The Von Economo Neurons: From Cells to Behavior

Citation

Watson, Karli Kiiko (2006) The Von Economo Neurons: From Cells to Behavior. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FZ94-DW76. https://resolver.caltech.edu/CaltechETD:etd-05252006-224259

Abstract

The von Economo neurons are one of the few known specializations to hominoid cortical microcircuitry. The recent emergence of this cell type, as well as its localization to subregions of the frontal cortex, suggest its involvement in sophisticated cognitive behaviors. Studies of this cell may thus provide insights into human uniqueness and origin and may additionally be relevant to the treatment and understanding of mental illness.

The first section of this thesis investigates the anatomical details of these cells, including their structure and surface receptor expression. Using a Golgi preparation of a human postmortem brain, I describe the dendritic architecture of this unique population of neurons. We found that, in contrast to layer 5 pyramidal neurons, the von Economo neurons have sparse dendritic trees with symmetric apical and basal components. This confirms that the von Economo cells in both ACC and FI share the architectural characteristics of a single population, and that this population is distinct from other layer 5 neurons. I additionally used immunohistochemistry to probe the receptor expression on these cells, and found that the von Economo neurons strongly express the dopamine D3 and D5 receptors, as well as serotonin-1b and serotonin-2b receptors. Together, these results provide the first detailed anatomical description of a neuron type unique to great apes and humans.

In the second part of this thesis, I explore whether a behavioral stimulus, humor, activates the regions in which this cell occurs. Humor is a hallmark of social discourse and usually depends on the convergence of fast, intuitive assessments with a slow "re-interpretation" of the humor. Because of these characteristics, we thought it likely that humor would activate FI and ACC in addition to other regions in the brain. I used event-related fMRI to differentiate brain activity induced by the hedonic similarities and cognitive differences inherent in cartoons depicting two kinds of humor: visual humor (sight gags) and language-based humor. I found that the brain networks recruited during a humorous experience did indeed include FI and ACC, and that the profile of activation differs according to the type of humor being processed.

Taken together, these projects significantly expand on our knowledge of these unusual cells, and provide a basis that allows us to hypothesize about their function. In the conclusion of this paper, we propose that the role of the von Economo neurons is to facilitate fast decision making in the context of high uncertainty, such as during social interaction.

Thesis Files