[Visual hallucinosis and hyperhedonism in pontine and thalamic infarction]

The syndrome of peduncular hallucinosis in characterized by transient visual hallucinations which often consist in animated and mobile characters or animals, and which are often associated with disordered sleep. Although vivid and life) like, these hallucinations are generally not mistaken for reality. In view of the associated neurological symptoms, this syndrome was first believed to occur only with lesions of the mesencephalon. Lesions restricted to the mesencephalon have been identified with MRI in a few cases and were demonstrated by pathological verification in one patient with this syndrome. We describe a patient who experienced very similar hallucinations following a unilateral infarct restricted to the cerebellum, rostral protuberance and posterior thalamus. No lesion was seen in the mesencephalon with MRI. This case confirms that the lesions responsible for peduncular hallucinosis are not restricted to the mesencephalon, which suggests that several interconnected neural structures are probably involved in the genesis of this type of visual hallucinations. During the days following the stroke, our patient also experienced transient sensations of pleasure which he considered as abnormal. In view of the site of the lesions in this case, the visual hallucinations may be explained by a disinhibition of ponto-geniculo-occipital waves. A transient activation of reward-system pathways traveling in the brainstem ventral tegmentum may have contributed to the occurrence of the abnormal sensations of pleasure.