Delayed early proprioceptive information processing in schizophrenia

Abnormal ERPs and Brain Dynamics Mediate Basic Self Disturbance in Schizophrenia: A Review of EEG and MEG Studies

Background: Interest in disordered sense of self in schizophrenia has recently re-emerged in the literature. It has been proposed that there is a basic self disturbance, underlying the diagnostic symptoms of schizophrenia, in which the person's sense of being a bounded individual continuous through time loses stability. This disturbance has been documented phenomenologically and at the level of cognitive tasks. However, the neural correlates of basic self disorder in schizophrenia are poorly understood. Methods: A search of PubMed was used to identify studies on self and schizophrenia that reported EEG or MEG data. Results: Thirty-three studies were identified, 32 using EEG and one using MEG. Their operationalizations of the self were divided into six paradigms: self-monitoring for errors, proprioception, self-other integration, self-referential processing, aberrant salience, and source monitoring. Participants with schizophrenia were less accurate on self-referential processing tasks and had slower response times across most studies. Event-related potential amplitudes differed across many early and late components, with reduced N100 suppression in source monitoring paradigms being the most replicated finding. Several studies found differences in one or more frequency band, but no coherent overall finding emerged in this area. Various other measures of brain dynamics also showed differences in single studies. Only some of the study designs were adequate to establish a causal relationship between the self and EEG or MEG measures. Conclusion: The broad range of changes suggests a global self disturbance at the neuronal level, possibly carried over from the resting state. Further studies that successfully isolate self-related effects are warranted to better understand the temporal-dynamic and spatial-topographic basis of self disorder and its relationship to basic self disturbance on the phenomenological level.

Atypical visual and somatosensory adaptation in schizophrenia-spectrum disorders

Neurophysiological investigations in patients with schizophrenia consistently show early sensory processing deficits in the visual system. Importantly, comparable sensory deficits have also been established in healthy first-degree biological relatives of patients with schizophrenia and in first-episode drug-naive patients. The clear implication is that these measures are endophenotypic, related to the underlying genetic liability for schizophrenia. However, there is significant overlap between patient response distributions and those of healthy individuals without affected first-degree relatives. Here we sought to develop more sensitive measures of sensory dysfunction in this population, with an eye to establishing endophenotypic markers with better predictive capabilities. We used a sensory adaptation paradigm in which electrophysiological responses to basic visual and somatosensory stimuli presented at different rates (ranging from 250 to 2550 ms interstimulus intervals, in blocked presentations) were compared. Our main hypothesis was that adaptation would be substantially diminished in schizophrenia, and that this would be especially prevalent in the visual system. High-density event-related potential recordings showed amplitude reductions in sensory adaptation in patients with schizophrenia (N=15 Experiment 1, N=12 Experiment 2) compared with age-matched healthy controls (N=15 Experiment 1, N=12 Experiment 2), and this was seen for both sensory modalities. At the individual participant level, reduced adaptation was more robust for visual compared with somatosensory stimulation. These results point to significant impairments in short-term sensory plasticity across sensory modalities in schizophrenia. These simple-to-execute measures may prove valuable as candidate endophenotypes and will bear follow-up in future work.

Self-disorder and brain processing of proprioception in schizophrenia spectrum patients: a re-analysis

BACKGROUND

Anomalies of self-awareness (self-disorders, SDs) are theorized to be basic to schizophrenia psychopathology. We have previously observed dysfunction of brain processing of proprioception in schizophrenia spectrum disorders (SZS). We hypothesized that SDs could be associated with abnormalities of early contralateral proprioceptive evoked oscillatory brain activity.

METHODS

We investigated the association between proprioceptive evoked potential components and SDs in a re-analysis of data from a subsample (n = 12) of SZS patients who had previously been observed with deviant proprioceptive evoked potentials and interviewed with the Examination of Anomalous Self-Experience (EASE) scale.

RESULTS

Higher EASE scores (i.e. increased SD) were associated with lower peak parietal gamma frequencies and higher peak beta amplitudes over frontal and parietal electrodes in the left hemisphere following right-hand proprioceptive stimulation.

CONCLUSION

Disorders of self-awareness may be associated with dysfunction of early phases of somatosensory processing. The findings are potentially relevant to our understanding of the pathophysiology of schizophrenia, but further studies are needed.

Sensory encoding in Neuregulin 1 mutants

Schizophrenic patients show altered sensory perception as well as changes in electrical and magnetic brain responses to sustained, frequency-modulated sensory stimulation. Both the amplitude and temporal precision of the neural responses differ in patients as compared to control subjects, and these changes are most pronounced for stimulation at gamma frequencies (20-40 Hz). In addition, patients display enhanced spontaneous gamma oscillations, which has been interpreted as 'neural noise' that may interfere with normal stimulus processing. To investigate electrophysiological markers of aberrant sensory processing in a model of schizophrenia, we recorded neuronal activity in primary somatosensory cortex of mice heterozygous for the schizophrenia susceptibility gene Neuregulin 1. Sensory responses to sustained 20-70 Hz whisker stimulation were analyzed with respect to firing rates, spike precision (phase locking) and gamma oscillations, and compared to baseline conditions. The mutants displayed elevated spontaneous firing rates, a reduced gain in sensory-evoked spiking and gamma activity, and reduced spike precision of 20-40 Hz responses. These findings present the first in vivo evidence of the linkage between a genetic marker and altered stimulus encoding, thus suggesting a novel electrophysiological endophenotype of schizophrenia.

Schizophrenia as a self-disorder due to perceptual incoherence

The aim of this review is to describe the potential relationship between multisensory disintegration and self-disorders in schizophrenia spectrum disorders. Sensory processing impairments affecting multisensory integration have been demonstrated in schizophrenia. From a developmental perspective multisensory integration is considered to be crucial for normal self-experience. An impairment of multisensory integration is called 'perceptual incoherence'. We theorize that perceptual incoherence may evoke incoherent self-experiences including depersonalization, ambivalence, diminished sense of agency, and 'loosening of associations' between thoughts, feelings and actions that lie within the framework of 'self-disorders' as described by Sass and Parnas (2003). We postulate that subconscious attempts to restore perceptual coherence may induce hallucinations and delusions. Increased insight into mechanisms underlying 'self-disorders' may enhance our understanding of schizophrenia, improve recognition of early psychosis, and extend the range of therapeutic possibilities.

Impaired action self-monitoring in schizophrenia patients with auditory hallucinations

BACKGROUND

It has been suggested that the process of discriminating between inner and outer experiences underlies auditory hallucinations (AHs). The aim of the present study was to investigate whether discrimination between imagined and performed action (i.e., action self monitoring) differed between schizophrenia patients with auditory hallucinations (AHs) and those without.

METHOD

Twenty-eight schizophrenia patients with AHs, twenty-six patients without AHs, and thirty-four healthy subjects were assessed with an action memory task. Simple actions were presented to the participant verbally (text) or non-verbally (icons). Some actions were physically performed and others were imagined. Following the learning phase, participants were presented with each action as well as new ones, were asked whether the action was presented verbally or non-verbally (action's presentation type discrimination), and whether the action was performed or imagined (self-monitoring). A confidence score related to self-monitoring responses was also obtained.

RESULTS

Patients with AHs more often remembered imagined actions as performed than patients without AHs and healthy controls. Schizophrenia patients made significantly more incorrect responses in action presentation type discrimination than healthy controls. Self-monitoring errors were followed by high confidence ratings in the schizophrenia group. No differences between patients with and without AH in old/new recognition emerged.

CONCLUSIONS

Our study suggests that action self-monitoring deficits but not impairments in discriminating presentation type are related to AHs. In the schizophrenia group, action-self monitoring errors were associated with overconfidence.

A step toward an objective quantification of subtle neurological signs in schizophrenia

Numerous reports have emphasized the value of neurological soft signs (NSS) as endophenotypic markers in schizophrenia. NSS also appear as useful prognostic predictors for functional outcome, response and tolerance to antipsychotics. Although several standardized scales have been proposed and offer fair inter-rater reliability, they still rely on the experience and accuracy of the investigators. This study was designed to assess NSS objectively. We evaluated 27 patients who met the Diagnostic and Statistical Manual, fourth edition (DSM-IV) criteria for schizophrenia and 15 healthy controls using a standardized examination encompassing a 23-item NSS scale as well as an assessment of parkinsonism and dyskinesia. Movements were then recorded using inertia sensors while the patients were performing a selection of motor items from the aforementioned scale (balance tasks, rapid alternative movements, rigidity). To our knowledge, this study is the first to provide an objective assessment of specific NSS in schizophrenia using inertial sensors. The results objectively demonstrate impairments in patients with schizophrenia when balance relies on proprioceptive information, with specific differences in groups of patients based on their NSS scores. Inertia sensors are promising, inexpensive and 'easy-to-use' tools that could improve the assessment of motor and sensory impairments in patients with schizophrenia in daily clinical practice, especially when the dysfunction is subtle.

Schizophrenia, myelination, and delayed corollary discharges: a hypothesis

Any etiological theory of schizophrenia must account for at least 3 distinctive features of the disorder, namely its excessive dopamine neurotransmission, its frequent periadolescent onset, and its bizarre, pathognomonic symptoms. In this article, we theorize that each of these features could arise from a single underlying cause--namely abnormal myelination of late-developing frontal white matter fasciculi. Specifically, we suggest that abnormalities in frontal myelination result in conduction delays in the efference copies initiated by willed actions. These conduction delays cause the resulting corollary discharges to be generated too late to suppress the sensory consequences of the willed actions. The resulting ambiguity as to the origins of these actions represents a phenomenologically and neurophysiologically significant prediction error. On a phenomenological level, the perception of salience in a self-generated action leads to confusion as to its origins and, consequently, passivity experiences and auditory hallucinations. On a neurophysiological level, this prediction error leads to the increased activity of dopaminergic neurons in the midbrain. This dopaminergic activity causes previously insignificant events to be perceived as salient, which exacerbates the budding hallucinations and passivity experiences and triggers additional first-rank symptoms such as delusions of reference. The article concludes with a discussion of the implications of the theory and some testable predictions which may form a worthwhile basis for future research.

Movement-related potentials point towards an impaired tuning of reafferent sensory feedback by preceding motor activation in schizophrenia

The link between focal motor system activation and reafferent sensory feedback is thought to be crucial for the perception that a movement is actively performed. In this article, we examine how schizophrenia affects the relationship between motor and somatosensory system activation. Movement-related potential source analysis allowed us to separate and compare motor activation deficits and reafferent feedback processing. We analyzed lateralized movement-related potentials during choice reaction movements in 16 subjects with schizophrenia/schizoaffective disorder. These subjects had partial remissions with predominantly negative symptoms and were compared to an age-matched healthy control group. In the schizophrenia/schizoaffective group, dipole source analysis indicated a significantly reduced lateralized sensorimotor activation immediately preceding movement execution. In contrast, activation by reafferent feedback was relatively unimpaired. Subjects with schizophrenia/schizoaffective disorder lacked a focal motor and reafferent sensory processing correlation, which can be identified through a significantly different regression slope from healthy controls. Reduced action-related motor system activation in subjects with schizophrenia/schizoaffective disorder was associated with preserved activation by reafferent sensory feedback. Most importantly, motor-sensory tuning, i.e. a specific enhancement of sensory information necessary to monitor movements, could not be found in subjects with schizophrenia/schizoaffective disorder. Our data provide further evidence for disturbed motor-sensory interactions in schizophrenia.

Attenuation of beta and gamma oscillations in schizophrenia spectrum patients following hand posture perturbation

Several electroencephalographic (EEG) studies in schizophrenia report that the patients have reduced evoked gamma activity following visual and auditory stimulation. Somatosensory gamma activity has not previously been examined. It has been suggested that a dysfunction basic to schizophrenia spectrum traits would involve proprioceptive information processing and this has recently been supported by the finding of diminished latency of early proprioceptive evoked potentials in a sample of chronic schizophrenia patients. The proprioceptive stimulus used previously, and presently, consisted of an abrupt increase of weight on a hand-held load. Eighteen first-time admitted schizophrenia spectrum patients and 18 healthy matched comparison subjects were included. Proprioceptive evoked potentials were recorded as 64-channels EEG for 120 trials in two runs differing in sequence. Contra-lateral evoked beta (latency 90 ms, frequency 21 Hz) and gamma (latency 70 ms, frequency 32 Hz) oscillations were attenuated in the patient group. The healthy comparison subjects had increased gamma amplitude in the left hemisphere in the regular sequence, a phenomenon not seen in the patients. The deviant findings were unexpectedly more circumscribed in the schizophrenia than in the schizotypal personality disorder (SPD) patients. Future studies should include several concurrent psychophysiological measures.

The phenomenological critique and self-disturbance: implications for ultra-high risk ("prodrome") research

Recent years have witnessed widespread interest in the early phase of schizophrenia and other psychotic disorders. Strategies have been introduced to attempt to identify individuals in the prepsychotic or prodromal phase. The most widely used of these approaches is the ultra-high risk (UHR) approach, which combines known trait and state risk factors for psychotic disorder. However, researchers guided by phenomenological theory have argued that modern psychiatry's neglect of subjective experience has compromised researchers' understanding of psychotic disorder and has thereby limited efforts at prospective and early identification. Phenomenological research indicates that disturbance of the basic sense of self may be a core marker of psychotic vulnerability, particularly of schizophrenia spectrum disorders. It is argued that identifying self-disturbance in the UHR population may provide a means of further "closing in" on individuals truly at high risk of psychotic disorder, thus supplementing the UHR identification approach. This would be of practical value in the sense of reducing inclusion of "false-positive" cases in UHR samples and of theoretical value in the sense of shedding light on core features of psychotic pathology. The strong explanatory power and empirical findings to date invite further research into the role of self-disturbance as a phenotypic vulnerability marker for psychotic disorder.