Auditory event-related potentials dissociate early and late memory processes

Event-related potentials (ERPs) to environmental sounds were recorded from 15 young control subjects in an auditory recognition memory task. Subjects listened to a continuous string of binaurally presented sounds, 20% of which were presented once and 80% were repeated. Of the repeated sounds, some repeated immediately after the initial presentation (2 sec; short delay repetition) while others repeated after 2–6 intervening sounds (4–12 sec; long delay repetition). Subjects were instructed to indicate whether they had heard the sounds before by pressing a “yes” or “no” button.The initial stimulus presentation and long delay repetition stimuli generated both an N4 component and a prolonged latency P3 component while the short delay repetition stimuli elicited no N4 component and an earlier latency P3 component. Subjects' responses were faster and more accurate for short delay repetition. All stimuli generated a sustained frontal negative component (SFN). These data indicate that auditory recognition memory for environmental sounds may involve two processes. The P3 generated by both short and long delay repetition stimuli may index activation of a neocortical template matching system. The N4 generated by initial stimulus presentations and long delay repetition is proposed to measure additional activation of limbic memory systems at long retention intervals.     

Brain mechanism of selective listening reflected by event-related potentials

Stimulus selection during selective listening on the basis of simple physical stimulus features is reflected by an event-related potential (ERP) component called the processing negativity (PN). PN has been proposed to indicate a matching or comparison process between the physical features of the stimulus and an ‘attentional trace’, an actively formed and maintained temporary neuronal representation of the features defining the relevant stimuli. According to this theory, the smaller is the difference between the eliciting stimulus and that represented by the attentional trace, the longer time is the stimulus processed, and thus the larger in amplitude and longer in duration is the PN elicited. The relevant stimuli, perfectly matching with the attentional trace, and therefore eliciting the largest and longest-duration PN, are selected for further processing. In the present study, the relevant and irrelevant stimuli differed in pitch, and the magnitude of this pitch separation was varied between different stimulus blocks. The results support the afore-mentioned matching or comparison hypothesis of selective attention by showing that PN is not elicited only by the relevant stimuli but even by irrelevant stimuli, and further that the latter PN is larger in amplitude and longer in duration the more similar the irrelevant stimuli are to the relevant stimuli. This PN, however, was smaller than that to the relevant stimuli even for very small separations, reflecting high accuracy of the discrimination function of the attentional trace mechanism proposed to underly selective listening. The termination of the PN to the irrelevant stimuli was followed by a positivity which thus partly explained the difference (Nd) between the ERPs to the relevant and irrelevant stimuli.     

Age-related changes in event-related potentials in visual discrimination tasks

Visual event-related potentials and reaction times in physical and semantic discrimination tasks were studied in 29 normal subjects between the ages of 21 and 74 years. The NA, N2 and P3 components of the evoked potential, and simple and GO/NOGO reaction times were observed in both kinds of discrimination. Significant age-related slowing of the GO/NOGO reaction time was observed only in the semantic discrimination task. The N2 and P3 latencies elicited by both the physical and semantic stimuli were significantly and positively correlated with age, although there was no significant correlation between the NA latency and age. The interpeak latency between N2 and P3 showed no age-related changes. The decline of cognitive information processing with advancing age was evident from the classification of a perceived event as reflected by the N2 component.     

Age-related changes in human middle latency auditory evoked potentials

We recorded middle latency auditory evoked potentials (MAEPs) in young (20–40 years) and elderly (60–80 years) subjects with normal hearing. The Pa component was prolonged in latency and markedly enhanced in amplitude in the elderly subjects. No changes were found in Na, or in the binaural interaction of the MAEP. Differences in Pa amplitude and latency were not due exclusively to changes in auditory thresholds, since they were not duplicated by changes in stimulus intensity, and persisted when MAEPs from selected young and old subjects were compared at similar SPL levels. The enhancement of Pa amplitude appears to reflect age-related central modifications in auditory processing.     

Amplitude modulation of steady-state visual evoked potentials by event-related potentials in a working memory task

Previous studies have shown that the amplitude and phase of the steady-state visual-evoked potential (SSVEP) can be influenced by a cognitive task, yet the mechanism of this influence has not been understood. As the event-related potential (ERP) is the direct neural electric response to a cognitive task, studying the relationship between the SSVEP and ERP would be meaningful in understanding this underlying mechanism. In this work, the traditional average method was applied to extract the ERP directly, following the stimulus of a working memory task, while a technique named steady-state probe topography was utilized to estimate the SSVEP under the simultaneous stimulus of an 8.3-Hz flicker and a working memory task; a comparison between the ERP and SSVEP was completed. The results show that the ERP can modulate the SSVEP amplitude, and for regions where both SSVEP and ERP are strong, the modulation depth is large.     

The effects of physical and semantic incongruites on auditory event-related potentials

Twenty subjects listened to a series of simple sentences, spoken by a male voice, in which the last word was on occassions either made semantically incongruous or was unexpectedly spoken by a female voice. Averages of ERPs to the last words revealed that a consistent late negative compenent (N456) was associated with semantic incongruity and a late positive component (P416) with physical (voice) incongruity. The results were consistent with thise in the visual modality by Kutas and Hillyard (1980a,b) and are interpreted in terms of the facilitatory and inhibitory effects of contextual priming on the processing of the words concerned. In a subsidiary experiment 6 subjects were required to repeat the last words of the same set of sentences as rapidly as possible. Verbal response latency increased by 62 msec to physically incongruous words and by 185 msec to semantically incongruous words.     

Interstimulus interval and auditory event-related potentials in children: evidence for multiple generators

In the present study, the component structure of auditory event-related potentials (ERP) was studied in children of 7–9 years old by presenting stimuli with different interstimulus intervals (ISI). A short-term auditory sensory memory, as reflected by ISI effects on ERPs, was also studied. Auditory ERPs were recorded to brief unattended 1000 Hz frequent, `standard' and 1100 Hz rare, `deviant' (probability 0.1) tone stimuli with ISIs of 350, 700 and 1400 ms (in separate blocks). With the 350 ms-ISI, the ERP waveform to the standard stimulus consisted of P100-N250 peaks. With the two longer ISIs, in addition, the frontocentral N160 and N460 peaks were observed. Results suggested that N160, found with the longer ISIs, is a correlate of the adult auditory N1. In difference waves, obtained by subtracting ERP to standard stimuli from ERP to deviant stimuli, two negativities were revealed. The first was the mismatch negativity (MMN), which is elicited by any discriminable change in repetitive auditory input. The MMN data suggested that neural traces of auditory sensory memory lasted for at least 1400 ms, probably considerably longer, as no MMN attenuation was found across the ISIs used. The second, later negativity was similar to MMN in all aspects, except for the scalp distribution, which was posterior to that of the MMN.     

Topographic analysis of auditory event-related potentials associated with acoustic and semantic processing

The topography of auditory event-related potentials (ERPs) was examined during 3 kinds of tasks: selection of a specified real word or nonsense syllable from a list; simple detection of each of the same stimuli without discrimination; and classification of a set of words according to a specified semantic category. The potentials that were associated with the additional processing required by the discriminative tasks were disclosed by subtracting the wave forms obtained in the detection condition from those obtained during discriminative performance. Difference wave forms were also derived between the semantic classification and verbal discriminative ERP to delineate the changes associated with the extraction of word meaning.The topography of the ERP associated with stimulus detection was comparable to that found in previous studies of evoked potentials to non-speech stimuli. This distribution was consistent with 2 cortical generators, one within the supratemporal plane and the other on the lateral surface of the superior temporal gyrus. When discriminative performance was required on the basis of acoustic stimulus properties, the topography of the difference wave form that reflected this discriminative processing extended more posteriorly over temporal cortex. Semantic processing elicited a further posterior extension of ERP components by 330 msec after stimulus onset, as well as longer latency potentials that were not present in the verbal selection task. These differences imply that a more extensive portion of language cortex is engaged in semantic classification than in verbal identification.     

Working memory in young schoolchildren: A study using event-related potentials

Event-related potentials (ERPs) were used to study working memory operations in young school-children. The type of information has proved to determine the specificity of encoding and retrieval processes in working memory. The formation of the trace and its comparison with new information for phonological stimuli requires involvement of the frontal cortical areas, whereas visual patterns are characterized by an enhanced late positive complex in the caudal areas.     

Age-related changes in the relationship between learning progress and auditory working memory characteristics

In order to explore the relationship between learning progress and working memory characteristics, the psychoacoustic testing of 42 persons (20-65 years old) of medical staff taught a novel science (informatics) was carried out. The subjects were divided into three age groups: 20-35, 36-50, and 51-65-year-olds. Acoustical test consisted of a set of 12 target words (professional informatics terms) presented through headphones and subsequent presentation of a random succession of 12 target and 12 masking words (all of them being professional informatics terms). Listeners had to recognize the target words. The stepwise linear regression analysis revealed a link between the progress in acquisition of the new material and characteristics of acoustical working memory, whose role in learning progress increased with age. Because the memory efficiency reduction was found in subjects older than 35 years, it was supposed that age-related changes in characteristics of the acoustical working memory were responsible for the decline in ability to learn novel material.     

Age-related alteration of PKC, a key enzyme in memory processes

Brain aging is characterized by a progressive decline of the cognitive and memory functions. It is becoming increasingly clear that protein phosphorylation and, in particular, the activity of the calcium-phospholipid-dependent protein kinase C (PKC) may be one of the fundamental cellular changes associated with memory function. PKC is a multigene family of enzymes highly expressed in brain tissues. The activation of kinase C is coupled with its translocation from the cytosol to different intracellular sites and recent studies have demonstrated the key role played by several anchoring proteins in this mechanism. PKC-phosphorylating activity appears to be impaired during senescence at brain level in a strain-dependent fashion in rodents. Whereas the levels of the various isoforms do not show age-related alterations, the enzyme translocation upon phorbol-ester treatment is deficitary among all strains investigated. Anchoring proteins may contribute to this activation deficit. We discuss also modifications of the PKC system in Alzheimer's disease that may be related to pathological alterations in neurotransmission. A better insight of the different factors controlling brain-PKC activation may be important not only for elucidating the molecular basis of neuronal transmission, but also for identifying new approaches for correcting or even preventing age-dependent changes in brain function.     

Age differences of event-related potentials in the perception of successive and spatial components of auditory information

The perception of spatial and successive contexts of auditory information develops during child ontogeny. We compared event-related potentials (ERPs) recorded in 5- to 6-year-old children (N = 15) and adults (N = 15) in response to a digital series with omitted digits to explore age differences in the perception of successive auditory information. In addition, ERPs in response to the sound of a falling drop presented binaurally were obtained to examine the spatial content of auditory information. The ERPs obtained from the omitted digits significantly differed in the amplitude and latency of the N200 and P300 components between adults and children, which supports the hypothesis that the perception of a successive auditory structure is less automatic in children compared to adults. Although no significant differences were found in adults, the sound of a falling drop presented to the left ears of children elicited ERPs with earlier latencies and higher amplitudes of the P300 and N400 components in the right temporal area. Stimulation of the right ear caused an increasing amplitude of the N100 component in children. Thus, the observed differences in the auditory ERPs of children and adults reflect developmental changes in the perception of spatial and successive auditory information.     

Selective attention and memory: evoked potentials in visual and auditory verbal competition

The brain mechanisms of the selective verbal attention were studied using evoked potential (EP) technique. It was shown that the late "cognitive" EP components (400-800 ms) related to memory function were more positive to the words presented via a relevant sensory channel and more negative to irrelevant words. The hypothesis is advanced that words delivered via two competing sensory channels, such as visual and auditory, are perceived, i.e., the subject sees and hears them. However, irrelevant signals are not stored in episodic memory due to the active inhibition of the information transmission to the hippocampal structures.     

Short- and middle-latency auditory evoked potentials in abstinent chronic alcoholics: preliminary findings

Short- and middle-latency auditory evoked potentials (BAEPs and MAEPs) were studied in 15 chronic alcoholic patients after 1 month's abstinence and compared with those of 15 healthy controls, matching the patients pairwise for sex and age. Most of the parameters studied varied more within the alcoholic group than within the control group. The BAEP results agree with previous reports; in the alcoholic group, BAEP peak V was significantly delayed and the inter-peak intervals, III–V and I–V, were lengthened. The latencies of the MAEP components Na and Pa, on the other hand, were significantly shortened. These findings suggest that chronic abusive consumption of alcohol may bring about structural and/or neurochemical alterations at various levels in the auditory pathway.     

Mismatch negativity in the auditory event-related potentials in response to abrupt and smooth displacements of virtual sound source

The work investigated event-related potentials, mismatch negativity (MMN), and P3a component under dichotic stimulation with deviant stimuli simulating abrupt or smooth displacement of auditory images to the left or to the right from the head midline by means of interaural time delay introduced into the deviant stimuli. Repetitive standard stimuli were localized near the head midline. All deviant stimuli elicited mismatch negativity and P3a component. It was shown the MMN for smooth deviant motion was lower than that for the abrupt deviant displacement. MMN amplitude for both deviant types obviously depended on interaural time delay, which confirms that MMN might be considered as a measure of the auditory system spatial discriminative ability. The P3a component demonstrated the same amplitude dependences as the MMN. The results obtained are discussed in respect to manifestation of the processes underlying the auditory motion detection in the event-related potentials.     

Gender differences in chemosensory perception and event-related potentials

The present study investigated chemosensory gender differences by means of ratings of total nasal chemosensory intensity, unpleasantness and sensory irritation and simultaneous recordings of chemosensory event-related potentials (CSERPs) for three concentrations of the olfactory/trigeminal stimulus pyridine in 19 women and 17 men, all young adults. Results show that, compared to men, women gave higher intensity and unpleasantness ratings, in particular for the highest stimulus concentration. The gender differences in perceived intensity are reflected in the signal-to-noise ratio of the individual CSERP averages, revealing more identifiable early components (P1, N1) in women than in men. The late positive component, labeled P2/P3, displayed larger amplitudes at all electrode sites and shorter latencies at Cz, in women compared to men. The effects of increased pyridine concentration on perception (larger in women) and CSERPs (similar across gender) imply that the two measures involve partially different neural processing. CSERP component identifiability is proposed here as a general means of assessing signal-to-noise ratio of the CSERPs.     

Brainstem auditory evoked potentials in the rabbit.

Eight white New Zealand rabbits were submitted to auditory stimulation in order to obtain normative BAEP parameters. A monaural alternating 0.1 ms click stimulation at 20 Hz, 90 dB was used. Two series of 1000 responses were averaged (10 ms time-base, 160-3000 Hz band-pass) and highly reproducible peaks were obtained. Peaks P1, P2, P3, P4 were obtained in all ipsilateral recordings, whereas peak P5 was detectable in only 6 animals. In contralateral recordings P1 was absent and the following peaks were similar to those of ipsilateral recordings. Normative values of absolute and interpeak latencies, peak amplitudes and amplitude ratios were obtained. The procedure was repeated 24 hours after basal recordings and measures of test-retest variability were obtained.     

Auditory event-related potentials and brain dysfunction in sleep apnea

Auditory event-related potentials (ERPs) were recorded from 14 subjects with obstructive sleep apnea (OSA) before and after treatment with nasal continuous positive airway pressure (nCPAP). After 2 nights of treatment, there was dramatic improvement in the sleep patterns of the OSA patients, improvements in measures of apnea severity and oxygenation, and decrease in daytime sleepiness. The results of neuropsychological tests of a broad range of cognitive functions failed to confirm the patients' subjective reports of improvement in psychological functioning after treatment. The latencies of the N2 and P3 components were significantly prolonged prior to treatment, and there was a trend towards smaller N2 and P3 amplitude in the apneic subjects. The latency of P3 (but not N2) changed with treatment, decreasing almost to normative values. The results suggest that ERPs may be useful in documenting neural dysfunction in patients with OSA, in evaluating treatment efficacy, and possibly in determining the causes of the daytime symptoms of OSA.     

Reactivity and event-related potentials during attentional tests in athletes

A series of attentional tests involving reaction times (RTs) was administered to 12 high-level young (age 17-18 years) volleyball players. During the tests, event-related potentials were recorded by electroencephalogram. In a simple reaction-time test (SRT), the subjects had to respond to a letter that appeared on a white screen. Other tests (attentional shifting tests) consisted of a go/no-go reaction time and a choice reaction time (CRT), divided into a short-latency CRT and a long-latency CRT. In the pre-stimulus period of these tests, there is a shift from broad attention to selective attention, represented by a crowding of black points on the computer screen, followed by the appearance of a letter in the centre of the crowding. The results show that RT increased from SRT to CRT. In the attentional shifting tests, averaged waves of event-related potentials showed a contingent-negative-variation-like wave that was closely related to selective attention (selective attention wave, SAW) before the onset of the stimulus. After the stimulus, a P3 complex was recorded. Correlations were found between the SAW amplitude and P3 latency and amplitude, and between these parameters and RT and its variability. Higher SAW and P3 amplitudes were accompanied by a shorter RT and a lower variability. The characteristics and the correlations that exist between the various parameters are consistent with a possible use of these tests in the analysis of the attentional styles of athletes, and in the evaluation of their progress with training.