Von Economo neuron
Spindle or Von Economo neurons (VENs) occur in primates (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).
Neuronal Type: Projection Neuron
VENs are 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).  Its large apical axon and high-volume, elongated soma is similar to that of the fast-conducting, cortical pyramidal neuron, but the VEN lacks the pyramidal neuron's large array of basal dendrites and the average VEN is 4.6 times larger than the average layer 5 pyramidal cell.  VENs are relatively rare, and thought to make up 1-2% of the Layer 5 neurons in ACC.  In FI, VENs are 30% more numerous in the right hemisphere than the left. 
- Neurotransmitter Receptors: vasopressin 1a, dopamine d3, serotonin 2b 
Though currently unknown where VENs ultimately project to, studies in monkeys indicate that ACC and FI connect to a wide range of areas: prefrontal, orbitofrontal, insular and anterior temporal cortices, amygdala, hypothalamus, and various thalamic nuclei.
Ontogeny and Phylogeny
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. The adult number is attained by 4 years of age. 
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 observed in the great apes (humans, gorillas, chimpanzees, bonobos, and orangutans). 
Among hominids, 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 of VENs, they are found in humans, bonobos, chimpanzees, gorillas, and orangutans. In humans and bonobos, VENs are distributed in clusters of 3-6 neurons, while in other apes they show no such pattern of distribution. 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 in cetaceans.  VENs may not have the same function in both sorts of organism, however. 
"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." 
Function and Behavior
The FI and ACC, where VENs are located, have been implicated in social reasoning, 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 of these purported functions in the areas in which VENs are located, and because their morphology suggests them as fast projection neurons, researchers have speculated that VENs have an important role to play in intuition, which allows us to overcome uncertainty, make quick decisions, and resolve cognitive dissonance. 
Because they evolved recently, VENs may be particularly susceptible to dysfunction. Abnormal VEN development has been implicated in autism  and selective degeneration of VENs has been observed in Alzheimer's and dementia .
 Von Economo, C. and Koskinas, G. (1925) Die Cytoarchitectonik der Hirnrinde des erwachsenen Menschen, Springer
 Nimchinsky, E.A. et al. (1995) Spindle neurons of the human anterior cingulate cortex. J. Comp. Neurol. 355, 27–37
 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
 Allman, J. et al. (2002) Two phylogenetic specializations in the human brain. Neuroscientist 8, 335–345
 Sherwood, C.C. et al. (2003) Evolution of specialized pyramidal neurons in primate visual and motor cortex. Brain Behav. Evol. 61, 28–44
 Allman, J.M. et al. (2005) Intuition and autism: a possible role for Von Economo neurons. TRENDS in Cognitive Sciences 9:8, 367-373
 Fajardo, C. et al. (2008) Von Economo neurons are present in the dorsolateral (dysgranular) prefrontal cortex of humans. Neuroscience Letters 435:3, 215-218
 Watson, K. K., et al. (2006) Dendritic architecture of the von Economo neurons. Neuroscience. 141:1107-1112.
 Balter, M. (2006) Well-Wired Whales. ScienceNOW Daily News. November 27, 2006. http://sciencenow.sciencemag.org/cgi/content/full/2006/1127/1
 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
 Seeley, W. W., et al. (2006) Early frontotemporal dementia targets neurons unique to apes and humans. Ann. Neurol. 60(6):660-667.