Long Association Fibers
SUPERIOR LONGITUDINAL FASCICULUS
- Anatomy - Bidirectional pathway that connects the parietal and frontal cortices.
- Further subcategorized into, from rostral to caudal, SLF I, II, and III.
- Function - Wide variety of cognitive functions; notably, it communicates spatial information between the frontal and parietal lobes.
ARCUATE FASCICULUS
- Anatomy - Originates in the posterior superior temporal area and passes forward to the frontal lobe.
- Function - The ability to repeat language, called language conduction, has historically been assigned to the arcuate fasciculus (and still commonly is).
- Language conduction requires the transmission of language from the superior temporal reception area to the frontal motor speech output area. Modern evidence suggests that the arcuate fasciculus is actually more generally involved in the spatial orientation of sound and that the superior longitudinal fasciculus (specifically SLF III), the middle longitudinal fasciculus, and the extreme capsule, instead, transmit language conduction.
UNCINATE FASCICULUS:
- Anatomy - Connects the orbital prefrontal cortex and anterior cingulate gyrus with the anterior temporal lobe.
- Function - Combines processed somatosensory information (auditory, visual, gustatory) with emotional response regulation to assist in decision-making processes.
CINGULUM
- Anatomy - The main white matter bundle of the limbic system. Projects bidirectionally through the limbic lobe - from the cingulate gyrus around the posterior end of the corpus callosum back forward through the parahippocampal gyrus.
- Function - Plays an important role in emotional processing.
MIDDLE LONGITUDINAL FASCICULUS
- Anatomy - From the posterior end of the superior temporal gyrus to the temporal pole (It is not the medial longitudinal fasciculus of the brainstem).
- Function - Connects paralimbic, associative, and prefrontal cortices.
INFERIOR LONGITUDINAL FASCICULUS
- Anatomy - From the antero-inferior temporal lobe to the parieto- occipital lobe.
- Function - The major white matter bundle of the ventral occipitotemporal visual pathway, which is responsible for object recognition and identification the so-called what pathway.
FRONTO-OCCIPITAL FASCICULUS
- Anatomy - From the parieto-occipital area to the prefrontal area.
- Function - The where pathway corollary to the ventral occipitotemporal what pathway; it transmits visual spatial information to the frontal motor areas to guide movement.
EXTREME CAPSULE
- Anatomy - Spans from the middle temporal area to the ventral prefrontal cortex. It is discretely situated between the claustrum and the insula (as opposed to the external capsule, which is situated between the claustrum and the putamen) and is most easily viewed on coronal radiographic imaging.
- Function - Plays a role in language, specifically in syntax and grammar, and as discussed above, conduction aphasia may at least partially be due to dysfunction within this white matter bundle.