Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Neurobiology and Anatomy, 2012.
The limbic system was conceived as a set of cortical and subcortical
neural regions responsible for emotional processing. Since ‘limbic system’
was coined by Paul MacLean, this concept has been criticized for its nonspecificity,
yet remains highly influential for affective neuroscience. This
doctoral thesis studied the functional and structural relationships between
limbic structures by inspecting: 1.) a functional incentive processing network,
and; 2.) anatomic cortico-amygdala-striatal circuits.
Experiment 1 used functional magnetic resonance imaging (fMRI) to
examine the effective connectivity of an a priori designated network
composed of the nucleus accumbens, anterior insula, and medial thalamus
during incentive anticipation in healthy human adults and adolescents.
Results demonstrated that the best-fit model involved all possible anatomic
connections across the three regions, and that, across the whole task, the
thalamus and insula significantly influenced the nucleus accumbens. The
network was used similarly during loss and gain anticipation, and between
adults and adolescents.
In Experiment 2, the prefrontal and insula cortical inputs, and striatal
outputs, of amygdala subregions were charted following the placement of
bidirectional tracers in the macaque amygdala. Results demonstrated three
main cortico-amygdala-striatal circuits that were organized according to
degree of cortical laminar differentiation, and associated striatal outputs to,
and beyond, the rostral ventral striatum. These circuits were layered in a
hierarchical fashion in the amygdala such that the ventral amygdala hosted
only one or two of these circuits, while the dorsal amygdala hosted all three
circuits.
These experiments provide further detail on the ‘system’ of the limbic
system, and additionally give definition to subsystems of the limbic system.
While the ‘limbic system’ as a whole may be vaguely defined, further research
on limbic subsystems may reveal the combination of influences responsible
for specific emotional processes.
