Test-retest reliability of mismatch negativity for duration, frequency and intensity changes.

OBJECTIVES: The test-retest reliabilities of the mismatch negativity (MMN) elicited by deviances in sound duration, frequency, and intensity were compared. METHODS: The MMN was recorded with a 64-channel electroencephalograph (EEG) from 15 healthy adult subjects in two sessions over intervals of 1-27 days. During the recordings, subjects watched a silent movie while they were presented with one long stimulus sequence consisting of 6 types of tones. The standard tone (P = 0.8) of 75 ms in duration consisted of 3 lowest harmonic partials with 500 Hz as the fundamental frequency. Each of the 5 different deviant tones was presented with P = 0.04: frequency deviants (+/-5%, +/-10%), duration deviants (-66%, -33%), and intensity deviants (- 15 dB). RESULTS: The 66% duration decrement elicited MMN with the most replicable amplitude (r = 0.78) and latency (r = 0.76) among the deviances tested. CONCLUSIONS: Since these reliabilities considerably exceed those reported previously, these data support the use of the duration decrement deviance presented with spectrally rich tones while investigating the integrity of the patients' cognitive brain functions using the MMN.

Brain responses reveal the learning of foreign language phonemes.

Learning to speak a new language requires the formation of recognition patterns for the speech sounds specific to the newly acquired language. The present study demonstrates the dynamic nature of cortical memory representations for phonemes in adults by using the mismatch negativity (MMN) event-related potential. We studied Hungarian and Finnish subjects, dividing the Hungarians into a naive (no knowledge of Finnish) and a fluent (in Finnish) group. We found that the MMN for a contrast between two Finnish phonemes was elicited in the fluent Hungarians but not in the naive Hungarians. This result indicates that the fluent Hungarians developed cortical memory representations for the Finnish phoneme system that enabled them to preattentively categorize phonemes specific to this language.

Pre-attentive detection of vowel contrasts utilizes both phonetic and auditory memory representations.

Event-related brain potentials (ERP) were recorded to infrequent changes of a synthesized vowel (standard) to another vowel (deviant) in speakers of Hungarian and Finnish language, which are remotely related to each other with rather similar vowel systems. Both language groups were presented with identical stimuli. One standard-deviant pair represented an across-vowel category contrast in Hungarian, but a within-category contrast in Finnish, with the other pair having the reversed role in the two languages. Both within- and across-category contrasts elicited the mismatch negativity (MMN) ERP component in the native speakers of either language. The MMN amplitude was larger in across- than within-category contrasts in both language groups. These results suggest that the pre-attentive change-detection process generating the MMN utilized both auditory (sensory) and phonetic (categorical) representations of the test vowels.

Enhanced brain activity preceding voluntary movement in early blind humans.

Effects of blindness on movement-related brain activity were investigated by measuring from the scalp movement-related potentials (MRPs) associated with self-paced button presses in blind and sighted young adults. The blind subjects had lost their vision at an early age due to a deficit in the peripheral visual system. The negative slope (NS') of MRP at about 400 ms prior to movement and the preceding readiness potential (RP) were larger in the blind than in the sighted subjects, but were similarly distributed on the scalp in these groups. The results suggest functional changes in the blind subjects' brain activity, presumably, in the cortical areas involved in preparation and initiation of voluntary movement.

The mismatch negativity for duration decrement of auditory stimuli in healthy subjects.

The amplitude and latency of the mismatch negativity (MMN) elicited by occasional shorter-duration tones (25 and 50 ms) in a sequence of 75 ms standard tones were studied in 40 healthy subjects (9-84 years). The replicability and age dependence of the MMN-responses were determined. The 25 ms deviant tone evoked a clear response in 39 of the subjects, while the 50 ms deviant tone evoked an observable MMN only in 32 of the subjects. The MMN peak amplitude for the 25 ms deviants was significantly larger than for the 50 ms deviants. There was no significant difference in the peak latencies (measured from stimulus offset). For the 25 ms deviant, the amplitude diminished with increasing age. The MMN curves for the 25 ms deviant, measured on separate days in 14 subjects, looked very replicable. As a result of noise and filtering effect, the product-moment correlations were poor. The results indicate that the signal-to-noise ratio for the MMN to 25 ms deviants, obtained even in a 25 min recording session, is large enough for clinical use and individual diagnostics when undetectable (or very low amplitude) MMN is used as a sign of pathology. However, judged from the low correlation coefficients, despite the good replicability in visual evaluation, better methods for MMN quantification have to be used for clinical follow-up.

Effects of naltrexone and ethanol on auditory event-related brain potentials.

Acute effects of ethanol (0.55 g/kg) and the opioid antagonist naltrexone (50 mg) on auditory event-related brain potentials (ERP) (i.e., electrical brain activity time-locked to sensory stimuli) were investigated in 13 healthy social drinkers, using a double-blind, placebo-controlled, design. The subjects' task was to attend to tones presented to a designated ear while ignoring tones to the other, and to detect deviant tones among the attended tones. When administered alone, naltrexone significantly reduced the amplitude of the later part of negative difference (Nd[l]), suggesting impaired selective attention. However, this effect might have been caused by naltrexone-induced nausea. Ethanol, when ingested alone, attenuated the amplitude of the N1, and increased the peak latencies of the mismatch negativity (MMN) and N2b that have been suggested to reflect automatic change detection in audition and allocation of attentional resources to processing of stimulus deviance, respectively. In contrast, the P1 amplitude was augmented by alcohol, but only when the tones were attended. When ethanol and naltrexone were simultaneously ingested, however, the alcohol-induced P1 amplitude augmentation was canceled, thus tentatively suggesting opioidergic mediation of this alcohol effect. In contrast, the MMN peak latency was increased significantly more in the interaction condition than in the ethanol condition, thus suggesting that the detrimental effects of alcohol on involuntary attention switching were augmented by naltrexone. Furthermore, the N2b amplitude was significantly suppressed in the interaction condition, suggesting attentional impairment.

Hemispheric lateralization in preattentive processing of speech sounds.

Event-related magnetoencephalographic (MEG) responses to infrequently presented spoken deviant syllables [di] and [ba] among repetitive standard [da)]syllables were recorded in subjects who either attended to these stimuli in order to discriminate the [ba] syllables or ignored them while attending a silent movie. In both conditions, the deviant syllables elicited a mismatch response (MMNm, the magnetic counterpart of mismatch negativity), which was stronger in the left than in the right auditory cortex, indicating left-hemispheric dominance in speech processing already at a preattentive processing level.

Rate effect and mismatch responses in the somatosensory system: ERP-recordings in humans.

In the first experiment, somatosensory event-related potentials (SERPs) were recorded to tactile pulses and vibration bursts applied to the left middle finger in trains of 4-8 stimuli with 1 s intervals. In addition to the negative N140 deflection, also the positive P50, P100 and P300 waves attenuated in amplitude with stimulus repetition. These decreases were immediate, there being no marked further amplitude attenuation after the second stimulus. The locus of this rate effect appears not to be the primary SI or SII, but rather prefrontal cortices or some deeper structures. In the second experiment, vibratory stimuli of different frequencies or at different skin sites were presented using the oddball paradigm. When the deviant stimulus was a high-frequency vibration burst, it elicited a distinct N250 deflection, probably analogous to the auditory N2b. When the deviation was a change in the stimulation site, no N250 deflection but instead an extra negativity between 100-200 ms latency, probably analogous to the auditory mismatch negativity, was observed.

Electrophysiological evidence for cross-modal plasticity in humans with early- and late-onset blindness.

It is commonly believed that sensory deprivation can lead to cross-modal reorganization in an immature but not in a mature brain. The results of the present study suggest, however, that plasticity between sensory modalities is possible even in adults: activity indicating involvement of parietal or occipital brain areas in pitch-change discrimination was found in individuals blinded after childhood. Event-related brain potentials of early blinded (before the age of 2 years), late-blinded (12-28 years of age), and sighted adults were recorded to stimulus sequences consisting of standard tones occasionally replaced by deviant tones. Even when participants were not attending to auditory stimuli, the deviant tones elicited the mismatch negativity (MMN) in each group. There were no significant MMN front-back scalp distribution differences among the groups. However, when participants were detecting deviant stimuli, these stimuli elicited N2 and P3 waves that were posterior in distribution in both groups of blind participants relative to those of the sighted participants. These results suggest that cross-modal reorganization may occur even in the mature human brain.

Language-specific phoneme representations revealed by electric and magnetic brain responses.

There is considerable debate about whether the early processing of sounds depends on whether they form part of speech. Proponents of such speech specificity postulate the existence of language-dependent memory traces, which are activated in the processing of speech but not when equally complex, acoustic non-speech stimuli are processed. Here we report the existence of these traces in the human brain. We presented to Finnish subjects the Finnish phoneme prototype /e/ as the frequent stimulus, and other Finnish phoneme prototypes or a non-prototype (the Estonian prototype /õ/) as the infrequent stimulus. We found that the brain's automatic change-detection response, reflected electrically as the mismatch negativity (MMN), was enhanced when the infrequent, deviant stimulus was a prototype (the Finnish /ö/) relative to when it was a non-prototype (the Estonian /õ/). These phonemic traces, revealed by MMN, are language-specific, as /õ/ caused enhancement of MMN in Estonians. Whole-head magnetic recordings located the source of this native-language, phoneme-related response enhancement, and thus the language-specific memory traces, in the auditory cortex of the left hemisphere.

Low dose of ethanol suppresses mismatch negativity of auditory event-related potentials.

The acute effect of a low dose of ethanol (0.5 g/kg) on attention and auditory event-related potentials (ERPs) was investigated in 10 social drinkers using a single-blind, placebo-controlled cross-over design. A dichotic listening task, in which the subjects were instructed to attend selectively to stimuli to one ear while ignoring stimuli to the other, was used. The amplitudes of N1, P2, and the mismatch negativity (MMN) were significantly diminished by alcohol. The latencies of the MMN and N2b were also significantly increased after alcohol ingestion. The novel finding of the significant (> 60% reduction in amplitude) suppression of the MMN can be interpreted as indicating disturbed preconscious detection of acoustic changes outside the scope of attention. Because this is a prerequisite to an attentional shift, the MMN suppression may be related to increased risk for accidents after alcohol ingestion. The same dose of alcohol that suppressed the MMN left intact selective attention and conscious "target" detection, as reflected by the processing negativity and P3 deflections, thus suggesting that the automatic functions of human information processing are more sensitive to alcohol than the controlled, attentional functions.