Mismatch negativity for speech sounds in temporal lobe epilepsy

The mismatch negativity (MMN) is an electrophysiological trace of change detection, measured by electroencephalography (EEG), and is a reliable marker for pre-attentive auditory sensory memory. We used a phonetic oddball paradigm in patients with temporal lobe epilepsy (TLE) to elicit the MMN response at fronto-central sites and the mismatch positivity (MMP) response at mastoid sites. The MMN in 26 patients was compared with that of 26 age- and gender-matched healthy control participants. Electroencephalography responses were recorded during the presentation of speech sounds: the vowels 'a' and 'o' in alternation. Average waveforms were obtained for standard and deviant trials. We found that the MMP response at bilateral mastoid sites was reduced, whereas the MMN response at fronto-central sites did not change significantly. These results support the view that the MMN is generated by separable sources in the frontal and temporal lobes and that these sources are differentially affected by TLE.

Evidence for a dual versus single origin of the MMNs evoked by cued versus cueless deviants

OBJECTIVE

This study was designed to separately test the effect of the cued/cueless nature of deviant stimuli and that of temporal distance between sound and deviance onsets on the mismatch negativity (MMN) as well as to look for discrepancies between behavioural discrimination performances and MMN amplitude when deviants are cueless.

METHODS

Ten healthy adults passively listened to stimuli that were contrasted by the presence or absence of a frequency sweep starting early or late within the sound. Discrimination performances were collected after the electrophysiological sessions.

RESULTS

MMNs were much larger for cued than for cueless deviants. The temporal distance between sound and deviance onsets affected MMNs evoked by both cued and cueless deviants, even to the point of abolishing the MMN when cueless deviance occurred late in the stimulus. Behavioural data were at ceiling levels for all conditions, contrasting with the absence of MMN evoked by cueless deviants with late onset.

CONCLUSIONS

Two mechanisms contribute to the MMN evoked by cued deviants: the memory comparison process and the adaptation/fresh-afferent one. Within the temporal window of integration, the delay at which each component disappears is different.

SIGNIFICANCE

Comparing waveforms evoked by cued versus cueless deviants provides a fairly simple way of isolating the MMN memory-based component.

Effects of experimentally induced low back pain on the sit-to-stand movement and electroencephalographic contingent negative variation

It is becoming increasingly evident that people with chronic, recurrent low back pain (LBP) exhibit changes in cerebrocortical activity that associate with altered postural coordination, suggesting a need for a better understanding of how the experience of LBP alters postural coordination and cerebrocortical activity. To characterize changes in postural coordination and pre-movement cerebrocortical activity related to the experience of acutely induced LBP, 14 healthy participants with no history of LBP performed sit-to-stand movements in 3 sequential conditions: (1) without experimentally induced LBP; NoPain1, (2) with movement-associated LBP induced by electrocutaneous stimulation; Pain, and (3) again without induced LBP; NoPain2. The Pain condition elicited altered muscle activation and redistributed forces under the seat and feet prior to movement, decreased peak vertical force exerted under the feet during weight transfer, longer movement times, as well as decreased and earlier peak hip extension. Stepwise regression models demonstrated that electroencephalographic amplitudes of contingent negative variation during the Pain condition significantly correlated with the participants' change in sit-to-stand measures between the NoPain1 and Pain conditions, as well as with the subsequent difference in sit-to-stand measures between the NoPain1 and NoPain2 conditions. The results, therefore, identify the contingent negative variation as a correlate for the extent of an individual's LBP-related movement modifications and to the subsequent change in movement patterns from before to after the experience of acutely induced LBP, thereby providing a direction for future studies aimed to understand the neural mechanisms underlying the development of altered movement patterns with LBP.

Successful deep brain stimulation of the nucleus accumbens in severe alcohol dependence is associated with changed performance monitoring

Following recent advances in neuromodulation therapy for mental disorders, we treated one patient with severe alcohol addiction with deep brain stimulation (DBS) of the nucleus accumbens (NAc). Before and one year following the surgery, we assessed the effects of DBS within the NAc on the addiction as well as on psychometric scores and electrophysiological measures of cognitive control. In our patient, DBS achieved normalization of addictive behavior and craving. An electrophysiological marker of error processing (the error-related negativity) linked to anterior mid-cingulate cortex (aMCC) functioning was altered through DBS, an effect that could be reversed by periods without stimulation. Thus, this case supports the hypothesis that DBS of the NAc could have a positive effect on addiction trough a normalization of craving associated with aMCC dysfunction.

Differential effects of chronic cannabis use on preattentional cognitive functioning in abstinent schizophrenic patients and healthy subjects

INTRODUCTION

A number of studies indicate a higher risk for psychosis as well as for neurocognitive deficits in healthy cannabis users. However, little is known about the impact of cannabis use on outcome in schizophrenia. In fact, there is growing evidence that cannabis-using schizophrenic patients may show preserved or even better neurocognitive performance compared to schizophrenic non-users.

METHODS

We measured mismatch negativity (MMN) to investigate preattentional neurocognitive functioning in long-term abstinent chronic cannabis users with (SZCA n=27) and without schizophrenia (COCA n=32) compared to schizophrenic patients (SZ n=26) and healthy controls (CO n=34) without any chronic drug use.

RESULTS

Healthy cannabis users showed reduced frontal MMN compared to controls (p=0.036). In contrast, cannabis-using schizophrenic patients showed increased frontal MMN compared to schizophrenic patients without cannabis use (p=0.038). Comparing non-cannabis users, schizophrenic patients showed reduced frontal MMN (p=0.001). No significant differences were found between CO and SZCA (p=0.27), and COCA and SZCA (p=0.50).

CONCLUSION

Results suggest that chronic cannabis use may have different effects on preattentional neurocognitive functioning in schizophrenic patients when compared to healthy subjects. This may be related to preexisting differences in the endocannabinoid system between schizophrenic patients and healthy subjects. However, due to the naturalistic design of the study, the results must be interpreted with caution.

Individual differences in substance dependence: at the intersection of brain, behaviour and cognition

Recent theories of drug dependence propose that the transition from occasional recreational substance use to harmful use and dependence results from the impact of disrupted midbrain dopamine signals for reinforcement learning on frontal brain areas that implement cognitive control and decision-making. We investigated this hypothesis in humans using electrophysiological and behavioral measures believed to assay the integrity of midbrain dopamine system and its neural targets. Our investigation revealed two groups of dependent individuals, one characterized by disrupted dopamine-dependent reward learning and the other by disrupted error learning associated with depression-proneness. These results highlight important neurobiological and behavioral differences between two classes of dependent users that can inform the development of individually tailored treatment programs.

Evidence of deficient central speech processing in children with specific language impairment: the T-complex

OBJECTIVE

This paper examined neurophysiological correlates of speech in children with language impairment (LI) and typical language development (TLD) across four experiments using different speech stimuli and tasks.

METHODS

The T-complex event-related potential (ERP) components and other ERP components (e.g., mismatch negativity [MMN]; N400) were examined. A subset of the children participated in more than one of the experiments.

RESULTS

73% of the children with LI had poor T-complex measures compared to only 13% of children with TLD. The T-complex measures were more comparable, in terms of indicating typical versus deviant processing, to neurophysiological measures of language processing, such as lexical discrimination, than to other measures of auditory and speech processing, such as the MMN. Only one LI child showed no poor measures and 64% showed three or more poor neurophysiological measures. However, 50% of children with TLD showed no poor neurophysiological measures, and 82% of the TLD children showed no more than two poor measures.

CONCLUSIONS

These results suggest that poor auditory processing, as measured by the T-complex, is a marker for LI and that multiple deficits serve to mark LI.

SIGNIFICANCE

The T-complex measures, indexing secondary auditory cortex, reflect an important aspect of processing in speech and language development.

Social status determines how we monitor and evaluate our performance

Since people with low status are more likely to experience social evaluative threat and are therefore more inclined to monitor for these threats and inhibit approach behaviour, we expected that low-status subjects would be more engaged in evaluating their own performance, compared with high-status subjects. We created a highly salient social hierarchy based on the performance of a simple time estimation task. Subjects could achieve high, middle or low status while performing this task simultaneously with other two players who were either higher or lower in status. Subjects received feedback on their own performance, as well as on the performance of the other two players simultaneously. Electroencephalography (EEG) was recorded from all three participants. The results showed that medial frontal negativity (an event-related potential reflecting performance evaluation) was significantly enhanced for low-status subjects. Implications for status-related differences in goal-directed behaviour are discussed.

MMN responsivity to manipulations of frequency and duration deviants in chronic, clozapine-treated schizophrenia patients

Event-related potential (ERP) probing of abnormal sensory processes in schizophrenia with the mismatch negativity (MMN) has shown impairments in auditory change detection, but knowledge of the acoustic features leading to this deficit is incomplete. Changes in the duration and frequency properties of sound stimuli result in diminished MMNs in schizophrenia but it is unclear as to whether this reduced responsiveness is seen with more subtle changes in sound frequency. In a sample of 19 healthy controls and 21 patients with chronic schizophrenia treated with clozapine, MMN was assessed in response to tone frequency changes of 5%, 10% and 20%, and to tone duration changes. Patients exhibited reduced amplitudes and shorter latencies than controls to all frequency changes, and attenuated amplitudes to tone duration increments and decrements. Clozapine dose was related to MMN, with increasing dose being positively associated with frequency-MMN amplitudes (10% ∆f, 20% ∆f) and negatively associated with the amplitude and latency of duration-MMNs. These data support the well-established findings of auditory sensory abnormality in schizophrenia and underscore the sensitivity of MMN to relatively small auditory change detection deficits that may appear to characterize chronic schizophrenia.

Pre-attentive and attentive processing of French vowels

This study aimed at investigating the effects of acoustic distance and of speaker variability on the pre-attentive and attentive perception of French vowels by French adult speakers. The electroencephalogram (EEG) was recorded while participants watched a silent movie (Passive condition) and discriminated deviant vowels (Active condition). The auditory sequence included 4 French vowels, /u/ (standard) and /o/, /y/ and /ø/ as deviants, produced by 3 different speakers. As the vowel /o/ is closer to /u/ than the other deviants in acoustic distance, we predicted smaller mismatch negativity (MMN) and smaller N1 component, as well as higher error rate and longer reaction times. Results were in line with these predictions. Moreover, the MMN was elicited by all deviant vowels independently of speaker variability. By contrast, the Vowel by Speaker interaction was significant in the Active listening condition thereby showing that subtle within-category differences are processed at the attentive level. These results suggest that while vowels are categorized pre-attentively according to phonemic representations and independently of speaker variability, participants are sensitive to between-speaker differences when they focus attention on vowel processing.

Increased error-related brain activity in generalized anxiety disorder

The error-related negativity (ERN) is a negative deflection approximately 50ms following an erroneous response, and is thought to reflect activity of the anterior cingulate cortex (ACC), a region of the medial prefrontal cortex implicated in the pathophysiology of a number of affective disorders, including generalized anxiety disorder (GAD). Pathological worry, the hallmark of GAD, has been linked to increased error-related brain activity, although no studies to date have examined the ERN among a clinical GAD sample. The present study measured electrocortical indices of error monitoring in a well-characterized, medication-free GAD sample. Brain activity was recorded in 17 GAD and 24 control subjects. The GAD group was characterized by a larger ERN and an increased difference between error and correct trials; a larger ERN was associated with increased self-reported anxiety and depression symptoms. Individuals with GAD have exaggerated early neural responses to errors, consistent with fMRI work implicating ACC abnormalities in GAD.

Subjective and model-estimated reward prediction: association with the feedback-related negativity (FRN) and reward prediction error in a reinforcement learning task

In this study, we examined whether the feedback-related negativity (FRN) is associated with both subjective and objective (model-estimated) reward prediction errors (RPE) per trial in a reinforcement learning task in healthy adults (n=25). The level of RPE was assessed by 1) subjective ratings per trial and by 2) a computational model of reinforcement learning. As results, model-estimated RPE was highly correlated with subjective RPE (r=.82), and the grand-averaged ERP waves based on the trials with high and low model-estimated RPE showed the significant difference only in the time period of the FRN component (p<.05). Regardless of the time course of learning, FRN was associated with both subjective and model-estimated RPEs within subject (r=.47, p<.001; r=.40, p<.05) and between subjects (r=.33, p<.05; r=.41, p<.005) only in the Learnable condition where the internal reward prediction varied enough with a behavior-reward contingency.

Deep brain stimulation of the lateral cerebellar nucleus produces frequency-specific alterations in motor evoked potentials in the rat in vivo

The cerebral cortex is tightly and reciprocally linked to the cerebellum and the ascending dentato-thalalmo-cortical pathway influences widespread cortical regions. Using a rodent model of middle cerebral artery stroke, we showed previously that chronic, 20 Hz stimulation of the contralateral lateral cerebellar nucleus (LCN) improved motor recovery, while 50 Hz stimulation did not. Using motor evoked potentials (MEP) elicited by intracortical microstimulation, we now show the effect of LCN stimulation on motor cortex excitability as a function of pulse frequency in propofol-anesthetized rats. MEPs were recorded serially, at 15-s intervals, with cerebellar stimulation delivered in 10-min blocks at rates of 20, 30, 40, 50 or 100 Hz. Stimulation at 20, 30, 40 or 50 Hz enhanced the average MEP response across the block, with the maximal overall increase observed during 30 Hz stimulation. However, the effect varied as a function of both repeated trials within the block and LCN stimulation frequency, such that 40 Hz and 50 Hz stimulation showed a reduced effect over time. Stimulation at 100 Hz produced a transient increase in MEP amplitude in some animals; however the overall effect across the block was a trend towards reduced cortical excitability. These results suggest that direct stimulation of the LCN can yield frequency-dependent changes in cortical excitability and may provide a therapeutic approach to modulating cortical activity for the treatment of strokes or other focal cortical lesions, movement disorders and epilepsy.

Differential effects of age and executive functions on the resolution of the contingent negative variation: a reexamination of the frontal aging theory

The "frontal aging theory" assumes the deterioration of executive/inhibitory functions as causal factors for the cognitive decline in human aging. The contingent negative variation resolution (CNV-R) is an electroencephalographic potential elicited after the second (informative) stimulus in warned Go/NoGo tasks requiring a response to one type of stimulus (Go) but not to the other (NoGo). Whereas the CNV-R across conditions is a measure of executive functions, the augmented potential in the NoGo condition is a specific measure of inhibitory processes. The aim was to examine the presumed linkage between executive processes and the CNV-R with special regard to inhibition in the NoGo condition, and to test whether any effects of age on this potential can be explained by a failure of (inhibitory) executive functions. Nineteen young and 15 elderly non-demented healthy volunteers were examined in a Go/NoGo CNV-R paradigm and on a test of executive functions focussed on set shifting (Trail Making test). Results showed: (1) Better executive functions are associated with higher amplitudes of the CNV-R across conditions. (2) The CNV-R is higher for elderly than younger subjects; this increment is much stronger in the NoGo condition. In conclusion, the CNV-R across conditions reflects executive processes such as the shift of motor set. A higher CNV-R for elderly subjects (particularly of the inhibition-related NoGo CNV-R) indicates that this group is not impaired in the available amount of executive control but may exert such control for task demands where young subjects do not require it.

Event-Related Potential Findings in Healthy Extremely Pre-Term (< Week 29) Children at Age 10

Ten healthy extremely pre-term (EPT) children, born before gestational week 29, were tested at age 10 using mismatch negativity (MMN) and a three-tone odd-ball task; the results were then compared to age-matched full-term controls. We found no difference in MMN. By contrast, EPT children had generally shorter N1 latencies and larger P2 amplitudes, possibly indicating a more stimulus-driven response mode. However, P300 parameters, indicative of controlled attention, were unaffected.

Relationships between sensory "gating out" and sensory "gating in" of auditory evoked potentials in schizophrenia: a pilot study

The interrelationship between the ability to inhibit incoming redundant input (gating out) and the ability of the brain to respond when the stimulus changes (gating in), has not been extensively examined. We administered a battery of auditory evoked potential tests to a group of chronic, medicated schizophrenia patients (N=12) and a group of healthy subjects (N=12) in order to examine relationships between "gating out" measures (suppression with repetition of the P50, N100, and P200 evoked responses), and the mismatch negativity (MMN) and the P300 event related potentials as measures of "gating in". Gating ratios for N100 and P200 in a visual attention paired-click task differed significantly between groups. Mismatch negativity and P300 potential amplitudes were also significantly reduced in the patient group. When including all subjects (N=24) a negative correlation was found between the P50 gating and the amplitude of the MMN. In healthy subjects this correlation was significantly stronger compared to schizophrenia patients. While no significant correlation was noted between the amplitudes of the P300 and any gating measures when all 24 subjects were included, a significant negative correlation was seen between the P200 gating and the P300 amplitudes in schizophrenia patients; an opposite trend was noted in healthy subjects. Finally, a positive correlation was seen between the P300 and MMN (to abstract deviance) amplitudes in healthy subjects, but the opposite was found in patients. These results suggest that further study of these interrelationships could inform the understanding of information processing abnormalities in schizophrenia.

The real-time link between person perception and action: brain potential evidence for dynamic continuity

Using event-related potentials, we investigated how the brain extracts information from another's face and translates it into relevant action in real time. In Study 1, participants made between-hand sex categorizations of sex-typical and sex-atypical faces. Sex-atypical faces evoked negativity between 250 and 550 ms (N300/N400 effects), reflecting the integration of accumulating sex-category knowledge into a coherent sex-category interpretation. Additionally, the lateralized readiness potential revealed that the motor cortex began preparing for a correct hand response while social category knowledge was still gradually evolving in parallel. In Study 2, participants made between-hand eye-color categorizations as part of go/no-go trials that were contingent on a target's sex. On no-go trials, although the hand did not actually move, information about eye color partially prepared the motor cortex to move the hand before perception of sex had finalized. Together, these findings demonstrate the dynamic continuity between person perception and action, such that ongoing results from face processing are immediately and continuously cascaded into the motor system over time. The preparation of action begins based on tentative perceptions of another's face before perceivers have finished interpreting what they just saw.

Multiple forms of learning yield temporally distinct electrophysiological repetition effects

Prior experience with a stimulus leads to multiple forms of learning that facilitate subsequent behavior (repetition priming) and neural processing (repetition suppression). Learning can occur at the level of stimulus-specific features (stimulus learning), associations between stimuli and selected decisions (stimulus-decision learning), and associations between stimuli and selected responses (stimulus-response learning). Although recent functional magnetic resonance imaging results suggest that these distinct forms of learning are associated with repetition suppression (neural priming) in dissociable regions of frontal and temporal cortex, a critical question is how these different forms of learning influence cortical response dynamics. Here, electroencephalography (EEG) measured the temporal structure of neural responses when participants classified novel and repeated stimuli, using a design that isolated the effects of distinct levels of learning. Event-related potential and spectral EEG analyses revealed electrophysiological effects due to stimulus, stimulus-decision, and stimulus-response learning, demonstrating experience-dependent cortical modulation at multiple levels of representation. Stimulus-level learning modulated cortical dynamics earlier in the temporal-processing stream relative to stimulus-decision and stimulus-response learning. These findings indicate that repeated stimulus processing, including the mapping of stimuli to decisions and actions, is influenced by stimulus-level and associative learning mechanisms that yield multiple forms of experience-dependent cortical plasticity.

Infant attention and visual preferences: converging evidence from behavior, event-related potentials, and cortical source localization

In this study, we had 3 major goals. The 1st goal was to establish a link between behavioral and event-related potential (ERP) measures of infant attention and recognition memory. To assess the distribution of infant visual preferences throughout ERP testing, we designed a new experimental procedure that embeds a behavioral measure (paired comparison trials) in the modified-oddball ERP procedure. The 2nd goal was to measure infant ERPs during the paired comparison trials. Independent component analysis (ICA) was used to identify and to remove eye-movement components from the electroencephalographic data, thus allowing for the analysis of ERP components during paired comparison trials. The 3rd goal was to localize the cortical sources of infant visual preferences. Equivalent current dipole analysis was performed on the ICA components related to experimental events. Infants who demonstrated novelty preferences in paired comparison trials demonstrated greater amplitude Negative central ERP components across tasks than infants who did not demonstrate novelty preferences. Visual preference also interacted with attention and stimulus type. The cortical sources of infant visual preferences were localized to inferior and superior prefrontal cortex and to the anterior cingulate cortex.

Automatic and controlled aspects of lexical associative processing in the two cerebral hemispheres

Associative processing in the cerebral hemispheres was examined using ERPs and visual half-field (VF) methods. Associative strength was manipulated using asymmetrically associated pairs: viewed in one order (forward), there was a strong prime-to-target association, but in the backward order, predictability was weak. N400 priming was greater for forward than backward pairs in both VFs and not different across VF, suggesting similar semantic representations and automatic meaning activation in the two hemispheres. However, a frontal P2 enhancement for forward pairs restricted to the LH suggests that it uses context to predict likely upcoming words. Also, greater late positive complex priming for backward pairs in the LH than the RH reveals a LH advantage for strategically reshaping meaning activation for weakly related and/or non-canonically ordered pairs. The results link asymmetries in word processing with those observed at the sentence level.

Decisions to shoot in a weapon identification task: The influence of cultural stereotypes and perceived threat on false positive errors

The decision to shoot a gun engages executive control processes that can be biased by cultural stereotypes and perceived threat. The neural locus of the decision to shoot is likely to be found in the anterior cingulate cortex (ACC), where cognition and affect converge. Male military cadets at Norwich University (N=37) performed a weapon identification task in which they made rapid decisions to shoot when images of guns appeared briefly on a computer screen. Reaction times, error rates, and electroencephalogram (EEG) activity were recorded. Cadets reacted more quickly and accurately when guns were primed by images of Middle-Eastern males wearing traditional clothing. However, cadets also made more false positive errors when tools were primed by these images. Error-related negativity (ERN) was measured for each response. Deeper ERNs were found in the medial-frontal cortex following false positive responses. Cadets who made fewer errors also produced deeper ERNs, indicating stronger executive control. Pupil size was used to measure autonomic arousal related to perceived threat. Images of Middle-Eastern males in traditional clothing produced larger pupil sizes. An image of Osama bin Laden induced the largest pupil size, as would be predicted for the exemplar of Middle East terrorism. Cadets who showed greater increases in pupil size also made more false positive errors. Regression analyses were performed to evaluate predictions based on current models of perceived threat, stereotype activation, and cognitive control. Measures of pupil size (perceived threat) and ERN (cognitive control) explained significant proportions of the variance in false positive errors to Middle-Eastern males in traditional clothing, while measures of reaction time, signal detection response bias, and stimulus discriminability explained most of the remaining variance.

Classical conditioning in the vegetative and minimally conscious state

Pavlovian trace conditioning depends on the temporal gap between the conditioned and unconditioned stimuli. It requires, in mammals, functional medial temporal lobe structures and, in humans, explicit knowledge of the temporal contingency. It is therefore considered to be a plausible objective test to assess awareness without relying on explicit reports. We found that individuals with disorders of consciousness (DOCs), despite being unable to report awareness explicitly, were able to learn this procedure. Learning was specific and showed an anticipatory electromyographic response to the aversive conditioning stimulus, which was substantially stronger than to the control stimulus and was augmented as the aversive stimulus approached. The amount of learning correlated with the degree of cortical atrophy and was a good indicator of recovery. None of these effects were observed in control subjects under the effect of anesthesia (propofol). Our results suggest that individuals with DOCs might have partially preserved conscious processing, which cannot be mediated by explicit reports and is not detected by behavioral assessment.

Hemispheric differences in auditory oddball responses during monaural versus binaural stimulation

Hemispheric lateralization of early event-related potentials (ERPs; e.g. N1) is largely based on anatomy of the afferent pathway; lateralization of later auditory ERPs (P2/N2, P250, P3b) is less clear. Using 257-channel EEG, the present study examined hemispheric laterality of auditory ERPs by comparing binaural and monaural versions of an auditory oddball task. N1 showed a contralateral bias over auditory cortex in both hemispheres as a function of ear of stimulation, although right hemisphere sources were activated regardless of which ear received input. Beginning around N1 and continuing through the time of P3b, right hemisphere temporal-parietal and frontal areas were more activated than their left hemisphere counterparts for stimulus evaluation/comparison and target detection. P250 and P3b component amplitudes, topographies, and source estimations were significantly influenced by ear of stimulation, with right hemisphere activity being stronger. This was particularly true for anterior temporal and inferior frontal sources which were more strongly associated with the later, more cognitive components (P250, P3b). Results are consistent with theories of a right hemisphere network that is prominently involved in sustained attention, stimulus evaluation, target detection, and working memory/context updating.