Auditory sensory memory and working memory skills: Association between frontal MMN and performance scores.

OBJECTIVE: Memory is the faculty responsible for encoding, storing and retrieving information, comprising several sub-systems such as sensory memory (SM) and working memory (WM). Some previous studies exclusively using clinical population revealed associations between these two memory systems. Here we aimed at investigating the relation between modality-general WM performance and auditory SM formation indexed by magnetic mismatch negativity (MMN) responses in a healthy population of young adults. METHODS: Using magnetoencephalography (MEG), we recorded MMN amplitudes to changes related to six acoustic features (pitch, timbre, location, intensity, slide, and rhythm) inserted in a 4-tone sequence in 86 adult participants who were watching a silent movie. After the MEG recordings, participants were administered the WM primary subtests (Spatial Span and Letter Number Sequencing) of Wechsler Memory Scale (WMS). RESULTS: We found significant correlations between frontal MMN amplitudes to intensity and slide deviants and WM performance. In case of intensity, the relation was revealed in all participants, while for slide only in individuals with a musical background. CONCLUSIONS: Automatic neural responses to auditory feature changes are increased in individuals with higher visual WM performance. SIGNIFICANCE: Conscious WM abilities might be linked to pre-attentive sensory-specific neural skills of prediction and short-term storage of environmental regularities.

The neural basis of aberrant speech and audition in autism spectrum disorders.

Autism spectrum disorders (ASD) are characterized by deficits in communication and social behavior and by narrow interests. Individuals belonging to this spectrum have abnormalities in various aspects of language, ranging from semantic-pragmatic deficits to the absence of speech. They also have aberrant perception, especially in the auditory domain, with both hypo- and hypersensitive features. Neurophysiological approaches with high temporal resolution have given novel insight into the processes underlying perception and language in ASD. Neurophysiological recordings, which are feasible for investigating infants and individuals with no speech, have shown that the representation of and attention to language has an abnormal developmental path in ASD. Even the basic mechanisms for fluent speech perception are degraded at a low level of neural speech analysis. Furthermore, neural correlates of perception and some traits typical of subgroups of individuals on this spectrum have helped in understanding the diversity on this spectrum.

The mismatch negativity (MMN)--a unique window to disturbed central auditory processing in ageing and different clinical conditions.

In this article, we review clinical research using the mismatch negativity (MMN), a change-detection response of the brain elicited even in the absence of attention or behavioural task. In these studies, the MMN was usually elicited by employing occasional frequency, duration or speech-sound changes in repetitive background stimulation while the patient was reading or watching videos. It was found that in a large number of different neuropsychiatric, neurological and neurodevelopmental disorders, as well as in normal ageing, the MMN amplitude was attenuated and peak latency prolonged. Besides indexing decreased discrimination accuracy, these effects may also reflect, depending on the specific stimulus paradigm used, decreased sensory-memory duration, abnormal perception or attention control or, most importantly, cognitive decline. In fact, MMN deficiency appears to index cognitive decline irrespective of the specific symptomatologies and aetiologies of the different disorders involved.

Dose-related effects of memantine on a mismatch negativity-like response in anesthetized rats.

Memantine is a low-affinity NMDA receptor antagonist that is used in the treatment of Alzheimer's disease to alleviate the cognitive symptoms of the disease. In humans, memantine has been shown to facilitate auditory change detection as reflected in the mismatch negativity (MMN) response recorded in the frontal cortex. In the present study we investigated the effects of memantine on the auditory MMN-like responses recorded in anesthetized rats. Saline, a low (3 mg/kg) or a high (10 mg/kg) dose of memantine was i.p. injected into the animals. Auditory MMN-like responses were recorded during the presentation of a repeated tone of one frequency (standard, P=0.956) that was rarely replaced by a tone of another frequency (deviant, P=0.044). The low dose of memantine did not observably affect the amplitude of the auditory MMN-like response, but it prolonged the duration of the response relative to saline. The high dose of memantine, in contrast, blocked the generation of the auditory MMN-like response. The findings suggest that memantine may, with appropriate doses, facilitate already this early stage of auditory processing.

The perception of invariant speech features in children with autism.

We investigated whether the good pitch-discrimination abilities reported in individuals with autism have adverse effects on their speech perception by compromising their ability to extract invariant phonetic features from speech input. The MMN, a brain response reflecting sound-discrimination processes, was recorded from children with autism and their controls for phoneme-category and pitch changes in speech stimuli under two different conditions: (a) when all the other features of the standard and deviant stimuli were kept constant, and (b) when constant variation with respect to an irrelevant feature was introduced to the standard and deviant stimuli. Children with autism had enhanced MMNs for pitch changes in both conditions, as well as for phoneme-category changes in the constant-feature condition. However, when the phoneme-category changes occurred in phonemes having pitch variation, the MMN enhancement was abolished in autistic children. This suggests that children with autism lose their advantage in phoneme discrimination when the context of the stimuli is speech-like and requires abstracting invariant speech features from varying input.

The mismatch negativity (MMN) in basic research of central auditory processing: a review.

In the present article, the basic research using the mismatch negativity (MMN) and analogous results obtained by using the magnetoencephalography (MEG) and other brain-imaging technologies is reviewed. This response is elicited by any discriminable change in auditory stimulation but recent studies extended the notion of the MMN even to higher-order cognitive processes such as those involving grammar and semantic meaning. Moreover, MMN data also show the presence of automatic intelligent processes such as stimulus anticipation at the level of auditory cortex. In addition, the MMN enables one to establish the brain processes underlying the initiation of attention switch to, conscious perception of, sound change in an unattended stimulus stream.

Psychosocial stress attenuates general sound processing and duration change detection.

An EEG-compatible adaptation of the Trier Social Stress Test was developed to induce psychosocial stress in healthy subjects while investigating their auditory processing of unattended sounds and salivary levels of the stress hormone cortisol. The mismatch negativity (MMN) and N1/P2 were assessed using a multifeature paradigm, while subjects were attending to visual tasks with high or low attentional workload. Only the responses to duration change were affected by the stress manipulation. Cortisol levels during stress were inversely related to the MMN amplitudes of duration deviants. During anticipatory stress, responses to the standard tones (general sound processing) increased, but their amplitude was not correlated with cortisol levels. We found that psychosocial stressor anticipation attenuates both general and deviance-specific sound processing, suggesting that cortisol interferes with cortical memory-trace formation.

Atypical pattern of discriminating sound features in adults with Asperger syndrome as reflected by the mismatch negativity.

Asperger syndrome, which belongs to the autistic spectrum of disorders, is characterized by deficits of social interaction and abnormal perception, like hypo- or hypersensitivity in reacting to sounds and discriminating certain sound features. We determined auditory feature discrimination in adults with Asperger syndrome with the mismatch negativity (MMN), a neural response which is an index of cortical change detection. We recorded MMN for five different sound features (duration, frequency, intensity, location, and gap). Our results suggest hypersensitive auditory change detection in Asperger syndrome, as reflected in the enhanced MMN for deviant sounds with a gap or shorter duration, and speeded MMN elicitation for frequency changes.

Speech- and sound-segmentation in dyslexia: evidence for a multiple-level cortical impairment.

Developmental dyslexia involves deficits in the visual and auditory domains, but is primarily characterized by an inability to translate the written linguistic code to the sound structure. Recent research has shown that auditory dysfunctions in dyslexia might originate from impairments in early pre-attentive processes, which affect behavioral discrimination. Previous studies have shown that whereas dyslexic individuals are deficient in discriminating sound distinctions involving consonants or simple pitch changes, discrimination of other sound aspects, such as tone duration, is intact. We hypothesized that such contrasts that can be discriminated by dyslexic individuals when heard in isolation are difficult to identify when occurring within words or structurally similar complex sound patterns. In the current study, we addressed how segments of pseudo-words and their non-speech counterparts are processed in dyslexia. We assessed the detection of long-duration differences in segments of these stimuli and identified the brain processes that could be associated with the behavioral results. Consistent with previous studies, we found no early cortical sound-duration discrimination deficit in dyslexia. However, differences between impaired and non-impaired readers were found in the brain processes associated with sound-change recognition as well as in the behavioral performance. This suggests that even when the early, automatic, sound discrimination processes are intact in dyslexic individuals, deficits in the later, attention-dependent processes may lead to impaired perception of speech and other complex sounds.

Auditory perception and attention as reflected by the brain event-related potentials in children with Asperger syndrome.

OBJECTIVE: Language development is delayed and deviant in individuals with autism, but proceeds quite normally in those with Asperger syndrome (AS). We investigated auditory-discrimination and orienting in children with AS using an event-related potential (ERP) paradigm that was previously applied to children with autism. METHODS: ERPs were measured to pitch, duration, and phonetic changes in vowels and to corresponding changes in non-speech sounds. Active sound discrimination was evaluated with a sound-identification task. RESULTS: The mismatch negativity (MMN), indexing sound-discrimination accuracy, showed right-hemisphere dominance in the AS group, but not in the controls. Furthermore, the children with AS had diminished MMN-amplitudes and decreased hit rates for duration changes. In contrast, their MMN to speech pitch changes was parietally enhanced. The P3a, reflecting involuntary orienting to changes, was diminished in the children with AS for speech pitch and phoneme changes, but not for the corresponding non-speech changes. CONCLUSIONS: The children with AS differ from controls with respect to their sound-discrimination and orienting abilities. SIGNIFICANCE: The results of the children with AS are relatively similar to those earlier obtained from children with autism using the same paradigm, although these clinical groups differ markedly in their language development.

Selective tuning of cortical sound-feature processing by language experience.

In 'quantity-languages', such as Japanese or Finnish, sound duration is linguistically relevant. We showed that quantity-language speakers were superior to speakers of a non-quantity language in discriminating the duration of even non-speech sounds. In contrast, there was no group difference in the discrimination of sound frequency. This result, obtained both by behavioural and neural indices at attentive and automatic levels of processing, indicates precise feature-specific tuning of the auditory-cortex functions by the mother tongue.

Evaluation of multi-attribute auditory discrimination in dyslexia with the mismatch negativity.

OBJECTIVE: Dyslexia is associated with impairments in the phonological system or with more general auditory dysfunctions. We determined the discrimination of 5 sound contrasts (pitch, duration, intensity, location, and the presence of a gap) in dyslexia with the mismatch negativity (MMN). METHODS: We compared MMNs of 9 adult dyslexic and 11 control subjects with a new 5-deviant paradigm which enables one to assess the discrimination of each of these features in 15 min. Also, a control oddball condition with pitch and duration deviants was included. In the new paradigm, all deviant stimuli are presented in the same stimulus block so that the standard stimuli, of which there are 50%, alternate with the deviant stimuli. RESULTS: In the 5-deviant paradigm, a diminished pitch-MMN and an enhanced location-MMN were found in dyslexic individuals. Furthermore, pitch and duration MMNs in this and in the oddball paradigms suggested that smaller MMNs are elicited in the new than oddball paradigm in dyslexic subjects. CONCLUSIONS: Pitch discrimination is impaired in dyslexia. However, location discrimination, not addressed previously with MMN, is enhanced. Furthermore, dyslexic subjects are more impaired in detecting changes in sound streams with than without variation. SIGNIFICANCE: In dyslexia research, the new 5-deviant MMN paradigm is feasible and even more sensitive than the traditional oddball paradigm.

Similarities in the phenotype of the auditory neural substrate in children with Asperger syndrome and their parents.

Asperger syndrome (AS) is a developmental disorder of brain function characterized by deficits in social interaction including difficulties in understanding emotional expressions. Children with AS share some of the behavioural characteristics with their parents and AS seems to run particularly in the male members of the same families. The aim of the present study was to determine whether similarities could be found between children with AS and their parents at central auditory processing. It was found that in children with AS the sound encoding, as reflected by the exogenous components of event-related potentials, was similarly abnormal as in both their mothers and fathers. However, their abnormal cortical auditory discrimination, as indexed by the prolonged latency of the mismatch negativity, resembled that of their fathers but not that of their mothers. The present results suggest that complex genetic mechanisms may contribute to auditory abnormalities encountered in children with AS.

Neurophysiological evidence for cortical discrimination impairment of prosody in Asperger syndrome.

Asperger syndrome (AS), belonging to the autism spectrum of disorders, is one of the pervasive developmental disorders. Individuals with AS usually have normal development of formal speech but pronounced problems in perceiving and producing speech prosody. The present study addressed the discrimination of speech prosody in AS by recording the mismatch negativity (MMN) and behavioural responses to natural utterances with different emotional connotations. MMN responses were abnormal in the adults with AS in several ways. In these subjects, fewer significantly elicited MMNs, diminished MMN amplitudes, as well as prolonged latencies were found. In addition, the MMN generator loci differed between the subjects with AS and control subjects. These findings were predominant over the right cerebral hemisphere. These results show impaired neurobiological basis for speech-prosody processing at an early, pre-attentive auditory discrimination stage in AS.

Electrophysiological evidence of enhanced distractibility in ADHD children.

Abnormal involuntary attention leading to enhanced distractibility may account for different behavioral and cognitive problems in children with attention deficit hyperactivity disorder (ADHD). This was investigated in the present experiment by recording event-related brain potentials (ERPs) to distracting novel sounds during performance of a visual discrimination task. The overall performance in the visual task was less accurate in the ADHD children than in the control children, and the ADHD children had a higher number of omitted responses following novel sounds. In both groups, the distracting novel sounds elicited a biphasic P3a ERP component and a subsequent frontal Late Negativity (LN). The early phase of P3a (180-240 ms) had significantly smaller amplitudes over the fronto-central left-hemisphere recording sites in the ADHD children than in the control group presumably due to an overlapping enhanced left-hemisphere dominant negative ERP component elicited in the ADHD group. Moreover, the late phase of P3a (300-350 ms) was significantly larger over the left parietal scalp areas in the ADHD children than in the controls. The LN had a smaller amplitude and shorter latency over the frontal scalp in the ADHD group than in the controls. In conclusion, the ERP and behavioral effects caused by the novel sounds reveal deficient control of involuntary attention in ADHD children that may underlie their abnormal distractibility.

The effect of different noise types on the speech and non-speech elicited mismatch negativity.

The effect of different types of real-life noise on the central auditory processing of speech and non-speech sounds was evaluated by the means of mismatch negativity and behavioral responses. Subjects (19-34 years old; 6 males, 4 females) were presented, in separate conditions, with either speech or non-speech stimuli of approximately equal complexity in five background conditions: babble noise, industrial noise, traffic noise, wide band noise, and silent condition. Whereas there were no effects of stimuli or noise on the behavioral responses, the MMN results revealed that speech and non-speech sounds are processed differently both in silent and noisy conditions. Speech processing was more affected than non-speech processing in all noise conditions. Moreover, different noise types had a differential effect on the pre-attentive discrimination, as reflected in MMN, on speech and non-speech sounds. Babble and industrial noises dramatically reduced the MMN amplitudes for both stimulus types, while traffic noise affected only speech stimuli.

Auditory event-related potential indices of increased distractibility in children with major depression.

OBJECTIVE: Children with major depression (MD) exhibit short-term memory and concentration deficits. Using auditory event-related potentials (ERPs), we aimed to determine whether these problems could be caused by a dysfunction in auditory sensory memory, attentional orienting, or both. METHODS: The subjects were 10 treatment-naïve children with MD and 10 controls. Sound sequences, consisting of frequent stimuli (syllable /ka/, P = 0.08), infrequent deviant stimuli (/ta/, P = 0.01 ), and novel sounds ( P = 0.01 ) were played through loudspeakers while the children watched silent videos and ignored the sound stimuli. Auditory sensory memory was studied by eliciting the ERPs mismatch negativity (MMN) and late discriminative negativity (LDN), and the P3a was used as an index of involuntary attention switch. RESULTS: The children with MD had shorter MMN and LDN latencies than the controls. The late component of the P3a (lP3a) was enhanced in amplitude in the patients as compared with that in the controls. CONCLUSIONS: Auditory sensory memory appears to function normally in children with MD. However, the ERP findings indicated enhanced sensory sensitivity and attentional distractibility in these children. This increased distractibility might underlie the concentration difficulties that compromise school performance in children with MD.

Event-related potentials associated with sound discrimination versus novelty detection in children.

In children, deviant sounds in an oddball paradigm elicit a mismatch negativity (MMN) indexing discrimination of sound change and late difference negativity (LDN) with unknown functional significance. Salient sounds elicit an ERP index if orienting, P3a, and a late negative component, Nc. We compared children's responses elicited by moderate sound changes and novel sounds to examine the relationships between MMN and LDN, and LDN and Nc. Two components of the Nc, the Nc1 and Nc2, were identified. The scalp topography of LDN differed from those of the MMN and Nc1. Children's early P3a appeared mature but late P3a lacked frontal predominance. The findings suggested that LDN is not linked with either the sensory or attentional processing. It might reflect cognitive, albeit preattentive, processing of sound change. The Nc1 appears to reflect cognitive attentive processing of salient stimuli and the Nc2 might reflect reorienting after distraction.

Auditory hemodynamic studies of newborn infants using near-infrared spectroscopic imaging.

The noninvasive study of tissue blood volume and oxygenation using near-infrared light is a new and actively developing technology. We have used near-infrared spectroscopic imaging (NIRSI) to study hemodynamic responses on the auditory cortices evoked by auditory stimulation. Ten healthy newborn infants were studied. The otoacoustic emission hearing test was performed for each infant. Pulse oximetry was used to monitor the heart rate during the measurement, video recording was used to monitor motion artifacts, and the eye movements were noted in order to determine sleep stage. A 16-channel frequency-domain optical imaging system developed in our laboratory was used for NIRSI measurements. The stimuli were presented in trains of seven 1 kHz beeps with 700-ms inter-stimulus intervals. The stimulus trains were separated by 25-s silent periods in order to allow for the hemodynamic delay. In 3/8 cases, we obtained a clear bilateral increase in [HbO/sub 2/], and in two additional cases, a clear response on one hemisphere. The mean change in [HbO/sub 2/] was +0.9+/-0.9muM and the mean change in [Hb] was -0.3+/-0.4muM for those channels producing the largest response for each subject. No statistically significant response was found in 3/8 cases.

Mismatch negativity indexes auditory temporal resolution: evidence from event-related potential (ERP) and event-related field (ERF) recordings.

This study examined auditory temporal resolution as indexed by gap detection using the mismatch negativity (MMN) component of the auditory event-related potential (ERP) and its magnetic counterpart (MMNm). ERPs were recorded in 10 subjects who were presented with auditory stimuli. These stimuli were presented in sequences of repetitive continuous 'standard' sinusoidal tones interspersed with infrequently occurring 'deviant' stimuli that differed from standards only in that they contained a silent gap midway in the stimulus. The gap size varied in separate stimulus blocks and was either 3, 5 or 7 ms. The stimuli were presented monaurally either to the left or the right ear. In a separate session, event-related magnetic fields (ERFs) were recorded from eight subjects using a similar paradigm but with gap sizes of 3, 7 or 11 ms and with binaural stimulation. Both ERP and ERF recordings showed that the smallest gap size (3 ms) did not elicit as large or reliable MMN or MMNm as did the larger ones. There were no differences in the laterality of the MMN as might be predicted on the basis of previous behavioural studies, but this result is likely a reflection of differences in task requirements. Nonetheless, the findings suggest that MMN and MMNm successfully index auditory temporal resolution thresholds, as measures that are independent of attention.