Visual phenomena evoked by electrical stimulation of the human brain stem

19 visual effects have been elicited out of 9,383 sites during stimulation mapping for physiological localization during stereotactic surgery. It is proposed that three visual pathways can be recognized during subcortical electrical stimulation in man. The optic tract and geniculocalcarine pathway, projecting to area 17, are recognizable by the production of contralateral coloured phosphenes. The tectopulvinar pathway projecting to areas 18 and 19 is recognizable by the eliciting of contralateral or bilateral colourless phosphenes or 'negative' visual effects, the latter presumably reflecting inhibitory collicular influences. Finally, deep responses, consisting of apparent movement of the visual fields, intermingled with 'negative' visual and oculomotor effects, suggest activation of a visual-oculomotor coordinating system.