Heikki Lang

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.

Dissimilar age influences on two ERP waveforms (LPC and N400) reflecting semantic context effect

Age-related changes in semantic context effects were examined using late event-related brain potentials (ERPs). Auditory ERPs to semantically congruous and incongruous final words in spoken sentences were recorded in 16 children (aged 5-11 years) and 16 adults. Previous findings concerning age-related effects on N400 were replicated: the N400 effect was significantly larger in children than in adults. The main new finding was that a late positive component (LPC) following N400 and modulated by semantic context in adults was not found in children. Thus, the common generalization that semantic context effects decline with age holds only for ERP components occurring in the N400 time window or earlier. The cognitive function reflected by the semantic LPC we observed is not clear, but it seems to have a role different from that of the N400, although in adults the components often co-exist as an N400-LPC complex.

Event-Related Desynchronization evoked by auditory stimuli

SummaryEvent-Related Desynchronization (ERD) and Synchronization (ERS) of several EEG alpha frequencies was studied in 19 subjects during the presentation of linguistic and/or melodic auditory stimuli. The stimulus length was 1300 msec (+/−100 msec) and the interstimulus interval was 2000 msec. A significant ERD was found during auditory stimulation in the 8–10 Hz and 10–12 Hz alpha frequency bands, and there were also significant differences in the spatiotemporal pattern of the ERD between these frequency bands. Significant ERD was elicited also in the 10–11 and 11–12 Hz frequency bands by auditory stimulation. There were no significant differences between these one-hertz frequency bands. The subjects were assigned to two analysis groups according to their individual alpha peak frequency (10–11 or 11–12 Hz) at rest. The ERD in these groups reached statistical significance and there were significant differences between the groups. The ERD of the two groups differed significantly also when their EEG data was studied in the 10–12 Hz frequency band. The results from this study show that ERD is not modality-specific, i.e., it can be elicited also by auditory stimuli. Moreover, they indicate that it is important to control over interindividual variation in the EEG when studying the ERD phenomenon.

Automatic auditory word perception as measured by 40 Hz EEG responses

OBJECTIVES Here we report the existence of automatic speech perception in man, revealed by 40 Hz EEG responses. METHODS We presented to Finnish subjects the Finnish word /tu:li/(wind) as the standard stimulus and another Finnish word /tuli/(fire) as the deviant stimulus using a passive auditory oddball task. The experiment was also conducted with pseudowords as stimuli. RESULTS We observed a global significant increase in 40 Hz EEG power at 600 ms after stimulus onset for words, but not for pseudowords. CONCLUSIONS Our results indicate that the memory representation of the standard verbal stimuli, even if unattended, might not merely be based on the physical features of the stimuli: if a semantic representation exists, then the brain processes it pre-attentively.

Cortical processing of vowels and tones as measured by event-related desynchronization.

SummaryEvent-Related Desynchronization (ERD) and Synchronization (ERS) were studied in 20 normal subjects during a Sternberg-type auditory memory-scanning paradigm. Half of the subjects performed the experiment with vowels and the other half with tones as stimuli. The stimuli consisted of 100 msec long synthesized vowels and 100 msec long tones produced by eight different synthesized instruments. In this paradigm each trial started with the presentation of a visual warning signal, after which a four-stimulus set was presented for memorization whereafter a probe stimulus was presented and identified by the subject as belonging or not belonging to the memorized set. The ERD/ERS of the lower (8–10 Hz) and upper (10–12 Hz) alpha frequency bands differed in their reactivity to stimulus type; the differences between the two frequency bands reached statistical significance only in the case of vowels. The presentation of the memory set elicited ERS which was more pronounced in the 10–12 Hz frequency band and greater for vowels than for tones. On the other hand, the presentation of the probe elicited ERD which was greater for vowels than for tones, especially in the upper alpha frequency band. The results of this exploratory study suggest that ERD is closely related to memory processes and that the ERD/ERS-technique might provide a valuable tool for future reseach encompassing more complex auditory stimulation like speech and music.

Alpha rhythm in classical migraine (migraine with aura): abnormalities in the headache-free interval.

The alpha rhythm of 18 patients with classical migraine (migraine with aura) was studied by EEG spectrum analysis for evidence of neural abnormalities during the asymptomatic period. The temporal relationship of the findings to attacks was studied by serial records in 11 cases. Increased frequency dispersion and frequency asymmetries of the alpha rhythm were found. The records were, however, mostly normal when separated from attacks by at least 10 asymptomatic days. The abnormalities increased significantly before the onset of prodromal symptoms and clearly outlasted the headache phase. The results give evidence of a fluctuating asymmetric neural disorder in classical migraine.

AMYGDALOID AFTERDISCHARGE AND GALVANIC SKIN RESPONSE.

Abstract 1. 1. The investigation was carried out on lightly anesthetized cats which were immobilised by succinylcholine. Recording and stimulation were made in the basolateral part of the amygdaloid nucleus. GSR was recorded from the volar surface of the fore paw by a DC-coupled amplifier. 2. 2. Tonic GSR accompanied the afterdischarge recorded from the amygdaloid nucleus. The duration of these phenomena always showed a certain temporal correlation. When the stimulation was subliminal for the afterdischarge the GSR was typically phasic or missing altogether. 3. 3. Xylocaine (3 mg/kg, i.v.) shortened the amygdaloid afterdischarge and GSR equally, but had no essential effect on the amplitude of GSR. Nembutal (10 mg/kg, i.v.) had a weaker effect on the duration of the afterdischarge, but distinctly lowered the amplitude of GSR and especially influenced its tonic character. 4. 4. If the stimulation intensity was clearly above the threshold value a minor elevation of the blood pressure and changes of the heart rate sometimes occurred during the amygdaloid afterdischarge and tonic GSR. 5. 5. The possibility that the sympathicotonic GSR is a secondary phenomenon caused by projection of AA to the brain-stem, is discussed.

The MMN amplitude increases in hypnosis: a case study

The neural mechanisms associated with hypnosis were investigated in a single highly hypnotizable subject by measuring the mismatch negativity (MMN) component of auditory ERP, reflecting the preattentive discrimination of change in stimulus flow, in normal baseline state and under hypnosis. It has been proposed that the frontal inhibition associated with hypnosis can be measured as a decrease in MMN. ERPs were elicited using the passive oddball paradigm with standard and deviant sine tone stimuli of 500 and 553Hz, respectively. The measurement was repeated in five separate sessions. In hypnosis the MMN was significantly larger compared to baseline. The results indicate that hypnosis can give rise to altered information processing in the brain even at a relatively early, i.e. preattentive level and that the larger MMN measured under hypnosis does not support frontal inhibition theory.

Toxic encephalopathy with hyperammonaemia during high-dose salicylate therapy

High‐dose, long‐term aspirin therapy easily overloads the patients individual capacity to metabolize salicylates and may lead to complex metabolic disturbances including fulminant hepatic failure, hyperammonemia and toxic metabolic encephalopathy.

Tone duration discrimination in Parkinson's disease

Patients with Parkinsons disease (PD) and healthy controls took a computerized test of tone duration discrimination (TDD) using pairs of tones of 0.4-1.6 sec duration, presented at intervals of 0.5-4 sec. In PD patients as well as controls, TDD was impaired by even slight degrees of cognitive deterioration. PD yielded impaired TDD in females, but not in males. This suggests that the dopamine-powered biological clock, which is vulnerable to PD, is more important for the processing of durations in the 1-sec range in women than in men.