Kalevi Reinikainen

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.

Event-related brain potential of human newborns to pitch change of an acoustic stimulus ☆

We report here event-related potentials (ERPs) of human newborns to occasional pitch changes in a repetitive sequence of tone pips. These pitch changes elicited a large slow negative ERP component which resembles the mismatch negativity (MMN) generated by the adult brain under similar conditions. This MMN-type of negativity in newborns suggests that already at this early ontogenetic stage the brain monitors the acoustic environment for a possible change in any of its repetitive aspects. Apart from its theoretical interest, this finding might provide a new way to test the development of the central nervous system and to diagnose cerebral dysfunction at a very early stage.

Mismatch negativity to change in spatial location of an auditory stimulus

Auditory stimulus blocks were presented to 12 reading subjects. Each block consisted of 2 types, standard (P = 90%) and deviant stimuli (P = 10%), delivered in a random order. The only difference between these stimuli was their spatial location of origin. The subject always heard the standards as coming straight in front and the deviants from an angle of either 10, 45, or 90 degrees to the right of the standards. The spatial locations were produced via earphones by introducing for low-frequency (600 Hz) tones an interaural phase difference and for high-frequency (3000 Hz) tones an interaural intensity difference. Standard and deviant stimuli were also delivered in more natural, free-field, conditions via differently positioned loudspeakers. The deviant tones elicited an event-related brain potential component called the mismatch negativity (MMN), followed by a P3a component. Thus changes in spatial location of an auditory stimulus produced by following either one of the two main principles of human sound localization elicited the MMN. Consequently, it was concluded that the spatial location of a sound source is coded in the hypothesized neuronal stimulus traces reflected by the MMN and, further, that a change in this location is automatically detected by the brain by means of the MMN generator process.

Temporal window of integration revealed by MMN to sound omission

THE central auditory system for event perception involves the integrating mechanism of sequential information addressed by the present study. The mismatch negativity (MMN) component of the event-related potentials (ERP) reflects the automatic detection of sound change. ERPs to occasionally omitted stimuli were measured when sequences with constant stimulus onset asynchronies (SOAs) were presented. In separate blocks, the SOA was from 100 to 350 ms. A clear MMN was elicited by a stimulus omission in a sequence of regularly spaced tone pips only when the SOA was shorter than 150 ms, yielding an estimate for the duration of the temporal window of integration used the perceptual segregation of auditory events.

Frequency and location specificity of the human vertex N1 wave

Test tones of 1000 Hz subjectively located in the middle of the head were randomly presented with equiprobable intervening tones. The latter stimulus was constant within a stimulus block. The frequency of the intervening stimulus varied between different blocks from 578 Hz to 1728 Hz and its location varied in parallel with the frequency along the left-right dimension through 7 different locations. The constant inter-stimulus interval was 460 msec. The EEG was recorded at Cz and Fz. The N1 wave elicited by the test stimuli was smaller the smaller was the separation between the two stimuli in frequency or location. These results were interpreted in terms of stimulus-specifically adapted detector activity. The more the test and intervening stimuli resemble each other the greater is the overlap between the respective feature-detector populations activated and, therefore, the smaller is the N1 amplitude. Thus the sensory-specific component of the N1 wave generated in the primary auditory areas at least in part reflects detector activity. The selective frequency adaptation was much more specific in the present study than in the previous ones and suggested that the N1 component recorded was generated by highly frequency-specific neurons. The frequency and location effects were independent, i.e., the frequency effect was rather similar for different location separations, and vice versa. Thus, evidence for separate detectors for frequency and location of an auditory stimulus was obtained.

Human somatosensory evoked potentials to mechanical pulses and vibration: contributions of SI and SII somatosensory cortices to P50 and P100 components ☆

Somatosensory evoked potentials (SEPs) were measured to short tactile pulses and vibratory stimuli applied to the fingertip to determine the characteristics and scalp topography of different early and late SEP components to these types of stimulus. The measurements were obtained from 3 homologous contra- and ipsilateral locations and from the vertex. In 2 subjects the SEPs were measured from 23 recording locations. The subjects were reading during the experiments. The first distinct contralateral response was an anteriorly negative and centrally as well as posteriorly positive peak at about 50 msec latency (P50). Largest P50 responses with shortest peak latencies were measured to single tactile pulses. We suggest that P50 is probably generated in the contralateral SI cortex. The P50 was followed by a distinct negative deflection (N70) in the middle and posterior recording locations on the contralateral hemisphere, which reversed its polarity in the frontal records. This peak was also seen ipsilaterally. At about 100 msec latency a distinct bilateral positive P100 peak was obtained. This peak was most prominent to vibratory stimuli, and especially to high frequency vibration. Comparisons with recent intracortical SEP studies in primates and MEG studies in humans suggest that P100 might be best accounted for by bilateral generators in SII cortices. The early components were followed by a negative N140 wave and by a slow, positive wave with a maximum at about 300 msec. Both waves had an asymmetrical distribution. The N140 wave occurred bilaterally, but was largest contralaterally, and often had two peaks at posterior recording locations. The slow positivity was largest at the vertex and at mid-posterior recording sites.

Maturation of mismatch negativity in infants

The mismatch negativity (MMN) is a pre-attentive change-specific component of the event-related brain potentials (ERPs). During the last decade this response has been intensively studied in adults, but investigations in children and especially in infants are still rare. Recent studies, however, have shown that MMN is also elicited in infants in response to changes in pure tones as well as in phonemes. The present study compared MMN in pre-term infants (conceptional age at the time of recording, 30-35 weeks), full-term newborns and full-term 3-month-old infants. Stimuli were Klatt-synthesized Finnish vowels /y/ and /i/. Previous studies have reported larger MMN amplitudes in school-age children compared with those obtained in adults. According to the results, however, the infant MMN amplitude seems to resemble that of adults. No significant differences in MMN amplitudes were found between the three age groups either. The mean MMN latency, however, decreased significantly with age, although in 3-month-old infants it was not much longer than in a previous study conducted in adults with the same stimuli.

Selective tuning of the left and right auditory cortices during spatially directed attention.

Effects of spatially directed auditory attention on human brain activity, as indicated by changes in regional cerebral blood flow (rCBF), were measured with positron emission tomography (PET). Subjects attended to left-ear tones, right-ear tones, or foveal visual stimuli presented at rapid rates in three concurrent stimulus sequences. It was found that attending selectively to the right-ear input activated the auditory cortex predominantly in the left hemisphere and vice versa. This selective tuning of the left and right auditory cortices according to the direction of attention was presumably controlled by executive attention mechanisms of the frontal cortex, where enhanced activation during auditory attention was also observed.

Auditory sensory memory impairment in Alzheimer's disease: an event-related potential study.

Auditory event-related potentials (ERP) were recorded from 10 healthy older subjects and 9 patients with Alzheimers disease (AD) to investigate whether auditory sensory memory is impaired in AD. Standard (85%) and deviant (15%) tones were presented in random order with interstimulus intervals (ISI) of 1 s or 3 s in separate blocks. Deviant tones elicited a specific ERP component called mismatch negativity (MMN) which reflects automatic stimulus change detection and thus presumably, the neural basis of sensory memory in audition. The MMN amplitude decreased as a function of the ISI more in the AD group than in the control group. This suggests that the memory trace decays faster in the AD patients than in age-matched healthy controls.

Auditory and somatosensory event-related brain potentials in early blind humans.

Previous event-related potential (ERP) studies have suggested a possible participation of the visual cortex of the blind in auditory processing. In the present study, somatosensory and auditory ERPs of blind and sighted subjects were recorded when subjects were instructed to attend to stimuli of one modality and to ignore those of the other. Both modalities were stimulated with frequent (“standard”) and infrequent (“deviant”) stimuli, which differed from one another in their spatial locus of origin. In the sighted, deviant stimuli of the attended modality elicited N2 type of deflections (auditory N2b and somatosensory N250) over the lateral scalp areas. In contrast, in the blind, these ERP components were centroposteriorly distributed, suggesting an involvement of posterior brain areas in auditory and somatosensory stimulus discrimination. In addition, the mismatch negativity, elicited by deviant auditory stimuli even when the somatosensory stimuli were attended, was larger in the blind than in the sighted. This appears to indicate enhanced automatic processing of auditory stimulus changes in the blind. Thus, the present data suggest several compensatory changes in both auditory and somatosensory modalities after the onset of early visual deprivation.