New insights in the limbic modulation of visual inputs: the role of the inferior longitudinal fasciculus and the Li-Am bundle.

Recent anatomical and DTI data demonstrated new aspects in the subcortical occipito-temporal connections. Although a direct (inferior longitudinal fasciculus, ILF) pathway has been previously described, its fine description is still matter of debate. Moreover, a fast and direct subcortical connection between the limbic system and the occipital lobe has been previously recognized in many functional studies but it still remains poorly documented by anatomical images. We provided for the first time an extensive and detailed anatomical description of the ILF subcortical segmentation. We dissected four human hemispheres with modified Klingler's technique, from the basal to the lateral occipito-temporal surface in the two steps, tracking the ILF fibers until their cortical termination. Pictures of this direct temporo-occipital pathway are discussed in the light of recent literature regarding anatomy and functions of occipito-temporal areas. The dissection confirmed the classical originating branches of ILF and allowed a fine description of two main subcomponent of this bundle, both characterized by separate hierarchical distribution: a dorsal ILF and a ventral ILF. Moreover, a direct pathway between lingual cortex and amygdala, not previously demonstrated, is here described with anatomical images. Even if preliminary in results, this is the first fine description of ILF's subcomponents. The complex but clearly segregated organization of the fibers of this bundle (dILF and vILF) supports different level of functions mediated by visual recognition. Moreover, the newly described direct pathway from lingual to amygdala (Li-Am), seems involved in the limbic modulation of visual processing, so it may support physiological conditions the crucial role of this connection in human social cognition. In pathological conditions, on the other hand, this may be one of the hyperactivated pathways in temporo-occipital epileptic and nonepileptic syndromes.