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Paleoneurobiology is the study of brain evolution by analysis of brain
endocast An endocast is the internal cast of a hollow object, often referring to the cranial vault in the study of brain development in humans and other organisms. Endocasts can be artificially made for examining the properties of a hollow, inaccessible sp ...
s to determine endocranial traits and volumes. Considered a subdivision of
neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, developme ...
, paleoneurobiology combines techniques from other fields of study including
paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...
and
archaeology Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landsca ...
. It reveals specific insight concerning
human evolution Human evolution is the evolutionary process within the history of primates that led to the emergence of '' Homo sapiens'' as a distinct species of the hominid family, which includes the great apes. This process involved the gradual development o ...
. 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
bone A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
s that support movement. Fossil
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
s and their endocasts can be compared to each other, to the skulls and fossils of recently deceased individuals, and even compared to those of other species to make inferences about functional
anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
,
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemical ...
and
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...
. Paleoneurobiology is in large part influenced by developments in
neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, developme ...
as a whole; without substantial knowledge about current functionality, it would be impossible to make inferences about the functionality of ancient
brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a ve ...
s. Hominid paleoneurobiology refers specifically to the study of brain evolution by directly examining the
fossil record A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
of humans and their closest hominid relatives (defined as species more closely related to humans than chimpanzees). Paleoneurobiologists analyze endocasts that reproduce details of the external
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...
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 Ancient Greece ( el, Ἑλλάς, Hellás) was a northeastern Mediterranean civilization, existing from the Greek Dark Ages of the 12th–9th centuries BC to the end of classical antiquity ( AD 600), that comprised a loose collection of cult ...
began to focus on studies of the brain and the relationship between the
optic nerve In neuroanatomy, the optic nerve, also known as the second cranial nerve, cranial nerve II, or simply CN II, is a paired cranial nerve that transmits visual information from the retina to the brain. In humans, the optic nerve is derived fro ...
and the brain. Studies of brain evolution, however, did not come about until much later in human history. Comparative anatomy began its emergence in the latter part of the 19th century. Two main views of life sprung forth;
rationalism In philosophy, rationalism is the epistemological view that "regards reason as the chief source and test of knowledge" or "any view appealing to reason as a source of knowledge or justification".Lacey, A.R. (1996), ''A Dictionary of Philosophy ...
and
transcendentalism Transcendentalism is a philosophical movement that developed in the late 1820s and 1830s in New England. "Transcendentalism is an American literary, political, and philosophical movement of the early nineteenth century, centered around Ralph Wald ...
. These formed the basis for the thought of scientists in this period. Georges Cuvier and Étienne Geoffroy St. Hilaire were leaders in the new field of comparative anatomy. Cuvier 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, in contrast, 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. Geoffroy was one of the first to look for homologies in organs across species, though he believed that this was evidence of a universal plan rather than descent with modification. The late part of the 19th century in comparative anatomy was heavily influenced by the work of
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended ...
in the ''
On the Origin of Species ''On the Origin of Species'' (or, more completely, ''On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life''),The book's full original title was ''On the Origin of Species by Me ...
'' 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 led to a shift in trying to understand how different parts of the brain evolved. The next major innovation that helped to bring about paleoneurobiology was the
microscope A microscope () is a laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic means being invisi ...
. Although the microscope was invented in the 17th century, it was only used in biology in the beginning in the late 19th century. The techniques of observing brain cells under a microscope took a long time to refine. In 1873, with this tool in hand,
Camillo Golgi Camillo Golgi (; 7 July 184321 January 1926) was an Italian biologist and pathologist known for his works on the central nervous system. He studied medicine at the University of Pavia (where he later spent most of his professional career) betwee ...
began to cellularly detail the brain and employ 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 paper influenced Tilly Edinger and she later became the founder of paleoneurobiology.


Tilly Edinger

Ottilie "Tilly" Edinger was born in
Frankfurt Frankfurt, officially Frankfurt am Main (; Hessian: , " Frank ford on the Main"), is the most populous city in the German state of Hesse. Its 791,000 inhabitants as of 2022 make it the fifth-most populous city in Germany. Located on it ...
, Germany, in 1897. Her father Ludwig Edinger, himself a pioneer in comparative neurology, provided Tilly with invaluable exposure to his field and the scientific community at large. Tilly had many private tutors before attending Schiller-Schule, the only secondary school for girls in Frankfurt at that time. Tilly Edinger continued her schooling with university studies in
zoology Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and ...
,
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ea ...
, and paleontology. While preparing her doctoral dissertation, Edinger encountered a natural brain endocast of ''
Nothosaurus ''Nothosaurus'' ("false lizard", from the Ancient Greek (), "illegitimate", and (), "lizard") is an extinct genus of sauropterygian reptile from the Triassic period, approximately 240–210 million years ago, with fossils being distributed fro ...
'', a marine reptile from the Mesozoic era. Edinger's first paper, published in 1921, centered on the characteristics of the ''Nothosaurus'' specimen. Prior to the publication of her work, inferences about the evolution of the vertebrate brain were made exclusively through comparative anatomy of extant fish, amphibian, reptile, bird, and mammal brains. Tilly Edinger's background in
neurology Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...
and paleontology paved the way for her to integrate comparative anatomy and stratigraphic sequence, thus introducing the concept of time to neurology and creating the field of paleoneurobiology. The field was formally defined with the publication of ''Die fossilen Gehirne'' (''Fossil Brains'') in 1929 which compiled knowledge on the subject that had previously been scattered in a wide variety of journals and treated as isolated events. While still in Germany, Edinger began studying extant species from a paleoneurobiological perspective by making inferences about evolutionary brain development in seacows using stratigraphic and comparative anatomical evidence. Edinger continued her research in Nazi Germany until the night of November 9, 1938, when thousands of Jews were killed or imprisoned in what became known as
Kristallnacht () or the Night of Broken Glass, also called the November pogrom(s) (german: Novemberpogrome, ), was a pogrom against Jews carried out by the Nazi Party's (SA) paramilitary and (SS) paramilitary forces along with some participation fro ...
. Although a visa was not immediately available for immigration to the United States, with the help of friends and colleagues who valued her work, Edinger was able to immigrate to London where she translated German medical texts into English. Eventually her visa quota number was called and she was able to immigrate to the United States where she took on a position as a research fellow at Harvard's
Museum of Comparative Zoology A museum ( ; plural museums or, rarely, musea) is a building or institution that cares for and displays a collection of artifacts and other objects of artistic, cultural, historical, or scientific importance. Many public museums make thes ...
. Her contributions to the field of paleoneurobiology include determining the extent to which endocasts reflect the anatomy of ancient brains, the adequacy of comparative anatomy to interpret brain evolution, the ability of brain endocasts to predict the lifestyles of extinct organisms, and if brain size has increased over geological time; topics which are still being explored today. In her later years, Edinger corresponded with the next generation of paleoneurobiologists, which insured that the work from her 50-year career continued into the future. The pinnacle accomplishment of her career was the compilation of an annotated bibliography of paleoneurobiological papers published between 1804 and 1966. The bibliography, ''Paleoneurology 1804–1966'', was completed and published by colleagues posthumously in 1975 due to the untimely death of Edinger from injuries sustained during a traffic accident in 1967.


Conflict between Holloway and Falk

Paleoneurobiologists Ralph L. Holloway and
Dean Falk Dean Falk (born June 25, 1944) is an American academic neuroanthropologist who specializes in the evolution of the brain and cognition in higher primates. She is the Hale G. Smith Professor of Anthropology and a Distinguished Research Professor ...
disagree about the interpretation of a depression on the ''
Australopithecus afarensis ''Australopithecus afarensis'' is an extinct species of australopithecine which lived from about 3.9–2.9 million years ago (mya) in the Pliocene of East Africa. The first fossils were discovered in the 1930s, but major fossil finds would not ...
'' AL 162-28 endocast. Holloway argues that the depression is a result of lipping at the
lambdoid suture The lambdoid suture (or lambdoidal suture) is a dense, fibrous connective tissue joint on the posterior aspect of the skull that connects the parietal bones with the occipital bone. It is continuous with the occipitomastoid suture. Structure T ...
and that the sulcal patterns indicate cerebral organization moving toward a more human pattern, while Falk insists that the depression is the lunate sulcus in a position that is indicative of an ape-like sulcal pattern. The debate between these two scientists is not hinged solely on the AL 162-28 endocast, but rather extends to all
australopithecine Australopithecina or Hominina is a subtribe in the tribe Hominini. The members of the subtribe are generally ''Australopithecus'' (cladistically including the genera ''Homo'', '' Paranthropus'', and ''Kenyanthropus''), and it typically includ ...
fossils, with Holloway insisting on the presence of hominid sulcal features, and Falk maintaining that the features are pongid in nature. The debate between Holloway and Falk is so intense that between 1983 and 1985, they published four papers on the identification of the medial end of the lunate sulcus of the Taung endocast (''Australopithecus africanus''), which only further strengthened the division between each scientist's respective opinion. Although there have been no definitive conclusions about the fossils in question, many techniques were created or critically analyzed and refined as a result of the conflict. These new techniques in endocast analysis included 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.


Brain endocasts

A brain endocast is the imprintation of the inner features of a cranium that captures the details created from pressure exerted on the skull by the brain itself. Endocasts can be formed naturally by
sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to the ...
through the cranial foramina which becomes rock-hard due to calcium deposition over time, or artificially by creating a mold from silicon or latex that is then filled with plaster-of-Paris while sitting in a water bath to equalize forces and retain the original shape. Natural endocasts are very rare; most of those that are studied are the result of artificial methods. Although the name implies that it is a copy of the once living brain, endocasts rarely exhibit convolutions due to buffering by the
pia mater Pia mater ( or ),Entry "pia mater"
in
arachnoid mater, and
dura mater In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. ...
that once surrounded and protected the brain tissue. Furthermore, not all endocasts are created from a complete cranial fossil and subsequently, the missing parts are approximated based on similar fossils. In some cases, fragments from several fossils of the same species are used to construct a single endocast. More recently, computed tomography has played a large role in reconstructing endocasts. The procedure is non-invasive and has the advantage of being able to analyze a fossil in record time with little risk of damaging the fossil under review. CT imaging is achieved through the application of x-rays to produce tomographs, or sectional density images, which are similar to the images produced during MRI scans. CT scans use slices approximately 1 mm thick to reconstruct a virtual model of the specimen. This method is especially useful when a fossil cranium is occupied by a natural endocast that cannot be removed without destroying the skeletal portions of the fossil. Because the cranium and its contents are of different densities, the endocranial cavity and its unique traits can be reconstructed virtually. Radiographic technique such as computed tomographic imaging, or CT scans, coupled with computer programming have been used to analyze brain endocasts from 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.


Methods of research

Paleoneurobiology 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 no clear landmarks to use as reference points. Furthermore, the only clear reference plane is the
sagittal plane The sagittal plane (; also known as the longitudinal plane) is an anatomical plane that divides the body into right and left sections. It is perpendicular to the transverse and coronal planes. The plane may be in the center of the body and div ...
one, which is marked by distinct cerebral asymmetries. Since the obtaining of clear data from fossil details is usually very difficult, much debate arises over interpretations. Experience is often an important factor in endocast analysis. Therefore, a large portion of the field of paleoneurobiology arises out of developing more detailed procedures that increase the resolution and the reliability of interpretations.


Overall brain volume

Statistical analysis of brain endocasts gives information on the increases in overall brain volume ("endocranial volume"). Because endocasts are not exact replicas, or exact casts, of a once-living brain, computer algorithms and CT scans are needed to calculate endocranial volume. The calculated endocranial volume includes the meninges,
cerebrospinal fluid Cerebrospinal fluid (CSF) is a clear, colorless body fluid found within the tissue that surrounds the brain and spinal cord of all vertebrates. CSF is produced by specialised ependymal cells in the choroid plexus of the ventricles of the ...
, and
cranial nerves Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and f ...
. Therefore, these volumes end up larger than the once-living brain. This information is useful for calculating relative brain size, RBS, and
encephalization quotient Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed to predicted brain mass for an animal of a given size, based on nonlinear regress ...
, 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 = \frac Brain volume is prominent in the scientific literature for discussing taxonomic identification, behavioral complexity, intelligence, and dissimilar rates of evolution. In modern humans, cranial capacity can vary by as much as 1000 cc, without any correlation to behavior. This degree of variation is almost equivalent to the total increase in volume from australopithecine fossils to modern humans, and brings into question the validity of relying on cranial capacity as a measurement of sophistication. Many paleoneurobiologists measure cranial capacity via the submersion method, in which displacement of water in a beaker is taken as the volume of the endocast. Scientists who believe that this method is not accurate enough will use a similar procedure in which a beaker with a spout is filled until it is full. The water displaced by the endocast is then weighed to determine the endocast volume. Although both of these techniques are significantly more precise than previous methods, scientists are optimistic that more advanced techniques such as computed tomography will provide greater accuracy of volume measurements.


Morphometric analysis

Morphometric Morphometrics (from Greek μορϕή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...
analysis relies on chord and arc measurements of the endocast surface. Length, width,
bregma The bregma is the anatomical point on the skull at which the coronal suture is intersected perpendicularly by the sagittal suture. Structure The bregma is located at the intersection of the coronal suture and the sagittal suture on the superi ...
-
basion The foramen magnum ( la, great hole) is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblon ...
, and height measurements of an endocast are taken with spreading
caliper A caliper (British spelling also calliper, or in plurale tantum sense a pair of calipers) is a device used to measure the dimensions of an object. Many types of calipers permit reading out a measurement on a ruled scale, a dial, or a digital d ...
s.
Frontal lobe The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove be ...
,
parietal lobe The parietal lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The parietal lobe is positioned above the temporal lobe and behind the frontal lobe and central sulcus. The parietal lobe integrates sensory informa ...
, and
occipital lobe The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the vi ...
chord length (the length of the lobe at its widest point along the midsagittal plane) are measured using a dioptograph in which landmarks are projected onto a two-dimensional surface. Measurements may be skewed if the orientation of the endocast has not been properly determined before the dioptograph is made. Geometric morphometrics (systems of coordinates superimposed over the measurements of the endocast) are often applied to allow comparison between specimens of varying size. Measurements may also be taken in reference to
Broca's area Broca's area, or the Broca area (, also , ), is a region in the frontal lobe of the dominant hemisphere, usually the left, of the brain with functions linked to speech production. Language processing has been linked to Broca's area since Pierr ...
, height of the endocast at 25% intervals of the maximum length, and the vault module (
mean There are several kinds of mean in mathematics, especially in statistics. Each mean serves to summarize a given group of data, often to better understand the overall value (magnitude and sign) of a given data set. For a data set, the '' ari ...
of maximum length, width, and middle height). Although other measurements may be taken, the choice of landmarks are not always consistent between studies.


Convolution pattern and cerebral organization

Convolutions, the individual
gyri In neuroanatomy, a gyrus (pl. gyri) is a ridge on the cerebral cortex. It is generally surrounded by one or more sulci (depressions or furrows; sg. ''sulcus''). Gyri and sulci create the folded appearance of the brain in humans and other m ...
and
sulci Sulci or Sulki (in Greek , Steph. B., Ptol.; , Strabo; , Paus.), was one of the most considerable cities of ancient Sardinia, situated in the southwest corner of the island, on a small island, now called Isola di Sant'Antioco, which is, how ...
that compose the folds of the brain, are the most difficult aspect of an endocast to accurately assess. The surface of the brain is often referred to as smooth and fuzzy, due to the meninges and
vasculature The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
that cover the brain's surface. It is possible to observe underlying gyri and sulci patterns if an endocast is accurately or preserved, but the uncertainty associated with these patterns often leads to controversy. Because the
robust australopithecine ''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: '' P. robustus'' and '' P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be synonymous with ''Austr ...
fossils show these details, convolutions are included in the study of endocasts whenever appropriate.


Asymmetry

The degree of asymmetry between right and left hemispheres is a point of interest to most paleoneurobiologists because it could be linked to handedness or language development of the specimen. Asymmetries occur due to
hemispherical A sphere () is a Geometry, geometrical object that is a solid geometry, three-dimensional analogue to a two-dimensional circle. A sphere is the Locus (mathematics), set of points that are all at the same distance from a given point in three ...
specialization and are observed in both a qualitative and quantitative manner. The unevenness of the hemispheres, known as a petalia, is characterized by a lobe that is wider and/or protruding beyond the contralateral lobe. For example, a right-handed person typically has larger left occipital lobe and right frontal lobes than the contralateral lobes. Petalias also occur due to specialization in the communication centers of the frontal cortex of the brain in modern humans. Petalias in the occipital lobe are easier to detect than those in the frontal lobe. 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. Some gorillas have shown strong petalias, but they are not found in combination with other petalias as is almost always the case in humans. Scientists use the presence of petalias to show sophistication, but they are not a definitive indicator of evolution toward a more human brain.


Meningeal patterns

Although the meninges have no link to behavior, they are still studied within the realm of paleoneurobiology due to the high degree of conservation of meningeal patterns within a species which may serve as a way to determine
taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
and
phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spe ...
.


Endocranial vasculature

Because meningeal blood vessels comprise part of the outermost layer of the brain, they often leave vascular grooves in the cranial cavity that are captured in endocasts. Endocranial vasculature originates around the foramina in the skull and in a living body would supply blood to the calvaria and
dura mater In neuroanatomy, dura mater is a thick membrane made of dense irregular connective tissue that surrounds the brain and spinal cord. It is the outermost of the three layers of membrane called the meninges that protect the central nervous system. ...
. The vasculature is so well preserved in some fossils that terminal branches of the
circulatory system The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
can be observed. Analysis of cranial vasculature concentrates on the anterior meningeal system of the frontal region, the middle meningeal system of the parieto-temporal and part of the anterior occipital region, and the cerebellar fossa system of the cerebellar region. In the course of hominid evolution, the middle meningeal system has undergone the most change. Although cranial vasculature has been exhaustively studied in the last century, there has been no consensus on an identification scheme for the branches and patterns of the vascular system resulting from little overlap of results between studies. As such, endocranial vasculature is better suited for inferring the amount of blood delivered to different parts of the brain.


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.


Significance

The study of paleoneurobiology allows researchers to examine the
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
ary nature of human
encephalization Encephalization quotient (EQ), encephalization level (EL), or just encephalization is a relative brain size measure that is defined as the ratio between observed to predicted brain mass for an animal of a given size, based on nonlinear regressi ...
. Traditionally, paleoneurobiologists 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. The limited scale and completeness of the fossil record inhibits the ability of paleoneurobiology to accurately document the course of brain evolution. Further, fossil preservation is necessary to ensure accuracy of the endocasts studied.
Weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...
,
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
, 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 quantify and describe, further complicating the observations made from the study of endocasts. Additionally, paleoneurobiology provides very little insight into the actual
anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...
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 genus ''
Homo ''Homo'' () is the genus that emerged in the (otherwise extinct) genus '' Australopithecus'' that encompasses the extant species ''Homo sapiens'' ( modern humans), plus several extinct species classified as either ancestral to or closely relat ...
''. These limitations of paleoneurobiology are currently being dealt with by the development of more advanced tools to refine the study of endocasts.


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

Scientist J. Ghika believes use of paleoneurobiology is the best way to analyze several neurodegeneration leading to diseases such as
Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...
,
dyskinesias Dyskinesia refers to a category of movement disorders that are characterized by involuntary muscle movements, including movements similar to tics or chorea and diminished voluntary movements. Dyskinesia can be anything from a slight tremor of t ...
, gait disorders,
Paget's disease of bone Paget's disease of bone (commonly known as Paget's disease or, historically, osteitis deformans) is a condition involving cellular remodeling and deformity of one or more bones. The affected bones show signs of dysregulated bone remodeling at the ...
,
dysautonomia Dysautonomia or autonomic dysfunction is a condition in which the autonomic nervous system (ANS) does not work properly. This may affect the functioning of the heart, bladder, intestines, sweat glands, pupils, and blood vessels. Dysautonomia ha ...
and so on. A past study by S.I. Rapoport on Alzheimer's disease in Homo sapiens has shown the importance in using a darwinian perspective to better understand this disease itself and its symptoms. The aim is to determine the genetic mechanisms that lead to focal or asymmetrical brain atrophy resulting in syndromic presentations that affect gait, hand movements (any sort of locomotion), language, cognition, mood and behavior disorders.


See also

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Evolution of nervous systems The evolution of nervous systems dates back to the first development of nervous systems in animals (or metazoans). Neurons developed as specialized electrical signaling cells in multicellular animals, adapting the mechanism of action potentials ...
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Paleobiology Paleobiology (or palaeobiology) is an interdisciplinary field that combines the methods and findings found in both the earth sciences and the life sciences. Paleobiology is not to be confused with geobiology, which focuses more on the interactio ...
* Paleoanthropology *
Paleontology Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...


References

{{Neuroscience Neuroscience
Neurology Neurology (from el, νεῦρον (neûron), "string, nerve" and the suffix -logia, "study of") is the branch of medicine dealing with the diagnosis and treatment of all categories of conditions and disease involving the brain, the spinal ...