Paleoneurology
Encyclopedia
Paleoneurology is the study of brain evolution by analysis of brain endocasts to determine endocranial traits and volumes. The cranium is unique in that it grows in response to the growth of brain tissue rather than genetic guidance, as is the case with bones that support movement. Fossil skulls can be compared with each other as well as the skulls of recently deceased individuals and even those of other species to make inferences about functional anatomy, physiology and phylogeny. Paleoneurology is in a large part influenced by current developments in neuroscience as a whole; without substantial knowledge about current functionality, it is impossible to make inferences about the functionality of ancient brains. Advances in technology are also necessary for proper analysis to be made.
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.
, paleoneurology combines techniques from other fields of study including paleontology
and archaeology
.
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 descent 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.
ary 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.
. 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.
s. 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.
, cerebrospinal 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..
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.
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
Latex
Latex is the stable dispersion of polymer microparticles in an aqueous medium. Latexes may be natural or synthetic.Latex as found in nature is a milky fluid found in 10% of all flowering plants . It is a complex emulsion consisting of proteins, alkaloids, starches, sugars, oils, tannins, resins,...
or silicone
Silicone
Silicones are inert, synthetic compounds with a variety of forms and uses. Typically heat-resistant and rubber-like, they are used in sealants, adhesives, lubricants, medical applications , cookware, and insulation....
. 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 neuroscienceNeuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
, paleoneurology combines techniques from other fields of study including paleontology
Paleontology
Paleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
and archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
.
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
Rationalism
In epistemology and in its modern sense, rationalism is "any view appealing to reason as a source of knowledge or justification" . In more technical terms, it is a method or a theory "in which the criterion of the truth is not sensory but intellectual and deductive"...
and transcendentalism
Transcendentalism
Transcendentalism is a philosophical movement that developed in the 1830s and 1840s in the New England region of the United States as a protest against the general state of culture and society, and in particular, the state of intellectualism at Harvard University and the doctrine of the Unitarian...
. 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
Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of organisms. It is closely related to evolutionary biology and phylogeny .-Description:...
. 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
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
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 descent 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
Camillo Golgi
Camillo Golgi was an Italian physician, pathologist, scientist, and Nobel laureate.-Biography:Camillo Golgi was born in the village of Corteno, Lombardy, then part of the Austrian Empire. The village is now named Corteno Golgi in his honour. His father was a physician and district medical officer...
began to cellularly detail the brain and look at techniques to perfect axonal microscoping. Ludwig Edinger
Ludwig Edinger
Ludwig Edinger was an influential German anatomist and neurologist and co-founder of the University of Frankfurt. In 1914 he was also appointed the first German professor of neurology....
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.
Significance
The study of paleoneurology allows researchers to examine the evolutionEvolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary nature of human encephalization
Encephalization
Encephalization is defined as the amount of brain mass exceeding that related to an animal's total body mass. Quantifying an animal's encephalization has been argued to be directly related to that animal's level of intelligence. Aristotle wrote in 335 B.C...
. 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
Lobes of the brain
Brain lobes were originally a purely anatomical classification, but have been shown also to be related to different brain functions. The telencephalon , the largest portion of the human brain, is divided into lobes, but so is the cerebellum...
, 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 gorillaWestern Gorilla
The western gorilla is a great ape and the most populous species of the genus Gorilla.-Taxonomy:Nearly all of the individuals of this taxon belong to the western lowland gorilla subspecies whose population is approximately 95,000 individuals...
. 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
Homo
Homo may refer to:*the Greek prefix ὅμο-, meaning "the same"*the Latin for man, human being*Homo, the taxonomical genus including modern humans...
genus.
These limitations of paleoneurology are currently being dealt with by the development of more advanced tools to refine the study of endocasts.
General
Paleoneurology revolves around the analysis of endocastEndocast
An endocast is the internal cast of a hollow object, often specifically used for an endocasts of the cranial vault. Endocasts can be man-made for examining the properties of a hollow, inaccessible space, or occur naturally through fossilisation....
s. 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 meningesMeninges
The meninges is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system.-Dura...
, cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...
, and cranial nerves
Cranial nerves
Cranial nerves are nerves that emerge directly from the brain, in contrast to spinal nerves, which emerge from segments of the spinal cord. In humans, there are traditionally twelve pairs of 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 gyriGyrus
A gyrus is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci .-Notable gyri:* Superior frontal gyrus, lat. gyrus frontalis superior* Middle frontal gyrus, lat. gyrus frontalis medius...
and sulci
Sulcus
Sulcus may refer to:* Sulcus , a groove, crevice or furrow in medicine, botany, and zoology* Sulcus , a long parallel groove on a planet or a moon-See also:...
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.