Research Groups

Sommer group

My aim is to improve future perspectives for patients with schizophrenia and other complex brain disorders. I am an optimist and see many possibilities for improvement, based on new knowledge from basic research, performed by my group and others. Special emphasis is put on prevention and personalized medicine. I have broad interest in methods like imaging, post-mortem analyses, epidemiology and treatment studies. So far I have pursued my goal in three ways:

  1. By optimising currently existing therapies, such as antipsychotic regimen, cognitive-behavioural therapy and psycho-education
  2. By investigating re-purposing drugs that have shown efficacy in other disorders, such as simvastatin, clonidine, prednisolone and raloxifen
  3. By better understanding the different symptoms of brain disorders and designing new treatment strategies based on newly acquired knowledge, such as focal brain stimulation, manipulations of the gut-brain axis and designing new drugs in concert with pharmaceutical companies.

My methods to better understand common symptoms of complex brain disorders are broad and include various brain imaging techniques (EEG, MEG, DTI, fMRI, sMRI, MRS, PET), phenomenology, epidemiology, focal brain stimulation (rTMS, tDCS), (epi)genetics, immuno-histochemy and proof of concept studies. I have made important progress in the understanding hallucinations. In addition, my group recently developed a biomarker based on analysis of spontaneous speech, to be used for diagnosis, prognosis and treatment monitoring.

  • People
  • Publications
  • Grants
  • Hallucinations
  • Psychosis
  • Schizophrenia
  • Depression
  • Media
  • Presentations
  • Iris Sommer MD PhD Visit

    professor of cognitive aspects of neurological and psychiatric disorders

    Research fields

    psychosis, hallucinations, transdiagnostic symptoms

    PhD students
    Jenny Borkent MSc
    Janna de Boer MD
    Shiral Gangadin MSc
    Moni Germann
    Caitlyn Kruiper MSc
    Mascha Linszen MD
    Kim Maijer MD
    Peter Martens MD
    Lyliana Nasib MSc
    Jasper Nuninga MSc
    Priscilla Oomen MSc
    postdoctoral fellows
    Marieke Begemann PhD
    Sanne Brederoo MSc
    Maya Schutte PhD
    • All Publications: mepa page or  pdf Selected Publications:
      1. Nuninga JO, Mandl RCW, Boks MP, Bakker S, Somers M, Heringa SM, Nieuwdorp W, Hoogduin H, Kahn RS, Luijten P, Sommer IEC. Volume increase in the dentate gyrus after electroconvulsive therapy in depressed patients as measured with 7T. Molecular Psychiatry. Mar 12, 2019. Pdf. This study shows neurogenesis to underlie the anti-depressive effect of ECT. 
      2. Kahn RS, Sommer IE, Meyer-Lindenberg A, Weinberger DRW, van Os J, Murray M, O’Donnovan M, Correll C, Cannon T, Kane J, Insel T. Schizophrenia. Nature Reviews Disease Primer Nov 12, 2015. Pdf. State-of-the-art paper on schizophrenia with world-leading authors.
      3. Blom JD, Sommer IE, Koops S, Sacks OMD. Prosopometamorphopsia and facial hallucinations. The Lancet 2014 384(9958):1998. Pdf.
      4. Sommer IE, Diederen KM, Blom JD, Willems A, Kushan L, Slotema K, Boks MP, Daalman K, Hoek HW, Neggers SF, Kahn RS. Auditory verbal hallucinations predominantly activate the right inferior frontal area. Brain. 2008;131(Pt 12):3169-77. Pdf. This study showed the right hemisphere language structures active during auditory verbal hallucinations.
      5. Sommer IE, Ramsey NF, Bouma A, Kahn RS. Cerebral mirror-imaging in a monozygotic twin. The Lancet. 1999 Oct 23;354(9188):1445-6. Pdf. This study showed opposite dominance for language in monozygotic twins.
  • Ongoing projects:

    Grants Year of award
    Hersenstichting 2018
    Stichting MS Research 2018
    ZONMW, Goed Gebruik Geneesmiddelen GG2 2018
    Stanley Foundation 2018
    QNRF NPRP11S-0119-180341 2018
    ZONMW, Goed Gebruik 2017
  • Understanding Hallucinations

    Understanding Hallucinations is a collaborative efforts to investigate phenomenology, cognition and underlying mechanisms of hallucinating patients with diverse disorders. We have so far included participants with schizophrenia, affective psychosis, post traumatic stress disorder, personality disorder, Parkinsons’ disease, Alzheimers’ disease, dementia with Lewy Bodies, hearing loss, vision loss, delirium and post-surgical status. Such broad inclusion was possible through fruitful collaborations with the Alzheimer Center Vumc, Parnassia, Neurology Department UMCG and Diaconnessen and Antonius hospital.

    Direct comparison of phenomenology was made possible by designing a questionnaire that can be used across diagnoses, see 

    2016 Public Project

    In 2016 we launched a large online investigation together with Weekend van de Wetenschap (a national organization to stimulate public interest in science) and NEMO Science museum. Phenomenology of hallucinations is assessed through the website and cognition is tested by measuring speed and accuracy on two tests. Drug use, sleep, loneliness and atopy is inquired and hearing loss is assessed. So far over 10.000 participants have completed this online test.

    tDCS for hallucinations

    When patients experience auditory hallucinations, we see extensive activation of language production and perception areas of both hemispheres. Focal stimulation with transcranial magnetic stimulation and transcranial direct current stimulation can reduce activity in local areas directly underlying the skull. This study provides 10 treatment sessions in an attempt to decrease frequency and severity of auditory hallucinations. The study includes in UMCU, Parnassia and Bergen (Norway)

  • Discontinue study

    Antipsychotic medication is effective in preventing relapse after a first psychosis. However, long-term dopamine blockade produces undesired effects on cognition and motivation. The discontinue study balances advantages and disadvantages of maintenance treatment on the long run in 512 patients who reached remission after a first psychosis. This project is a collaboration of 22 large institutes in the Netherlands, joined in the Psychosis Consortium.


    Following the important work of Dr. Oranje, assessing the influence of norepinephrine agonists on ERPs, this study adds low dose clonidine to standard antipsychotic treatment in order to improve symptoms and cognition. CATs study includes in UMCU, Altrecht and GGZ Centraal.

  • Immune studies

    Two randomized control studies assess the safety and efficacy of augmentation with anti-inflammatory drugs in people with schizophrenia-spectrum disorder. The main outcome is symptom severity. Important secondary outcomes are general functioning, side-effects, brain volume, PK11195-binding (PET), peripheral inflammation and cognition. The simvastatine study includes in AMC, UMCG, GGZ Ingeest, Altrecht, Reinier van Arkel stichting, GGZ Centraal, Arkin and GGZ NoorHolland Noord. On May 11 a symposium is organized to celebrate the 100st inclusion. The prednisolone study is including in UMCU, Yulius, GGZ Delfland, ZN Antwerpen and Bergen (Norway).



    It has long been known that women with schizophrenia have much better prognosis than men, but this advantage is lost after menopause. Several small studies found efficacy on symptoms and cognition of estrogen or estrogen derives. This study investigates the safety and efficacy of augmentation with raloxiphene in men and women with schizophrenia-spectrum disorders. The study includes in UMCU, AMC, GGZ Centraal, GGZ Eindhoven and ZN Antwerpen.

  • 7-ECT for severe depression is the most effective treatment of all psychiatric interventions. Yet we only partly understand its mechanism of action. This study measures, structure, function and circulation of key brain structures before and after ECT in patients with unipolar and bipolar depression.

  • Our group is active in Dutch and international media. Please find a selection of our newspaper articles and TV and radio items.


    In addition, we are proud to have produced five podcasts on several types of hallucinations. These are short stories told by the people who experience the hallucinations, followed by a brief psychiatric explanation. Maayke Klaver, M.Sc. created these podcasts in collaboration with NEMO and Kennislink.
    You can listen to our podcast via Soundcloud:

    For the UMCG podcastseries The Genezers(The Healers) we hear the story of Carolien Jansen who after suffering years from heavy depression is treated with Electro Compulsive Therapy. You can find this podcast here.



    • 26-09-2016 – Introduction of public investigation (RTL late night)

    • Iris Sommer over de invloed van sport op hersenen

    • Iris Sommer over hallucinaties

    • Iris Sommer over risico’s van sport op onze hersenen

    • Iris Sommer over hallucineren tijdens koorts

    • Iris Sommer over hallucinaties bij jonge ouders


  • Our group regularly provides presentations about hallucinations, psychosis, focal stimulation, brain disorders or about specific projects. Some examples of presentations can be viewed through the links below.
    For booking of presentation by Iris, please contact Speakers Academy.

    Previous presentations

    • Lowlands Science 2016

    • Tivoli Vredenburg – Betweter Festival 2016

    • Opening national psychiatry congress 2016

    • Hearing voices

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