[not in handout, see intranet]
Allman, J. M., Watson, K. K., Tetreault, N. A., & Hakeem, A. Y. (2005). Intuition and autism: a possible role for Von Economo neurons. Trends in Cognitive Sciences, 9(8), 367-373.
Von Economo neurons (VENs) are a recently evolved cell type which may be involved in the fast intuitive assessment of complex situations. As such, they could be part of the circuitry supporting human social networks. We propose that the VENs relay an output of fronto-insular and anterior cingulate cortex to the parts of frontal and temporal cortex associated with theory-of-mind, where fast intuitions are melded with slower, deliberative judgments. The VENs emerge mainly after birth and increase in number until age 4 yrs. We propose that in autism spectrum disorders the VENs fail to develop normally, and that this failure might be partially responsible for the associated social disabilities that result from faulty intuition.
[not in handout, see intranet]
Elston et al. (2006). Specializations of the granular prefrontal cortex of primates: Implications for cognitive processing. Anatomical Record Part a-Discoveries in Molecular Cellular and Evolutionary Biology, 288A(1), 26-35.
The biological underpinnings of human intelligence remain enigmatic. There remains the greatest confusion and controversy regarding mechanisms that enable humans to conceptualize, plan, and prioritize, and why they are set apart from other animals in their cognitive abilities. Here we demonstrate that the basic neuronal building block of the cerebral cortex, the pyramidal cell, is characterized by marked differences in structure among primate species. Moreover, comparison of the complexity of neuron structure with the size of the cortical area/region in which the cells are located revealed that trends in the granular prefrontal cortex (gPFC) were dramatically different to those in visual cortex. More specifically, pyramidal cells in the gPFC of humans had a disproportionately high number of spines. As neuron structure determines both its biophysical properties and connectivity, differences in the complexity in dendritic structure observed here endow neurons with different computational abilities. Furthermore, cortical circuits composed of neurons with distinguishable morphologies will likely be characterized by different functional capabilities. We propose that 1. circuitry in V1, V2, and gPFC within any given species differs in its functional capabilities and 2. there are dramatic differences in the functional capabilities of gPFC circuitry in different species, which are central to the different cognitive styles of primates. In particular, the highly branched, spinous neurons in the human gPFC may be a key component of human intelligence. (C) 2005 Wiley-Liss, Inc.
Hakeem, A. Y., Hof, P. R., Sherwood, C. C., Switzer, R. C., Rasmussen, L. E. L., & Allman, J. M. (2005). Brain of the African elephant (Loxodonta africana): Neuroanatomy from magnetic resonance images. Anatomical Record Part a-Discoveries in Molecular Cellular and Evolutionary Biology, 287A(1), 1117-1127.
We acquired magnetic resonance images of the brain of an adult African elephant, Loxodonta afficana, in the axial and parasagittal planes and produced anatomically labeled images. We quantified the volume of the whole brain (3,886.7 cm(3)) and of the neocortical and cerebellar gray and white matter. The white matter-to-gray matter ratio in the elephant neocortex and cerebellum is in keeping with that expected for a brain of this size. The ratio of neocortical gray matter volume to corpus callosum crosssectional area is similar in the elephant and human brains (108 and 93.7, respectively), emphasizing the difference between terrestrial mammals and cetaceans, which have a very small corpus callosum relative to the volume of neocortical gray matter (ratio of 181-287 in our sample). Finally, the elephant has an unusually large and convoluted hippocampus compared to primates and especially to cetaceans. This may be related to the extremely long social and chemical memory of elephants. (c) 2005 Wiley-Liss, Inc.
Phillips, K. A., & Sherwood, C. C. (2005). Primary motor cortex asymmetry is correlated with handedness in Capuchin monkeys (Cebus apella). Behavioral Neuroscience, 119(6), 1701-1704.
Humans exhibit a population-wide tendency toward right-handedness, and structural asymmetries of the primary motor cortex are associated with hand preference. Reported are similar asymmetries correlated with hand preference in a New World monkey (Cebus apella) that does not display population-level handedness. Asymmetry of central sulcus depth is significantly different between left-handed and right-handed individuals as determined by a coordinated bimanual task. Left-handed individuals have a deeper central sulcus in the contralateral hemisphere; right-handed individuals have a more symmetrical central sulcus depth. Cerebral hemispheric specialization for hand preference is not uniquely human and may be more common among primates in general.
[not in handout, see intranet]
Sherwood et al. (2006). Evolution of increased glia-neuron ratios in the human frontal cortex. PNAS, 103(37), 13606-13611. listed in wk 10 references
Evidence from comparative studies of gene expression and evolution suggest that human neocortical neurons may be characterized by unusually high levels of energy metabolism. The current study examined whether there is a disproportionate increase in glial cell density in the human frontal cortex in comparison with other anthropoid primate species (New World monkeys, Old World monkeys, and hominoids) to support greater metabolic demands. Among 18 species of anthropoids, humans displayed the greatest departure from allometric scaling expectations for the density of glia relative to neurons in layer II/III of dorsolateral prefrontal cortex (area 9L). However, the human glia-neuron ratio in this prefrontal region did not differ significantly from predictions based on brain size. Further analyses of glia-neuron ratios across frontal areas 4, 9L, 32, and 44 in a sample of humans, chimpanzees, and macaque monkeys showed that regions involved in specialized human cognitive functions, such as "theory of mind" (area 32[in anterior cingulate]) and language (area 44) have not evolved differentially higher requirements for metabolic support. Taken together, these findings suggest that greater metabolic consumption of human neocortical neurons relates to the energetic costs of maintaining long-range projecting axons in the context of an enlarged brain.
Watson, K. K., Jones, T. K., & Allman, J. M. (2006). Dendritic architecture of the von Economo neurons. Neuroscience, 141(3), 1107-1112.
The von Economo neurons are one of the few known specializations to hominoid cortical microcircuitry. Here, using a Golgi preparation of a human postmortem brain, we describe the dendritic architecture of this unique population of neurons. We have found that, in contrast to layer 5 pyramidal neurons, the von Economo neurons have sparse dendritic trees and symmetric apical and basal components. This result provides the first detailed anatomical description of a neuron type unique to great apes and humans. [but large whales have them too.]