Visual hallucinatory syndromes: past, present, and future

In 1936, two clinical rewiews, one by de Morsier, the other by L'Hermitte and de Ajuriaguerra, formulated an approach to visual hallucinations that continues to this day. Breaking with previous traditions, the papers championed visual hallucinations as worthy of study in their own right, de-emphasizing the clinical significance of their visual contents and distancing them from visual illusions. De Morsier described a set of visual hallucinatory syndromes based on the wider neurological and psychiatric context, many of which remain relevant today; however, one - the Charles Bonnet Syndrome - sparked 70 years of controversy over the role of the eye. Here, the history of visual hallucinatory syndromes and the eye dispute is reviewed, together with advances in perceptual neuroscience that question core assumptions of our current approach. From a neurobiological perspective, three syndromes emerge that relate to specific dysfunctions of afferent cholinergic and serotonergic visual circuitry and promise future therapeutic advances.