by Aaron Jonas Stutz
How does an animal body achieve a sense of where it is and where it’s going? Today’s announcement of the Nobel Prize in Physiology or Medicine recognizes foundational scientific brain research in proprioception. This term in psychology may not be a familiar one, but perception (a more familiar “ception” word) wouldn’t be possible without proprioception, which is the central nervous system’s monitoring of the body’s relationship–in part and in whole–to its surroundings.
This year’s Nobel Prize in Physiology or Medicine was awarded to three researchers. John O’Keefe’s groundbreaking laboratory work on rats established that the hippocampus–a basal structure of the vertebrate cerebrum in the brain that is also known to be important for creating and maintaining memory–includes neurons that network together, dynamically mapping boundaries in a room as the animal moves around horizontally. It is notable that these neurons–which O’Keefe named “place cells”–respond to the position of the body, as well as dynamically perceived visual-spatial information. It is further notable that grid cell networks in the hippocampus constitute a joint iconic and indexical representation system. Spatial structures surrounding the animal are saliently and simply represented in a very small part of the brain. Yet, the iconic mapping–via place cell activation patterns–occurs in real time, shifting with the position and orientation of the animal’s head, so that the map auto-indexically orients the animal to those salient spatial features. The more recent work by May-Britt and Edvard Moser expands our understanding of how this dynamic joint iconic-indexical mapping works. The Mosers and their colleagues have been examining a more specific portion of the hippocampus, called the entorhinal cortex, layers of which have neurons connecting to hippocampal place cell networks, while also incorporating more complex sets of grid cells, linked to head-positioning cells. These complex neural networks, organized in several layers in the entorhinal cortex, allow:
(1) rapid updating of spatial boundaries surrounding the body
(2) updating of the position of the head in relation to those extrasomatic boundaries
(3) integration of position and spatially iconic grid maps as they change over time, providing velocity information
(4) feedback of velocity information to the grid mapping and positioning networks, modulating their sensitivity (encouraging more rapid map and positioning updating at higher velocities)
The life and social sciences (which do not logically have clear subject-matter boundaries) are continuing to undergo two rapid, technologically driven revolutions: the genomic and the neuroscience transformations. Of course, the work recognized by the Nobel Committee this year focuses on the latter. It is worth thinking, though, about the evolutionary aspects of proprioception, which is carried out in important part via the hippocampus and entorhinal cortex. The fact that specialized networks of neurons develop in different parts of the brain is now well-established. That rat and human hippocampi and entorhinal cortices function similarly to map the body’s surroundings and index it’s position within those surroundings … well, that suggests something else. Important aspects of human proprioception have been evolutionarily conserved from the very early mammalian ancestor we share with rats (from at least the time of the last dinosaurs, around 65 million years ago). Yet, we don’t know what protein coding and RNA regulatory regions in our DNA (that is, the two main parts of our DNA that build and maintain our bodies and their capacity to interact–in part or in whole–with our somatic and extrasomatic environment) have been shaped by natural selection to influence such structurally specialized, yet sufficiently networked brains. Nor do we know how functionally specialized neurons and the specialized networks they constitute are developmentally determined by corresponding networks of dynamically activated DNA loci. (For here, the question is not whether neural networks are programmed by DNA or simply emerge through interaction with the environment. Our neurons would not survive over our typically long lifetimes without DNA in their nuclei chemically interacting with the cellular and extracellular environments. Thus, the question must be how DNA and the neurons that contain said DNA strands interact throughout the organism’s life, in a complex feedback system.)
Yet, even as we concentrate on thinking about our neurons, the neural networks they make up, the brain structures in they’re organized in, and the DNA within them that mutually shapes their early-life development and subsequent maintence, our hippocampi and entorhinal cortices are vigilantly keeping tabs on ourselves … in our surroundings. And this–proprioception, that is–is an important concrete part of our sense of self that is so basic, we don’t notice we’re perceiving it.
Key Citations and Links
Gapenne, O. (2014). The co-constitution of the self and the world: action and proprioceptive coupling. Frontiers in Psychology, 5, 594. doi:10.3389/fpsyg.2014.00594
O’Keefe, J., & Nadel, L. (1978). The hippocampus as a cognitive map. Clarendon Press.
Sargolini, F., Fyhn, M., Hafting, T., McNaughton, B. L., Witter, M. P., Moser, M.-B., & Moser, E. I. (2006). Conjunctive Representation of Position, Direction, and Velocity in Entorhinal Cortex. Science, 312(5774), 758–762. doi:10.1126/science.1125572