Brian Schilder is a PhD candidate from George Washington University. He was awarded a Leakey Foundation Research Grant during our fall 2016 cycle for his project entitled “The evolution of the hippocampus and adult neurogenesis: Novel insights into the origins of human memory.”
Memories do more than simply provide us humans the pleasure of reminiscing about pleasant past experiences. Our ability to consciously access our memories plays a critical role in shaping our sense of self-identity. It allows us to envision future experiences and how we might make these visions a reality. To be sure, many other animals have memory, in the sense that their nervous systems store information about past experiences such that it can adaptively influence behavior later on. But much like other homologous systems, the form and complexity of memory varies considerably across species. The hippocampus is a brain structure that is critical for the storage and recall of long-term memories as well as spatial navigation in all mammals. However, only in humans is it known to additionally mediate episodic memory, the capacity to recall specific personal experiences and imagine future scenarios. This uniquely flexible and complex form of memory may have first emerged in our hominin ancestors to meet the demands of increasingly challenging environments, expanded home ranges, and novel hunting/foraging strategies. Recent evidence suggests that the human whole-hippocampus has become evolutionarily specialized compared to those of NHPs in terms of relative size, neuronal structure and distribution, and gene expression. However, it is well known that the hippocampus is composed of molecularly and functionally distinct subfields. The hippocampus is also one of the only brain regions that maintains the ability to generate new neurons (known as adult hippocampal neurogenesis (AHN)) throughout one’s lifetime, which is necessary for efficient memory storage.
For these reasons, my project will investigate the origins of human memory by comparing the hippocampal subfields of humans to those of non-human primates (NHPs) at the levels of neuroanatomy, gene expression, and genetics. In Part I. I will compare the relative size hippocampal subfields and degree of adult neurogenesis in humans to those of NHPs, as well as search for ecological factors that correlate with these features. In Part II. I will use whole-transcriptome technology to compare the gene expression patterns of human hippocampal subfields to those of NHPs, in terms of both differential expression (gene upregulation and downregulation) and gene co-expression networks (groups of genes that together serve a function). In Part III. I will investigate whether these potential differences in neuroanatomy and gene expression can be attributed to evolutionary changes in the genome.
These findings will provide novel insights into the neurobiological basis of certain human-specific memory-related abilities and the ecological factors that may have driven their emergence. Furthermore, this project will identify neurobiological targets that may render humans uniquely susceptible to certain neurological diseases and disorders known to affect the hippocampus (e.g. Alzheimer’s disease, Autism spectrum disorder). Upon publication in peer-reviewed scientific journals, the resulting large dataset will be made publically available online to facilitate further research and discoveries. I also look forward to continuing my engagement in programs to promote public understanding of and excitement for neuroscience, genetics and human evolution.