Methods of research Paleoneurobiology

1 methods of research

1.1 overall brain volume
1.2 morphometric analysis
1.3 convolution pattern , cerebral organization
1.4 asymmetry
1.5 meningeal patterns
1.6 endocranial vasculature
1.7 relative lobe size

methods of research

sagittal view of human brain through mri

paleoneurobiology revolves around analysis of endocasts. of analysis focused on interpreting sulcal patterns, difficult because traces hardly recognizable, , there no clear landmarks use reference points. furthermore, clear reference plane sagittal plane one, marked distinct cerebral asymmetries. since obtaining of clear data fossil details difficult, debate arises on interpretations. experience important factor in endocast analysis. therefore, large portion of field of paleoneurobiology arises out of developing more detailed procedures increase resolution , reliability of interpretations.

overall brain volume

statistical analysis of brain endocasts gives information on increases in overall brain volume ( endocranial volume ). because endocasts not exact replicas, or exact casts, of once-living brain, computer algorithms , ct scans needed calculate endocranial volume. calculated endocranial volume includes meninges, cerebrospinal fluid, , cranial nerves. therefore, these volumes end larger once-living brain. information useful calculating relative brain size, rbs, , encephalization quotient, eq. corresponding body weight of subject must known calculated rbs. rbs calculated dividing weight of brain body weight. eq can determined several different ways depending on data set used. example, holloway , post calculate eq following equation:

e
q
=
brainweight



0.12

⋅

bodyweight

0.66





{\displaystyle eq=\operatorname {brainweight} \over \operatorname {0.12} \cdot \operatorname {bodyweight} ^{0.66}}

brain volume prominent in scientific literature discussing taxonomic identification, behavioral complexity, intelligence, , dissimilar rates of evolution. in modern humans, cranial capacity can vary as 1000 cc, without correlation behavior. degree of variation equivalent total increase in volume australopithecine fossils modern humans, , brings question validity of relying on cranial capacity measurement of sophistication.

many paleoneurobiologists measure cranial capacity via submersion method, in displacement of water in beaker taken volume of endocast. scientists believe method not accurate enough use similar procedure in beaker spout filled until full. water displaced endocast weighed determine endocast volume. although both of these techniques more precise previous methods, scientists optimistic more advanced techniques such computed tomography provide greater accuracy of volume measurements.

morphometric analysis

morphometric analysis relies on chord , arc measurements of endocast surface. length, width, bregma-basion, , height measurements of endocast taken spreading calipers. frontal lobe, parietal lobe, , occipital lobe chord length (the length of lobe @ widest point along midsagittal plane) measured using dioptograph in landmarks projected onto two-dimensional surface. measurements may skewed if orientation of endocast has not been determined before dioptograph made. geometric morphometrics (systems of coordinates superimposed on measurements of endocast) applied allow comparison between specimens of varying size. measurements may taken in reference broca s area, height of endocast @ 25% intervals of maximum length, , vault module (mean of maximum length, width, , middle height). although other measurements may taken, choice of landmarks not consistent between studies.

convolution pattern , cerebral organization

convolutions, individual gyri , sulci compose folds of brain, difficult aspect of endocast accurately assess. surface of brain referred smooth , fuzzy, due meninges , vasculature cover brain s surface. possible observe underlying gyri , sulci patterns if endocast accurately or preserved, uncertainty associated these patterns leads controversy. because robust australopithecine fossils show these details, convolutions included in study of endocasts whenever appropriate.

asymmetry

the degree of asymmetry between right , left hemispheres point of interest paleoneurobiologists because linked handedness or language development of specimen. asymmetries occur due hemispherical specialization , observed in both qualitative , quantitative manner. unevenness of hemispheres, known petalia, characterized lobe wider and/or protruding beyond contralateral lobe. example, right-handed person typically has larger left occipital lobe , right frontal lobes contralateral lobes. petalias occur due specialization in communication centers of frontal cortex of brain in modern humans. petalias in occipital lobe easier detect in frontal lobe. asymmetries have been documented on homo erectus specimens such homo redolfensis specimen 1.8 million years ago resemble same asymmetries modern humans. gorillas have shown strong petalias, not found in combination other petalias case in humans. scientists use presence of petalias show sophistication, not definitive indicator of evolution toward more human brain.

meningeal patterns

although meninges have no link behavior, still studied within realm of paleoneurobiology due high degree of conservation of meningeal patterns within species may serve way determine taxonomy , phylogeny.

endocranial vasculature

because meningeal blood vessels comprise part of outermost layer of brain, leave vascular grooves in cranial cavity captured in endocasts. endocranial vasculature originates around foramina in skull , in living body supply blood calvaria , dura mater. vasculature preserved in fossils terminal branches of circulatory system can observed. analysis of cranial vasculature concentrates on anterior meningeal system of frontal region, middle meningeal system of parieto-temporal , part of anterior occipital region, , cerebellar fossa system of cerebellar region. in course of hominid evolution, middle meningeal system has undergone change. although cranial vasculature has been exhaustively studied in last century, there has been no consensus on identification scheme branches , patterns of vascular system resulting little overlap of results between studies. such, endocranial vasculature better suited inferring amount of blood delivered different parts of brain.

relative lobe size

it impossible determine accurate location of central or precentral sulci endocast. still can provide rough idea of lobe sizes.