Paleoneurology is the study of the cranial capacities of various extinct vertebrates in order to establish possible theories about the brain evolution of various species. One of the best means of study is by the use of
endocasts, which are casting of the brain for which the cranial cavity serves as a mold. Endocasts of mammals are usually remarkable, lifelike replicas of brains.
Many people take it for granted that human beings are the most evolved, intelligent beings on earth. Paleoneurology seeks to examine that claim and offer evidence for its validity by analyzing the evolution of brain capacity and its respective functioning. It is a relatively new branch of neuroscience, developing out of a need for an evolutionary based study of known facts about vertebrate brains. The science is rooted in neurology, paleoanthropology and primatology. Along with the use of brain endocasts, paleonuerologists also study comparative primate neuroanatomy in order to determine which mental capacities humans have that primates do not in order to isolate which areas of the brain are responsible for such things as language and abstract thought. As such, paleoneurology is attempting to find what makes us human.
The first brain structure appeared in reptiles about 500 mya. This simple hindbrain directed breathing, heartbeat regulation, motor movements, and other simple skills. As brains have evolved throughout time, species have tended to maintain these basic structures. The human brain contains this simple hindbrain region, which is called the protereptilin brain, and it controls most homeostatic functions in humans. In our brains, these regions contain the pons and medulla structures.
Around 250 mya after the development of the hindbrain, the paleomammalian brain appeared in organisms. This area of the brain is usually called the limbic system, and contains the hippocampus and the cerebellum. It controls the more complex actions of emotional and sexual responses as well as fighting and defense mechanisms.
The cerebrum, which is the most recent development in brain evolution, emerged around 200 mya. Higher cognitive functions are controlled by this area, like thought processes and linguistic expression.
Aside from analyzing the basic development of the brain over time, paleoneurologists study the variations in brain size in different species. This method of study is currently debated in the field, as size itself is often considered an unreliable standard of comparison with respect to intelligence. Across species of mammals, the number of brain cells itself is actually very consistent, what is different are the connections among them. One thing agreed upon by many experts in the field is the fact that as the brain evolves, more folds develop in the neocortex, which is the surface of the cerebrum. This particular characteristic of the brain allows for a larger overall surface area for the execution of mental functions. The prefrontal cortex has been identified as being central to the ability to relate and connect experiences and to therefore think about relate past, present, and future events in terms of making choices.
Lateralization of brain function is unique to human beings, and is one of the main reasons why our cognitive abilities have advanced. Lateralization is a result of the split of the human brain into two hemispheres. Each half of the brain controls certain things, and the result is that the right hemisphere has evolved to handle creative thinking, while the left hemisphere controls rational and analytic thinking. Lateralization results in our ability to integrate these capacities so that we can execute complex sequences of behavior, such as those involved in language comprehension and production.
The origin of lateralization is uncertain. Certain experts think that it evolved as a result of bipedalism; when early human ancestors began to walk upright, the nervous system was reorganized, and this resulted in such a development.
Paleoneurology is a fascinating thing to study. One of the things that is most interesting to me is the recent analysis of the brain of dolphin species. Their brains are larger than human brains, but beyond that, folds in the neocortex are more numerous, indicating a potential for higher cognitive functioning. All of this data can lead to the conclusion that dolphins are more intelligent than human beings. This conclusion is obviously contested, but it is interesting nonetheless.
The science is useful in terms of its integration of so many disciplines into one field that, I think, has the potential to tell us a lot about ourselves and our minds from a biological and evolutionary perspective.
Sources:
http://www.arts.uwaterloo.ca/~acheyne/evolbrn.html
http://brainmuseum.org/evolution/paleo/
http://serendip.brynmawr.edu/bb/neuro/neuro98/202s98-paper1/O'Hare.html