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Auditory Hallucinations in Psychiatric Illness: Page 3 of 3

Auditory Hallucinations in Psychiatric Illness: Page 3 of 3

Theoretical frameworks of auditory hallucinations

The exact processes that underlie auditory hallucinations remain largely unknown. There are 2 principal avenues of research: one focuses on neuroanatomical networks using techniques such as positron emission tomography and functional MRI. The other focuses on cognitive and psychological processes and the exploration of mental events involved in auditory hallucinations.

A common formulation suggests that auditory verbal hallucinations represent an impairment in language processing and, particularly, inner speech processes, whereby the internal and silent dialogue that healthy people engage in is no longer interpreted as coming from the self but instead as having an external alien origin. There is support for this language hypothesis of auditory hallucinations from neuroimaging studies. These show that the experience of auditory hallucinations engages brain regions, such as the primary auditory cortex and Broca area (Figure), that are associated with language comprehension and production. This suggests that hallucinatory experiences are associated with listening to external speech in the absence of external sounds.23,24

An explanation of why these experiences are not perceived as self-generated posits that audi-tory hallucinations arise because persons who have the hallucinations fail to distinguish between internal and external events. According to Frith’s self-monitoring theory,25 this arises because of deficits in internal self-monitoring mechanisms that compare the expected with the actual sensations that arise from the patient’s intentions. This abnormality also applies to inner speech processes and leads to the misclassification of internal events as external and misattribution to an external agent.

By contrast, Bentall and Slade26 have proposed that individuals with hallucinations use a different set of judgment criteria from healthy people when deciding whether an event is real, and they are more willing to accept that a perceptual experience is true. This bias essentially involves a greater willingness to believe that an event is real on the basis of less evidence.

According to the context memory hypothesis of auditory hallucinations, the failure to identify events as self-generated arises because of specific deficits in episodic memory for remembering the details associated with particular past memory events. These specific deficits in memory cause confusion about the origins of the experience.27-29 In support of this hypothesis, findings indicate that patients with auditory hallucinations tend to misidentify the origins and source of stimuli during ongoing events and during memory events.27-30 In addition, imaging studies have shown abnormalities in brain regions associated with memory integration in individuals with schizophrenia.31-33

The lack of voluntary control over the experience is a key feature of auditory hallucinations, which might explain why self-generated inner speech is classified as external in origin.33 According to this proposal, hallucinations are experienced when verbal thoughts are unintended and unwanted. Because deficits in cognitive processes, such as inhibitory control, are thought to render people more susceptible to intrusive and recurrent unwanted thoughts, studies have linked auditory hallucinations with deficits in cognitive inhibition.29

From a neuroanatomical point of view, deficits in the prefrontal cortex of patients with auditory hallucinations are consistent with the hypothesis of cognitive inhibitory deficits. Functional disconnectivity between the frontal and posterior areas of the brain in hallucinating patients may result in a lack of modulatory control of the frontal cortex over activities generated by the posterior brain areas so that events that arise from the temporal/parietal areas are not regulated normally.32,34

Recent advances in the neurosciences provide clues to why patients report an auditory experience in the absence of any perceptual input. Spontaneous activity in the early sensory cortices may in fact form the basis for the original signal. Early neuronal computation systems are known to interpret this activity and engage in decision-making processes to determine whether a percept has been detected.35 A brain system that is abnormally tuned in to internal acoustic experiences may therefore report an auditory perception in the absence of any external sound. Ford and colleagues36 recently suggested that patients with auditory hallucinations may have excessive attentional focus toward internally generated events—the brains of persons who have auditory hallucinations may therefore be overinterpreting spontaneous sensory activity that is largely ignored in healthy brains.

Cognitive impairments are not the only factors responsible for auditory hallucinations. Psychological factors such as metacognitive biases, beliefs, and attributions concerning the origins and intent of voices also play a critical modulatory role in shaping the experience of hallucinations.16,19,37 The role of environmental cues and reinforcement factors through avoidance strategies must also be incorporated in any explanations of auditory hallucinations. These factors do not explain how hallucinations occur in the first place, but they have strong explanatory power when accounting for individual differences in how the voices are experienced.

Treatment of auditory hallucinations

The presence of hallucinations does not necessarily imply a need for medical treatment if the experience is not intrusive and does not interfere with everyday activities. When treatment is required, antipsychotic medication is usually the treatment of choice in organic and psychiatric conditions. Clinicians should provide information and discuss the benefits and adverse effects of each drug, including a drug’s potential to cause symptoms that include the extrapyramidal syndrome and metabolic syndrome. In view of such adverse effects, clinicians need to monitor the physical health of patients regularly.

Few studies have compared the efficacy of different neuroleptic treatments, and hallucinations often persist despite intensive and prolonged psychopharmacological treatment.38 Another biological method that has been researched in recent years is repetitive transcranial magnetic stimulation (rTMS), which plays a role in altering neural activity over language cortical regions. Used as an adjunct to antipsychotic medication, studies show that rTMS can reduce the frequency and severity of auditory hallucinations in treatment-resistant cases.39,40

Many psychological treatments target the idiosyncratic ways that individuals respond to an abnormal perceptual experience, based on the understanding that this influences their coping strategies and emotional response.16,19,37 Studies show that some patients respond well to cognitive-behavioral therapy, where the focus is on evaluating and monitoring one’s perceptions, beliefs, and reasoning; promoting alternative ways of coping; and reducing distress. Anxiety reduction strategies are particularly effective in reducing the impact of voices.41-43 Evidence also suggests that a combination of family and psychological interventions, as well as medication, may be the most beneficial treatment for auditory hallucinations.44

There is increasing evidence that peer support groups (voice-hearers networks; http://www.intervoiceonline.org) can help alleviate the impact of voices. Self-help groups often encourage patients to take responsibility for their hallucinatory experience, to accept the voices, and to cope with them. A series of investigations showed that accepting hallucinations as an aspect of the normal human condition is one of the most difficult steps to take, but that the acceptance process and lack of resistance lead to successful adaptation to hearing voices and a change in the relationship with the voices.45

Because cognitive dysfunctions have been shown to underlie auditory hallucinations, cognitive deficits are becoming targets of treatment with cognitive remediation strategies, although these interventions are at a very early stage of development. By focusing on deficits found to be linked to auditory hallucinations, recent trials have focused on the convergence between theory and practice.46-48 For example, in their study, Favrod and colleagues48 taught patients techniques to help them recognize the source of the voices; beneficial outcomes were maintained at 1-month follow-up.

Conclusion

Auditory hallucinations are much more than false perceptions. The combination of personalized contents and interpretational processes contributes to a dynamic and emotionally charged experience that can be better described as a belief system rooted in a perceptual experience. Auditory hallucinations are most likely to arise because of an interaction between perceptual, cognitive, and biological vulnerability as well as affective factors and contextual influences. In addition, the interpretation of these experiences combined with delusional elaboration makes auditory hallucinations a complex and truly individualized phenomenon. Understanding their complexity can lead to useful insights for therapy.

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References

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