Brain networks of spatial awareness: evidence from diffusion tensor imaging tractography

Area of Science:

• Neuroscience
• Neurology
• Neuroimaging

Background:

• Left unilateral neglect is classically linked to right hemisphere cortical lesions, particularly in the inferior parietal region.
• Recent research suggests long-range white matter tracts are crucial for spatial awareness, involving distributed brain networks.
• Damage to the superior longitudinal fasciculus (SLF) and inferior longitudinal fasciculus (ILF) has been previously associated with neglect.

Purpose of the Study:

• To investigate the role of white matter tracts, including the inferior fronto-occipital fasciculus (IFOF), in the manifestation of left unilateral neglect.
• To determine if superficial cortical damage alone is sufficient to cause neglect, or if white matter integrity is also critical.

Main Methods:

• Four right-handed patients with right hemisphere strokes underwent high-definition anatomical MRI with diffusion tensor imaging (DTI).
• DTI tractography was used to visualize the SLF, ILF, and IFOF.
• Patients completed a pencil and paper neglect battery test.

Main Results:

• Two patients with parietal and temporal cortical damage but intact fasciculi showed no neglect symptoms.
• Two patients exhibiting left neglect had superficial inferior parietal cortex damage and white matter damage involving the IFOF.
• The IFOF, a pathway not previously linked to neglect, was implicated in the affected patients.

Conclusions:

• Superficial damage to the inferior parietal cortex may not be sufficient to cause visual neglect.
• Lesions to the IFOF, connecting ventral occipital and frontal regions, may contribute to neglect by disrupting top-down modulation of visual areas.