|Allman Lab Research|
Mechanisms of Economic and Social Decision-Making
One of our goals is to explore the mechanisms of economic and social
decision-making. Much of our investigation has focused on the role of
anterior cingulate and fronto-insular cortex, which we have found to
contain a population of large bipolar neurons, the Von Economo (spindle)
cells. These neurons are present only in humans and apes and are much
more abundant in humans than in apes. They thus represent a recent
development in hominoid evolution. We think that the Von Economo
neurons are part of the circuitry responsible for rapid intuitive choice
in complex social situations.
Anatomical structure and location of Von Economo neurons Our lab has investigated the anatomical structure of the Von Economo (spindle) neurons in anterior cingulate and fronto-insular cortex. Based on functional imaging studies of these brain areas and our studies of the expression of neurotransmitter receptors on these cells, we think they participate in fast, intuitive social decision-making. We have found that the Von Economo neurons emerge mainly in the first three years after birth. We also have evidence that in autistic subjects the Von Economo neurons are abnormally located, possibly as a result of a migration defect. This abnormality may be at least partially responsible for defective social intuition in autism. Brain structures activated during auction bidding In collaboration with David Grether, Charles Plott, Daniel Rowe, and Martin Sereno we have used fMRI to map the brain structures activated during auction bidding. These inculde the frontal polar cortex (Brodmann's area 10) and anterior cingulate cortex. The frontal polar cortex appears to be involved in strategic thinking and cost-benefit analyses, and the anterior cingulate cortex in error recognition and focused problem solving. Both cortical areas have undergone recent evolutionary change, and ACC contains Von Economo neurons. Decision-making in young vs. elderly subjects In most tests, elderly subjects are similar in performance to young subjects, with two interesting exceptions. First, the elderly subjects are more accurate in judging the accuracy of their own beliefs, which is an aspect of wisdom. Second, the elderly subjects are much less prone than young subjects to be come overconfident when engaged in gambling tasks. This overconfidence in young subjects leads them to persist in making disadvantageous decisions in the face of financial losses. This study was performed by Dr. Allman and former Allman Lab member Stephanie Kovalchik, in collaboration with Colin Camerer, Charles Plott, and David Grether. Agenesis of the corpus callosum
In collaboration with Ralph Adolphs and Lynn Paul, we have been investigating the anatomic structure of the brains of subjects with agenesis of the corpus callosum. This congenital failure of formation of the major pathway connecting the two halves of the brain is fairly common and is associated with abnormal social behavior and decision-making. Our data show there is a substantial reduction of all fiber systems in agenesis, and that the structure of anterior cingulate cortex is grossly abnormal in these subjects.
Neural mechanisms of humor To investigate the neural mechanisms of humor we presented cartoons to subjects in the MRI scanner and asked them to rate how funny each was. We found that activity in fronto-insular cortex (FI) is strongly related to how funny the subject rated a cartoon. We also found that verbal humor engages speech cortex, which is also activated by syntactic errors, while sight gags activate higher order visual cortical areas. Fronto-insular cortex lesions Undergraduate Corinna Zygourakis, in collaboration with Ralph Adolphs, has been investigating the deficits in social cognition that result from lesions in fronto-insular cortex. Subjects were drawn from the Iowa Patient Registry, which is a population of carefully documented neurological cases. Corinna developed a test based on film clips depicting various emotional states by first showing these clips to normal subjects to establish a baseline, then showing them to patients with FI lesions. Lesions patients had deficits in the interpretation of emotional states, particularly for the complex social emotions.
Aye-aye We performed a multi-modal analysis of tissue volume and microstructure in the brain of the aye-aye (Daubentonia madagascariensis). We scanned the left hemisphere of an aye-aye brain using t2-weighted structural magnetic resonance imaging and diffusion-tensor imaging prior to histological processing and staining for myelinated fibers. Measurements of brain structure volumes in our specimen are consistent with those reported in the literature: the aye-aye has a very large brain for its body size, its visual structures (V1 and LGN) are reduced in volume, and its olfactory lobe is increased in volume. This trade-off between visual and olfactory reliance is a reflection of the nocturnal extractive foraging behavior practiced by Daubentonia. Additionally, frontal cortex volume is large in the aye-aye, a feature that could also be related to its complex foraging behavior and increased sensorimotor intelligence. Gross brain components appear to scale propportionally in the aye-aye. Finally, our analysis of white matter fiber structure in the anterior cingulum bundle demonstrates a strong correlation between fiber spread as measured from histological sections and fiber spread as measured from diffusion-tensor imaging. African elephant We acquired magnetic resonance images (MRI) of the brain of an adult African elephant, Loxodonta africana, in the axial and parasagittal planes and produced anatomically labeled images. The elephant has an unusually large and convoluted hippocampus compared to primates and especially to cetaceans. We quantified the volume of the whole brain and of the neocortical and cerebellar gray and white matter. The white matter to gray matter ratio in the elephant neocortex and cerebellum are in keeping with that expected for a brain of this size. The ratio of neocortical gray matter volume to corpus callosum cross-sectional area is similar in the elephant and human brains, emphasizing the difference between terrestrial mammals and cetaceans, which have a very small corpus callosum relative to the volume of neocortical gray matter.