Von Economo Neurons, Intuition, and Phylogeny

A class of bipolar neurons, known as Von Economo neurons (VEN), are found in layer Vb of human neocortex. VEN morphology is very simple: they have a large apical dendrite as do cortical pyramidal neurons but lack the collection of basal dendrites. They possess the high-volume, elongated cell body that is typical of fast-conducting projection neurons, and preliminary tract-tracing indicates that they are such, although the array of their projections has not been elucidated. Interestingly, VENs are found in a select few cortical areas that receive inputs from numerous brain regions; the fronto-insular cortex (FI) and anterior cingulate cortex (ACC). Thus, VEN morphology and anatomical location suggest that these cells are positioned to receive an array of diverse information in parallel and then compress it for speedy processing.

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Figure 2. Location of the frontoinsular cortex (FI) and anterior cingulate cortex (ACC) on coronal brain sections.

VENs may play a role in intuition. The FI and ACC, where VENs are located, are active during social situations; when we experience humor, trust, empathy, guilt, when we engage in deception, or when we must determine another's mental state. All of these scenarios carry a high degree of uncertainty. Intuition allows us to overcome uncertainty, to make quick decisions based upon our prior experiences when we do not have the time to conduct a proper cost-benefit analysis. Intuition is frequently described as the "gut feeling" or "going with your gut", which is especially interesting because the ACC and FI are literally involved in processing the conscious monitoring of visceral activity. VENs are the logical candidates to mediate these processes due to their morphological specifications and anatomical locations.

Perhaps the most intriguing characteristic of VENs is their phylogeny. An analysis of over 30 mammalian species (including monotremes, marsupials, insectivores, micro- and megachiropterans, rodents, carnivores, artiodactyls, and cetaceans) failed to find VENs in any neocortical region examined, including the ACC or its equivalent. In a wide survey of primates, including numerous species of prosimians, both New and Old World monkeys, lesser apes (gibbons), and the great apes (orangs, gorillas, both the common and bonobo chimpanzee, and humans,) VENs were only observed in the great apes.


Figure 3. Primate cladogram detailing the species examined for VENs. Species in red have VENs in the FI. Pongids have VENs in the ACC only. Click on the image for something readable.

VENs were common to both FI and ACC in all Hominidae but were found infrequently in the Pongid (orang) ACC, and were completely absent from the Pongid FI. Of the hominids, humans have the highest absolute numbers of VENs, and the highest percentage of VENs relative to total neurons. Humans and bonobos are similar in that they display a clustered pattern of VEN distribution, while the other apes do not.


Figure 4. Von Economo neurons in layer Vb of the anterior cingulate cortex in human (A), bonobo (B), common chimpanzee (C), gorilla (D), and orangutan (E). In all of these species the VENs display similar morphology and apparent somatic size. Note the clusters of VENs in the through-focus photomontage from the human and in the bonobo, whereas isolated neurons are observed in the three other great apes. (F-H) No VENs are present in the anterior cingulate cortex of the white-handed gibbon (F), Patas monkey (G), or ring-tailed lemur (H). [Bar = 50 µm (A), 80 µm (B-E and H), and 120 µm (F and G).]

Phylogeny

VENs represent a phylogenic specialization of the hominid line, thus they have arisen in the last 12-15 million years. As such, natural selection has had only a short time to refine their functional role, suggesting that they may be particularly susceptible to dysfunction. Perhaps unsurprisingly, VENs have been implicated in autism and may be selectively vulnerable to degeneration in Alzheimer's Disease.

The phylogeny of VENs make sense given their evolutionary context. The great apes are highly social animals that must engage in rapid decision-making to navigate complex social environs. Of the great apes, the most solitary is the orangutan. Similarly, they display the fewest VENs. Humans and bonobos have arguably the most complex social interactions, and display not only high numbers of VENs but also a similar clustered distribution, whereas in the common chimpanzee, gorilla, and orang, VENs are found in isolated arrangements. The evolutionary context also provides a framework for future research into the common origins of intuitive processing in great apes and its neurobiological underpinnings, and the role of VENs in dysfunctional brain states and neurodegenerative diseases.

Bonus Section: Implications for Intelligent Design Creationism

The existence of VENs raises difficult questions for the Intelligent Design Creationism movement. Do VENs suggest common ancestry? The IDC movement is split over whether humans shared a common ancestor with apes, and of course ID itself is consistent with either (or any) possible answer, but provides no actual explanation. If an IDC argues that VENs are the product of common ancestry, how does the IDC distinguish common ancestry from design? Will we finally get an internally consistent set of criteria for distinguishing the two? Somehow I doubt it.

If the IDC argues that they are not a product of common ancestry but indicative of design from a common body plan, what have we gained scientifically? Can we make inquiries into the teleological subtext of common design? Unfortunately no. According to the ID crowd, the identity and motivations of a designer are not subject to investigation. This means that we cannot distinguish between one common designer for all great ape species, individual designers for each species who share common "parts", or--as the commonality between species might also suggest-- A designer for Homo and Pan paniscus, a slightly-less-skilled designer for Pan troglodytes and Gorilla gorilla, and an inept designer for Pongo who pilfered the design from the troglo-and-gorilla designer, perhaps by reverse engineering or sending covert rhesus monkey corporate spies to steal the blueprints...

...except those stupid monkeys only stole the blueprint for the ACC.

So, once again, the ID crowd is at a scientific dead end.



PNAS Vol. 96, Issue 9, 5268-5273, April 27, 1999
Trends Cogn Sci. 2005 Aug;9(8):367-73. Review
J. Chem. Neuroanat. 1999:16, 77-116