Deafferentation as a cause of hallucinations

PURPOSE OF REVIEW: The association between hallucinations and sensory loss, especially vision- and hearing-impairment, has been firmly established over the past years. The deafferentation theory, a decrease of the threshold for activation in the brain and the consequential imbalance between excitatory and inhibitory brain networks, is hypothesized to underly this relationship. Here we review the studies investigating this theory with a focus on the most recent literature to better understand the contribution of sensory loss to hallucinations. RECENT FINDINGS: A large cross-sectional study has recently confirmed the relationship between auditory impairment and deafferentation. However, the underlying mechanisms of deafferentation are still under debate, with hyperexcitability and deviations in bottom-up and top-down processes being the most likely explanations. Social isolation following sensory impairment increases the risk for hallucinations. Better knowledge and awareness about the contribution of deafferentation and loneliness would benefit diagnosis and treatment of hallucinations. SUMMARY: Studies imply activity in higher order areas, corresponding to the functional mapping of sensory system, and a general state of higher excitability as neurobiological explanation. Auditory deafferentation, tinnitus and other auditory hallucinations, likely lie on a continuum. Social isolation mediates psychotic symptoms in sensory-impaired individuals. Currently, there is no standard treatment for deafferentation hallucinations

Spontaneous brain activity underlying auditory hallucinations in the hearing-impaired

Auditory hallucinations, the perception of a sound without a corresponding source, are common in people with hearing impairment. Two forms can be distinguished: simple (i.e., tinnitus) and complex hallucinations (speech and music). Little is known about the precise mechanisms underlying these types of hallucinations. Here we tested the assumption that spontaneous activity in the auditory pathways, following deafferentation, underlies these hallucinations and is related to their phenomenology. By extracting (fractional) Amplitude of Low Frequency Fluctuation [(f)ALFF] scores from resting state fMRI of 18 hearing impaired patients with complex hallucinations (voices or music), 18 hearing impaired patients with simple hallucinations (tinnitus or murmuring), and 20 controls with normal hearing, we investigated differences in spontaneous brain activity between these groups. Spontaneous activity in the anterior and posterior cingulate cortex of hearing-impaired groups was significantly higher than in the controls. The group with complex hallucinations showed elevated activity in the bilateral temporal cortex including Wernicke's area, while spontaneous activity of the group with simple hallucinations was mainly located in the cerebellum. These results suggest a decrease in error monitoring in both hearing-impaired groups. Spontaneous activity of language-related areas only in complex hallucinations suggests that the manifestation of the spontaneous activity represents the phenomenology of the hallucination. The link between cerebellar activity and simple hallucinations, such as tinnitus, is new and may have consequences for treatment. (C) 2020 The Author(s). Published by Elsevier Ltd

Time varying dynamics of hallucinations in clinical and non-clinical voice-hearers

Auditory verbal hallucinations (AVH) are frequently associated with psychotic disorders, yet also occur in non-clinical voice-hearers. AVH in this group are similar to those within clinical voice-hearers in terms of several phenomenological aspects, but non-clinical voice-hearers report to have more control over their AVH and attribute less emotional valence to them. These dissimilarities may stem from differences on the neurobiological level, as it is still under debate whether the mechanisms involved in AVH are the same in clinical and non-clinical voice-hearers. In this study, 21 clinical and 21 non-clinical voice-hearers indicated the onset and offsets of AVH during an fMRI scan. Using a method called leading eigenvector dynamics analysis (LEiDA), we examined time-varying dynamics of functional connectivity involved in AVH with a sub-second temporal resolution. We assessed differences between groups, and between hallucination and rest periods in dwell time, switching frequency, probability of occurrence, and transition probabilities of nine recurrent states of functional connectivity with a permutation ANOVA. Deviations in dwell times, switching frequencies, and switch probabilities in the hallucination period indicated more erratic dynamics during this condition regardless of their clinical status. Post-hoc analyses of the dwell times exhibited the most distinct differences between the rest and hallucination condition for the non-clinical sample, suggesting stronger differences between the two conditions in this group. Overall, these findings suggest that the neurobiological mechanisms involved in AVH are similar in clinical and non-clinical individuals.</p

Hallucinations in Hearing Impairment: How Informed Are Clinicians?

Background and Hypothesis: Patients with hearing impairment (HI) may experience hearing sounds without external sources, ranging from random meaningless noises (tinnitus) to music and other auditory hallucinations (AHs) with meaningful qualities. To ensure appropriate assessment and management, clinicians need to be aware of these phenomena. However, sensory impairment studies have shown that such clinical awareness is low. Study Design: An online survey was conducted investigating awareness of AHs among clinicians and their opinions about these hallucinations. Study Results: In total, 125 clinicians (68.8% audiologists; 18.4% Ear-Nose-Throat [ENT] specialists) across 10 countries participated in the survey. The majority (96.8%) was at least slightly aware of AHs in HI. About 69.6% of participants reported encountering patients with AHs less than once every 6 months in their clinic. Awareness was significantly associated with clinicians’ belief that patients feel anxious about their hallucinations (β = .018, t(118) = 2.47, P < .01), their belief that clinicians should be more aware of these hallucinations (β =.018, t(118) = 2.60, P < .01), and with confidence of clinicians in their skills to assess them (β = .017, t(118) = 2.63, P < .01). Clinicians felt underequipped to treat AHs (Median = 31; U = 1838; PFDRadj < .01). Conclusions: Awareness of AHs among the surveyed clinicians was high. Yet, the low frequency of encounters with hallucinating patients and their belief in music as the most commonly perceived sound suggest unreported cases. Clinicians in this study expressed a lack of confidence regarding the assessment and treatment of AHs and welcome more information

Hallucinations and other psychotic experiences across diagnoses:A comparison of phenomenological features

Although psychotic experiences are prevalent across many psychiatric, neurological, and medical disorders, investigation of these symptoms has largely been restricted to diagnostic categories. This study aims to examine phenomenological similarities and differences across a range of diagnoses. We assessed frequency, severity and phenomenology of psychotic experiences in 350 outpatients including; participants with schizophrenia spectrum disorders, hearing impairment, Parkinson's disease, Lewy Body Dementia, Alzheimer's disease, visual impairment, posttraumatic stress disorder, borderline personality disorder, and participants with recent major surgery. Psychotic phenomena were explored between these groups using the Questionnaire for Psychotic Experiences (QPE). Participants with major psychiatric disorders reported a combination of several psychotic experiences, and more severe experiences compared to all other disorders. Participants with recent major surgery or visual impairment experienced isolated visual hallucinations. Participants with hearing impairment reported isolated auditory hallucinations, whereas the neurodegenerative disorders reported visual hallucinations, occasionally in combination with hallucinations in another modality or delusions. The phenomenology between neurodegenerative disorders, and within major psychiatric disorders showed many similarities. Our findings indicate that the phenomenology of psychotic experiences is not diagnosis specific, but may rather point to the existence of various subtypes across diagnoses. These subtypes could have a different underlying etiology requiring specific treatment