Effects of sleep onset on the mismatch negativity (MMN) to frequency deviants using a rapid rate of presentation

This study examined the effects of sleep onset-the transition from a waking, conscious state to one of sleep and unconsciousness-on the mismatch negativity (MMN) following frequency deviants when a rapid rate of stimulus presentation is employed. The MMN is thought to reflect a brief-lasting sensory memory. Rapid rates of stimulus presentation should guard the sensory memory from fading. A 1,000 Hz standard stimulus was presented every 150 ms. At random, on 6.6% of the trials, the standard was changed to either a large 2,000 or a small 1,100 Hz deviant. During alert wakefulness (when subject ignored the stimuli and read a book), the large deviant elicited a larger deviant related negativity (DRN) than did the small deviant. This negativity may be a composite of both N1 and MMN activity while that following the small deviant is probably a 'true' MMN. The large deviant continued to elicit a DRN in relaxed wakefulness (eyes closed) and Stages 1 and 2 of sleep, although it was much reduced in amplitude. A significant MMN was recorded for the small deviant only in alert wakefulness. The failure to observe an MMN to small deviance and the attenuation of the DRN to large deviance at sleep onset therefore is probably not due to a decay of sensory memory. It is more likely that cortical encoding of both the standard and deviant is weakened during sleep onset because of prior thalamic inhibition of sensory input.     

The mismatch negativity during natural sleep: intensity deviants.

Auditory event-related potentials (ERPs) were recorded from 7 subjects who slept for a single night in the laboratory. An 'oddball' sequence of brief tone pips, differing in intensity, was used. Frequently occurring 70 dB 'standards' were presented with infrequent 80 dB intensity increment deviants and 60 dB intensity decrement deviants. The probability of each deviant was 0.1. Stimuli were presented in a random sequence every 600 ms while subjects were awake but inattentive and during stages 2 and REM of sleep. During wakefulness, the intensity increments elicited a broad fronto-central negativity with two discernable peaks. The first, peaking at approximately 120 ms, showed a polarity inversion at the mastoid and likely represented a summation of the N1 wave and the mismatch negativity (MMN). The second, peaking at approximately 330 ms, may have reflected an enhanced N2b component. In REM sleep, the increment deviants elicited a small amplitude 100-200 ms negativity but its amplitude was not significantly larger than the baseline level. It was followed by a larger and significant 300-450 ms negativity but this was considered too delayed to represent the MMN. The decrement deviants elicited a small amplitude, but statistically non-significant, MMN-like wave during both wakefulness and in REM sleep. A MMN-like wave was absent in stage 2 sleep.     

Right hemisphere dominance of different mismatch negativities

Auditory stimulus blocks were presented to 10 reading subjects. Each block consisted of 2 types of stimulus, standard (P = 90%) and deviant (P = 10%), delivered in a random order with short constant inter-stimulus intervals. The standard stimuli were 600 Hz, 80 dB SPL 50 msec sine wave bursts. In different blocks, the deviant stimuli differed from the standards either in frequency (650 Hz), intensity (70 dB) or duration (20 msec). Left- and right-ear stimulations were used in separate blocks. Event-related brain potentials (ERPs) were recorded with 16 electrodes over both hemispheres. All the different types of deviant stimuli elicited an ERP component called the mismatch negativity (MMN). The MMN was larger over the right hemisphere irrespective of the ear stimulated whereas the N1 component, elicited by both standards, and deviants, was larger over the hemisphere contralateral to the ear stimulated. The results provide further evidence for the view that the MMN reflects a neural mismatch process with a memory trace which automatically codes the physical features of the repetitive stimuli.     

The effect of visual task difficulty and attentional direction on the detection of acoustic change as indexed by the Mismatch Negativity

Näätänen's model of auditory processing purports that attention does not affect the MMN. The present study investigates this claim through two different manipulations. First, the effect of visual task difficulty on the passively elicited MMN is assessed. Second, the MMNs elicited by stimuli under attended and ignored conditions are compared. In Experiment 1, subjects were presented with mixed sequences of equiprobable auditory and visual stimuli. The auditory stimuli consisted of standard (80 dB SPL 1000 Hz), frequency deviant (1050 Hz), and intensity deviant (70 dB SPL) tone pips. In a first instance, subjects were instructed to ignore the auditory stimulation and engage in an easy and difficult visual discrimination task (focused condition). Subsequently, they were asked to attend to both modalities and detect visual and auditory deviant stimuli (divided condition). The results indicate that the passively elicited MMN to frequency and intensity deviants did not significantly vary with visual task difficulty, in spite of the fact that the easy and difficult tasks showed a wide variation in performance. The manipulation of the attentional direction (focused vs. divided conditions) did result in a significant effect on the MMN elicited by the intensity, but not frequency, deviant. The intensity MMN was larger at frontal sites when subjects' attention was directed to both modalities as compared to only the visual modality. The attentional effect on the MMN to the intensity deviants only may be due to the specific deviant feature or the poorer perceptual discriminability of this deviant from the standard. Experiment 2 was designed to address this issue. The methods of Experiment 2 were identical to those of Experiment 1 with the exception that the intensity deviant (60 dB SPL) was made to be more perceptible than the frequency deviant (1016 Hz) when compared to the standard stimulus (80 dB SPL 1000 Hz). The results of Experiment 2 also demonstrated that the passively elicited MMN was not affected by large variations in visual task difficulty; this provides convincing evidence that the MMN is independent of visual task demands. Similarly to Experiment 1, the direction of attention again had a significant effect on the MMN. In Experiment 2, however, the frequency MMN (and not the intensity MMN) was larger at frontal sites during divided attention compared to focused visual attention. The most parsimonious explanation of these results is that attention enhances the discriminability of the deviant from the standard background stimulation. As such, small acoustic changes would benefit from attention whereas the discriminability of larger changes may not be significantly enhanced.     

Individual differences in mismatch negativity measures of involuntary attention shift.

OBJECTIVE: The purpose of this study was to compare the automatic detection of deviance in introverts and extraverts. Event-related potentials were recorded to standard and deviant stimuli. These were presented either rapidly or slowly. Stimuli that are presented slowly may intrude into consciousness. METHODS: Twenty subjects were tested and divided into introverted and extraverted groups. A 500 Hz standard stimulus was presented on 85% of trials. On the remaining 15% of trials, a 750 Hz deviant was presented. In separate conditions, stimuli were presented rapidly (every 500 ms) or slowly (every 1500 ms). Subjects ignored the stimuli while reading. RESULTS: The deviant stimulus elicited a mismatch negativity (MMN) in both conditions. No inter-group differences in the MMN emerged when a rapid rate of presentation was employed. When a slower rate was employed, a late negativity was significantly larger for the extraverted than the introverted group. This was followed by a late positive wave. CONCLUSION: The late negative-positive complex is thought to reflect intrusiveness. It would therefore appear that extraverts are more distractible than introverts when stimuli are presented slowly.     

The vanishing point of the mismatch negativity at sleep onset.

OBJECTIVE: To determine when the mismatch negativity (MMN) disappears at sleep onset, event-related potentials (ERPs) were recorded continuously from wakefulness to sleep. METHODS: Ten healthy young students were told to fall asleep ignoring the tones presented through a loudspeaker above their head. Standard (1000 Hz, P=0.90), high deviant (1200 Hz, P=0.05), and low deviant (1050 Hz, P=0.05) tones were presented in a quasirandom order with a fixed stimulus onset asynchrony of 500 ms. ERP waveforms were obtained separately for 5 successive stages characterized by typical electroencephalographic (EEG) patterns of the sleep onset period. The EEG staging was made manually with very short (5 s) scoring epochs. RESULTS: The MMN appeared in wakefulness and in the early phase of stage 1 sleep (EEG stage II) but disappeared when low-voltage theta waves emerged after alpha flattening (EEG stage III). Instead, P240 and N360 developed particularly for high deviant tones. CONCLUSIONS: Concurrently with the disappearance of alpha waves, the automatic change detection system in wakefulness seems to stop operating and a different sleep-specific system becomes dominant.     

Primary task demands modulate P3a amplitude

Auditory event-related brain potentials (ERPs) were recorded from 10 subjects in two different conditions: (1) subjects were required to reorder five visually presented letters in order to form a word and provide a verbal response (task condition); (2) subjects were presented with a control stimulus with the same physical characteristics as the experimental stimulus, but containing just one type of letter (i.e., AAAAA). Subjects had to verbally respond to such stimuli by saying "A" (control condition). Tones of 1000 Hz (standard) and 1050 Hz (deviant) were also presented to the subjects in a 85%-15% probability paradigm 2 s before, during and 8 s after the presentation of the visual stimuli. Recordings were obtained from Fpz, Fz, Cz and Pz vs. linked ears. Auditory ERPs to the auditory stimuli after the presentation of the visual letter string and during the performance of the task were averaged for the standard and deviant tones in both conditions. Only correct responses were considered for the averages. The N100 was affected by stimulus type (standard vs. deviant) but not by condition (task vs. control); however, larger P3a waves were observed during the control than during the task condition. No significant differences between conditions were observed in the mismatch negativity (MMN) latency range. These results suggest that primary task demands modulate involuntary attention processing.     

A modified oddball paradigm "cross-modal delayed response" and the research on mismatch negativity

A modified oddball paradigm was developed to facilitate the focus of attention and to minimize target effects on deviant-related components of auditory and visual event-related potentials (ERPs) elicited with long interstimulus intervals. Subjects were required to focus on either the visual or auditory stimulus in each stimulus block. Deviant-related components were obtained by subtracting ERPs of the standard stimulus from that of the deviant stimulus for each modality with each stimulus condition. Results showed that auditory mismatch negativity (MMN) and a visual early deviant related negativity (DRN1) were elicited both when stimuli were attended and unattended. In contrast, N2b and P3 were produced only under the attended condition. In comparison of attended MMN and unattended MMN at three time windows (100-150 ms, 150-200 ms, and 200-250 ms) of MMN zone, different scalp distributions were shown, depending on the time windows. This result suggests that the attended auditory MMN is a mixed wave, consisting of genuine MMN, N2b, and possible P165. The effect of attention on MMN may stem from the contamination of these overlapping components. With the present paradigm, at least three sensory memory traces have to be maintained simultaneously in multiple sensory modalities to support automatic processing.     

Spatial Properties of Mismatch Negativity in Patients with Disorders of Consciousness

In recent decades, event-related potentials have been used for the clinical electrophysiological assessment of patients with disorders of consciousness (DOCs). In this paper, an oddball paradigm with two types of frequency-deviant stimulus (standard stimuli were pure tones of 1000 Hz; small deviant stimuli were pure tones of 1050 Hz; large deviant stimuli were pure tones of 1200 Hz) was applied to elicit mismatch negativity (MMN) in 30 patients with DOCs diagnosed using the JFK Coma Recovery Scale-Revised (CRS-R). The results showed that the peak amplitudes of MMN elicited by both large and small deviant stimuli were significantly different from baseline. In terms of the spatial properties of MMN, a significant interaction effect between conditions (small and large deviant stimuli) and electrode nodes was centered at the frontocentral area. Furthermore, correlation coefficients were calculated between MMN amplitudes and CRS-R scores for each electrode among all participants to generate topographic maps. Meanwhile, a significant negative correlation between the MMN amplitudes elicited by large deviant stimuli and the CRS-R scores was also found at the frontocentral area. In consequence, our results combine the above spatial properties of MMN in patients with DOCs, and provide a more precise location (frontocentral area) at which to evaluate the correlation between clinical electrophysiological assessment and the level of consciousness.     

Differential auditory processing continues during sleep.

Auditory evoked potentials (AEPs) were used to examine selective stimulus processing in sleep. In waking, repetitive stimuli generate exogenous P1, N1 and P2 components of the auditory evoked potential (AEP). Deviant stimuli generate endogenous cognitive components including the mismatch negativity (MMN), N2 and P3 components. We examined long-latency auditory evoked potentials elicited by repetitive and deviant stimuli during waking and stage II-IV sleep to assess whether stimulus deviance is detected during sleep. The waking P1, N1b and P2 had maximal amplitudes at fronto-central scalp sites, with additional peaks (N1a, N1c) at temporal sites. Deviant tones generated a frontal maximal MMN, and complex novel tones generated an additional P3 component maximal at centro-parietal sites. During stages II-IV sleep N1a, b, c amplitudes were reduced. During stage II sleep all stimuli generated increased P2 amplitudes and a late negative component (N340). Deviant stimuli generated greater P2 and N340 amplitudes than frequent stimuli in stage II sleep, as well as an additional P420 component. In stage III-IV sleep the P420 was absent and the AEP was dominated by a negativity of long duration whose amplitude increased in response to deviant stimuli. These data indicate that auditory evoked activity changes from wakefulness to sleep. The differential response to deviant sounds observed during waking and all sleep stages supports the theory that selective processing of auditory stimuli persists during sleep.     

"...and were instructed to read a self-selected book while ignoring the auditory stimuli": the effects of task demands on the mismatch negativity.

OBJECTIVE: The Mismatch Negativity (MMN) is commonly recorded while the subject is reading, and instructed to ignore the auditory stimuli. It is generally assumed that the demands of the diversion task will have no effect on the MMN. Several studies, however, have reported that a diversion task presumably requiring strong attentional focus is associated with a smaller MMN than that elicited during a less demanding task. This study examines the effect of variations in the classical reading paradigm on the MMN. METHODS: In Experiment 1, event-related potentials (ERP) were recorded while subjects were presented with standard (80 dB SPL 1000 Hz) and frequency deviant (1050 Hz) stimuli. Subjects were instructed to ignore the tone pips and, in separate conditions, engage in different tasks. They were asked to read a text or to sit passively. Subjects were informed that they would subsequently be queried or not about the content of the reading. In Experiment 2, the auditory sequence included the same standard (80 dB SPL 1000 Hz) but the deviant was changed to an intensity decrement (70 dB SPL). A different sample of subjects was again asked to ignore the auditory stimuli and engage in different reading tasks that would or not be followed by query. RESULTS: In all task conditions, MMN was elicited by the frequency and intensity change. The intensity MMN did not significantly vary with task. A significant effect of task was, however, found for the frequency MMN. Its amplitude was largest when subjects were later queried about their reading. CONCLUSIONS: This finding is counter-intuitive in light of previous research on the attentional modulation of the MMN. The pattern of frequency MMN results may relate to the differences in cortical excitability across tasks. SIGNIFICANCE: The present results indicate that the nature of the diversion task may affect the MMN. The choice of diversion task during MMN recording should thus be carefully considered.     

Mismatch negativity evoked by the McGurk-MacDonald effect: a phonetic representation within short-term memory.

OBJECTIVES: The McGurk-MacDonald illusory percept is obtained by dubbing an incongruent articulatory movement on an auditory phoneme. This type of audiovisual speech perception contributes to the assessment of theories of speech perception. The mismatch negativity (MMN) reflects the detection of a deviant stimulus within the auditory short-term memory and besides an acoustic component, possesses, under certain conditions, a phonetic one. The present study assessed the existence of an MMN evoked by McGurk-MacDonald percepts elicited by audiovisual stimuli with constant auditory components. METHODS: Cortical evoked potentials were recorded using the oddball paradigm on 8 adults in 3 experimental conditions: auditory alone, visual alone and audiovisual stimulation. Obtaining illusory percepts was confirmed in an additional psychophysical condition. RESULTS: The auditory deviant syllables and the audiovisual incongruent syllables elicited a significant MMN at Fz. In the visual condition, no negativity was observed either at Fz, or at O(z). CONCLUSIONS: An MMN can be evoked by visual articulatory deviants, provided they are presented in a suitable auditory context leading to a phonetically significant interaction. The recording of an MMN elicited by illusory McGurk percepts suggests that audiovisual integration mechanisms in speech take place rather early during the perceptual processes.     

Mismatch negativity to inclusions of noise within complex spectrotemporal sound patterns.

Event-related potentials to complex spectrotemporal sound patterns were recorded during non-attend conditions. A high-intensity noise deviant elicited a large negative wave. This is probably a combined mismatch negativity (MMN) and N2b since it was followed by a large amplitude frontal positive wave (P3a). When the noise intensity was reduced, a smaller amplitude negative wave was elicited. This probably corresponds to a true MMN since it was not followed by the positive wave. These findings are consistent with previous research in which N2b is elicited in non-attend conditions when the deviant stimulus was particularly difficult to ignore. These findings demonstrate that complex spectrotemporal sound patterns are represented in auditory memory and that inclusions of noise within these complex stimuli can be passively discriminated.     

Generalization of the generation of an MMN by illusory McGurk percepts: voiceless consonants.

OBJECTIVE: The existence of a Mismatch Negativity (MMN) evoked by McGurk percepts elicited by audiovisual syllables with constant auditory components has been previously demonstrated with voiced consonants [Clin. Neurophysiol. 113 (2002) 495]. The present study aimed at generalizing such results with voiceless consonants. In a first experiment, the MMN was computed using the classical subtraction method (standard minus deviant). Since results showed a possible contamination by exogenous visual components, a technique preventing from including those components in the differential waveform was used in a second experiment (deviant in sequence minus deviant presented alone). METHODS: Cortical evoked potentials were recorded using the oddball paradigm on eight adults in three experimental conditions (auditory alone, visual alone and audiovisual) for experiment one and in two conditions (visual alone and audiovisual) for experiment two. Obtaining illusory percepts was confirmed in additional psychophysical experiments. RESULTS: Significant MMNs were recorded in the three conditions of experiment one, whereas only the audiovisual condition of experiment two gave rise to a significant MMN. CONCLUSIONS: Provided that the MMN is computed with deviant stimuli only, the present results confirm the elicitation of genuine audiovisual MMN. Possible refractoriness effects and N2b confound have, however, to be controlled for in further studies.     

Stability of mismatch negativities in children.

OBJECTIVES AND METHODS: Mismatch negativities (MMN) to frequency and duration changes in a series of repetitive tones and to two different consonant-vowel syllables (ba and ga, standard da) were recorded in a test and retest session in 15 children aged 7-11 years. Reliability within one session and stability between the sessions of MMN amplitudes and the ERP-components P1 and N1 were determined by correlation coefficients. RESULTS: Mean amplitudes of the grand averages showed a decrease of MMN during the second test session in a late latency window (400-500 ms) for the frequency MMN and of the MMN elicited by speech stimuli. The individual stability reached significance only for the duration deviant and one of the syllables. Compared to results found in adults with similar stimulus conditions the stability of the MMN in children seems to be somewhat lower. The components P1 and N1 to both stimulus types (tone and speech), however, showed a high reliability and individual stability. CONCLUSION: While MMN is a useful tool to study processing deficits in groups of children, as e.g. in language-impaired children, MMN as a individual diagnostic measure should be interpreted very cautiously.     

Mismatch negativity to inclusions and omissions of stimulus features

Two experiments were run to determine the effects of addition or removal of a stimulus feature on mismatch negativity (MMN). In the first experiment, a deviant stimulus was constructed by adding a click to a white noise standard stimulus. In the second experiment, the deviant was constructed by subtracting the click from the standard. In different conditions, the intensity of the click was varied. When the deviant was constructed by the addition of a click, a significant MMN was evident in those conditions in which click-to-noise ratio exceeded 1.0. When the deviant was constructed by the subtraction of the click, a significant negativity was found only when the click-to-noise ratio was very large. However, this negativity was accompanied by only a small polarity inversion at the mastoid. The MMN is thus best elicited when the deviant stimulus contains a new afferent element not present in the standard stimulus.     

Abnormal mismatch negativity in women with sexual assault-related posttraumatic stress disorder.

BACKGROUND: Disturbances in sensory processing have been hypothesized in individuals with posttraumatic stress disorder (PTSD). The authors investigated this possibility by using mismatch negativity (MMN), an event-related potential (ERP) that reflects the operation of a preconscious cortical detector of stimulus change. METHODS: Thirteen medication-free women with sexual assault-related PTSD were compared with 16 age-matched, healthy comparison women without PTSD. ERPs were elicited by regularly presented "standard" auditory stimuli and by infrequently occurring "deviant" auditory stimuli, which differed slightly in frequency. The MMN was identified in the subtraction waveforms as the difference between ERPs elicited by the deviant and standard stimuli. Group comparisons of P50, N1, P2, and N2 to the standard and to the deviant stimuli, and of the MMN in the subtraction waveform were performed. RESULTS: The amplitude of the MMN was significantly greater in the PTSD compared to the non-PTSD women. MMN was significantly correlated with the total Mississippi PTSD Symptom Scale score in the PTSD group. No significant group differences were noted in P50, N1, or P2 responding. Significant group differences in N2 were due to the increased MMN in PTSD subjects. CONCLUSIONS: The data provide evidence for abnormalities in preconscious auditory sensory memory in PTSD, whereas earlier studies have reported abnormalities in conscious processing. These data suggest an increased sensitivity to stimulus changes in PTSD and implicate the auditory cortex in the pathophysiology of the disorder.     

The role of large-scale memory organization in the mismatch negativity event-related brain potential

The mismatch negativity (MMN) component of event-related brain potentials is elicited by infrequent changes in regular acoustic sequences even if the participant is not actively listening to the sound sequence. Therefore, the MMN is assumed to result from a preattentive process in which an incoming sound is checked against the automatically detected regularities of the auditory sequence and is found to violate them. For example, presenting a discriminably different (deviant) sound within the sequence of a repetitive (standard) sound elicits the MMN. In the present article, we tested whether the memory organization of the auditory sequence can affect the preattentive change detection indexed by the MMN. In Experiment 1, trains of six standard tones were presented with a short, 0.5-sec stimulus onset asynchrony (SOA) between tones in the train. This was followed by a variable SOA between the last standard and the deviant tone (the "irregular presentation" condition). Of 12 participants displaying an MMN at the 0.5-sec predeviant SOA, it was elicited by 11 with the 2-sec predeviant SOA, in 5 participants with the 7-sec SOA, and in none with the 10-sec SOA. In Experiment 2, we repeated the 7-sec irregular predeviant SOA condition, along with a "regular presentation" condition in which the SOA between any two tones was 7 sec. MMN was elicited in about half of the participants (9 out of 16) in the irregular presentation condition, whereas in the regular presentation condition, MMN was elicited in all participants. These results cannot be explained on the basis of memory-strength decay but can be interpreted in terms of automatic, auditory preperceptual grouping principles. In the irregular presentation condition, the close grouping of standards may cause them to become irrelevant to the mismatch process when the deviant tone is presented after a long silent break. Because the MMN indexes preattentive auditory processing, the present results provide evidence that large-scale preperceptual organization of auditory events occurs despite attention being directed away from the auditory stimuli.     

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's area 45) is involved in early stages of processing repeating sounds and sound changes.     

Neurophysiological evidence of memory traces for words in the human brain

Mismatch negativity (MMN), an index of experience-dependent memory traces, was used to investigate the processing of lexical contrasts in the human brain. The MMN was elicited either by rare words presented among repetitive words or pseudowords, or by pseudowords presented among words. Phonetic and phonological contrasts were identical in all conditions. MMNs elicited by both word deviants were larger than that elicited by the deviant pseudoword. The presence of lexical contrast did not significantly alter the word-elicited MMNs, which were, however, distinct in amplitude and topography from the MMN evoked by pseudowords. Thus, our results indicate the existence of word-related MMN enhancement largely independent of the lexical status of the standard stimulus. This enhancement may reflect the presence of a long-term memory trace for a spoken word.