Neuroanatomy of the white matter

Question 1

White matter fasciculi

Answer 1

• Each fasciculi has a name and associated function depending on which cortical area they connect.
• Not random.
• As the brain develops, connections are formed and some are eliminated between specific brain areas to form networks.

Question 2

Commissural fibres

Answer 2

The Corpus Callosum
• The largest commisural bundle
• Connects the two hemispheres together

The Anterior Commissure (AC)
• Connects areas of the temporal cortex as well as subcortical structures (amygdala) and olfactory bulbs

Question 3

Division of the Corpus Callosum

Answer 3

Genu and rostrum: Connect the Orbitofrontal and Prefrontal areas

Rostral Body: Connects the Premotor and Supplementary motor areas

Anterior Midbody: Connects the Sensori-motor areas

Posterior Midbody: Connects Parietal areas

Isthmus: Connects the Posterior Parietal and Superior Temporal areas

Splenium: Connects Occipital and Inferior Temporal area.

Question 4

Association fibres

Answer 4

Intra-hemispheric: information transfer from
one brain area to another
• Superior longitudinal fasciculus: connect frontal
to parietal areas (3 branches)
• Arcuate fasciculus: connect frontal to posterior
temporal areas
• Middle longitudinal fasciculus: Connect temporal to Parietal area
• Fronto-Temporal Extreme Capsule fasciculus:
Connects Frontal to Anterior-Mid Temporal area

• Uncinate fasciculus: Connect orbitofrontal and anterior temporal areas
• Inferior longitudinal fasciculus: Occipito-temporal connections
• (Inferior Fronto-Occipital Fasciculus (IFOF): occipito-frontal connections)

Question 5

Projection fibres

Answer 5

Ascending and descending fiber tracts from and to the cortex
• External capsule → motor cortex primarily to putamen (unidirectional)
• Internal capsule → a massive white matter highway connecting cortex with subcortical structures, the brainstem, and the spinal cord and vice versa, i.e. bidirectional

Question 6

Tractography limitations/challenges

Answer 6

• Where there are crossing fibres
• Where several fibre tract run in parallel within a same white matter area
• Cannot detect if there is a synapse

Question 7

Research example: The language tracts

Answer 7

• The Arcuate Fasciculus (AF) is a white matter tract connecting the posterior temporal region (Wernicke’s area) involved in the comprehension of language with the
inferior frontal gyrus (IFG; Broca’s region), involved in the production of language.
• Several studies have used diffusion imaging tractography to reconstruct and study it.

Question 8

Common impairments in stroke patients

Answer 8

-motor deficits: upper or lower limb weakness
-dysphagia: difficulty swallowing
-visual impairments: e.g. neglect
-language deficits: aphasia
▪ Depend on where the stroke happens, and which brain areas are affected
▪ The location and extent of the lesion affects the symptom severity

Question 9

Aphasia

Answer 9

• A disorder caused by damage to the areas of the brain that support our ability to comprehend and produce speech.
• Usually caused by stroke, tumor, traumatic brain injury or degenerative brain disease
• Leads to difficulties in speaking, understanding, reading and writing.