Central nervous system disorders

VI./1.3.: Association tracts

These tracts make connections between different areas of the same hemisphere. Their task is to coordinate the functions belonging to different cortical areas. Based on the fact that this can happen within a certain functional system or between several of these, uni-and multimodal associations can be distinguished. Thus the association tracts may consist of quite short fibre bundles, these are the short association fibres (e.g. between the different Broadmann areas of the visual cortex) or long bundles connecting different lobes, these are the long association fibres. The latter can be made visible especially well with the fibre dissection technique.

Such fasciculi, that connect different lobes and are macroscopically easy to dissect, are the fasciculus frontooccipitalis (superior et inferior), a fasciculus temporooccipitalis, and deeper and medial from the insula the fasciculus longitudinalis inferior (seu uncinatus), which mainly connects the basal sections of the frontal and temporal lobe.

The fasciculus arcuatus seu frontotemporalis can be interpreted as the caudal bundle of the fasciculus longitudinalis superior. Similar to the former, this also connects the frontal and temporal lobe, but their more superior gyri. Higher fibres of the fasciculus longitudinalis superior reach the occipital lobe, too.

The cingulum embraces the fibres radiating laterally from the corpus callosum. In older textbooks besides the word cingulum we can find in under another name, the felicitous fornix periphericus. (Fibres of the fornix between the septum pellucidum and the hippocampus formation are also commonly reckoned among association tracts.)

Bundles connecting neighbouring gyri are called fibrae arcuatae (propriae) or „U”-fibres.

The gyrus angularis and supramarginalis, located on the parietal, temporal and occipital lobes’ border, play a particularly important associative role, as these have extensive subcortical associative connections with distant cortical areas.