Complex visual hallucinations triggered by eye closure and condition-specific release phenomenon

The pathogenesis of complex visual hallucination by suppression of inhibitory cortical input to visual association areas is considered as the "release phenomenon". A 79 year-old man without dementia or hallucinations history experienced complex visual hallucinations in the right lower quadrantanopia area after traumatic subdural hematoma (SDH) of the left occipital region. The vivid hallucinations were only triggered only by eye closure. Serial Tc- 99m single photon emission computed tomography studies were performed to explore the phenomenon. By semi-quantitative measurement of the parietal-occipital region in three different settings, we suggested that hyperperfusion in the left parieto-occipital region was related to hallucination during eye closure. In conclusions, release phenomenon in lesions that caused dysregulation between external perception and internal image production may be one possible mechanism in triggering visual hallucinations during eye closure.