Von Economo neuron

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Figure 1. Photomicrographs of soma and proximal dendrites of (a) a pyramidal and (b) the VENs stained with the Golgi method. Photomicrogaphs are montages taken of several planes and/or fields of view. Scale bar applies to both images. Source: [6]

Contents

Basic information

Figure 2. Von Economo neuron compared to Pyramidal neuron. Source: [12]

Spindle or Von Economo neurons (VENs) are bipolar neurons in the anterior cingulate, frontoinsular, and dorsoloteral prefrontal cortices of great apes (humans, gorillas, chimpanzees, bonobos, and orangutans), and while previously thought to be unique to the great apes, have more recently been found in cetaceans (humpback, fin, killer, and sperm whales) [8]. Because of their morphology and anatomical location, it has been speculated that VENs may play an important role in intuitive choice in social situations and that their dysfunction may be a factor in autism and Alzheimer's. VENs were first described by Constantin Von Economo in 1925, and their exclusivity to the great apes was discovered by John Allman, Patrick Hof, and others, in 1999.

Neuronal Type: Projection Neuron


Anatomy

VENs are large, bipolar neurons with one large apical axon and a single basal dendrite. They are found exclusively in layer Vb of the anterior cingulate cortex (ACC) and frontoinsular cortex (FI), and have also recently been identified in human dorsolateral prefrontal cortex (DLPFC) (Brodmann area 9). [9] Its large apical axon and high-volume, elongated soma is similar to that of the cortical pyramidal neuron, but the VEN lacks the pyramidal neuron's numerous basal dendrites, instead receiving inputs from a comparatively small subset of cortex; the average VEN is also 4.6 times larger than the average layer 5 pyramidal cell. [6] Pyramidal neurons conduct information from the cortex to other parts of the central nervous system. Their structural similarity to pyramidal neurons suggests that VENs may play a similar functional role, and because the speed at which neurons conduct information typically co-varies with the diameter of their axon, the large VENs may do so very quickly compared to other neurons. [5] VENs are relatively rare, comprising 1-2% of the total neurons in layer 5 of the ACC. [2] In FI, VENs are 30% more numerous in the right hemisphere than the left, a hempispherization that occurs in the first four years of postnatal development in humans. [5]

Figure 3. Regions of the brain containing Von Economo neurons (VENs). (a) A lateral view of the brain, with fronto-insular cortex (FI) shown in red. (b) A medial view of the brain, with anterior cingulate cortex (ACC) shown in red. Adapted from Von Economo and Koskinas [1]. Source: [5]

Molecular profile

  • Neurotransmitter Receptors: vasopressin 1a, dopamine d3, serotonin 2b [5]

Synaptic Connections

Though currently unknown where VENs ultimately project to, ACC and FI connect to numerous anatomical areas: prefrontal, orbitofrontal, insular and anterior temporal cortices, amygdala, hypothalamus, and various thalamic nuclei. Allman and others have speculated that VENs project information processed in FI and ACC to other parts of the brain, including Brodmann's area 10, in frontopolar cortex. [11]

Ontogeny and Phylogeny

Figure 4. Primate cladogram detailing the species examined for VENs. Species in red have VENs in the FI. Pongids have VENs in the ACC only. Source: [12]
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Figure 5. 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). Source: [3]

VENs develop late both ontogenetically and phylogenetically.

Ontogenetically, VENs first appear in the 35th week of gestation; at birth only about 15% of the postnatal number are present, and at 4 years old, the adult number are present. [5]

Analyses of over 30 mammalian species have failed to find VENs except in primates and cetaceans. Among primates (including the lesser apes (gibbons)) VENs have only been found in the great apes (humans, gorillas, chimpanzees, bonobos, and orangutans). [3]

Among the great apes, humans have the most VENs, both in terms of absolute number and relative percentage compared to total number of neurons. In decreasing order of total number, VENs are found in humans, bonobos, chimpanzees, gorillas, and orangutans. Unlike in the other species exhibiting them, VENs in humans and bonobos are distributed in clusters of 3-6 neurons. In analyses of total number of VENs present in FI of both hemispheres, the average adult human was found to have 193,000 cells, a 4 year old human child had 184,000, the average human newborn had 28,200, a gorilla had 16,710, a bonobo had 2,159, and a chimpanzee had 1,808. [3,4]

That their relative abundance and clustering in species co-varies with a species' phylogenetic proximity to humans has led to speculation that VENs are important to evolution and cognition. That they occur in hominids and pongids (but no other primates) suggests that VENs evolved relatively recently: approximately 15-20 million years ago, prior to the evolutionary divergence of orangutans and hominids. [3,4] Their recent discovery in some whales suggests a second, independent evolution of VENs, though they may not have the same function in both apes and cetaceans [10].

Function and Behavior

The FI and ACC, where VENs are located, are thought to be implicated in social reasoning, empathy, emotion, and monitoring of visceral autonomic activity, among other functions. ACC projects to the frontopolar cortex, which has been implicated in cognitive dissonance and uncertainty. Because their morphology suggests them as fast-projection neurons, and because of the functions of the areas they are thought to receive information from and project information to, it is speculated that VENs have an important role to play in intuition, which allows one to overcome uncertainty, make quick decisions, and resolve cognitive dissonance. [5]

Abnormal VEN development has been implicated in autism [5] and selective degeneration of VENs has been observed in Alzheimer's and dementia [7].

References

[1] Von Economo, C. and Koskinas, G. (1925) Die Cytoarchitectonik der Hirnrinde des erwachsenen Menschen, Springer

[2] Nimchinsky, E.A. et al. (1995) Spindle neurons of the human anterior cingulate cortex. J. Comp. Neurol. 355, 27–37

[3] Nimchinsky, E.A. et al. (1999) A neuronal morphologic type unique to humans and great apes. Proc. Natl. Acad. Sci. U. S. A. 96, 5268–5273

[4] Allman, J. et al. (2002) Two phylogenetic specializations in the human brain. Neuroscientist 8, 335–345

[5] Allman, J.M. et al. (2005) Intuition and autism: a possible role for Von Economo neurons. TRENDS in Cognitive Sciences 9:8, 367-373

[6] Watson, K. K., et al. (2006) Dendritic architecture of the von Economo neurons. Neuroscience. 141:1107-1112

[7] Seeley, W. W., et al. (2006) Early frontotemporal dementia targets neurons unique to apes and humans. Ann. Neurol. 60:6, 660-667

[8] Hof, P. and Van Der Gucht, E. (2007) Structure of the cerebral cortex of the humpback whale, Megaptera novaeangliae (Cetacea, Mysticeti, Balaenopteridae). The Anatomical Record 290, 1-31

[9] Fajardo, C. et al. (2008) Von Economo neurons are present in the dorsolateral (dysgranular) prefrontal cortex of humans. Neuroscience Letters 435:3, 215-218

[10] Balter, M. (2006) Well-Wired Whales. ScienceNOW Daily News. November 27, 2006 http://sciencenow.sciencemag.org/cgi/content/full/2006/1127/1

[11] Balter, M. (2007) NEUROANATOMY: Brain Evolution Studies Go Micro. Science 315:5816, 1208 - 1211 http://www.sciencemag.org/cgi/content/full/315/5816/1208

[12] http://neurotransponder.blogspot.com/2005/12/von-economo-neurons-intuition-and.html