Impaired visual object recognition and dorsal/ventral stream interaction in schizophrenia

BACKGROUND: Schizophrenia is associated with well-documented deficits in high-order cognitive processes such as attention and executive functioning. The integrity of sensory-level processing, however, has been evaluated only to a limited degree. Our study evaluated the ability of patients with schizophrenia to recognize complete objects based on fragmentary information, a process termed perceptual closure. Perceptual closure processes are indexed by closure negativity (N(cl)), a recently defined event-related potential (ERP) component that is generated within the visual association cortex. This study assessed the neural integrity of perceptual closure processes in schizophrenia by examining N(cl) generation. Generation of the preceding positive (P1) and negative (N1) ERP components was also examined. METHODS: We evaluated 16 patients with chronic schizophrenia and 16 healthy comparison subjects. Successively less fragmented images were presented during high-density ERP recording, which permitted the monitoring of brain activity during perceptual closure processes prior to object recognition. Analyses were performed at parieto-occipital and occipitotemporal sites consistent with dorsal and ventral stream generators of P1, N1, and N(cl). RESULTS: Patients with schizophrenia showed significant impairment in the ability to recognize fragmented objects, along with impaired generation of N(cl). The amplitude of visual P1 was significantly reduced, particularly over dorsal stream sites. In contrast, the generation of visual N1 was intact. CONCLUSIONS: Patients with schizophrenia are profoundly impaired in perceptual closure as indicated by both impaired performance and impaired N(cl) generation. The selective impairment in dorsal stream P1 is consistent with prior reports of impaired magnocellular processing in schizophrenia. By contrast, intact ventral N1 generation suggests that the initial stages of ventral stream processing are relatively preserved and that impaired magnocellular dorsal stream functioning in schizophrenia may lead to secondary dysregulation of ventral stream object recognition processing.     

Electrophysiological indices of automatic and controlled auditory information processing in first-episode, recent-onset and chronic schizophrenia.

BACKGROUND: Deficits in amplitudes of auditory event-related potentials (ERP) indexing preattentive, automatic (mismatch negativity, MMN) and controlled, attention-dependent (N2, P3) auditory information processing have been well described in chronic schizophrenia. Normal MMN, but deficient N2 and P3 have been reported in first-episode patients. No study has investigated these ERPs concurrently in first-episode patients; thus, reported differences in MMN, N2 and P3 generation may reflect differences in patient samples rather than genuine differences in abnormal generation of these ERPs. METHODS: We recorded MMN, N2 and P3 in 26 first-episode patients, 25 recent-onset patients within 1.5 to 5 years after first admission, 25 chronic patients and 39 healthy controls. RESULTS: Recent-onset and chronic, but not first-episode patients showed reduced MMN. However, among first-episode patients those with low premorbid educational achievement demonstrated significantly reduced MMN. All patient groups showed pronounced N2 deficits and, to a variable extent, abnormalities in P3 generation. CONCLUSIONS: Abnormalities in N2 and P3 generation appear to reflect premorbid neuropathology, whereas MMN deficits may index both ongoing disease processes associated with illness progression as well as premorbid neurocognitive impairment. ERPs may provide tools to assess static and progressive neuropathology in schizophrenia. These findings need confirmation in longitudinal studies.     

Cognitive impairments in patients with first episode psychosis: The relationship between neurophysiological and neuropsychological assessments

Cognitive deficits in schizophrenia have been widely reported. Neurophysiological and neuropsychological assessments have been conducted to study these impairments. Event-related potentials (ERPs) are relevant markers of cognitive deficits in schizophrenia, and reductions in specific ERP components have been found. The MATRICS Consensus Cognitive Battery (MCCB) was developed to obtain a consensus battery for the assessment of cognitive deficits in schizophrenia. Here, we aimed to study modulations of several ERP components in first episode psychosis (FEP). We also examined neuropsychological deficits using the MCCB, and correlations between ERP and MCCB impairments. Thirty-eight FEP patients were compared to thirty-eight healthy controls. The following ERP components were examined: P1, N1, MMN, P2, early-P3 and late-P3. We used an auditory three-stimulus oddball paradigm, with standard (60%), target (20%) and distractor (20%) stimuli. FEP patients showed significantly lower amplitudes of P2, early-P3 and late-P3 components. FEP patients also showed significant deficits in all the MCCB cognitive domains. Finally, correlational analyses found strong associations between amplitudes of P2, early-P3 and late-P3 components and MCCB tests for attention and speed of processing. These findings indicate that deficits in late auditory ERP components are present in FEP, whereas early components are preserved. These reductions in late ERP components were related to attentional deficits in FEP as assessed by MCCB. These findings indicate that MCCB is a valid battery for studying cognitive impairments in the initial stages of schizophrenia, and highlight the utility of converging neurophysiological and neuropsychological measures to examine attentional impairments in schizophrenia.     

Profile of auditory information-processing deficits in schizophrenia

Schizophrenia patients exhibit abnormalities in several different auditory event-related potential (ERP) measures. It is unclear how these abnormalities relate to each other, since multiple measures are rarely acquired from the same sample. This study addressed two related questions: 1) Are specific auditory ERP measures differentially impaired in schizophrenia? 2) Do abnormalities co-aggregate within the same patients? Nine auditory ERP measures were acquired in a single testing session from 23 schizophrenia patients and 22 healthy subjects. Hierarchical oblique factor analysis revealed that these measures aggregated into four factors, with each loading primarily on a single factor. Patient deficits were observed for two independent factors: N100/mismatch negativity (MMN) and P3a/P3b. N100/MMN abnormalities were associated with symptoms of alogia and formal thought disorder. P3a/P3b abnormalities were associated with avolition, attentional disturbances and delusions. We conclude that deficits in different ERP measures of early sensory processing at the level of the auditory cortex co-occur in patients. These likely represent a single differential deficit indexing the physiological abnormality underlying impaired language and verbal processing. This is relatively independent of a higher cortical deficit that mediates cognitive stimulus evaluation and underlies deficits in motivation, attention and reality testing. Such multidimensional profiling of ERP abnormalities may help to clarify the clinical and genetic heterogeneity of schizophrenia.     

An Event-Related Potential Investigation of Early Visual Processing Deficits During Face Perception in Youth at Clinical High Risk for Psychosis

Impairments in early visual face perception are well documented in patients with schizophrenia. Specifically, event-related potential (ERP) research in patients with schizophrenia has demonstrated deficits in early sensory processing of stimulus properties (P1 component) and the structural encoding of faces (N170 component). However, it is not well understood if similar impairments are present in individuals at clinical high risk (CHR) for psychosis (ie, those in the putative prodromal stage of the illness). Thus, it is unknown if face perception deficits are the result of illness onset or are present in the high-risk period for the illness. The present study used the ERP technique to examine neural activation when viewing facial emotion expressions and objects in 44 CHR and 47 control adolescents and young adults (N = 91). P1 amplitude was similar across groups, indicating that early sensory processing impairments did not substantially contribute to face perception deficits in CHR youth. CHR youth exhibited reduced N170 amplitude compared to controls when viewing faces but not objects, implicating a specific deficit in the structural encoding of faces rather than a general perceptual deficit. Further, whereas controls demonstrated the expected face-selective N170 effect (ie, larger amplitude for faces than objects), CHR youth did not, which suggests that facial emotion expressions do not elicit the expected preferential perceptual processing for critical social information in individuals at CHR for psychosis. Together, these findings provide valuable information regarding the specific impairments contributing to face perception deficits in the high-risk period where treatment stands to aid in preventing illness progression.     

P300 reduction and prolongation with illness duration in schizophrenia.

BACKGROUND: The P300 component of the auditory event-related potential (ERP) is both reduced in amplitude and delayed in schizophrenia. P300 is prolonged and, less consistently, reduced with normal aging. Additional latency delays are observed in neurodegenerative disorders. We asked whether P300 is reduced and delayed with longer illness duration in schizophrenia, consistent with a neurodegenerative process. METHODS: P300 amplitude and latency were recorded to infrequent auditory target stimuli from 35 men with schizophrenia (DSM-III-R) and 26 control men. Effects of current age, age of onset, and duration of illness on P300 were assessed using regression analysis. RESULTS: P300 amplitude showed no age-related decrease in either group; however, among schizophrenic participants, P300 amplitude correlated positively with onset age and negatively with illness duration. P300 latency correlated positively with age in schizophrenic participants and also tended to increase with age in controls. Slopes of the latency-age relationships were significantly greater in schizophrenic participants than in control participants. Latency also correlated positively with illness duration but showed no relationship to onset age. CONCLUSIONS: P300 amplitude and latency are reduced and delayed with longer illness duration in schizophrenia, consistent with a progressive pathophysiological process. Reduced P300 amplitude may also be a marker of an early onset variant of schizophrenia.     

Visual information processing deficits as biomarkers of vulnerability to schizophrenia: An event-related potential study in schizotypy

We aimed to clarify the importance of early visual processing deficits for the formation of cognitive deficits in the schizophrenia spectrum. We carried out an event-related potential (ERP) study using a computerised delayed matching to sample working memory (WM) task on a sample of volunteers with high and low scores on the Schizotypal Personality Questionnaire (SPQ). The amplitudes of the visual ERPs to the encoding and retrieval stimuli in the task were measured using the BESA software. The hypothesis was that the high schizotypes would have deficits in early visual processing (reduced P1 amplitude) and working memory similar to those observed in schizophrenia. The high schizotypy group identified fewer previously encoded target cues than the low schizotypy group in the WM task and their mean cue-evoked P1 amplitudes were significantly reduced, both in the encoding and the retrieval phases of the task. Accuracy on the WM task correlated with the P1 amplitude. None of the later components (N1 and P2) were significantly different between the groups, nor were there differences in performance on the CANTAB tests. The results are compatible with the hypothesis that trait vulnerability to schizophrenia is associated with impaired early visual processing which may contribute to impaired cognitive memory performance. However, the high schizotypes are apparently able to compensate for the visual processing deficits and perform normally when stimuli are presented for longer as in the CANTAB tasks. This study adds to growing evidence that the schizophrenia spectrum is characterized by early sensory abnormalities.     

Auditory recovery cycle dysfunction in schizophrenia: a study using event-related potentials

Previous event-related potential (ERP) studies reported evidence of impaired auditory information processing in patients with schizophrenia. The recovery cycle of the auditory N1 ERP component was measured in 17 patients with schizophrenia and 17 age- and sex-matched healthy volunteers. Subjects performed a visual distraction task while listening to 80-dB SPL, 1000-Hz tone pairs, presented with intra-pair intervals of 1, 3, 5 or 7 s, with inter-pair intervals of 9-13 s. Patients with schizophrenia had significantly reduced N1 amplitudes for S1 stimuli compared with healthy volunteers. For N1 amplitudes elicited by S2 stimuli, there was a significant group effect whilst the main effect of intra-pair interval was not significant. These results provide additional evidence of inhibitory auditory processing deficits in schizophrenia.     

Visual sensory processing deficits in patients with bipolar disorder revealed through high-density electrical mapping

Background

Etiological commonalities are apparent between bipolar disorder and schizophrenia. For example, it is becoming clear that both populations show similar electrophysiological deficits in the auditory domain. Recent studies have also shown robust visual sensory processing deficits in patients with schizophrenia using the event-related potential technique, but this has not been formally tested in those with bipolar disorder. Our goal here was to assess whether early visual sensory processing in patients with bipolar disorder, as indexed by decreased amplitude of the P1 component of the visual evoked potential (VEP), would show a similar deficit to that seen in those with schizophrenia. Since the P1 deficit has already been established as an endophenotype in schizophrenia, a finding of commonality between disorders would raise the possibility that it represents a measure of common genetic liability.

Methods

We visually presented isolated-check stimuli to euthymic patients with a diagnosis of bipolar disorder and age-matched healthy controls within a simple go/no-go task and recorded VEPs using high-density (72-channel) electroencephalography.

Results

The P1 VEP amplitude was substantially reduced in patients with bipolar disorder, with an effect size of f = 0.56 (large according to Cohen’s criteria).

Limitations

Our sample size was relatively small and as such, did not allow for an examination of potential relations between the physiologic measures and clinical measures.

Conclusion

This reduction in P1 amplitude among patients with bipolar disorder represents a dysfunction in early visual processing that is highly similar to that found repeatedly in patients with schizophrenia and their healthy first-degree relatives. Since the P1 deficit has been related to susceptibility genes for schizophrenia, our results raise the possibility that the deficit may in fact be more broadly related to the development of psychosis and that it merits further investigation as a candidate endophenotype for bipolar disorder.     

Mismatch negativity (MMN) in multiple sclerosis: an event-related potentials study in 46 patients.

OBJECTIVE: To assess pre-attentive detection mechanisms indexed by MMN component of auditory Event-Related Potentials (ERPs) in Multiple Sclerosis (MS) patients. METHODS: 46 MS patients (mean age 43.7 years, mean disease duration 10.1 years, mean EDSS 4.6) and 46 matched controls were assessed with ERPs elicited by a passive oddball paradigm using duration deviants. Auditory P50, N1, P2 components were recorded. MMN and P3a components were calculated as the difference potential between deviants and standard stimuli. Eighteen of these 46 patients underwent also global psychometrical assessment and were sorted in cognitively normal and impaired patients. ERPs of these two groups of patients were compared. RESULTS: MS patients showed reduced MMN and P3a areas as compared to controls, besides exogenous N1-P2 complex amplitude reduction. Among the 18 patients investigated with neuropsychological testings, six were cognitively impaired and 12 cognitively unimpaired. Patients with a global cognitive impairment had reduced MMN as compared to cognitively unimpaired patients. CONCLUSIONS: Auditory MMN and P3a components of auditory ERPs are altered in MS patients. MMN alterations are more pronounced in cognitively impaired patients. SIGNIFICANCE: MMN and P3a areas reduction suggests that MS patients are prone to pre-attentive auditory information processing deficits, besides previously described controlled information processing difficulties. Moreover, MMN alterations may represent an objective index of cognitive disturbances in MS patients.     

Trait and state aspects of P300 amplitude reduction in schizophrenia: a retrospective longitudinal study.

BACKGROUND: The P300 component of the auditory event-related brain potential (ERP) is consistently reduced in schizophrenia. Longitudinal data are examined to determine whether P300 amplitude is a trait marker of schizophrenia or a state marker tracking clinical fluctuations over time. METHODS: Schizophrenic men (DSM-III-R) (n = 36) received ERP and the Brief Psychiatric Rating Scale (BPRS) assessments on multiple occasions, at varying intervals, under varying medication states. Automatically elicited auditory P3a and effortfully elicited auditory and visual P3b amplitudes were assessed. Brief Psychiatric Rating Scale scores were regressed on P300 amplitude within patients using both multiple regression models and nonparametric analyses of individual patient slopes. Event related brain potentials in patients were compared to ERPs from 34 age-matched control men, and stability of P300 over time was estimated with intraclass correlations. RESULTS: P300 amplitude, regardless of elicitation method or sensory modality, tracked BPRS Total and positive symptom scores over time, decreasing with symptom exacerbations and increasing with improvements. In addition, effortful auditory and visual P3b amplitudes tracked negative symptoms, and automatic auditory P3a tracked depression-anxiety symptoms. When analyses were limited to unmedicated occasions, auditory P3a and P3b persisted in tracking BPRS Total scores, with additional tracking of positive symptoms by P3b and mood symptoms by P3a. Mean auditory and visual P3bs, averaged over all measurement occasions for each individual, were inversely related to mean negative symptoms. Auditory P3a and P3b, but not visual P3b, amplitudes were smaller in patients than control subjects, even when patients were least symptomatic. P300 amplitudes showed high test-retest reliability in control subjects and patients and moderate stability over time in patients. CONCLUSIONS: Auditory, and possibly visual, P300 amplitudes track fluctuations in clinical state, but only auditory P300 amplitude is a trait marker of schizophrenia.     

Auditory P300 in high-risk, recent-onset and chronic schizophrenia

BACKGROUND: The present study examined the integrity of the P300 component of the event-related potential (ERP) in patients at high imminent risk for schizophrenia in relation to healthy comparison subjects and patients in the recent-onset and chronic stages of schizophrenia. METHODS: The P300 was recorded by using an auditory oddball task in 10 patients clinically considered at risk of being prodromally symptomatic for schizophrenia, 10 patients with recent-onset schizophrenia, 14 patients with chronic schizophrenia, 14 young healthy comparison subjects, who were age-matched to the high-risk and recent-onset schizophrenia groups, and 14 older healthy comparison subjects, who were age-matched to the chronic schizophrenia group. RESULTS: High-risk subjects displayed smaller than normal P300 amplitudes at the parietal, centroparietal and central scalp locations. The observed P300 amplitude abnormalities in high-risk subjects were severe, being comparable in magnitude to the abnormalities seen in recent-onset and chronic schizophrenia subjects. However, whereas high-risk subjects showed P300 amplitude abnormalities that were bilaterally symmetrical, subjects with recent-onset schizophrenia and, particularly, subjects with chronic schizophrenia exhibited abnormalities that were markedly larger over the left temporal scalp sites. CONCLUSIONS: Patients at high imminent risk for developing a first florid psychotic episode seem to manifest auditory P300 amplitude abnormalities that are similar, but not identical, to those observed in patients in the recent-onset and chronic stages of schizophrenia. These results support the idea that auditory P300 abnormalities in schizophrenia reflect a primary cognitive and pathophysiological feature of the illness.     

Phonetic mismatch negativity predicts verbal memory deficits in schizophrenia

Deficits in auditory sensory memory at the electrophysiological level as indexed by mismatch negativity and those in auditory verbal memory at the neuropsychological level have been independently demonstrated in previous studies of schizophrenia. We predicted a specific association between these indices in schizophrenia. Mismatch negativities elicited by change in tone duration and phoneme duration were recorded in 23 schizophrenia patients, who were also evaluated for auditory verbal memory and executive function. Lower amplitude of mismatch negativity under the phoneme-duration condition was significantly associated with worse verbal memory. Phoneme-duration mismatch negativity was not correlated with executive function, nor was tone-duration mismatch negativity correlated with verbal memory. These results suggest that electrophysiological auditory sensory memory dysfunction underlies the basis for neuropsychological auditory verbal memory deficits in schizophrenia.     

Enhanced attention-dependent auditory processing by electroconvulsive therapy in psychotic depression

There is a lack of knowledge about the effect of electroconvulsive therapy (ECT) on auditory event-related potentials (ERPs) in severe psychotic depression. The aim of this study was to investigate both the effect of ECT on attention-dependent ERP (P300) and the correlation of P300 values with depression level. We recorded the auditory ERPs of 23 patients expressing psychotic symptoms and fulfilling the DSM-III-R criteria for treatment-resistant severe major depressive episode before and a week after successful bitemporal ECT. The clinical status was assessed with Hamilton (Ham-D) and Montgomery and Asberg (MADRS) depression scales. ECT was clinically very effective with these scales. On the level of auditory processing, ECT increased P300 amplitude with no significant effect on latency. Small amplitudes over the left hemisphere before treatment were associated with bigger Ham-D-score decrement. ECT produces a significant increase in brain activity at the level of attention-dependent auditory processing in severe depression. The change in electrical responses seems to represent a largely independent variable from the clinical assessment scales, even if the recovery rate was remarkable, because the change in overall symptom scores did not correlate with the P300 changes.     

Different patterns of auditory information processing deficits in chronic schizophrenia and bipolar disorder with psychotic features

With the development of DSM-V and ICD-11 the definitions of psychiatric disorders are under re-evaluation. The emphasis is shifted from distinct disorders to clusters defined not only by symptomatology, but also by underlying neurobiology and cognitive deficits. Bipolar disorder I (BD-I) and schizophrenia (SZ) are of special interest since their differential diagnosis is often problematic and they partially overlap in measures ranging from genetics to neurophysiology. Event-related potentials (ERPs) are one of the most studied factors but the results are still controversial, primarily in BD-I, where ERPs reflecting different stages of auditory information processing have been much less investigated. In this study, we aimed at investigating the changes of five auditory event-related potentials (P50 and N100 suppression, duration and pitch deviant mismatch negativity (MMN) and P3b) in 20 SZ and 20 BD-I patients with a history of psychosis and 21 healthy control subjects. Our data revealed substantial differences between the two patient groups. Only patients with SZ demonstrated impaired N100 suppression, shorter duration deviant MMN latency and attenuated P3b amplitude, while prolonged pitch deviant MMN latency was found to be characteristic of the BD-I group. No shared ERP abnormalities were observed among the patient groups. Our results indicate that SZ and BD-I are characterized by highly different neurophysiological profiles when measured in the same laboratory setting.     

Mismatch negativity in schizophrenia: a meta-analysis

BACKGROUND: Mismatch negativity (MMN) is an auditory event-related potential that provides an index of automatic context-dependent information processing and auditory sensory memory. Many studies have reported abnormalities in the generation of MMN in schizophrenia. The objective of this study was to assess the magnitude of this deficit and associated factors. METHOD: Studies of MMN in schizophrenia were identified and included in a meta-analysis to estimate the mean effect size. Effects of duration of illness, gender ratio, age of patients, type of MMN (duration versus frequency MMN) and characteristics of the test paradigms (deviant probability, magnitude of standard-deviant difference) on effect size were assessed. RESULTS: Of 62 identified studies 32 met our inclusion criteria. The mean effect size was 0.99 (95% confidence intervals: 0.79, 1.29). Overall, no specific factor was significantly associated with MMN deficits, although MMN to stimuli differing in duration appeared more impaired in schizophrenia than MMN to frequency deviants. In addition, effect sizes of frequency MMN were significantly correlated with duration of illness. CONCLUSIONS: MMN deficits are a robust feature in chronic schizophrenia and indicate abnormalities in automatic context-dependent auditory information processing and auditory sensory memory in these patients. Reports of normal MMN in first-episode schizophrenia and the association of deficits in frequency MMN with illness duration suggest that MMN may index ongoing neuropathological changes in the auditory cortex in schizophrenia.     

Visual mismatch negativity among patients with schizophrenia

Event related potentials (ERPs) provide an insight into sensory and cognitive processes in health and disease. Studies of an ERP negative amplitude deflection elicited by a change in a series of auditory stimuli is known as mismatch negativity (MMN). The generation of MMN is impaired in schizophrenia. Its deficit is associated with lower everyday functioning and may be also interpreted as the marker of progression in schizophrenia. MMN elicited by visual stimuli (vMMN) was described by several research teams, but it has not been investigated in schizophrenia as yet. Using a motion-direction paradigm, we elicited visual MMN in 24 patients with schizophrenia and schizoaffective disorder. The vMMN was computed as differences in areas under curve of visual ERPs to standard and deviant motion-direction stimuli recorded from midline derivations at the interval of 100-200 ms. They were compared between groups of patients with schizophrenia and healthy controls. The significantly smaller vMMN indicated an impaired generation of mismatch negativity in patients with schizophrenia. In secondary analyses there was an association of vMMN impairment among patients with higher dose of medication, lower level of functioning and the presence of deficit syndrome. This impairment appears analogous to the impairment of MMN in the auditory domain and is probably related to early visual information processing. Its relationship to cognitive functioning of patients with schizophrenia deserves further attention.     

Early visual processing deficits in schizophrenia: impaired P1 generation revealed by high-density electrical mapping.

Integrity of early visual sensory processing in schizophrenia was assessed using the well characterized P1 and N1 components of the visual evoked potential (VEP) as our dependent measures. VEPs were recorded in response to successively less fragmented line drawings of common objects. P1 amplitudes were significantly reduced across all stimulus conditions for patients versus controls. Further, this decrement was relatively greater at parieto-occipital than occipito-temporal electrode sites. No differences in N1 amplitude were found. The finding of P1 deficits in patients, particularly over dorsal scalp, supports the view that schizophrenia is associated with impairment of early dorsal visual stream processing. On the other hand, the finding of normal N1 amplitudes in patients suggests that early stages of ventral stream processing may be relatively more intact. These results imply that the cognitive impairment seen in schizophrenia is not just due to deficits in higher order aspects of cognition but also encompasses significant deficits in early sensory processing.     

A high-density ERP study reveals latency,amplitude, and topographical differences in multiple sclerosis patients versus controls

ObjectiveTo quantify latency, amplitude and topographical differences in event-related potential (ERP) components between multiple sclerosis (MS) patients and controls and to compare ERP findings with results from the paced auditory serial addition test (PASAT).MethodsFifty-four subjects (17 relapsing remitting (RRMS) patients, 16 secondary progressive (SPMS) patients, and 21 controls) completed visual and auditory oddball tasks while data were recorded from 134 EEG channels. Latency and amplitude differences, calculated using composite mean amplitude measures, were tested using an ANOVA. Topographical differences were tested using statistical parametric mapping (SPM).ResultsIn the visual modality, P2, P3 amplitudes and N2 latency were significantly different across groups. In the auditory modality, P2, N2, and P3 latencies and N1 amplitude were significantly different across groups. There were no significant differences between RRMS and SPMS patients on any ERP component. There were topographical differences between MS patients and controls for both early and late components for the visual modality, but only in the early components for the auditory modality. PASAT score correlated significantly with auditory P3 latency for MS patients.ConclusionsThere were significant ERP differences between MS patients and controls.SignificanceThe present study indicated that both early sensory and later cognitive ERP components are impaired in MS patients relative to controls.     

Global-local visual processing in schizophrenia: evidence for an early visual processing deficit.

BACKGROUND: Abnormalities in early-stage visual processing might contribute to observed higher neurocognitive deficits in schizophrenia, but to date no clear link has been established. Schizophrenia has been associated with deficits in the magnocellular visual pathway, suggesting a relative bias for processing elemental (local) as opposed to configural (global) aspects of a hierarchical stimulus; however, global-local paradigm studies in schizophrenia have yielded mixed results. METHODS: In the current study, global-local and event-related potential (ERP) procedures were concomitantly used to assess temporal and spatial characteristics of hierarchical visual stimulus processing abnormalities. RESULTS: Patients (n = 24) had slower and less accurate responses to global stimuli than a healthy comparison group (n = 29). They exhibited a marked decrement in N150 ERP amplitude, which correlated with speed of response to global stimuli. They also failed to show an augmented P300 response to local stimuli. CONCLUSIONS: Behavioral and physiological data are consistent and support a global visual processing deficit in schizophrenia. This is manifest at a relatively early stage of visual processing and might relate to physiological disturbances in areas V3/V3a of the extrastriate cortex.