Stimulating the inferior fronto-occipital fasciculus elicits complex visual hallucinations

Complex visual hallucinations are vivid visual percepts (e.g. scenes, figures) that appear without an external stimulus. These percepts may be elicited during electrical brain stimulation (EBS) mapping, a procedure performed during evaluation and surgical treatment of patients with severe intractable focal epilepsy [1e3]. When evoked during EBS, these hallucinations usually involve mnemonic and affective content [1,2,4], and are typically induced in the occipital and temporal lobes [3,4] while only rarely in the frontal lobe regions [3,5]. It has been suggested that these multifaceted visual phenomena arise from the activation of widely distributed neural networks [1e3]. Yet, the specific white matter tracts involved in these networks remain unclear, especially in the frontal regions. Here we describe two patients who experienced complex visual hallucinations during electrostimulation of their orbitofrontal white matter tracts. By combining EBS findings with generalized Q-sampling imaging, we identify the inferior fronto-occipital fasciculus (IFOF) as the origin of these responses.