Hearing loss; the neglected risk factor for psychosis

Increased Central Auditory Gain and Decreased Parvalbumin-Positive Cortical Interneuron Density in the Df1/+ Mouse Model of Schizophrenia Correlate With Hearing Impairment

Background

Hearing impairment is a risk factor for schizophrenia. Patients with 22q11.2 deletion syndrome have a 25% to 30% risk of schizophrenia, and up to 60% also have varying degrees of hearing impairment, primarily from middle-ear inflammation. The Df1/+ mouse model of 22q11.2 deletion syndrome recapitulates many features of the human syndrome, including schizophrenia-relevant brain abnormalities and high interindividual variation in hearing ability. However, the relationship between brain abnormalities and hearing impairment in Df1/+ mice has not been examined.

Methods

We measured auditory brainstem responses, cortical auditory evoked potentials, and/or cortical parvalbumin-positive (PV+) interneuron density in over 70 adult mice (32 Df1/+, 39 wild-type). We also performed longitudinal auditory brainstem response measurements in an additional 20 animals (13 Df1/+, 7 wild-type) from 3 weeks of age.

Results

Electrophysiological markers of central auditory excitability were elevated in Df1/+ mice. PV+ interneurons, which are implicated in schizophrenia pathology, were reduced in density in the auditory cortex but not the secondary motor cortex. Both auditory brain abnormalities correlated with hearing impairment, which affected approximately 60% of adult Df1/+ mice and typically emerged before 6 weeks of age.

Conclusions

In the Df1/+ mouse model of 22q11.2 deletion syndrome, abnormalities in central auditory excitability and auditory cortical PV+ immunoreactivity correlate with hearing impairment. This is the first demonstration of cortical PV+ interneuron abnormalities correlating with hearing impairment in a mouse model of either schizophrenia or middle-ear inflammation.

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.

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.

Psychotic symptoms and sensory impairment: Findings from the 2014 adult psychiatric morbidity survey

PURPOSE

Hearing and visual impairment have been associated with psychosis. Mechanisms behind this are poorly understood. We tested whether i) self-reported hearing and visual impairments are associated with psychotic symptoms in the 2014 UK Adult Psychiatric Morbidity Survey; ii) the odds of having psychotic symptoms vary with self-perceived degree of impairments; and iii) reduced social functioning partially explains these associations.

METHODS

We analysed cross-sectional data using logistic regression. Hearing and visual impairment were the exposures, and screening positive on the Psychosis Screening Questionnaire was the outcome. We used structural equation modelling to assess mediation by social functioning, measured by the Social Functioning Questionnaire.

RESULTS

Psychotic symptoms were strongly associated with visual impairment (Adjusted Odds Ratio (AOR) 1.81, 95% Confidence Intervals (CI) 1.33 to 2.44), especially moderate visual impairment (AOR 2.75, 95% CI 1.78 to 4.24, p < .001). Psychotic symptoms were associated with a severe degree of hearing impairment (AOR 4.94, 95% CI 1.66 to 14.67, p = .004), and weakly associated with hearing impairment overall (AOR 1.50, 95% CI 1.10 to 2.04, p = .010). Social functioning accounted for approximately 50% of associations with both types of sensory impairment, but the confidence intervals around these estimates were broad.

CONCLUSIONS

Our findings suggest an association between psychosis and visual impairment, with the strongest evidence for moderate visual impairment; the findings also support a linear relationship between psychosis and degree of hearing impairment. Social functioning may mediate these relationships and be a potential target for intervention, alongside sensory correction. These should be investigated longitudinally.

Hallucinations and Strong Priors

Hallucinations, perceptions in the absence of objectively identifiable stimuli, illustrate the constructive nature of perception. Here, we highlight the role of prior beliefs as a critical elicitor of hallucinations. Recent empirical work from independent laboratories shows strong, overly precise priors can engender hallucinations in healthy subjects and that individuals who hallucinate in the real world are more susceptible to these laboratory phenomena. We consider these observations in light of work demonstrating apparently weak, or imprecise, priors in psychosis. Appreciating the interactions within and between hierarchies of inference can reconcile this apparent disconnect. Data from neural networks, human behavior, and neuroimaging support this contention. This work underlines the continuum from normal to aberrant perception, encouraging a more empathic approach to clinical hallucinations.

Auditory hallucinations in adults with hearing impairment: a large prevalence study

BACKGROUND

Similar to visual hallucinations in visually impaired patients, auditory hallucinations are often suggested to occur in adults with hearing impairment. However, research on this association is limited. This observational, cross-sectional study tested whether auditory hallucinations are associated with hearing impairment, by assessing their prevalence in an adult population with various degrees of objectified hearing impairment.

METHODS

Hallucination presence was determined in 1007 subjects aged 18-92, who were referred for audiometric testing to the Department of ENT-Audiology, University Medical Center Utrecht, the Netherlands. The presence and severity of hearing impairment were calculated using mean air conduction thresholds from the most recent pure tone audiometry.

RESULTS

Out of 829 participants with hearing impairment, 16.2% (n = 134) had experienced auditory hallucinations in the past 4 weeks; significantly more than the non-impaired group [5.8%; n = 10/173; p &lt; 0.001, odds ratio 3.2 (95% confidence interval 1.6-6.2)]. Prevalence of auditory hallucinations significantly increased with categorized severity of impairment, with rates up to 24% in the most profoundly impaired group (p &lt; 0.001). The corrected odds of hallucination presence increased 1.02 times for each dB of impairment in the best ear. Auditory hallucinations mostly consisted of voices (51%), music (36%), and doorbells or telephones (24%).

CONCLUSIONS

Our findings reveal that auditory hallucinations are common among patients with hearing impairment, and increase with impairment severity. Although more research on potential confounding factors is necessary, clinicians should be aware of this phenomenon, by inquiring after hallucinations in hearing-impaired patients and, conversely, assessing hearing impairment in patients with auditory hallucinations, since it may be a treatable factor.

Successful hearing improvement with direct acoustic stimulation in a patient with schizophrenia

OBJECTIVE

A direct acoustic cochlear implant provides its power directly to the inner ear by vibrating the perilymph via a conventional stapes prosthesis. Our experience with a patient with severe mixed hearing loss due to otosclerosis is described.Case reportThe patient, a 47-year-old male, had a pre-operative speech recognition score of 10 per cent and had been treated for many years for schizophrenia, both of which made him a poor candidate for a direct acoustic stimulation device. Nevertheless, the surgery was performed, which preserved the pre-operative bone conduction level and significantly improved hearing. His speech recognition score rose to 100 per cent. He uses the device all day and his auditory hallucinations have subsided. Improvement of schizophrenia symptoms has enabled the patient to reduce his psychiatric medications intake.

CONCLUSION

Hearing restoration was the main reason for the reduction of auditory hallucinations in our patient. Hearing loss is a potentially reversible risk factor for psychosis, but this association is often overlooked.

Increased risk of psychosis in patients with hearing impairment: Review and meta-analyses

Several studies suggest hearing impairment as a risk factor for psychosis. Hearing impairment is highly prevalent and potentially reversible, as it can be easily diagnosed and sometimes improved. Insight in the association between hearing impairment and psychosis can therefore contribute to prevention of psychosis. This paper provides meta-analyses of all epidemiologic evidence on the association between hearing impairment and psychosis and summarizes mechanisms that potentially underlie this relationship. Meta-analyses showed an increased risk of hearing impairment on all psychosis outcomes, such as hallucinations (OR 1.40(95%CI 1.18-1.65; n=227,005)), delusions (OR 1.55(95%CI 1.36-1.78; n=250,470)), psychotic symptoms (OR 2.23(95%CI 1.83-2.72; n=229,647) and delirium (OR 2.67(95%CI 2.05-3.48; n=12,432). Early exposure to hearing impairment elevated the risk of later development of schizophrenia (OR 3.15(95%CI 1.25-7.95; n=50,490)). Potential mechanisms underlying this association include loneliness, diminished theory of mind, disturbances of source monitoring and top-down processing and deafferentiation. Early assessment and treatment of hearing impairment in patients with (high risk of) psychosis may be essential in psychosis treatment and prevention.