Paleoneurobiology

Paleoneurobiology is the study of the brain’s evolution through the use of endocasts, or molds of the interior of the skull. Since the soft brain tissues cannot fossilize, endocasts allow scientists to study the impressions made by the brain on fossilized skulls. The field of paleoneurobiology involves the study of the brains of extinct hominids to explore their structure and makeup and see how they evolved over time. Johanna Gabrielle Ottilie Tilly Edinger, a German paleontologist, is considered the founder of paleoneurobiology. Born in 1897, Edinger researched the evolution of various animal brains. She began utilizing the concept of paleoneurobiology in the 1920s. Although endocasts had been used prior to her study, Edinger researched the relationship between the brain, its skull or braincase, and different vertebrate classes. She later went on to conduct comparisons over time, as well as between classes. In modern times, paleoneurobiology has received more widespread attention among the general public because of its potential to aid in the research of degenerative brain disorders, including Parkinson’s and Alzheimer’s diseases.

Background

Paleoneurobiology, sometimes called paleoneurology, sits at the intersection of neurology and paleontology and pulls from other sciences, including archaeology and physiology. Its first purpose is to explore the evolution of the human brain. However, in addition to exploring how ancient brains functioned, scientists are looking for ways to apply paleoneurobiology to more modern, degenerative brain issues. The brain has long been a topic of interest for scientists. Ancient Egyptians are believed to have been among the first to record brain studies as early as the seventeenth century BCE. Evidence also suggests that the ancient Greeks conducted their own studies around the sixth century BCE. However, it wasn’t until the late nineteenth century that comparative anatomy and brain studies, as they are more widely known, were conducted. Those studies were influenced by Charles Darwin’s 1859 publication On the Origin of Species. Around that time, microscopes became more commonly used in biology. At first, observing the brain under a microscope was challenging. However, the process was eventually refined and the microscope became a necessary tool for biologists.

Edinger was born on November 13, 1897, in Frankfurt, Germany. Her father, Ludwig, founded Frankfurt’s first neurological research institute, and heavily influenced his daughter’s career. Edinger obtained degrees in zoology, geology, and paleontology. After her father’s death, she sought advice and mentoring from Louis Dollo, a Belgian paleontologist. However, her interest in paleoneurobiology was likely influenced the most during her doctoral studies when she encountered a skull with a natural brain cast, which she referred to as a fossil brain. In 1921, Edinger began her professional career as a research assistant at the University of Frankfurt. In 1927, she took on a curatorial position at the Naturmuseum Senckenberg, where she stayed for more than a decade. It was there that she wrote her seminal piece on paleoneurobiology. In the 1930s, Edinger, who was Jewish, faced persecution from the Nazi regime. Following Kristallnacht, or the Night of Broken Glass in Germany on November 9, 1938, Edinger was no longer able to research at any public building. She was able to leave Germany in May of 1939 and traveled to London, England. One year later, she received a visa and moved to the United States, where Edinger was able to focus more on her paleoneurobiology work and further the work started by her father. She published her second major work, The Evolution of the Horse Brain, in 1948. Her work with horses challenged the work of many previous scientists.

Overview

Paleoneurobiology, which involves the analysis of the endocranial cavity of extinct species to better understand the evolution of the brain, is often thought of in terms of understanding the past. However, it may have applications in modern medicine. By using endocasts, scientists can better study the sulcal patterns, or grooves, of the brain. The brain’s surface features gyri, or bumps and ridges, and sulci, which are grooves around each gyrus. These vary between individuals though some general features are common. Because obtaining clear, useable information from fossils is challenging, much of paleoneurobiology focuses on developing better ways to obtain detail and precision from endocasts. Manmade endocasts rely on latex or silicone to recreate the brain and/or other soft tissues. Natural endocasts are created when sediments of some other material enter the cavity and recreate the brain. The more thorough the endocast, the more reliable and comprehensive the resulting analysis will be. This process is further complicated by external factors that impact the fossils directly. For example, fossils must be pristinely preserved to create the most detailed endocasts. However, even the most well-kept fossil is only as good as its condition after millions of years of weathering and other stresses. Once quality endocasts have been obtained, researchers can examine the braincase and its proportions, as well as regions like the frontal, parietal, temporal, and occipital lobes.

Endocasts provide the only direct evidence scientists can obtain about the brains of early humans and extinct creatures. Indirect evidence can be pulled from comparative neuroanatomy. Researchers have also proposed further studies surrounding the evolution of cognition and tertiary sulci. Scientists are particularly interested in the sulci and their relationship to functional utility. They have also begun exploring midsagittal brain shape and mental speed. Comparative studies have sought to discern cerebral differences between modern human subjects and extinct humans, but little significance has been found. Focus has also been placed on using paleoneurobiology to better understand degenerative brain issues, including Parkinson’s and Alzheimer’s diseases, as well as cognitive aging.

Bibliography

Beaudet, Amélie. “The Emergence of Language in the Hominin Lineage: Perspectives from Fossil Endocasts.” Frontiers in Human Neuroscience, vol. 11, 2017, DOI: 10.3389/fnhum.2017.00427. Accessed 17 Aug. 2023.

Bruner, Emiliano. “Human Paleoneurology: Shaping Cortical Evolution in Fossil Hominids.” Journal of Comparative Neurology, vol. 527, no. 10, 2019, pp. 1753–1765. pubmed.ncbi.nlm.nih.gov/30520032/. Accessed 13 Aug. 2023.

Bruner, Emiliano. “Paleoneurology.” Centro Nacional de Investigación Sobre la Evolución Humana, CENIEH, 23 Feb. 2022, www.cenieh.es/en/research/lines-of-research/paleoneurology. Accessed 13 Aug. 2023.

Buchholtz, Emily A., and Ernst-August Seyfarth. “The Study of ‘Fossil Brains’: Tilly Edinger (1897–1967) and the Beginnings of Paleoneurology.” BioScience, vol. 51, no. 8, 2001, pp. 674–682. academic.oup.com/bioscience/article/51/8/674/220658. Accessed 13 Aug. 2023.

Falk, Dean. “Chapter 12: Hominin Paleoneurology: Where Are We Now?” Progress in Brain Research, vol. 195, 2012, pp. 255–272. www.sciencedirect.com/science/article/abs/pii/B978044453860400012X. Accessed 13 Aug. 2023.

“I Want to Study Paleoneurology, but What Is It?” World of Paleoanthropology, 19 Apr. 2023, worldofpaleoanthropology.org/2023/04/19/i-want-to-study-paleoneurology-but-what-is-it/. Accessed 13 Aug. 2023.

Miller, Jacob A., and Kevin S. Weiner. “Unfolding the Evolution of Human Cognition.” Trends in Cognitive Sciences, vol. 26, no. 9, 2022, pp. 735–737. www.cell.com/action/showPdf?pii=S1364-6613%2822%2900139-5. Accessed 13 Aug. 2023.