The temporoinsular projection system: an anatomical study.

Area of Science:

• Neuroanatomy
• Brain Connectivity
• White Matter Tracts

Background:

• Functional connections between the insular cortex and amygdaloid complex are known.
• The precise anatomical pathways linking the amygdala and insula remain unclear.
• Previous descriptions of an amygdaloinsular fasciculus lack detailed anatomical documentation.

Purpose of the Study:

• To elucidate the anatomical pathway connecting the insular cortex and the mesial temporal lobe.
• To investigate the existence and detailed anatomy of the fasciculus amygdaloinsularis.
• To map the white matter connections between the insula and amygdala.

Main Methods:

• Fiber dissection technique applied to 14 post-mortem human brain specimens.
• Specimens were fixed and frozen prior to dissection.
• Progressive, stepwise dissections were performed to trace white matter tracts.

Main Results:

• The insula connects to the frontal, parietal, and temporal opercula via the extreme capsule's short association fibers.
• White matter fibers converge at the limen insulae, looping around the uncinate fasciculus towards the temporal pole and amygdala.
• Direct white matter connections between the insula and mesial temporal lobe create the appearance of a single amygdaloinsular fasciculus.

Conclusions:

• The insula and mesial temporal lobe are directly linked by white matter fibers within the extreme capsule.
• This pathway is part of the broader extreme capsule fiber network connecting the insular cortex to the temporal pole and amygdala.
• The authors propose the term "temporoinsular projection system" (TIPS) for this interconnected system.