Electrodermal activity in schizophrenia: a quantitative study using a short interstimulus paradigm

A continuous measure of phasic electrodermal activity

Electrodermal activity is characterized by the superposition of what appear to be single distinct skin conductance responses (SCRs). Classic trough-to-peak analysis of these responses is impeded by their apparent superposition. A deconvolution approach is proposed, which separates SC data into continuous signals of tonic and phasic activity. The resulting phasic activity shows a zero baseline, and overlapping SCRs are represented by predominantly distinct, compact impulses showing an average duration of less than 2 s. A time integration of the continuous measure of phasic activity is proposed as a straightforward indicator of event-related sympathetic activity. The quality and benefit of the proposed measure is demonstrated in an experiment with short interstimulus intervals as well as by means of a simulation study. The advances compared to previous decomposition methods are discussed.

Time-series analysis for rapid event-related skin conductance responses

Event-related skin conductance responses (SCRs) are traditionally analysed by comparing the amplitude of individual peaks against a pre-stimulus baseline. Many experimental manipulations in cognitive neuroscience dictate paradigms with short inter trial intervals, precluding accurate baseline estimation for SCR measurements. Here, we present a novel and general approach to SCR analysis, derived from methods used in neuroimaging that estimate responses using a linear convolution model. In effect, the method obviates peak-scoring and makes use of the full SCR. We demonstrate, across three experiments, that the method has face validity in analysing reactions to a loud white noise and emotional pictures, can be generalised to paradigms where the shape of the response function is unknown and can account for parametric trial-by-trial effects. We suggest our approach provides greater flexibility in analysing SCRs than existing methods.

Fronto-limbic and autonomic disjunctions to negative emotion distinguish schizophrenia subtypes

Schizophrenia patients show a disconnection in amygdala-medial prefrontal cortex and autonomic arousal systems for processing fear. Concurrent functional magnetic resonance imaging [fMRI] and skin conductance recording were used to determine whether these disturbances are specific to fear, or present in response to other signals of danger. We also examined whether these disturbances distinguish a specific symptom profile. During scanning, 27 schizophrenia (13 paranoid, 14 nonparanoid) and 22 matched healthy control subjects viewed standardized facial expressions of fear, anger and disgust (versus neutral). Skin conductance responses [SCRs]were acquired simultaneously to assess phasic increases in arousal. 'With-arousal' versus 'without-arousal' responses were analysed using non-parametric methods. For controls, 'with-arousal' responses were associated with emotion-specific activity for fear (amygdala), disgust (insula) and anger (anterior cingulate), together with common medial prefrontal cortex [MPFC] engagement, as predicted. Schizophrenia patients displayed abnormally increased phasic arousal, with concomitant reductions in emotion-specific regions and MPFC. These findings may reflect a general disconnection between central and autonomic systems for processing signals of danger. This disjunction was most apparent in patients with a profile of paranoia, coupled with poor social function and insight. Heightened autonomic sensitivity to signals of fear, threat or contamination, without effective neural mechanisms for appraisal, may underlie paranoid delusions which concern threat and contamination, and associated social and interpersonal difficulties.

INTEGRATING OBJECTIVE GENE-BRAIN-BEHAVIOR MARKERS OF PSYCHIATRIC DISORDERS

There is little consensus about which objective markers should be used to assess major psychiatric disorders, and predict/evaluate treatment response for these disorders. Clinical practice relies instead on subjective signs and symptoms, such that there is a "translational gap" between research findings and clinical practice. This gap arises from: a) a lack of integrative theoretical models which provide a basis for understanding links between gene-brain-behavior mechanisms and clinical entities; b) the reliance on studying one measure at a time so that linkages between markers are their specificity are not established; and c) the lack of a definitive understanding of what constitutes normative function. Here, we draw on a standardized methodology for acquiring multiple sources of genomic, brain and behavioral data in the same subjects, to propose candidate markers of selected psychiatric disorders: depression, post-traumatic stress disorder, schizophrenia, attention-deficit/hyperactivity disorder and dementia disorders. This methodology has been used to establish a standardized international database which provides a comprehensive framework and the basis for testing hypotheses derived from an integrative theoretical model of the brain. Using this normative base, we present preliminary findings for a number of disorders in relation to the proposed markers. Establishing these objective markers will be the first step towards determining their sensitivity, specificity and treatment prediction in individual patients.

Electrodermal responsivity distinguishes ERP activity and symptom profile in schizophrenia

BACKGROUND

Traditional averaging of late component Event Related Potentials (ERPs) might obscure important psychophysiological subprocesses underlying schizophrenia disturbances in cognitive functioning. One such subprocess could be the active orientation of attention to significant or novel stimuli. In this study, we used skin conductance responses (SCRs) to index orienting responses (ORs). ERP activity was examined in relation to concomitant ORs in a schizophrenia and nonpsychiatric control group. Schizophrenia responses were considered with respect to the Reality Distortion, Disorganisation and Psychomotor Poverty syndromes.

METHOD

Forty schizophrenia and 40 age and sex matched control subjects were tested. The three schizophrenia syndromes were derived from a principal component analysis of Positive and Negative Syndrome Scale (PANSS) ratings. Auditory ERPs (N100, N200, P200, P300) were elicited using a conventional auditory oddball paradigm, and electrodermal SCR data were acquired simultaneously.

RESULTS

ERP data were sub-averaged according to the presence/absence of an OR. For both 'with-' and 'without-OR' ERPs, schizophrenia subjects as a group showed reduced N100 (associated with vigilance level) and N200 (associated with response selection) amplitude, and for with-OR responses, they showed an additional reduction in P300 (context processing). Concerning schizophrenia syndromes, Reality Distortion was related primarily to frontal disturbances (earlier N100/N200 latency and decreased P200/P300 amplitude), and Psychomotor Poverty to a generally delayed P300 latency. Similarly delayed P300 in Disorganisation was explained by medication effects. There were no associations with syndromes for without-OR ERPs.

CONCLUSION

These results suggest that schizophrenia syndromes are dissociated with regard to both the direction and nature of speed of information processing disturbances, in relation to task-relevant information that produces active orientation.

ERPs associated with and without an "orienting reflex" in patients with schizophrenia

In this study, we measured traditional late components of the Event Related Potential (ERP: N 100, P 200, N 200 and P 300) in a conventional auditory oddball paradigm, but additionally and simultaneously assessed electrodermal "orienting reflexes (ORs)" in 40 patients with schizophrenia and 40 age and gender matched normal controls. The single epoch ERPs that did and did not evoke an OR, were sub-averaged separately. The control subjects (but not the patient group), revealed delayed P 300 latency in the ERP sub-averages without ORs (ERP-OR), compared with ERP sub-averages with ORs (ERP+OR). Between-group analysis showed reduced N 100, N 200 and P 300 amplitudes (as well as delayed P 300 latency) in the ERP+OR sub-average in patients with schizophrenia. In the ERP-OR sub-average, the patient group also had smaller N 100, N 200 and P 300 amplitudes, but larger P 200 amplitude (compared with normal controls). This study shows the potential to tease out physiologically based OR sub-processes, by simultaneous acquisition and analysis of ERPs and autonomic electrodermal activity. Such ERP sub-averages (based on autonomic responses) highlight that multiple processes overlap across the trial, and their delineation may elucidate more specific patterns of disturbance in schizophrenia, than traditional averaged measures.

Integrative psychophysiology

This paper attempts to provide an overview of the current status and some possible future directions of 'Integrative Psychophysiology'. Exemplar integrations are offered for: (i) the theory of some of the more cited models of the brain as a system; (ii) a numerical simulation of brain dynamics (highlighting the plausibility of exploring mechanisms at the whole brain scale); and (iii) an empirical profile of disturbances in patients with schizophrenia (reflecting a prototypical disorder of overall brain instability and suboptimal integrative information processing). These 'integrative' dimensions provide a frame of reference for considering interrelationships among brain dynamics and behaviour, in health and disease.

Skin conductance and schizophrenic symptomatology

Skin conductance is a psychophysiological parameter that reflects fundamental processes such as attention and arousal. The present study explored whether deviations in skin conductance activity are associated with severity of schizophrenic symptoms. For this purpose, Skin Conductance Responses (SCRs) to discrete stimuli (80 dB noises) and Skin Conductance Levels (SCLs) of 37 schizophrenic patients and 31 healthy volunteers were recorded. In accordance with previous studies, schizophrenic patients were found to be hyporesponsive compared to healthy controls. More specifically, almost half of the patients (46%) did not react with any SCR to the first 3 stimuli, whereas only 10% of the control group exhibited such a non-responding. Accordingly, the mean amplitude of the first 3 SCRs - as measured in u Siemens - was found to be significantly lower in patients compared to controls. As well, mean SCL was found to be (marginally) elevated in the patient group. This was especially the case for patients who did exhibit SCRs. In the patient group, a negative correlation was found between amplitude of SCRs and symptom severity. This association was mainly carried by a significant correlation between positive symptoms and reduced SCRs. The clinical relevance of these findings is discussed in detail.