# 17 - 3. White matter pathways

# 3. White matter pathways

© SPMM Course 
3. White matter pathways 
There are 3 major types of white matter pathways. Projection fibers run vertically connecting higher and 
lower centres of the brain. Association fibers interconnect different regions within the same hemisphere 
of the brain. Commissural fibers interconnect similar regions in 
the opposite hemisphere. 
Corpus callosum is the largest bundle of fibres that connect the two cerebral hemispheres; the other such 
bundles are anterior commissure (interconnects olfactory bulbs), posterior commissure (interconnects 
midbrain pretectal nuclei), hippocampal commissure and habenular commissure (interconnects posterior 
dorsal thalamic nuclei). 
The pericallosal artery derived from the anterior cerebral artery provides blood supply to the anterior 
aspect and most of the body of the corpus callosum. Left sided apraxia and agnosia may be seen in cases 
of vascular disruption. 
Posterior cerebral artery territory supplies splenium (posterior aspect of the corpus callosum) and 
disrupted supply here prevents right visual cortex accessing the dominant hemispheric processes such as 
language resulting in alexia and color anomia but with preserved ability to copy words as motor 
information is relayed via anterior corpus callosum 
Fornix is an important white mater tract that connects hippocampus to the hypothalamus via mammillary 
bodies. Thus, it relays cortical input to regulate neuroendocrine and autonomic systems. 
Arcuate fasciculus connects Broca’s and Wernicke’s areas. Damage results in conduction aphasia. 
Uncinate fasciculus is a major frontotemporal tract that connects orbitofrontal cortex to the anterior 
temporal lobes. It plays an important role in social cognition and language.