Monitoring the past and choosing the future: the prefrontal cortical influences on voluntary action.

Choosing between equivalent response options requires the resolution of ambiguity. One could facilitate such decisions by monitoring previous actions and implementing transient or arbitrary rules to differentiate response options. This would reduce the entropy of chosen actions. We examined voluntary action decisions during magnetoencephalography, identifying the spatiotemporal correlates of stimulus- and choice-entropy. Negative correlations between frontotemporal activity and entropy of past trials were observed after participants' responses, reflecting sequential monitoring of recent events. In contrast, choice entropy correlated negatively with prefrontal activity, before and after participants' response, consistent with transient activation of latent response-sets ahead of a decision and updating the monitor of recent decisions after responding. Individual differences in current choices were related to the strength of the prefrontal signals that reflect monitoring of the statistical regularities in previous events. Together, these results explain individual expressions of voluntary action, through differential engagement of prefrontal areas to guide sequential decisions.

Functional auditory disorders.

There are a number of auditory symptom syndromes that can develop without an organic basis. Some of these, such as nonorganic hearing loss, affect populations similar to those presenting with functional somatosensory and motor symptoms, while others, such as musical hallucination, affect populations with a significantly different demographic and require different treatment strategies. Many of these conditions owe their origin to measurably abnormal peripheral sensory pathology or brain network activity, but their pathological impact is often due, at least in part, to overamplification of the salience of these phenomena. For each syndrome, this chapter briefly outlines a definition, demographics, investigations, putative mechanisms, and treatment strategies. Consideration is given to what extent they can be considered to have a functional basis. Treatments are in many cases pragmatic and rudimentary, needing more work to be done in integrating insights from behavioral and cognitive psychology to auditory neuroscience. The audiology literature has historically equated the term functional with malingering, although this perception is, thankfully, slowly changing. These disorders transcend the disciplines of audiology, otorhinolaryngology, neurology and psychiatry, and a multidisciplinary approach is often rewarding.

Is musical hallucination an otological phenomenon? a review of the literature.

BACKGROUND: Musical hallucination is the subjective experience of hearing music, or aspects of music, when none is being played, and as such is a disorder of the processing of complex sounds. OBJECTIVE OF REVIEW: To determine the extent to which the otological system is responsible for musical hallucination, and to evaluate approaches to clinical management. TYPE OF REVIEW: A review of all studies and literature reviews pertaining to musical hallucination, supplemented by inclusion of informative case reports. SEARCH STRATEGY: A systematic search of multiple databases carried out on 22nd March 2009 was complemented by referral to the reference lists of included manuscripts. RESULTS: Although not always troublesome in itself, musical hallucination can be a marker of underlying pathology in the ear or brain, or indicate obsessive-compulsive traits or social isolation, and is likely to be clinically underreported. Associations have been reported with hearing loss, female gender, social isolation and being over 60 years of age, although it is rare even in this group, and these may well not be independent risk factors. Robust comparative analysis of these factors with controls has yet to be undertaken. Underlying causes include neurovascular pathology, psychiatric disorders and opioid medications, however these are absent in the majority of cases. CONCLUSIONS: This review supports the proposal that the otological system plays a role in the pathogenesis of musical hallucination. Hearing impairment may act as an initiating factor, and the primary dysfunction is overactivity of auditory association cortex, although an impairment of higher-level inhibition does also seem necessary. Once underlying sinister causes have been excluded, first line treatment should be explanation of the condition and optimisation of hearing. Medications have a role only in selected patient groups.