Abstract
The amygdala has attracted considerable research interest because of its potential involvement in various neuropsychiatric disorders. Recently, attempts have been made using magnetic resonance imaging (MRI) to evaluate the integrity of the axonal connections to and from the amygdala under pathological conditions. Although amygdalar pathways have been studied extensively in animal models, anatomical references for the human brain are limited to histology-based resources from a small number of slice locations, orientations and annotations. In the present study, we performed high-resolution (250 μm) MRI of postmortem human brains followed by serial histology sectioning. The histology data were used to identify amygdalar pathways, and the anatomical delineation of the assigned structures was extended into 3D using the MRI data. We were able to define the detailed anatomy of the stria terminalis and amygdalofugal pathway, as well as the anatomy of the nearby basal forebrain areas, including the substantia innominata. The present results will help us understand in detail the white matter structures associated with the amygdala, and will serve as an anatomical reference for the design of in vivo MRI studies and interpretation of their data.
Highlights
It is widely accepted that the amygdala is involved in various emotional responses, in which white matter connectivity plays an essential role
We describe the anatomy of these important areas using serial histology sections to provide anatomical landmarks and clarify the magnetic resonance imaging (MRI) contrast of the white matter associated with amygdalar pathways
For the white matter tracts, comparison of the histology sections and 3D trajectory information provided by tractography (Figure 3) greatly facilitated the structural assignment
Summary
It is widely accepted that the amygdala is involved in various emotional responses (reviewed by Amaral, 2003; Phelps and LeDoux, 2005), in which white matter connectivity plays an essential role. Amygdalar connectivity has been studied extensively using animal models, which have shown that the stria terminalis and amygdalofugal pathways serve two major connections of the amygdala. The stria terminalis is an efferent pathway that connects the amygdala to the septal area of the basal forebrain and hypothalamus. It is a poorly myelinated tract, 2–4 mm in diameter, which has only. Animal studies revealed that the amygdala has extensive connections to various cortical areas and the brainstem, but the exact locations of these axonal tracts have not been well defined in the human brain, probably because they do not form discrete and independent bundles
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