Schizophrenia: Symptoms, causes, tests and treatments

Schizophrenia is a psychiatric pathology belonging to the class of psychotic disorders. It is a very disabling and relatively common condition. There are around 600,000 sufferers in France and 0.7% of the population worldwide, i.e. around 23 million people affected. It generally begins in adolescence or young adulthood, with the first symptoms appearing between the ages of 15 and 25.
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What are the symptoms of schizophrenia?

The clinical picture of the disease varies greatly from one individual to another, with a wide range of possible symptoms. These can be classified into three groups: positive, negative and cognitive.

  • Positive” symptoms include delusions, feelings of persecution and a variety of sensory hallucinations affecting all the senses (hearing, smell, vision, etc.);
  • Negative” symptoms, which correspond to a reduction in normal functions, with affective and emotional blunting and apathy at the top of the list;
    Finally, “cognitive” or “dissociative” symptoms, characterised by a global disorganisation of thought associated with memory, attention or reasoning problems.
  • All these symptoms, and the disability they generate, are a huge burden for patients in their day-to-day social, professional and emotional lives. The risk of early death is multiplied by 2 or 3 in schizophrenic individuals compared with the general population. The suicide rate is also very high. 1 in 2 patients will attempt suicide at least once in their lifetime.


How is schizophrenia diagnosed?

Diagnosis of schizophrenia is difficult and often delayed. It is often made after a first psychotic or delusional episode. Today, there are three criteria that together define schizophrenia. Distortion of reality, characterised by delusional thoughts and hallucinations, emotional damage and disorganised thinking. The exclusion of other pathologies with which schizophrenia shares a certain number of symptoms, such as bipolar disorder or certain neurological pathologies, is also an important issue in the treatment of this disorder. The variety of symptoms and their similarity to other psychiatric conditions, as well as their fluctuation over time, make it difficult to diagnose schizophrenia, which can sometimes take a long time to be diagnosed.


What treatments are available for schizophrenia?

Treatments exist to help patients, but the wide range of symptoms makes them difficult to treat. Schizophrenia is mainly treated with neuroleptics, drugs that help control positive and negative symptoms, but are not effective against “cognitive” deficits. Up to a third of patients do not respond to these therapies. New therapeutic targets are therefore being actively sought to improve the treatment of schizophrenia, particularly cognitive deficits. Cognitive-behavioural therapies, for their part, are very useful for working with patients on their cognitive deficits and the risks of social isolation to which they may fall victim, in order to stabilise them in their daily lives.

A clinical trial currently underway at the Institut du Cerveau is seeking to treat drug-resistant auditory hallucinations with repeated transcranial magnetic stimulation (TMS), and to identify the brain mechanisms involved in the effect of this treatment using MRI.


Causes and mechanisms of schizophrenia

Today, many questions remain unanswered about the origin and pathophysiology of this disorder. While important elements concerning the role of genetics and the environment have been brought to light, the clear mechanisms for the development of the disease have yet to be elucidated.

Genetic risk factors increasing susceptibility to developing the disease have been identified, as have point mutations with probable effects on cerebral plasticity, the dynamics of cerebral connections and their adaptation to learning and life experiences.

Understanding these mechanisms is therefore essential in this disease. Several teams at the Institut du Cerveau are working on understanding the mechanisms of neuronal plasticity and sensory perception at the molecular, cellular and network levels


Anatomical changes have been observed in this pathology, with damage to the brain’s grey and white matter, as well as to its support cells such as oligodendrocytes, and to the myelin sheath, which is important in the transmission of nerve impulses. The impact of all these factors on brain function is still being studied.

Environmental factors have also been established, such as certain forms of stress which are thought to disrupt biological mechanisms in the brain, and the use of psychogenic substances such as cannabis (THC), particularly in adolescents.

Finally, the identification of markers for the development and progression of schizophrenia, which would represent a major advance in patient care, is a major hope for research.


Last updated May 2024.