Olfactory and gustatory hallucinations

Olfactory hallucinations (OHs) occur in healthy people, as the primary symptom in the condition phantosmia and as a secondary symptom in psychotic disorders, temporal lobe epilepsy, brain injury, and migraine among others. Gustatory hallucinations are rarer, poorly studied, and may co-occur with OHs as flavor hallucinations. OHs may differ across conditions in their time course, varying from brief bursts, reminiscent of normal olfactory experience, to persistent smells lasting hours or days in phantosmia. Notwithstanding, OHs are generally unpleasant and seem to be of real-world smells, there being no obvious parallel to the simple-versus-complex distinction applied to other hallucinations. In terms of cause, OHs may arise from damage to peripheral receptor systems, from damage or activation of central olfactory structures (especially the amygdala due to its involvement in olfactory hedonics), and from psychological causes, with recent evidence suggesting a role for source-monitoring failures in OHs experienced by psychotic individuals.