obtaining clear data from fossil details is usually very difficult, much debate arises over interpretations. Experience is a very important factor in endocast analysis. Therefore, a large portion of the field of paleoneurology arises out of developing more detailed procedures that increase the resolution and the reliability of interpretations.

Overall Brain Volume

Statistical analysis of brain endocasts give information on the increases in overall brain volume or endocranial volume. Because endocasts are not exact replicas, or exact casts, of once living brain, computer algorithms and CT scans are needed to calculate endocranial volume. The calculated endocranial volume includes the meninges, cerebral fluid, and cranial nerves. Therefore these volumes end up larger than the once living brain. This information is useful for calculating relative brain size, RBS, and encephalization quotient, EQ. The corresponding body weight of the subject must also be known to calculated RBS. RBS is calculated by dividing the weight of the brain by body weight. EQ can be determined several different ways depending on the data set used. For example, Holloway and Post calculate EQ by the following equation: EQ = Brain weight (of any species)/0.12 × Body weight^.66..

Convolution Pattern and Cerebral Organization

It is possible to observe underlying gyri and sulci patterns if an endocast is accurate or preserved. The surface of the brain is often referred to as smooth and fuzzy, which makes analysis inexact. Therefore, the lack of certainty in these patterns often leads to controversy.

Asymmetry

The degree of asymmetry between right and left hemispheres is a point of interest to most paleoneurologists because it could be linked to handedness of the specimen. Modern human brain show asymmetries in Broca's cap regions of the frontal cortex that correspond to different handedness. Certain asymmetries have been documented on Homo erectus specimens such as the Homo redolfensis specimen from 1.8 million years ago that resemble the same asymmetries from modern humans. It is possible that asymmetry can also lead to findings about language development.

Relative Lobe Size

It is impossible to determine accurate location of the central or precentral sulci from an endocast. Still it can provide a rough idea of lobe sizes.

Methodological Development

Controversy over different interpretations of the same endocasts has spurred developement of new research methods in the field of paleoneurology. For example, between 1983 and 1985 two paleoneurologists, Holloway and Falk, published at least four papers that bolstered their own original opinion on the analysis of an endocast prepared from Australopithecus afarensis, one of the oldest known hominids. These papers developed multiple techniques in endocast analysis including the use of stereoplotting to transfer sulci between differently shaped endocasts, measurement of indexes from photographs rather than directly from specimens, and confounding of measurements taken directly from specimens and those taken from photographs.

Current Research Advancements

Advancements in Radiographic Techniques

Radiographic technique such as computed tomographic imaging, or CT scans, coupled with computer programing have been used to analyze brain endocasts as early as 1906. Recent development of advanced computer graphics technology have allowed scientists to more accurately analyze of brain endocasts. M. Vannier and G. Conroy of Washington University School of Medicine have developed a system that images and analyzes surface morphologies in 3D. Scientists are able to encode surface landmarks that allows them to analyze sulcal length, cortical asymmetries and volume. Radiologist, paleoanthropologists, computer scientists in both the United States and Europe have collaborated to study such fossils using virtual techniques.

Studies of Interest

Brain Shape, Intelligence, and Cognitive Performance

Recent studies by Emiliano Bruner, Manuel Martin-Loechesb, Miguel Burgaletac, and Roberto Colomc have investigated the connection between midsagittal brain shape and mental speed. This study incorporated human subjects' cognitive testing in relationship to extinct humans. They used 2D from 102 MRI-scanned young adult human for comparison. Such correlations are small, suggesting that the influence of midsagittal brain geometry on individual cognitive performance is negligible but still provides useful information of evolutionary traits of the brain. Areas associated with the parietal cortex appear to be involved in relationships between brain geometry and mental speed.

Degenerative Diseases and Functional Disorder

Recent studies led by J. Ghika determine to understand the evolution of several neurodegenerative disease. The aim is to determine the genetic mechanisms that lead to focal or asymmetrical brain atrophy resulting in syndromic presentations that affect gait, hand, language, cognition, mood and behaviour disorders. Most risk-factors for neurodegenerative disease places highest priority on age, however, evolution may play a role.

Division of workload:

We have decided to schedule times that we can all meet to work together on the various parts of this project. We think that this is the best way for all of us to discuss and understand fully the topic so that we can create a cohesive article.