Memory template comparison processes in anhedonia and dysthymia

Dysfunction of visual novelty detection in physical but not social anhedonia in a non-clinical sample

Background/objective

Despite its obvious motivational impairment, anhedonia as a transdiagnostic psychopathological construct is accompanied by deficits in attention function. Previous studies have identified voluntary attention anomalies in anhedonia, but its involuntary attention has received less study.

Method

Using a visual novelty oddball task, the current event-related potential study assessed electrophysical correlates underlying mismatch detection in anhedonia with a non-clinical sample. Well-matched healthy control (N = 28; CNT), social anhedonia (N = 27; SA), and physical anhedonia (N = 26; PA) groups were presented standard, target, and perceptually novel stimuli while their EEG was recording.

Results

The PA group relative to the CNT group exhibited a reduced N2 to novel stimuli but not to target stimuli. In contrast, the SA group as compared to the other two groups showed comparable N2 responses to both target and novel stimuli. Control analyses indicated that these patterns were unaffected by depression symptoms.

Conclusions

These findings suggest that anhedonia is a heterogenous construct associated with impairments in early detection of visual novelty in physical but not social anhedonia, highlighting that dysfunction in involuntary attention may play a mediating role in the development, maintenance, and consequences of anhedonia-related psychopathology.

Blunted Flanker P300 Demonstrates Specificity to Depressive Symptoms in Females during Adolescence

Recent research suggests that depressive disorders in adults are characterized by reductions in flanker P300 amplitude, and that a reduced flanker P300 may also predict worst depressive trajectories over time. The current study extended this work to adolescence-and to evaluate the specificity of the relationship between flanker P300 to depressive symptoms versus anxiety symptoms, and whether the association between flanker P300 and depressive symptoms was moderated by biological sex. To this end, P300 amplitude, depression, anxiety, and sex were assessed in a large sample of 619 adolescents aged 11 to 14. Participants completed a speeded response flanker task while EEG was recorded, as well as self-reported measures of current depression and anxiety symptoms. Reduced P300 amplitude was related to both heightened depression and anxiety symptoms in zero-order correlations. Regression-based analyses suggest that reduced P300 was uniquely related to depressive symptoms. Furthermore, this negative association between P300 and depression was apparent in female adolescents, but not male adolescents. In sum, the current study suggests that flanker P300 amplitude may potentially serve as a neural marker specific to depression in females during adolescence.

Stimulus sequence context differentially modulates inhibition-related theta and delta band activity in a go/no-go task

Recent work suggests that dissociable activity in theta and delta frequency bands underlies several common ERP components, including the no-go N2/P3 complex, which can better index separable functional processes than traditional time-domain measures. Reports have also demonstrated that neural activity can be affected by stimulus sequence context information (i.e., the number and type of preceding stimuli). Stemming from prior work demonstrating that theta and delta index separable processes during response inhibition, the current study assessed sequence context in a go/no-go paradigm in which the number of go stimuli preceding each no-go was selectively manipulated. Principal component analysis of time-frequency representations revealed differential modulation of evoked theta and delta related to sequence context, where delta increased robustly with additional preceding go stimuli, while theta did not. Findings are consistent with the view that theta indexes simpler initial salience-related processes, while delta indexes more varied and complex processes related to a variety of task parameters.

Primary somatosensory contextual modulation is encoded by oscillation frequency change

OBJECTIVE

This study characterized thalamo-cortical communication by assessing the effect of context-dependent modulation on the very early somatosensory evoked high-frequency oscillations (HF oscillations).

METHODS

We applied electrical stimuli to the median nerve together with an auditory oddball paradigm, presenting standard and deviant target tones representing differential cognitive contexts to the constantly repeated electrical stimulation. Median nerve stimulation without auditory stimulation served as unimodal control.

RESULTS

A model consisting of one subcortical (near thalamus) and two cortical (Brodmann areas 1 and 3b) dipolar sources explained the measured HF oscillations. Both at subcortical and the cortical levels HF oscillations were significantly smaller during bimodal (somatosensory plus auditory) than unimodal (somatosensory only) stimulation. A delay differential equation model was developed to investigate interactions within the 3-node thalamo-cortical network. Importantly, a significant change in the eigenfrequency of Brodmann area 3b was related to the context-dependent modulation, while there was no change in the network coupling.

CONCLUSION

This model strongly suggests cortico-thalamic feedback from both cortical Brodmann areas 1 and 3b to the thalamus. With the 3-node network model, thalamo-cortical feedback could be described.

SIGNIFICANCE

Frequency encoding plays an important role in contextual modulation in the somatosensory thalamo-cortical network.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Thalamocortical changes in major depression probed by deconvolution and physiology-based modeling

Auditory event-related potentials (ERPs) have been extensively studied in patients with depression, but most studies have focused on purely phenomenological analysis methods, such as component scoring. In contrast, this study applies two recently developed physiology-based methods-fitting using a thalamocortical model of neuronal activity and waveform deconvolution - to data from a selective-attention task in four subject groups (49 patients with melancholic depression, 34 patients with non-melancholic depression, 111 participants with subclinical depressed mood, and 98 healthy controls), to yield insight into physiological differences in attentional processing between participants with major depression and controls. This approach found evidence that: participants with depressed mood, regardless of clinical status, shift from excitation in the thalamocortical system towards inhibition; that clinically depressed participants have decreased relative response amplitude between target and standard waveforms; and that patients with melancholic depression also have increased thalamocortical delays. These findings suggest possible physiological mechanisms underlying different depression subtypes, and may eventually prove useful in motivating new physiology-based diagnostic methods.

Somatosensory system deficits in schizophrenia revealed by MEG during a median-nerve oddball task

Although impairments related to somatosensory perception are common in schizophrenia, they have rarely been examined in functional imaging studies. In the present study, magnetoencephalography (MEG) was used to identify neural networks that support attention to somatosensory stimuli in healthy adults and abnormalities in these networks in patient with schizophrenia. A median-nerve oddball task was used to probe attention to somatosensory stimuli, and an advanced, high-resolution MEG source-imaging method was applied to assess activity throughout the brain. In nineteen healthy subjects, attention-related activation was seen in a sensorimotor network involving primary somatosensory (S1), secondary somatosensory (S2), primary motor (M1), pre-motor (PMA), and paracentral lobule (PCL) areas. A frontal-parietal-temporal "attention network", containing dorsal- and ventral-lateral prefrontal cortex (DLPFC and VLPFC), orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), superior parietal lobule (SPL), inferior parietal lobule (IPL)/supramarginal gyrus (SMG), and temporal lobe areas, was also activated. Seventeen individuals with schizophrenia showed early attention-related hyperactivations in S1 and M1 but hypo-activation in S1, S2, M1, and PMA at later latency in the sensorimotor network. Within this attention network, hypoactivation was found in SPL, DLPFC, orbitofrontal cortex, and the dorsal aspect of ACC. Hyperactivation was seen in SMG/IPL, frontal pole, and the ventral aspect of ACC in patients. These findings link attention-related somatosensory deficits to dysfunction in both sensorimotor and frontal-parietal-temporal networks in schizophrenia.

Auditory scene analysis: the interaction of stimulation rate and frequency separation on pre-attentive grouping

Segregation of auditory inputs into meaningful acoustic groups is a key element of auditory scene analysis. Previously, we showed that two interwoven sets of tones differing widely along multiple feature dimensions (duration, pitch and location) were pre-attentively separated into different groups, and that tones separated in this manner did not elicit the mismatch negativity component with respect to each other. Grouping was studied with human subjects using a stimulus rate too slow to induce streaming. Here, we varied the separation of tone sequences along a single feature dimension, i.e. frequency. Frequency differences were either 24 Hz (small) or 1054 Hz (large). Two relatively slow stimulus rates were used (2.7 or 1 tone/s) to explicitly investigate grouping outside the so-called 'streaming effect', which requires rates of about 4 tones/s or faster. Two tones were presented in a quasi-random manner with embedded trains of one to four identical tones in a row. Deviants were defined as frequency switches after trains of four identical tones. Mismatch negativity was only elicited for small frequency switches at the slower stimulation rate. The data indicate that pre-attentive grouping of tones occurred when the frequency difference that separated them was large, regardless of stimulation rate. For small frequency differences, inputs were only grouped separately when the stimulation rate was relatively fast.

Error-related event-related potentials in children with attention-deficit hyperactivity disorder, oppositional defiant disorder, reading disorder, and math disorder

We studied error-related negativity (ERN) and error positivity (Pe) during a discrimination task in 319 unmedicated children divided into subtypes of ADHD (Not-ADHD/inattentive/combined), learning disorder (Not-LD/reading/math/reading+math), and oppositional defiant disorder. Response-locked ERPs contained a frontocentral ERN and posterior Pe. Error-related negativity and positivity exhibited larger amplitude and later latency than corresponding waves for correct responses matched on reaction time. ADHD did not affect performance on the task. The ADHD/combined sample exceeded controls in ERN amplitude, perhaps reflecting patients' adaptive monitoring efforts. Compared with controls, subjects with reading disorder and reading+math disorder performed worse on the task and had marginally more negative correct-related negativities. In contrast, Pe/Pc was smaller in children with reading+math disorder than among subjects with reading disorder and Not-LD participants; this nonspecific finding is not attributable to error processing. The results reflect anomalies in error processing in these disorders but further research is needed to address inconsistencies in the literature.

Preattentively grouped tones do not elicit MMN with respect to each other

To promote preattenive grouping of two sets of tones, one set of tones with a combination of frequency and ear of delivery was intermixed with another set of tones with a different combination of frequency and ear of delivery. The ERPs elicited by tones delivered to one ear that were preceded by three or four tones delivered in a row to the other ear were associated with an enhanced N1, due to the changes in frequency and ear of delivery with respect to the immediately preceding tones. However, no mismatch negativity (MMN) was obtained, even though these tones differed from the previious tones on the two dimensions of frequency and ear of delivery. The data were interpreted to signify that preattentively grouped sets of tones do not elicit MMN with respect to one another. This implies that once acoustic input has been preattentively grouped, the MMN system is dedicated to detecting changes that occur within but not between preattentively grouped stimuli.

Effect of hedonic tone on event-related potential measures of cognitive processing

Anhedonia, the inability to experience pleasure, is a core feature of several psychiatric disorders such as schizophrenia, depression, and substance dependence. Furthermore, it has been suggested that anhedonia is an important predictor of schizophrenia. Anhedonia has been associated with information-processing deficits, especially attentional deficits, which may predispose for schizophrenia. In the present study, event-related potentials (ERPs) were used to examine the influence of hedonic tone on information-processing characteristics in a sample of healthy individuals. Thirty-five healthy subjects were divided into two groups based on their scores on the Snaith-Hamilton Pleasure Scale (SHAPS). Cognitive functions were measured during an active visual oddball paradigm. It was found that both early, middle and late ERP components of subjects with low levels of hedonic tone were attenuated compared with ERPs of subjects with high levels of hedonic tone. These findings suggest that decreased hedonic tone is associated with reductions in both automatic and effortful cognitive processing of relevant stimuli. Consequences of these findings for the vulnerability to psychopathology are discussed.

Abnormal asymmetry of N200 and P300 event-related potentials in subclinical depression

Sex differences for depression in prevalence and symptom profile may in part be due to differences between men and women in brain dysfunction associated with the disorder. Changes in event-related potential (ERP) measures similar to those seen in clinical populations are reported in subclinical or premorbid forms of depression. The current study investigates sex differences in ERPs associated with subclinical depression. One-hundred-and-forty healthy, right-handed adults (aged 20-60 years; screened to exclude clinical depression and psychosis) completed an auditory oddball task and the Depression Anxiety and Stress Scale (DASS). Seventy (n = 35 men) subclinically depressed (SD) (i.e. scoring >2 for depression on DASS) participants were matched for age and education with 70 (n = 35 men) participants showing no signs of depression (ND). Repeated measures multivariate analysis of variance was used to test for differences in N200 and P300 amplitude between SD and ND groups. ND, but not SD groups had asymmetry (R > L) of central N200 amplitude. Similar asymmetry was seen in ND, but not SD men at posterior sites. SD groups demonstrated left > right posterior P300 amplitude asymmetry due to P300 enhancement at left temporoparietal sites. Results support involvement of various cognitive mechanisms measured by P300 and N200 in subclinical depressive symptoms some of which may rely on sex.

Probability-independent and -dependent ERPs reflecting visual change detection

In ERP studies, two posterior components with different polarities have been identified as ERP correlates of visual change detection. To compare these components in terms of sensitivity to the preceding stimulus sequence, two peripheral stimuli of different colors (red and blue) were presented with equal (50:50) or different probabilities (20:80 or 80:20), while 12 participants performed shape discrimination at a central location. A posterior positivity at around 90-140 ms was observed with similar amplitude to all stimuli immediately preceded by a different stimulus. In contrast, a posterior negativity at around 140-180 ms was observed to increase in amplitude with increasing number of preceding different stimuli. These results suggest the existence of probability-independent and -dependent change processing in the human visual system. The functional significance is discussed in terms of memory-based comparison and stimulus-specific refractoriness.

PREDICTING SEVERITY OF NON-CLINICAL DEPRESSION: PRELIMINARY FINDINGS USING AN INTEGRATED APPROACH

INTRODUCTION

Depression is characterized by disturbances in affect, cognition, brain and body function, yet studies have tended to focus on single domains of dysfunction. An integrated approach may provide a more complete profile of the range of deficits characterized by depressed individuals, but it is unclear whether this approach is able to predict depression severity over and above that predicted by single tasks or domains of function. In this study, we examined the value of combining multiple domains of function in predicting depression severity.

METHODS

Participants contained in the International Brain Database, (http://www.brainresource.com) had completed three testing components including a web-based questionnaire of Personal History, the Brain Resource Cognition battery of Neuropsychological tests, Personality assessment and Psychophysiological testing. Two hundred and sixty six of these participants were able to be classified as either non-depressed, mild-moderately or severely (non-clinically) depressed, based on a depression screening questionnaire. Analysis of variance identified variables on which the categorized participants differed. Significant variables were then entered into a series of stepwise regressions to examine their ability to predict depression scores.

RESULTS

An integrated model including measures of affect (increased Neuroticism; decreased Emotional Intelligence), cognition (increased variability of reaction time during a working memory task; decreased "name the word component score" in the verbal interference task), brain (decreased left-lateralized P150 ERP component during a working memory task) and body function (increased negative skin conductance level gradient) were found to predict more of the variation in depression severity than any single domain of function.

DISCUSSION

On the basis of behavioral as well as Psychophysiological findings reported in this study, it was suggested that deficits in subclinically depressed individuals are more pronounced during automatic stages of stimulus processing, and that performance in these individuals may improve (to the level displayed by controls) when task demands are increased. Findings also suggest that it is important to consider disturbances across different domains of function in order to elucidate depression severity. Each domain may contribute unique explanatory information consistent with an integrative model of depression, taking into account the role of both behavior and underlying neural changes.

An ERP study of visual change detection: effects of magnitude of spatial frequency changes on the change-related posterior positivity

In event-related brain potential (ERP) studies using a visual S1-S2 matching task, change stimuli elicit a posterior positivity at around 100-200 ms. In the present study, we investigated the effects of magnitude of spatial frequency changes on change-related positivity. Each trial consisted of two sequentially presented stimuli (S1-S2), where S2 was either (1) the same as S1 (i.e., NO-change, p=.40), (2) different from S1 in spatial frequency only (SF-change, .40), (3) different in orientation only (OR-change, .10), or (4) different in both spatial frequency and orientation (BOTH-change, .10). Further, three magnitude conditions (Large, Medium, and Small) were used to examine the effect of the magnitude of the spatial frequency change. Participant's (N=12) task was to respond to S2 with a change in orientation (from vertical to horizontal, or from horizontal to vertical) regardless of the spatial frequency of the stimulus. Changes in the spatial frequency elicited change-related positivity at a latency range of about 120-180 ms, which was followed by a central negativity (N270) and a late positive component (LPC). The amplitude of the change-related positivity tends to be enhanced as the magnitude of the change is increased. These results support the notion that the change-related positivity reflects memory-based change detection in the human visual system.

The Neural Circuitry of Pre-attentive Auditory Change-detection: An fMRI Study of Pitch and Duration Mismatch Negativity generators

Electrophysiological studies have revealed a pre-attentive change-detection system in the auditory modality. This system emits a signal termed the mismatch negativity (MMN) when any detectable change in a regular pattern of auditory stimulation occurs. The precise intracranial sources underlying MMN generation, and in particular whether these vary as a function of the acoustic feature that changes, is a matter of some debate. Using functional magnetic resonance imaging, we show that anatomically distinct networks of auditory cortices are activated as a function of the deviating acoustic feature--in this case, tone frequency and tone duration--strongly supporting the hypothesis that MMN generators in auditory cortex are feature dependent. We also detail regions of the frontal and parietal cortices activated by change-detection processes. These regions also show feature dependence and we hypothesize that they reflect recruitment of attention-switching mechanisms.

Processing Tonal Modulations: An ERP Study

A common stylistic element of Western tonal music is the change of key within a musical sequence (known as modulation in musical terms). The aim of the present study was to investigate neural correlates of the cognitive processing of modulations with event-related brain potentials. Participants listened to sequences of chords that were infrequently modulating. Modulating chords elicited distinct effects in the event-related brain potentials: an early right anterior negativity reflecting the processing of a violation of musical regularities and a late frontal negativity taken to reflect processes of harmonic integration. Additionally, modulations elicited a tonic negative potential suggested to reflect cognitive processes characteristic for the processing of tonal modulations, namely, the restructuring of the “hierarchy of harmonic stability” (which specifies musical expectations), presumably entailing working memory operations. Participants were “nonmusicians”; results thus support the hypothesis that nonmusicians have a sophisticated (implicit) knowledge about musical regularities.

Psychophysiological Response Patterns of High and Low Alexithymics Under Mental and Emotional Load Conditions

Abstract Compared to normals or low alexithymics, high alexithymic subjects show a modified psychophysiological reactivity under experimental stress. This study aims to differentiate these effects under different load conditions (mental vs. emotional load, 5min each). High (N = 33) and low (N = 33) alexithymic subjects were identified by the German version of the Toronto-Alexithymia-Scale (TAS-20). Subjects were exposed to two tasks of the continuous performance test as a mental load condition and two unpleasant movie sequences as an emotional load condition. Heart rate and electrodermal activity (nonspecific skin conductance reactions) were continuously recorded during stimuli presentation. High alexithymic subjects showed a decreased number of nonspecific skin conductance reactions under all load conditions compared to low alexithymics. Initial heart rate acceleration of high alexithymic subjects under mental load was stronger, whereas under emotional load high alexithymic subjects showed a stronger initial heart rate deceleration. Results are discussed with respect to a modified processing of emotionally qualified information in alexithymics.

Effects of event probability and sequence on children with attention-deficit/hyperactivity, reading, and math disorder

BACKGROUND

We investigated the impact of stimulus probability and sequence on performance and event-related potentials of 310 children classified into 12 combinations of attention-deficit/hyperactivity disorder (Not-attention-deficit/hyperactivity disorder, Inattentive and Combined subtypes) with presence/absence of reading disorder and math disorder.

METHODS

Subjects pressed buttons to displays of the letters O and X, which were presented with probabilities of either .17/.83 or .50/.50. Greater response selection was required in the .17/.83 condition.

RESULTS

Stimulus probability had comparable effects on all diagnostic groups. The extent of mismatch between a stimulus and preceding events elicited less systematic increases in errors, P3b latency, and P3b amplitude among both attention-deficit/hyperactivity disorder subtypes than controls. Mismatch with preceding trials more greatly reduced math disorder and reading disorder + math disorder children's speed in the Rare task and accuracy in both conditions. Math disorder and reading disorder + math disorder subjects also registered less the effects of alternations of the infrequent O on N2 amplitude and on P3b latency.

CONCLUSIONS

Math disorder and reading disorder + math disorder youngsters' lower sensitivity to sequence irregularity in their event-related potentials along with greater disruption of performance suggest working memory deficits that adversely affected response selection. Comorbidity of attention-deficit/hyperactivity disorder and reading disorder did not affect the results.

The long and the short of it: influence of interstimulus interval on auditory P300 abnormalities in schizophrenia

Event-related brain potentials were recorded from 10 patients with DSM-IV schizophrenia (9 men) and 10 healthy control subjects (9 men) during the performance of two auditory oddball tasks, one using a 1.5 second interstimulus interval (ISI), the other using an 8 second ISI. P300 amplitude to target tones (.20 probability) and standard tones (.80 probability) were measured from midline electrodes Fz, Cz, and Pz. Results showed different effects of ISI in the two groups. Controls showed a slight decrease in P300 amplitude to targets but a marked increase in P300 to standards with the increase in ISI. In contrast, schizophrenic patients showed no change in the P300 to targets and a relatively small increase in P300 to standards with the ISI increase. Moreover, relative to the controls, P300 amplitude to targets was reduced in the schizophrenic patients at the short but not the long ISI. Implications for the cognitive significance of the P300 and its reduction in schizophrenia are discussed.

P300 stimulus sequence effects in children and adults

Immediate memory capability for 12 children (8 years) and 12 adults (21 years) was assessed electrophysiologically by using P300 event-related brain potential (ERP) stimulus sequences. These were derived from an auditory discrimination paradigm in which participants detected target stimuli in a series of target (T) and standard (S) tones that were varied by randomly presenting one of four sequence patterns (SSSS, TTTT, TTTS, SSST). Short-term memory capability was assessed behaviorally by recall performance of a 20-word list. Children and adults showed virtually identical P300 amplitude sequence patterns, such that for both groups component size increased systematically as the discrepancy between standard and target stimuli increased across sequence patterns. P300 latency evinced similar, albeit weaker, stimulus sequence effects, with children having longer component peak latencies. Memory recall performance was substantially weaker for the children than for adult participants, especially for recency effects. The findings suggest that immediate memory for stimulus sequences is fully developed in young children, although long-term memory is not.

Anhedonia in depression and schizophrenia: a reexamination

The purpose of this study was to utilize factor analysis to help determine whether anhedonia is a symptom of both depression and schizophrenia. Measures of depression, positive and negative symptoms of schizophrenia, and anhedonia were administered to a group of schizophrenic patients (N = 54) and to a group of patients with major depressive disorder (N = 27). The correlation matrix among the various scales was subjected to an oblique exploratory factor analysis. Three factors were extracted, accounting for three quarters of the variance. The first measured depression, the second measured positive symptoms, and the third measured negative symptoms. Anhedonia loaded significantly on the first factor but not on the third, suggesting that it is a symptom of depression rather than schizophrenia. These results were corroborated by means of confirmatory factor analysis. We conclude that anhedonia is a symptom of depression and that it only appears to be a symptom of schizophrenia because it is a component of emotional blunting which is indeed a negative symptom of schizophrenia.

Methylphenidate does not modify the impact of response frequency or stimulus sequence on performance and event-related potentials of children with attention deficit hyperactivity disorder

Twenty-six children with attention deficit/hyperactivity disorder (ADHD) participated in a double-blind trial consisting of 2 consecutive weeks each of placebo and methylphenidate (M = 26.92 mg/day = 0.78 mg/kg/day). As expected, stimulant therapy resulted in moderate weight loss, increased somatic complaints, and teacher and parent reports of reduced inattentiveness, aggression, and oppositionality. In both phases of the trial, patients were tested in a choice reaction time task assessing two aspects of the task that presumably affect response selection: response frequency (ratio of targets/nontargets = 25/75 vs. 50/50) and stimulus sequence (alternations vs. repetitions). Both manipulations yielded expected results on performance and event-related potentials (ERPs). Stimulant treatment increased accuracy and speed among younger children and curtailed variability of reaction time for the sample as a whole. However, methylphenidate did not affect ERPs. In combination, the results imply that the enhancement of performance by methylphenidate does not involve the demands of response selection examined in this study.

P300 sequence effects, probability, and interstimulus interval

Probability and interstimulus interval effects on P3(00) event-related potential (ERP) stimulus sequences were examined in 2 experiments. ERPs were elicited with an auditory-discrimination paradigm in which subjects were instructed to detect target stimuli from a series of target (T) and standard (S) tones that were varied by randomly presenting 1 of 4 sequence patterns (SS, TS, TT, ST). Experiment 1 manipulated target stimulus probability as either 0.33 or 0.67; Experiment 2 kept target probability at 0.33 and manipulated the interstimulus interval (ISI) as either 2 or 6 s. Increases in target stimulus probability produced smaller P300 amplitudes that were additive with stimulus sequence type. ISI did not reliably affect P300 amplitude, although ISI interacted with stimulus sequence. P300 latency from the stimulus sequences was influenced weakly by the probability and ISI factors, with few consistent sequence effects obtained for the N1, P2, and N2 potentials. The results suggest that even relatively short sequences can affect P300 amplitude in the same way as longer sequences: as the number of standard stimuli preceding the target increased, P300 amplitude increased. The theoretical implications of the findings are discussed in the context of applied testing situations.

P300 and probability: comparison of oddball and single-stimulus paradigms

The P300 event-related brain potential (ERP) was elicited with auditory stimuli in two different tasks. The oddball paradigm presented both target and standard stimuli; the single-stimulus paradigm presented a target but no standard tone stimulus, with the inter-target interval the same as that for the oddball condition. Target stimulus probability was manipulated in the oddball task in different conditions (0.10, 0.30, 0.50, 0.70, 0.90). The single-stimulus paradigm employed the same procedures such that the inter-target interval was identical as that for the oddball condition across changes in probability. P300 amplitude and latency were similar for both the oddball and single-stimulus procedures across probability levels. Correlations between the P300 values from each task mimicked those from test-retest comparisons for the oddball paradigm. The findings suggest that P300 from the single-stimulus paradigm responds to target stimulus probability in the same fashion as the traditional oddball. The implications of the single-stimulus technique are discussed in terms of applied contexts that require very simple ERP task conditions.

Interactions between Transient and Long-Term Auditory Memory as Reflected by the Mismatch Negativity

The mismatch negativity (MMN) event-related potential (ERP) component is elicited by any discriminable change in series of repetitive auditory stimuli. MMN is generated by a process registering the deviation of the incoming stimulus from the trace of the previous repetitive stimulus. Using MMN as a probe into auditory sensory memory, the present study addressed the question of whether the sensory memory representation is formed strictly on the basis of an automatic feature analysis of incoming sensory stimuli or information from long-term memory is also incorporated. Trains of 6 tone bursts (standards with up to 1 deviant per train) separated by 9.5-sec intertrain intervals were presented to subjects performing a visual tracking task and disregarding the auditory stimuli. Trains were grouped into stimulus blocks of 20 trains with a 2-min rest period between blocks. In the Constant-Standard Condition, both standard and deviant stimuli remained fixed across the session, encouraging the formation of a long-term memory representation. To eliminate the carryover of sensory storage from one train to the next, the first 3.6 sec of the intertrain interval was filled with 6 tones of random frequencies. In the Roving-Standard Condition, the standard changed from train to train and the intervening tones were omitted. It was found that MMN was elicited by deviants presented in Position 2 of the trains in the Constant-Standard Condition revealing that a single reminder of the constant standard reactivated the standard-stimulus representation. The MMN amplitude increased across trials within each stimulus block in the Constant- but not in the Roving-Standard Condition, demonstrating long-term learning in that condition (i.e., the standard-stimulus trace indexed by the MMN amplitude benefitted from the presentations of the constant standard in the previous trains). The present results suggest that the transient auditory sensory memory representation underlying the MMN is facilitated by a longer-term representation of the corresponding stimulus.

[Interindividual variability of exogenous and endogenous auditory evoked potentials in a condition of voluntary attention]

The use of P300 in psychopathology raises the important problem of the constitution of reference normative data and of the high variability of auditive ERP's in controls. To handle better this problem, we recorded 86 control subjects, using an auditory oddball paradigm with motor response. We analyzed the successive components of the ERP's evoked by target and standard stimuli (N1, P2, N2, P3a, P3b and slow wave negativity). Our results underlined the role of age, sex and psychological factors on the ERP's interindividual variability: P3 amplitude decreased and its latency increased with age, while its topography was more frontal in the older than in the younger subjects. The P300 occurrence after standard stimuli and P3 amplitude after target stimuli were different according to sex. Moreover, P300 amplitude, latency and topography were related to the subject's anxiety level. Finally, our results also propose new description modes of ERP's relying on P3a and P3b relative peak amplitude (P300 with prominent P3a or P3b), topographical predominance (frontal or parietal P300) and duration of the late positive complex (brief or long-lasting P300). These data will improve the clinical use of P300.