Fig 1.

Visual pathways. A, Retino-geniculo-calcarine tract. Optical information from the retina (1) passes along the optic nerve (2) through the optic chiasm (3) and optic tract (4) into the lateral geniculate nucleus of the thalamus (5), where it receives input from the superior colliculus (7) via the pulvinar (6) and then traverses the optic radiation (8 and 9) through the temporal lobe (13) into the visual cortex (10–12). B, Intersection of ascending pathways. Optical information in the retino-geniculo-calcarine tract (1–8 and 11) is modulated by ascending input from the pedunculopontine and parabrachial nuclei (9) and raphe nuclei (10) via the superior colliculus (7). Hashed areas show regions where interruptions are known to produce visual hallucinations: in the retino-geniculo-calcarine tract via deafferentation, in the thalamus through reducing signal-to-noise ratio, and in the ascending pathways via removal of inhibitory control. Reproduced with permission from Dr. Ramon Mocellin.