The perception of music without a stimulus, or musical hallucination, is reported in both organic and psychiatric disorders. It is most frequently described in the elderly with associated hearing loss and accompanied by some degree of insight. In this setting it is often referred to as ‘musical hallucinosis’. The aim of the authors was to present examples of this syndrome and review the current understanding of its neurobiological basis.

We describe three cases of persons experiencing musical hallucinosis in the context of hearing deficits with varying degrees of associated central nervous system abnormalities.

Putative neurobiological mechanisms, in particular those involving de-afferentation of a complex auditory recognition system by complete or partial deafness, are discussed in the light of current information from the literature.

Musical hallucinosis can be experienced in those patients with hearing impairment and is phenomenologically distinct for hallucinations described in psychiatric disorders.

In consultation-liaison settings, neuropsychiatrists are commonly asked to assess patients with hallucinatory syndromes and to differentiate ‘functional’ from ‘organic’ psychotic presentations.

The occurrence and management of visual hallucinations (VH) in healthy individuals, lesion states, neurodegenerative disorders, intoxication/withdrawal states and delirium are reviewed.

The presence of VH has been shown to predict a secondary rather than primary psychotic illness and an understanding of the neurobiology of the visual system – including how and where underlying neurotransmitter systems interact in visual processing and how perturbations can result in VH – allows for appropriate clinical assessment and management.

We describe the presentation of a young woman with long-standing complex partial seizures with occasional secondary generalization, who presented with complex visual hallucinations (CVHs) and delusions.

Routine biological workup including magnetic resonance imaging revealed an area of significant left-sided occipital gliosis. Video telemetry monitoring revealed a left occipital focus for the origin of the electrographic seizure discharge.

CVHs occur in a range of organic states, including epilepsy, and can be understood in terms of the underpinning neuroanatomy and neurotransmitter systems of the visual system.