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.
Comparative Anatomy
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.
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