Palinopsia: a review of the literature

When Left is One and Right is Double: An Experimental Investigation of Visual Allesthesia after Right Parietal Damage

Illusory visual phenomena, such as palinopsia, polyopsia or allesthesia, are rare manifestations of posterior cortical damage. Symptoms are characterized by illusory perceptions, ranging from isolated stationary objects to scenes and moving persons. Such illusions may appear while the original object is still in view, or become manifest with a delay and last for minutes, hours or even days. Some authors have suggested a disinhibited cortical response underlying visual illusions, but experimental studies supporting this hypothesis are lacking. Here, we examined a rare patient who after focal right parietal injury consistently reported a second stimulus on the left when briefly shown a target in his right hemifield. The patient perceived the illusory stimulus as less intense, and therefore concluded that it must have a different shape than the original stimulus. A masking experiment revealed that the frequency of the illusion was inversely related to the visibility of the original stimulus, suggesting that it depended on early, feedforward visual processing. We propose that illusory perceptions reflect the interplay of two physiological processes: a fast and automatic activation of contralateral, homotopic visual cortex after unilateral stimulation, and the lack of top-down inhibition following damage to the posterior parietal cortex.

Palinopsia Following Acute Unilateral Partial Vestibular Deafferentation: A Case Report

Palinopsia is defined as the persistence or reappearance of images after cessation of the visual stimulus. One patient presented episodes of palinopsia after the functional loss of the 3 semicircular canals of the right ear while the otolithic function was preserved. None of classical causes was identified in this patient, intoxications, brain tumors, migraines, psychiatric disorders, etc. For a movement to be perceived as a single event, central processes of temporal integration are necessary to correct the shift between the rapid vestibular information, and the slow visual information. However, it has been shown on animal models that vestibular inputs are slower than normal in case of peripheral deafferentation limited to the canalar function with preservation of the otolithic function, which is the case in this patient. Therefore, we hypothesize that episodes of palinopsia he presents result from the fact that temporal integration processes do not take into account the slower than normal vestibular information due to the peripheral disorder and continue to slow it down. Thus, the patient keeps the visual image in memory until the late arrival of the vestibular information.