Lateral asymmetries in auditory acuity distinguish hallucinating from nonhallucinating schizophrenic patients

Auditory perceptual discomfort and low-hearing tolerance in the first episode psychosis

Awareness of perceptual and sensory changes that might occur in visual, auditory, proprioception, and other senses, in the early stages towards the First Episode Psychosis (FEP), and their subsequent sensorial evolution as the disturb progresses deeper into an acute episode, might be a key element for interrupting the process. In the present study, we investigated hearing discomfort/tolerance to 16 given sound streams. Sixteen people diagnosed with FEP, participated in the experiment. Sixteen frequency sweeps varying in modulation envelopes (sawtooth, sine), order (ascending, descending), duration (4s, 8s), and range (50–8000 Hz, 2–8 kHz) were presented randomly, but always in the same sequence, to FEP and healthy controls (HC). The level of discomfort was estimated by the participant by making a mark across a continuous line whose extremes read “nothing bad” (left) and “too bad” (right). Results showed that ascending sine pure frequency sweeps (p < 0.01) and descending sine pure frequencies sweeps (p < 0.01) caused the maximum discomfort in FEP. Other variables also showed differences between FEP and HC, and FEP were always more intolerant to such pure frequency sweeps than HC. We conclude that this might be useful for very early assessment of people at risk, people with FEP, and people with schizophrenia.

Genome-wide association study and polygenic risk score analysis for hearing measures in children

An efficient auditory system contributes to cognitive and psychosocial development. A right ear advantage in hearing thresholds (HTs) has been described in adults and atypical patterns of left/right hearing threshold asymmetry (HTA) have been described for psychiatric and neurodevelopmental conditions. Previous genome-wide association studies (GWASs) on HT have mainly been conducted in elderly participants whose hearing is more likely to be affected by external environmental factors. Here, we investigated HT and HTA in a children population cohort (ALSPAC, n = 6,743). Better hearing was associated with better cognitive performance and higher socioeconomic status. At the group level, HTA suggested a left ear advantage (mean = -0.28 dB) that was mainly driven by females. SNP heritability for HT and HTA was 0.13 and 0.02, respectively (n = 4,989). We found a modest negative genetic correlation between HT and reading ability. GWAS for HT (n = 5,344) did not yield significant hits but polygenic risk scores for higher educational attainment (EA, ß = -1,564.72, p = .008) and schizophrenia (ß = -241.14, p = .004) were associated with lower HT, that is, better hearing. In summary, we report new data supporting associations between hearing measures and cognitive abilities at the behavioral level. Genetic analysis suggests shared biological pathways between cognitive and sensory systems and provides evidence for a positive outcome of genetic risk for schizophrenia.

Visual hallucinations, thalamocortical physiology and Lewy body disease: A review

One of the core diagnostic criteria for Dementia with Lewy Bodies (DLB) is the presence of visual hallucinations. The presence of hallucinations, along with fluctuations in the level of arousal and sleep disturbance, point to potential pathological mechanisms at the level of the thalamus. However, the potential role of thalamic dysfunction in DLB, particularly as it relates to the presence of formed visual hallucinations is not known. Here, we review the literature on the pathophysiology of DLB with respect to modern theories of thalamocortical function and attempt to derive an understanding of how such hallucinations arise. Based on the available literature, we propose that combined thalamic-thalamic reticular nucleus and thalamocortical pathology may explain the phenomenology of visual hallucinations in DLB. In particular, diminished α7 cholinergic activity in the thalamic reticular nucleus may critically disinhibit thalamocortical activity. Further, concentrated pathological changes within the posterior regions of the thalamus may explain the predilection for the hallucinations to be visual in nature.

The role of the primary auditory cortex in the neural mechanism of auditory verbal hallucinations

Auditory verbal hallucinations (AVHs) are a subjective experience of "hearing voices" in the absence of corresponding physical stimulation in the environment. The most remarkable feature of AVHs is their perceptual quality, that is, the experience is subjectively often as vivid as hearing an actual voice, as opposed to mental imagery or auditory memories. This has lead to propositions that dysregulation of the primary auditory cortex (PAC) is a crucial component of the neural mechanism of AVHs. One possible mechanism by which the PAC could give rise to the experience of hallucinations is aberrant patterns of neuronal activity whereby the PAC is overly sensitive to activation arising from internal processing, while being less responsive to external stimulation. In this paper, we review recent research relevant to the role of the PAC in the generation of AVHs. We present new data from a functional magnetic resonance imaging (fMRI) study, examining the responsivity of the left and right PAC to parametrical modulation of the intensity of auditory verbal stimulation, and corresponding attentional top-down control in non-clinical participants with AVHs, and non-clinical participants with no AVHs. Non-clinical hallucinators showed reduced activation to speech sounds but intact attentional modulation in the right PAC. Additionally, we present data from a group of schizophrenia patients with AVHs, who do not show attentional modulation of left or right PAC. The context-appropriate modulation of the PAC may be a protective factor in non-clinical hallucinations.

The role of the primary auditory cortex in the neural mechanism of auditory verbal hallucinations

Auditory verbal hallucinations (AVHs) are a subjective experience of “hearing voices” in the absence of corresponding physical stimulation in the environment. The most remarkable feature of AVHs is their perceptual quality, that is, the experience is subjectively often as vivid as hearing an actual voice, as opposed to mental imagery or auditory memories. This has lead to propositions that dysregulation of the primary auditory cortex (PAC) is a crucial component of the neural mechanism of AVHs. One possible mechanism by which the PAC could give rise to the experience of hallucinations is aberrant patterns of neuronal activity whereby the PAC is overly sensitive to activation arising from internal processing, while being less responsive to external stimulation. In this paper, we review recent research relevant to the role of the PAC in the generation of AVHs. We present new data from a functional magnetic resonance imaging (fMRI) study, examining the responsivity of the left and right PAC to parametrical modulation of the intensity of auditory verbal stimulation, and corresponding attentional top-down control in non-clinical participants with AVHs, and non-clinical participants with no AVHs. Non-clinical hallucinators showed reduced activation to speech sounds but intact attentional modulation in the right PAC. Additionally, we present data from a group of schizophrenia patients with AVHs, who do not show attentional modulation of left or right PAC. The context-appropriate modulation of the PAC may be a protective factor in non-clinical hallucinations.

Nicotine, Auditory Sensory Memory, and sustained Attention in a Human Ketamine Model of Schizophrenia: Moderating Influence of a Hallucinatory Trait

BACKGROUND

The procognitive actions of the nicotinic acetylcholine receptor (nAChR) agonist nicotine are believed, in part, to motivate the excessive cigarette smoking in schizophrenia, a disorder associated with deficits in multiple cognitive domains, including low-level auditory sensory processes and higher-order attention-dependent operations.

OBJECTIVES

As N-methyl-d-aspartate receptor (NMDAR) hypofunction has been shown to contribute to these cognitive impairments, the primary aims of this healthy volunteer study were to: (a) to shed light on the separate and interactive roles of nAChR and NMDAR systems in the modulation of auditory sensory memory (and sustained attention), as indexed by the auditory event-related brain potential - mismatch negativity (MMN), and (b) to examine how these effects are moderated by a predisposition to auditory hallucinations/delusions (HD).

METHODS

In a randomized, double-blind, placebo-controlled design involving a low intravenous dose of ketamine (0.04 mg/kg) and a 4 mg dose of nicotine gum, MMN, and performance on a rapid visual information processing (RVIP) task of sustained attention were examined in 24 healthy controls psychometrically stratified as being lower (L-HD, n = 12) or higher (H-HD) for HD propensity.

RESULTS

Ketamine significantly slowed MMN, and reduced MMN in H-HD, with amplitude attenuation being blocked by the co-administration of nicotine. Nicotine significantly enhanced response speed [reaction time (RT)] and accuracy (increased % hits and d' and reduced false alarms) on the RVIP, with improved performance accuracy being prevented when nicotine was administered with ketamine. Both % hits and d', as well as RT were poorer in H-HD (vs. L-HD) and while hit rate and d' was increased by nicotine in H-HD, RT was slowed by ketamine in L-HD.

CONCLUSIONS

Nicotine alleviated ketamine-induced sensory memory impairment and improved attention, particularly in individuals prone to HD.

Dysregulation of thalamic sensory "transmission" in schizophrenia: neurochemical vulnerability to hallucinations

Cholinergic arousal mechanisms predispose thalamic and cortical neurons to fire action potentials at gamma rhythms, which have a tendency to resonate in thalamocortical networks, thereby forming coherent assemblies under constraints of sensory input to specific thalamic nuclei, on the one hand, and prefrontal and limbic attentional mechanisms, on the other. Perception may be based on sustained assemblies of coherent gamma oscillations in thalamocortical circuits. In schizophrenia, the impact of sensory input on self-organization of thalamocortical activity may be generally reduced. As a result, processes underlying perception can become uncoupled from sensory input, particularly at times of hyperarousal, leading to domination of attentional mechanisms and the emergence of hallucinations. Evidence is reviewed that implicates excessive neuronal noise in specific thalamic nuclei in the generation of hallucinations in schizophrenia. Nicotinic receptor abnormalities, dopaminergic hyperactivity and glutamate-receptor hypofunction are reconciled within a model of psychotic symptom generation that places crucial emphasis on dysfunction of the reticular thalamic nucleus.

Does brain white matter growth expand the cortex like a balloon? Hypothesis and consequences

Horrobin (2001) has proposed that phospholipid metabolism is linked to human brain growth, and that deviations in the metabolism may be linked to creativity as well as mental disorders. The present literature review leads to a framework or model which states that brain white matter growth causes the overlying cortex to expand tangentially, like a balloon, and that this expansion affects the cortex's capacity to differentiate afferent signals. The neuroanatomical description of this model is based on publications linking human white matter growth and mass to the thickness of the overlying cortex, and of some linking cortical thickness and surface area (inversely). The link between the surface area of a cortical region and its differentiation capacity is based on previous work on hemispheric differences and functional lateralisation in the human auditory cortices. The link between differentiation capacity and inappropriate responses or "loose associations" is based on publications linking perceptual deficits and abnormal cortical structure, especially abnormal laterality. Finally, perceptual deficits have been linked to aspects of schizophrenia or other "disorders".

Unreality symptoms and volumetric measures of Heschl's gyrus and planum temporal in first-episode psychosis

BACKGROUND

Schizophrenia may involve dysfunction to primary auditory, speech, and language processes governed by the superior temporal gyrus (STG). These processes are implicated in hallucinations, delusions, and thought disorder. The current study explored the relationship between unreality symptoms (hallucinations and delusions) and specific STG substructures, including Heschl's gyrus (HG) and planum temporale (PT).

METHODS

Twenty-five right-handed men within their first episode of psychosis were assessed using the Positive and Negative Syndrome Scale (PANSS) for the presence of hallucinations and delusional behavior (a composite score of delusions, grandiosity, suspiciousness, and unusual thought content). T1-weighted magnetic resonance imaging (MRI) scans were acquired using a 1.5 Tesla scanner. Stereological measurements of HG and PT volume were obtained. Linear regression methods explored the relationship between regional volumes and symptoms.

RESULTS

Reductions in left HG were associated with hallucinations and delusions. Increases in left PT were associated with delusional behavior.

CONCLUSIONS

Current results implicate HG dysfunction in unreality symptoms in men with recent-onset schizophrenia.

Hallucinations: synchronisation of thalamocortical gamma oscillations underconstrained by sensory input

What we perceive is the product of an intrinsic process and not part of external physical reality. This notion is consistent with the philosophical position of transcendental idealism but also agrees with physiological findings on the thalamocortical system. gamma-Frequency rhythms of discharge activity from thalamic and cortical neurons are facilitated by cholinergic arousal and resonate in thalamocortical networks, thereby transiently forming assemblies of coherent gamma oscillations under constraints of sensory input and prefrontal attentional mechanisms. Perception and conscious experience may be based on such assemblies and sensory input to thalamic nuclei plays merely a constraining role in their formation. In schizophrenia, the ability of sensory input to modulate self-organisation of thalamocortical gamma activity may be generally reduced. If during arousal thalamocortical self-organisation is underconstrained by sensory input, then attentional mechanisms alone may determine the content of perception and hallucinations may arise.

Reduced pyramidal cell somal volume in auditory association cortex of subjects with schizophrenia

Subjects with schizophrenia have decreased gray matter volume of auditory association cortex in structural imaging studies, and exhibit deficits in auditory sensory memory processes subserved by this region. In dorsal prefrontal cortex (dPFC), similar in vivo observations of reduced regional volume and working memory deficits in subjects with schizophrenia have been related to reduced somal volume of deep layer 3 pyramidal cells. We hypothesized that deep layer 3 pyramidal cell somal volume would also be reduced in auditory association cortex (BA42) in schizophrenia. We used the nucleator to estimate the somal volume of pyramidal neurons in deep layer 3 of BA42 in 18 subjects with schizophrenia, each of whom was matched to one normal comparison subject for gender, age, and post-mortem interval. For all subject pairs, somal volume of pyramidal neurons in deep layer 3 of dPFC (BA9) had previously been determined. In BA42, somal volume was reduced by 13.1% in schizophrenic subjects (p=0.03). Reductions in somal volume were not associated with the history of antipsychotic use, alcohol dependence, schizoaffective disorder, or death by suicide. The percent change in somal volume within-subject pairs was highly correlated between BA42 and BA9 (r=0.67, p=0.002). Deep layer 3 pyramidal cell somal volume is reduced in BA42 of subjects with schizophrenia. This reduction may contribute to impairment in auditory function. The correlated reductions of somal volume in BA42 and BA9 suggest that a common factor may affect deep layer 3 pyramidal cells in both regions.

Are creativity and schizotypy products of a right hemisphere bias?

Prior research has shown associations between higher creativity (e.g., semantic association, verbal fluency), higher schizotypy (e.g., magical ideation), and relatively stronger right hemisphere laterality measures--when each of the three pairings has been studied individually. Our prior study related creativity and schizotypy to signal detection theory response criterion aspects of laterality. The present study attempted to integrate findings regarding these three constructs and to replicate the signal detection theory laterality results by providing measures of all three constructs in a within subjects design. Participants were 60 undergraduates who completed a test battery including two measures of creativity, three measures of schizotypy, a lateralized lexical decision task, and a dichotic listening task. Results are consistent with individual differences in creativity and schizotypy being partly related to a response criterion favoring right hemisphere, possibly nonconscious, processing. Dichotic listening results revealed a strong association of better right hemisphere (left ear) localization ability and creativity.

Abnormal peripheral auditory asymmetry in schizophrenia

OBJECTIVE

Auditory processing difficulties have been reported in schizophrenia. This study explores peripheral auditory function in patients with schizophrenia in whom certain early disturbances of auditory message filtering have been found and may be associated with certain abnormalities which are particularly localised in the left temporal lobe.

METHODS

Otoacoustic emissions, including click evoked and spontaneous emissions and measurements of functioning of the medial olivocochlear efferent system were obtained from 12 chronic schizophrenic patients and compared with normative data recorded from 12 normal controls.

RESULTS

Otoacoustic emission amplitudes and medial olivocochlear functioning were similar between the normal controls and schizophrenic patients; the schizophrenic patients did, however, differ from the normal controls in otoacoustic emission intensity and in medial olivocochlear asymmetry. A tendency to a higher number of spontaneous peaks, and a significantly higher click evoked otoacoustic emission response amplitude were found in the right ear compared with the left ear of schizophrenic patients. For the medial olivocochlear system, whereas normal controls showed greater attenuation in the right than in the left ear, schizophrenic patients lacked such an asymmetry.

CONCLUSION

In the absence of any attention task, the findings show disturbed peripheral lateralisation in schizophrenia of mechanisms involved in auditory information filtering. Such a lack of right ear advantage in medial olivocochlear functioning may thus be a peripheral reflection of central lateralisation anomalies.

Auditory hallucinations: phenomenology, neuropsychology and neuroimaging update

Auditory verbal hallucinations (AVHs) are a cardinal feature of psychosis. Recent research is reviewed which has attempted to advance our knowledge of the mechanisms underlying this symptom. Phenomenological surveys have confirmed the importance of the content of such hallucinations and their meaning to the voice-hearer. Psychological and neuroimaging studies of inner speech and source monitoring have provided a neuropsychological framework for AVHs as well as some novel therapeutic strategies. There have also been successful attempts to 'capture' neural activity coincident with the experience of hallucinations using PET, SPECT and functional magnetic resonance imaging (MRI). This body of knowledge in combination with work on in-vivo receptor binding (dopamine and GABA) provides the beginnings of a cognitive and neurophysiological understanding of this complex and intriguing phenomenon.

Hallucinations

Hallucinations, sensory perceptions without environmental stimuli, occur as simple experiences of auditory, gustatory, olfactory, tactile, or visual phenomena as well as mixed- or complex experiences of more than one simple phenomenon. The nature of the hallucination assists localization, differential diagnosis, and treatment planning. In particular, the presence of persistent visual hallucinations of persons with Parkinson's disease predicts dementia, rapid deterioration, permanent nursing home placement, and death. Hallucinations in persons with Alzheimer's disease are often associated with serious behavioral problems and predict a rapid cognitive decline. Theories of the etiology of hallucinations include (1) stimulation, e.g., neurochemical, electrical, seizure, and ephaptic, and (2) inhibition, e.g., destruction of normally inhibitory functions, resulting in disinhibition as in the Charles Bonnet and phantom limb syndromes. Functional neuroimaging procedures suggest anatomical associations for hallucinations. While hallucinations may be a symptom of medical, neurologic, and psychiatric disorders, they may also occur in a wide range of human experiences.

Functional asymmetries in schizophrenia and their relationship to cognitive performance

Previous accounts of cerebral dominance in schizophrenic patients have been conflicting. While many studies report decreased patterns of functional laterality in schizophrenic subjects, others report increases or no differences. Conceptual differences in the definition of laterality and its effects on behavior may be a reason for the poor concordance among studies. The present report addresses some of these problems and examines the hypothesis that schizophrenia may be associated with an alteration in normal patterns of functional laterality. In addition, the relationship between patterns of laterality and cognitive functioning was assessed. Twenty-one schizophrenic patients and 24 control subjects, all right-handed, were compared on two neuropsychological batteries, one designed to test cerebral dominance and the other, cognitive performance. Cerebral dominance was measured by two dichotic listening tests (verbal and nonverbal) and three motoric tests. Cognitive ability was assessed with a comprehensive neuropsychological battery. Schizophrenic and control subjects differed significantly in performance on laterality measures, but they did not differ in patterns of functional laterality when performance was taken into account. In addition, it was shown that the relationship between cognitive ability and laterality is complex, with some aspects of laterality appearing to be beneficial to cognitive ability.

Selected quantitative EEG (QEEG) and event-related potential (ERP) variables as discriminators for positive and negative schizophrenia

Heterogeneity is a major obstacle in the search for biological substrates in schizophrenia. The positive and negative distinction, even if too simplistic, may improve our understanding of underlying processes. Frontostriatal deficits have been related to negative symptoms, while dysfunction of the dominant temporal lobe appears more relevant to the generation of positive symptoms. Despite interactions between the subsystems, different neurophysiological profiles could be expected for patients predominantly affected at each of those levels. We performed discriminant analysis on 10 neurophysiological variables (hypothesis-related) in schizophrenic patients grouped by positive or negative symptoms (PANSS), obtaining a discriminant that correctly classified the sample. The function was then tested in a new sample of patients with schizophrenia, affective psychoses, and controls, classifying subjects with 78% sensitivity and 85% specificity. Our findings suggest that predominantly negative and positive schizophrenics have different neurophysiological profiles, which are consistent with the hypotheses of hypofrontality and temporal lobe dysfunction, respectively. A linear relation between discriminant scores and PANSS ratings might reflect coexisting pathologies or compensatory interactions in the mixed subgroup.