Researchers from Trinity College Dublin and the Royal College of Surgeons in Ireland (RCSI) have shown for the first time, the mental health significance of hallucinations in people with a history of seizures.
In a study published today, findings show that 8% of individuals with a history of seizures report hallucinations, including experiences of hearing or seeing things that are not based in reality.
And, most importantly of that 8%, 65% also met criteria for one or more mental health disorders and 53% had one or more suicide attempt.
The study is published in leading journal Epilepsia. As part of one of the longest running studies of mental health in the general population, researchers assessed a wide range of physical and mental health factors in 15,000 people living in the UK. Hallucinations are known to occur in a proportion of adults with seizures but may be erroneously viewed as ‘incidental’ symptoms of abnormal electrical activity in the brain and nothing more.
The findings of this study tell us that these symptoms are not just incidental in people with seizures; they are important markers of risk for mental ill health and for suicidal behaviour.
Dr Ian Kelleher, Research Associate Professor of Psychiatry, Trinity and Senior Author of the study said:
” People with epilepsy are known to be at increased risk of suicide. But among individuals with seizures, it’s hard to pick out who is most at risk. What this research shows is that people with seizures who report hallucinations are a particularly high-risk group for suicidal behaviour – about half of these individuals had one or more suicide attempt.
So, it’s important in epilepsy clinics to ask about hallucinations – and where someone endorses these symptoms, to carefully examine their mental state.”
In an Irish context, anecdotal evidence tells us that auditory and visual hallucinations are not routinely assessed in epilepsy clinics.
Kathryn Yates, RCSI, Study Author said:
“It’s not surprising that individuals with seizures have a higher rate of hallucinations – almost any disease that affects the brain is likely to increase risk of hallucinations.
However, it’s important to recognise that hallucinations don’t simply reflect abnormal electrical activity in individuals with epilepsy; they’re important markers of risk for mental health problems and suicidal behaviour.”
Dr Kelleher concluded:
“We’ll need further research to fully understand the significance of hallucinations in people with seizures.
But what’s clear from this work is that, for clinicians working with people with seizures, asking about auditory and visual hallucinations should be a routine part of their assessment.”
Hallucinations—erroneous perceptions that are not elicited by external stimuli—may manifest in every sensory modality1. In schizophrenia, auditory hallucinations (AHs) have been described as the dominant experiences, with occurrence rates ranging from 60% to 80%2.
Although visual hallucinations (VHs) have been largely neglected in psychiatric disorders, a systematic review showed evidence of a weighted mean of 27% of VHs in schizophrenia3.
In contrast to what can be observed in neurological or eye diseases, schizophrenia is characterized by very rare isolated VHs4, which typically co-occur with hallucinations in other sensory modalities5,6,7,8,9, notably with auditory hallucinations in up to 84% (later called “A+VH”10).
Impairments of the hippocampus, a medial temporal structure involved in mnesic and neuroplastic processes, have been repeatedly reported in schizophrenia.
Such changes include reductions in volume, increases in basal perfusion, activation deficits during declarative memory, and reductions in neurogenesis in the dentate gyrus (for a recent review, see ref. 11).
More precisely, hippocampal hyperactivity was regularly associated with auditory12,13, visual14, or multisensory hallucinations15. Beyond a strict local alteration, disrupted hippocampal oscillations were linked to functional changes in hallucinations-related network16, while we observed specific structural and functional hippocampal dysconnectivity patterns in patients with audio–visual hallucinations17.
The fact that some schizophrenia patients experience pure AH or A+VH experiences has been related to developmental factors. Several studies reported that the rate of VHs in schizophrenia was age-dependent18,19,20, and some authors proposed that they could be considered as a severity index of developmental abnormalities19, a theory in line with the neurodevelopmental model of schizophrenia, which considers this disorder as the end state of abnormal brain development starting years before its onset21.
This hypothesis was recently supported by the association of VHs with impaired cortical sulcation22, an indirect proxy of early deviations in brain development23,24.
Surprisingly, the question of a possible neurodevelopmental origin of hippocampal impairments in VHs has never been investigated. A classic marker of early atypical hippocampal development is incomplete hippocampal inversion (IHI)25,26,27.
IHI is a variant of the hippocampus anatomy, in which prominent features are round, verticalized, and medially positioned hippocampus28,29. Different terms have been used to refer to this atypical pattern, including “hippocampal malrotation”30,31,32, “abnormal hippocampal formation”29, or “developmental changes of the hippocampal formation”28.
IHI has been described in patients with seizures (with a prevalence of ~30–50%), particularly in the case of impaired cortical development and in temporal lobe epilepsy28,29,33,34.
However, IHI is not specific to epilepsy and has also been reported in healthy individuals, although with a lower frequency25,29,35. A recent study assessed the prevalence of IHI in the general population in a large sample of over 2000 subjects and reported more frequent IHIs in the left (17%) than in the right (6%) hemispheres36.
In this context, this study aimed to test the hypothesis of a neurodevelopmental hippocampal deviation specifically associated with VHs in schizophrenia. We compared healthy volunteers with two subgroups of carefully selected seizure-free schizophrenia patients experiencing frequent hallucinations: patients with pure AH (i.e., patients who had never reported visual hallucinations) and patients with A+VH. The matched subgroups of patients differed only in the presence or absence of VHs. This distinction appears crucial in testing for variable IHI in patients with hallucinations according to the sensory modality involved.
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