Automatic auditory information processing in sleep

STUDY OBJECTIVES: The mismatch negativity (MMN) component of the event-related potentials reflects the automatic detection of sound change. Only a few researchers have investigated the MMN elicitation during sleep in adult human and some of them reported that MMN amplitude was decreased in sleep compared to in waking. However, it is not clear that the decrease of MMN amplitude was due to increased drowsiness or long-term response decrement. Two experiments were conducted to clarify whether or not the MMN was elicited in each sleep stage. We presented auditory stimuli to subjects continuously from waking until sleep state (Experiment 1). Using the same experimental condition, we examined whether or not MMN amplitude was influenced by long-term stimulus presentation (80min.) and by vigilance level (Experiment 2). DESIGN: N/A SETTING: N/A PARTICIPANTS: N/A INTERVENTIONS: N/A MEASUREMENTS & RESULTS: Experiment 1: MMN was obtained in both drowsiness and REM sleep. MMN was significantly smaller in amplitude and shorter in latency in the both stages than in the waking state. However, MMN was not found in another sleep stage. Experiment 2: Amplitudes were no different among 0-20 min., 20-40 min., 60-80 min. But it was decreased in 40-60 min. and power value of alpha-wave was decreased in 40-60 min. CONCLUSIONS: To obtain the reliable data, by using the automatic spectral analysis, we confirmed that MMN was elicited in REM sleep. MMN was not influenced by long-term stimulation. The result suggested that auditory stimuli could be processed in the pre-attentive sensory memory even in REM sleep.     

Pre-attentive representation of sound duration in the human brain

Studies using a brain index for pre-attentive change detection, the mismatch negativity (MMN), suggested distinct neuronal populations for signaling changes in sound duration and frequency. However, these studies used only durations within the temporal window of loudness summation (ca. 200 ms) in which any duration change is accompanied by a loudness change. Hence, the present study employed stimulus durations both beyond and within this temporal window in order to examine the genuine duration representation in the brain. Magnetic mismatch responses (MMNm) for duration and frequency changes were compared with each other. The equivalent current dipole (ECD) of the duration MMNm was located in the auditory cortex slightly posterior to that for the frequency MMNm irrespective of stimulus duration. The results suggested separate memory representations for sound duration and frequency in the human brain.     

Attention and mismatch negativity

The mismatch negativity (MMN) component of the auditory event-related potential (ERP) is elicited by infrequent, physically deviant stimuli in a sequence of frequent homogeneous stimuli (standards). It has been suggested that the MMN is generated by an automatic (attention-independent) neural mismatch process with a memory trace that encodes the physical features of the standard stimulus. The proposed MMN independence of attention was addressed in the present study. Standard stimuli and two types of deviant stimuli, differing from standards either in frequency or intensity, were dichotically presented in random order and at a very rapid rate. The subject attended either to left-or right-ear stimuli, counting the number of a designated type of deviants in that ear. In the present conditions of very strongly focused attention, the MMN was elicited even by frequency change in the ignored input stream, and its amplitude was very similar to that of the MMN elicited by equivalent deviant stimuli (targets) in the attended input stream. In contrast, the MMN to intensity deviation was clearly attenuated in the absence of attention. This effect is, however, probably due to the attention effect on the MMN generator itself rather than the antecedent sensory-analysis and -storing functions.     

Mismatch negativity impairment associated with alcohol consumption in chronic alcoholics: a scalp current density study.

Previous studies, based on amplitude and latency measurements of auditory event-related brain potentials, yielded inconclusive results about the status of mismatch negativity (MMN) in chronic alcoholics. The present study explores scalp current density (SCD) dynamics during MMN latency range in alcoholics, and correlates electrical SCD results with clinical data of the patients. SCD was computed from 30 electrodes in 16 abstinent chronic alcoholics and 16 healthy control volunteers in a paradigm on MMN elicited by duration changes. Reduced activity was observed in left frontal and right anterior and posterior temporal areas during MMN in alcoholics. Alcohol consumption correlated negatively with SCD intensity in these regions. Delayed activation was observed in the left posterior temporal area in the patients. Alcohol abstinence duration correlated positively with SCD intensity in this region. These results point to an impairment of automatic brain processing mechanisms associated with auditory change detection in chronic alcoholism. The present results suggest a reorganization of the computational neurodynamics of automatic auditory change detection linked to the amount of alcohol consumed in abstinent chronic alcoholics.     

Circadian variations in time perception in rats

The hypothesis that time perception is determined by an internal clock's rate, which is sensitive to physiological circadian changes was examined. This hypothesis suggests that when body temperature and activity increase, clock rate increases causing overestimations of time and a decrease in time interval production. The following experiments examine this hypothesis with rats. Since rats are nocturnal, and body temperature is highest at night, time estimation should be longer and time production shorter than during the day. All experiments were run 24 hr a day under a 12:12 light:dark cycle. In the first experiment, rats discriminated among stimulus durations. Consistent with the hypothesis, both rats reliably judged standard durations as "longer" during the night than during the day. In Experiment 2, fixed-interval (FI) schedules of 60, 120 and 180 sec were used to examine circadian variations in time production. All seven rats produced longer postreinforcement pause (PRP) durations as FI length increased, and shorter PRP durations at night than during the day. However, absolute differences in PRP durations between day and night did not increase as FI duration increased, suggesting the PRP durations alone do not directly characterize proportional changes in internal clock rate. To more directly examine circadian variation in clock rate and the production of shorter intervals (i.e., between 1 and 16 sec) Experiment 3 used a lever holding procedure. Since this procedure requires the measured lever hold duration to meet or exceed the required hold duration, it more accurately characterizes the timing process.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Effects of Channel-Selective Attention on the Mismatch Negativity Wave Elicited by Deviant Tones

The mismatch negativity (MMN) is an event-related brain potential elicited by infrequent, physically deviant sounds in a sequence of repetitive auditory stimuli. Two dichotic listening experiments that were designed to optimize the selective focusing of attention provided a strong test of Näätänen's proposal that the MMN is unaffected by attention and reflects the operation of a strongly automatic mismatch detection system. In Experiment 1, tones were presented at intervals of 120-320 ms, and the deviant tones (intensity decrements) in both the attended and unattended ears elicited negative waves consistent in waveshape, latency, and distribution with previously described MMNs. In contrast to previous reports, however, the MMN elicited by the unattended-channel deviant was markedly reduced (peak amplitude of less than 1 μV) relative to the corresponding negative wave elicited by the attended-channel deviants (3–4 μV), as well as relative to previously reported MMNs (3–6 μV) elicited by comparable deviations in stimulus intensity. In Experiment 2, which employed interstimulus intervals of 65–205 ms, the unattended-channel MMN elicited by the deviant fainter tones was barely discernible, whereas the corresponding attended-channel negativity was again about 3-4 μV.
These findings call into question the assertion that the auditory mismatch detection process and the associated MMN wave are wholly independent of attentional influence. Rather, these data provide evidence that the processing of stimuli in unattended channels can be attenuated or gated at an early sensory level under conditions of highly focused auditory selective attention.     

Contextual effects in interval-duration judgements in vision, audition and touch

We examined the effect of temporal context on discrimination of intervals marked by auditory, visual and tactile stimuli. Subjects were asked to compare the duration of the interval immediately preceded by an irrelevant “distractor” stimulus with an interval with no distractor. For short interval durations, the presence of the distractor affected greatly the apparent duration of the test stimulus: short distractors caused the test interval to appear shorter and vice versa. For very short reference durations (≤100 ms), the contextual effects were large, changing perceived duration by up to a factor of two. The effect of distractors reduced steadily for longer reference durations, to zero effect for durations greater than 500 ms. We found similar results for intervals defined by visual flashes, auditory tones and brief finger vibrations, all falling to zero effect at 500 ms. Under appropriate conditions, there were strong cross-modal interactions, particularly from audition to vision. We also measured the Weber fractions for duration discrimination and showed that under the conditions of this experiment, Weber fractions decreased steadily with duration, following a square-root law, similarly for all three modalities. The magnitude of the effect of the distractors on apparent duration correlated well with Weber fraction, showing that when duration discrimination was relatively more precise, the context dependency was less. The results were well fit by a simple Bayesian model combining noisy estimates of duration with the action of a resonance-like mechanism that tended to regularize the sound sequence intervals.     

Auditory processing that leads to conscious perception: a unique window to central auditory processing opened by the mismatch negativity and related responses

In this review, we will present a model of brain events leading to conscious perception in audition. This represents an updated version of Näätänen's previous model of automatic and attentive central auditory processing. This revised model is mainly based on the mismatch negativity (MMN) and N1 indices of automatic processing, the processing negativity (PN) index of selective attention, and their magnetoencephalographic (MEG) and functional magnetic resonance imaging (fMRI) equivalents. Special attention is paid to determining the neural processes that might underlie conscious perception and the borderline between automatic and attention‐dependent processes in audition.     

Differential processing of duration changes within short and long sounds in humans

It has been postulated that there exist two different mechanisms of duration processing. Brief durations, shorter than 500 ms, are processed sensorially, whereas longer durations are processed via a cognitive mechanism. We investigated whether electrophysiological evidence for this distinction can be found. In particular, we measured the mismatch negativity (MMN) to auditory duration deviants (40% decrements) in blocks of short (200 ms) and long sounds (1000 ms) in Ignore and in Attend conditions. Our results show a typical MMN for long and short durations in the Attend condition, whereas no MMN was obtained for long durations in the Ignore condition. This interaction between duration and attention seems to reflect a breakdown of the sensorial mechanism of temporal processing at some critical duration of about 1 s when sounds are ignored.     

The temporal window of integration in elderly and young adults

Integration of information across time is an essential part of auditory processing. Evidence from a variety of experiments support the notion of an approximately 200-ms long time window following the onset of a sound, during which a unitary sound representation is formed (the temporal window of integration, TWI). The temporal resolution in the auditory system is assumed to decrease with aging suggesting that the duration of the TWI may be longer in elderly than young adults. The TWI duration was assessed in young and elderly adults using the oddball paradigm in which a regular auditory event (standard) is occasionally exchanged for a different event (deviant). Previous studies showed that when the stimulus onset asynchrony (SOA) exceeds the duration of the TWI, two successive deviations occurring infrequently in a repetitive sound sequence elicit two separate mismatch negativity (MMN) event-related brain potentials. However, only one MMN is elicited when the SOA is shorter than the TWI. Experiment 1 tested MMN elicitation for the second of two successive deviant sounds as a function of the SOA. Experiment 2 used the sound omission paradigm, in which MMN is only elicited by omissions when the SOA is shorter than the TWI. Again, MMN elicitation was tested by infrequent tone omissions as a function of the SOA. Results showed no significant differences between elderly and younger participants as a function of SOA. This suggests that the duration of the TWI is approximately between 200 and 250 ms in both groups of subjects. On the other hand, the lower MMN amplitudes elicited by frequency deviation in the elderly compared with the younger participants suggest that the specificity of frequency representation deteriorates with aging.     

Effect of deviance direction and calculation method on duration and frequency mismatch negativity (MMN)

The mismatch negativity (MMN) component of the auditory event-related potential (ERP) reflects the process of change detection in the auditory system. The present study investigated the effect of deviance direction (increment vs. decrement) and calculation method (traditional vs. same-stimulus) on the amplitude of MMN. MMN was recorded for increments and decrements in frequency and duration in 20 adults. The stimuli (standard/deviant) were 250 Hz/350 Hz (frequency MMN) and 200 ms/300 ms (duration MMN) for increment MMN and vice versa for decrement MMN. Amplitude of MMN was calculated in two ways: the traditional method (subtracting ERP to the standard from the deviant presented in the same block) and the same-stimulus method (subtracting ERP to identical stimuli presented as standard in one block and deviant in another block). We found that increments in frequency produced higher MMN amplitudes compared to decrements for both methods of calculation. For duration deviance, the decrement MMN was absent in the traditional method, while the decrement and increment MMN did not differ for the same-stimulus method. These findings suggest that the brain processes frequency increments and decrements in different ways. The results also suggest the use of same-stimulus method for the calculation of duration MMN when long duration stimuli are used.     

Modulation of the mismatch negativity (MMN) to vowel duration changes in native speakers of Finnish and German as a result of language experience.

While crucial for phoneme distinctions in the Finnish language, mere vowel duration is of lower relevance as a phonetically distinctive cue in the German language. To investigate the pre-attentive processing of vowel duration between these two languages, the mismatch negativity (MMN), a component of the auditory event-related potential (ERP) that is an index of automatic auditory change detection, was measured in Finnish and German native speakers for vowel duration changes embedded in the pseudoword sasa. Vowel duration changes thereby were presented as a shortening or a lengthening of either the first- or second-syllable vowel. An additional non-speech condition measured the MMN to duration and frequency changes in tones. In both language groups, diminished MMN amplitudes for the shortening of vowel duration in the word-final syllable suggested a generally more difficult discrimination of vowel duration in a word-final position. Further, shorter MMN latencies for the Finns than the Germans for vowel duration as well as tone duration deviants suggested a generally higher sensitivity to duration contrasts in the Finnish language group. No latency difference between the groups was found for tone frequency processing. Moreover, the Finns, but not the Germans, showed a leftward shift of the MMN scalp distribution for changes in vowel duration, whereas the MMN topography was highly similar between both groups in the tone condition. An enhanced phonetic processing of vowel duration changes and possibly an enhanced processing of sound duration in general is thus indicated for the Finns as a result of their extensive linguistic experience with phonetically distinctive vowel duration contrasts in the native language.     

The duration of a neuronal trace of an auditory stimulus as indicated by event-related potentials

Event-related brain potential studies have revealed a component called the mismatch negativity (MMN) in response to occasional deviant stimuli presented in a sequence of homogeneous repetitive, ‘standard’, stimuli. This negativity probably reflects an automatic neuronal-mismatch process with a neuronal representation of the standard stimulus. The present study aimed at determining the duration of the assumed neuronal representation by varying the inter-stimulus interval (ISI) of a stimulus block. It was assumed that a deviant stimulus can elicit a MMN only when the neuronal representation of the previous standard stimulus still exists. It was found that a clear MMN was elicited by the deviant stimulus when the ISI was 1 or 2 s, but not when the ISI was 4 or 8 s. This suggests that the duration of the neuronal representation involved was less than 4 s.     

Mismatch negativity results from bilateral asymmetric dipole sources in the frontal and temporal lobes

The event-related potential (ERP) reflecting auditory change detection (mismatch negativity, MMN) registers automatic selective processing of a deviant sound with respect to a working memory template resulting from a series of standard sounds. Controversy remains whether MMN can be generated in the frontal as well as the temporal cortex. Our aim was to see if frontal as well as temporal lobe dipoles could explain MMN recorded after pitch-deviants (Pd-MMN) and duration deviants (Dd-MMN). EEG recordings were taken from 32 sites in 14 healthy subjects during a passive 3-tone oddball presented during a simple visual discrimination and an active auditory discrimination condition. Both conditions were repeated after one month. The Pd-MMN was larger, peaked earlier and correlated better between sessions than the Dd-MMN. Two dipoles in the auditory cortex and two in the frontal lobe (left cingulate and right inferior frontal cortex) were found to be similarly placed for Pd- and Dd-MMN, and were well replicated on retest. This study confirms interactions between activity generated in the frontal and auditory temporal cortices in automatic attention-like processes that resemble initial brain imaging reports of unconscious visual change detection. The lack of interference between sessions shows that the situation is likely to be sensitive to treatment or illness effects on fronto-temporal interactions involving repeated measures.     

Memory-based or afferent processes in mismatch negativity (MMN): a review of the evidence

The mismatch negativity (MMN) is an electromagnetic response to any discriminable change in regular auditory input. This response is usually interpreted as being generated by an automatic cortical change‐detection process in which a difference is found between the current input and the representation of the regular aspects of the preceding auditory input. Recently, this interpretation was questioned by Jääskeläinen et al. (2004) who proposed that the MMN is a product of an N1 (N1a) difference wave emerging in the subtraction procedure used to visualize and quantify the MMN. We now evaluate this “adaptation hypothesis” of the MMN in the light of the available data. It is shown that the MMN cannot be accounted for by differential activation of the afferent N1 transient detectors by repetitive (“standard”) stimuli and deviant (“novel”) stimuli and that the presence of a memory representation of the standard is required for the elicitation of MMN.     

Effects of auditory hallucinations on the mismatch negativity (MMN) in schizophrenia as measured by a modified ‘optimal’ multi-feature paradigm

The recently developed Optimal-3 multi-feature MMN paradigm, a shortened version of the ‘optimal’ multi-feature MMN paradigm, allows for the focused recording of the most widely reported MMN deviants (frequency, duration, intensity) within an efficient and time-saving paradigm. The objective of this study was to examine MMN acoustic change detection in schizophrenia (SZ), and elucidate its association with auditory verbal hallucinations (AH), using the Optimal-3.

Methods

MMN to duration, frequency and intensity deviants were recorded in 12 SZ outpatients (SZs) with persistent AHs and 12 matched healthy controls (HC). Electrical activity was recorded from 32 scalp electrodes; MMN amplitudes and latencies for each deviant were compared between groups and were correlated with trait (PSYRATS) and state measures of AH severity and Positive and Negative Syndrome Scale (PANSS) ratings in SZs.

Results

SZs showed a significantly smaller duration MMN compared to HCs. Furthermore, in SZs attenuated duration MMN amplitudes were correlated with increased PSYRATS scores, as well as increased PANSS positive symptom, hallucination item and general psychoticism ratings, while attenuated intensity MMN amplitudes were correlated with increased PSYRATS scores.

Conclusions

This is the first study to examine MMN in SZ within the modified (Optimal-3) multi-feature MMN paradigm. This study corroborates previous research reporting a robust duration MMN deficit in SZ and supports previous findings suggesting that AHs may contribute to MMN deficits in SZ.     

Preattentive timing of empty intervals is from marker offset to onset

The internal marker hypothesis explains the superior timing performance for empty intervals over filled intervals by assuming that timing an empty interval starts from the offset of the first marker stimulus and stops at the onset of the second marker stimulus. Other models suggest that timing an empty interval is from first marker onset to second marker onset. We used an electrophysiological measure of preattentive change detection, the mismatch negativity (MMN), to examine processing of empty intervals. Participants watched a silent movie while a stream of auditory stimuli demarcating empty intervals was presented in the background. Most intervals were of the same duration (standards), but shorter intervals (deviants) were presented occasionally also. The pattern of MMN amplitudes obtained across five deviant conditions indicated that preattentive timing of empty intervals occurred from marker offset to onset.     

Nicotinic modulation of human auditory sensory memory: Evidence from mismatch negativity potentials.

Impairment in mismatch negativity (MMN) generation is a robust biological marker of schizophrenia. Understanding the physiological and pharmacological processes involved in its generation may therefore advance our understanding of this complex disorder. The present study tested if acute administration of nicotine modulates human auditory sensory memory as measured with MMN. ERP responses to tone duration deviants were recorded using a stimulation protocol with continuously changing (roving) standard stimuli in order to measure the effect of stimulus repetitions on encoding of new stimuli (MMN memory trace effect). Twenty healthy adult volunteers were randomly assigned to receive either a nicotine gum or placebo after a baseline ERP recording. Nicotine administration augmented MMN amplitude in the treatment group compared to the baseline recording, while no MMN change was found in the placebo group. The drug effect was due to a selective enhancement of a frontal positive potential to standard stimuli (from 80-200 ms post-stimulus), while the negativity to deviants remained unaffected. Furthermore, under nicotine stimulation this repetition positivity showed a more marked increase with stimulus repetition compared to baseline and placebo. These results have potential implications for schizophrenia by suggesting that nicotinic agonists could ameliorate patients' MMN deficits by improving stimulus encoding and sensory memory trace formation.     

The Processing of Temporal Intervals Reflected by CNV-Like Brain Potentials

The present study employed event-related potentials (ERPs) of the brain to improve the understanding of temporal processing. A reproduction paradigm was realized by presenting a visual stimulus (illuminated screen) for intervals of varying length. A few seconds after presentation of such standard intervals the visual stimulus was switched on again and subjects were asked to reproduce the duration of the standard interval by turning off the illumination after a corresponding interval had elapsed. The length of standard intervals varied randomly with each of the following lengths being presented 20 times: 1, 2, 3, 4, 6, and 8 s. Reproduction was accurate for standard intervals up to 3 s but deteriorated with increasing interval length. Brain potentials during reproduction intervals of 1-3 s differed from those recorded during the longer intervals. A CNV-like slow negative shift developed during the shorter reproduction intervals. Negatively was reduced or even absent, when subjects had to reproduce standard intervals of 4 s or longer. The ERP results suggest that intervals shorter than 3-4 s may evoke a processing mode that is qualitatively different from the one dominating when periods in the range of several seconds have to be processed.     

Mismatch negativity (MMN) reduction in schizophrenia-impaired prediction--error generation, estimation or salience?

The model of mismatch negativity (MMN) as a simple index of change detection has been superseded by a richer understanding of how this event-related potential (ERP) reflects the representation of the sound environment in the brain. Our conceptualization of why the MMN is altered in certain groups must also evolve along with a better understanding of the activities reflected by this component. The detection of change incorporates processes enabling an automatic registration of "sameness", a memory for such regularities and the application of this recent acoustic context to interpreting the present and future state of the environment. It also includes "weighting" the importance of this change to an organism's behaviour. In this light, the MMN has been considered a prediction error signal that occurs when the brain detects that the present state of the world violates a context-driven expectation about the environment. In this paper we revisit the consistent observation of reduced MMN amplitude in patients with schizophrenia. We review existing data to address whether the apparent deficit might reflect problems in prediction error generation, estimation or salience. Possible interpretations of MMN studies in schizophrenia are linked to dominant theories about the neurobiology of the illness.