7.2 VA Reading - Mori 2005 MRI Atlas of Human White Matter

Mori S, Wakana S, Nagae-Poetscher LM, can Zijl PCM (2005). MRI Atlas of Human White Matter. ELSEVIER.

Chapter 3: Three-Dimensional Atlas of Brain White Matter Tracts
White matter tracts can be divided into four groups:

1. Tracts in the brainstem
2. Projection fibers
   Connect cortical and subcortical gray matter
3. Association tracts
   Connect two cortical areas
4. Commissural tracts
   Connect two hemispheres

Tracts in the brainstem (5)

• Superior cerebellar peduncles: main efferent pathway from dentate nucleus of the cerebellum toward the thalamus
• Middle cerebellar peduncles: afferent and efferent connections to cerebellum, originated from caudal medullar and pass through pons
• Inferior cerebellar peduncles: efferent fibers from the pons to the cerebellum (pontocerebellar tracts)
• Corticospinal tract: descending pathway from the cortex
• Medial lemniscus: major pathway for ascending sensory fibers

Projection fibers (2): all penetrate the internal capsule either between the thalamus and the putamen or between the caudate and the putamen; form corona radiata when approachin gto the cortex

• Corticothalamic/thalamocortical fibers (collectively called thalamic radiations)
• Long corticofugal (corticoefferent) fibers
• corticopontine tracts
• corticoreticular tracts
• corticobulbar tracts
• corticospinal tracts

Association fibers (2)

• Short association fibers: connect areas within the same lobe, also include the fibers connecting adjacent gyri (U-fibers)
• Long association fibers: connect different lobes: connect limbic system (cingulum, fornix, stria terminalis)
• superior longitudinal fasciculus: located at the supero-lateral side of the putamen; form a large arc; send branches into the frontal, parietal, occipital, and temporal lobes
• inferior longitudinal fasciculus: connect occipital and temporal lobes
• superior fronto-occipital fasciculus: location is still unclear, most likely at the supero-lateral area of the caudate. Anteriorly occupies the superior edge of the anterior limb of the internal capsule and projects into the frontal lobe; posteriorly travels along the caudate nucleus and seems to merge into the corona radiata.
• inferior fronto-occipital fasciculus: connect frontal and occipital lobes
• uncinate fasciculus: connect the anterior temporal lobe (including the hippocampal formation) to the orbital cortex
• Cingulum: collect axons from the cingulate gyrus that travel immediately dorsal to the corpus callosum and along the ventral face of the hippocampus; large C-shaped trajectory; connect cingulate gyrus and entorhinal cortex
• Fornix: afferent and efferent pathways between the hippocampus and the septal area and the hypothalamus; C-shaped trajectory (smaller than cingulum)
• Stria terminalis: C-shaped trajectory (innermost), afferent and efferent pathways between the amygdala and the septal area and the hypothalamus.

Commissural fibers: mainly corpus callosum. By far the largest fiber bundle in the human brain

• Most interconnect homologous cortical areas in roughly mirror-image sites, but also a lot have heterotopic connections and end in asymmetrical areas.
• Research in monkeys show that the entire cortex is connected by the commissural fibers, but DTI-based tractography fails to reveal commissural connections to the lateral areas of the hemispheres.