Brain Camp Review – Von Economo Neurons
While at UCLA we had the pleasure of a lecture by Dr. John Allman of Caltech. Dr. Allman is a worldwide leader in the investigation of Von Economo neurons (VEN) or ‘spindle’ cells. While he was originally slated to give an introductory neuroanatomy lecture, he ended up spending much of the time discussing this very unique cell type.
Von Economo neurons are large bipolar cells that are found in cortical layer V of the anterior cingulate and fronto-insular regions. The cells have also been found in the gray matter of the ventral claustrum, near the amygdala. Originally discovered by Von Economo and Koskinas (1925) the cells are much larger [5x] than comparable layer V pyramidal cells. The size of these cells seems to indicate that they stand ready to send signals very quickly across long distances.
Von Economo cells are not ubiquitous across animal brains. Only humans, great apes, certain whales, and elephants have been shown to possess VENs. The relative number of cells varies by species, with humans having by far the greatest amount – over twice the number of our nearest evolutionary neighbor. One argument is that some aspect of VEN function is giving rise to the cognitive abilities that make us uniquely human.
Of interest developmentally is that not all Von Economo neurons are in place when we are born. Only 15% of the cells seem to be in place at birth. It takes several additional years for the number of cells to rise to adult-like levels. It is unknown if existing cell types are morphing into Von Economo neurons or if new neurons are migrating into place during this time. In either case, VEN development in somewhat protracted compared to other cell types.
In terms of pathology VENs seem to be particularly vulnerable to certain types of disease. In a paper by Seeley et al. (2006) they found that early fromtotemporal dementia resulted in a 74% loss of Von Economo neurons throughout the cingulate and insula. VENs that remained were dysmorphic and plagued with tau protein accumulation. Other neuron types were unaffected and a control group of Alzheimers patients did not show the same pattern of VEN loss.
What remains unknown is where the Von Economo neurons project to and what function(s) they support. Everybody likes to do some hand-waving in this regard. Some argue that VENs are projecting to frontopolar cortex, while others believe that VENs in the cingulate and insula are reciprocally connected. This anatomical uncertainty hasn’t stopped scientists from hypothesizing that these cells may (or may not) be linked to high-speed intuitive decision making and possibly higher-order social cognition. From my perspective there is still little support for this case and extrapolating region-level fMRI results to the function of a single cell type is going too far.
In summary I find Von Economo neurons very fascinating. Part of what draws me to cognitive neuroscience is the philosophical investigation into what processes make humans so unique compared to other animals. I do believe that the VENs are one part of this greater puzzle. I also want to believe that VENs play a role in intuitive thought and higher-order processes. However, I fear it will be some time before scientists are able to adequately demonstrate that link.
References and further reading:
The Allman Lab website
Allman JM, Hakeem AY, and Watson KK. (2002) “Two Phylogenetic Specializations in the Human Brain.” The Neuroscientist, 8(4): 35-346.
Allman JM, Watson KK, Tetreault NA, and Hakeen AY. (2005). “Intuition and autism: a possible role for Von Economo neurons.” Trends in Cognitive Sciences. 9(8): 367-373.
Seeley WW, Carlin DA, Allman JM, Macedo MN, Bush C, Miller BL, Dearmond SJ. (2006). “Early frontotemporal dementia targets neurons unique to apes and humans.” Annals of Neurology. 60(6): 660-667.
Von Economo C, and Koskinas. (1925). “Die Cytoarchtectonik der Hirnrinde des erwachsenen Menschen.”