A hallucination is a sensory perception that occurs without any external stimulus. In schizophrenia, hallucinations are a “positive” symptom, meaning they represent experiences added to a person’s reality. For the person experiencing them, the sights, sounds, or feelings are entirely real and can be profoundly disorienting.
The Sensory Experience of Hallucinations
Auditory hallucinations, particularly hearing voices, are the most common type experienced by individuals with schizophrenia, affecting an estimated 60% to 80% of them. These voices can manifest in various ways, from indistinct murmurs to clear commands or conversations. The content is often critical, persecutory, or threatening, causing significant distress. A person might hear one voice or several, which could be familiar or unknown.
Visual hallucinations, while less frequent than auditory ones, are also a significant part of the experience for many. These can range from seeing simple flashes of light to fully formed images of people or objects that are not present. The visions can be stationary, move, or even interact with the person, sometimes combining with auditory hallucinations if the figure begins to speak.
Other sensory domains can be affected, though this is much rarer. Tactile hallucinations involve the sensation of touch without a physical cause, such as the feeling of insects crawling on the skin. Olfactory hallucinations involve smelling odors that no one else can detect. Gustatory hallucinations are similar, causing a person to taste something, often metallic or bitter, that is not there.
The Brain’s Role in Hallucinations
The occurrence of hallucinations in schizophrenia is linked to biological processes involving chemical messengers called neurotransmitters. The dopamine hypothesis is a leading theory, suggesting that an excess of dopamine activity in certain neural pathways contributes to positive symptoms. This is supported by the fact that substances that increase dopamine can induce psychosis. Other neurotransmitters, including serotonin and glutamate, are also implicated.
Brain imaging technologies like functional magnetic resonance imaging (fMRI) provide further insight. During auditory hallucinations, studies show increased activity in the brain’s language and hearing centers, such as Broca’s area. This suggests the brain may be misinterpreting its own internal monologue as external voices. Similarly, during visual hallucinations, the visual cortex shows heightened activity, as if it were processing real sensory input.
Differentiating from Other Psychotic Experiences
While hallucinations are a hallmark of schizophrenia, they can also appear in other conditions. In severe episodes of bipolar disorder or depression, individuals may experience hallucinations that are often “mood-congruent.” For instance, a person with severe depression might hear voices that reinforce feelings of worthlessness. Hallucinations in schizophrenia can be more bizarre and less connected to the person’s emotional state.
The use of stimulants, cannabis, or hallucinogens can also trigger hallucinations. However, these experiences are temporary and resolve once the substance is cleared from the body. In contrast, hallucinations in schizophrenia are part of a chronic condition.
Neurological disorders such as Parkinson’s disease, dementia, or delirium can also cause hallucinations, which are frequently visual. The difference lies in the underlying pathology. In these conditions, the hallucinations are tied to neurodegenerative processes rather than the specific disruptions associated with schizophrenia.
Therapeutic and Medical Interventions
The primary medical treatment for managing hallucinations involves antipsychotic medications. These drugs work mainly by blocking dopamine D2 receptors, reducing the intensity and frequency of hallucinatory experiences. Second-generation antipsychotics also affect serotonin receptors, which can help address a broader range of symptoms. The goal is to make hallucinations less distressing, not necessarily to eliminate them.
Psychosocial therapies are also a component of treatment. Cognitive Behavioral Therapy for psychosis (CBTp) is a specialized talk therapy that helps individuals change how they react to their hallucinations. CBTp teaches coping strategies to reduce distress and improve daily functioning. Other supportive approaches include family therapy and social skills training.