Teija Kujala

The mismatch negativity in cognitive and clinical neuroscience: Theoretical and methodological considerations

Mismatch negativity (MMN) component of the event-related brain potentials has become popular in cognitive and clinical brain research during the recent years. It is an early response to a violation of an auditory rule such as an infrequent change in the physical feature of a repetitive sound. There is a lot of evidence on the association of the MMN parameters and behavioral discrimination ability, although this relationship is not always straight-forward. Since the MMN reflects sound discrimination accuracy, it can be used for probing how well different groups of individuals perceive sound differences, and how training or remediation affects this ability. In the present review, we first introduce some of the essential MMN findings in probing sound discrimination, memory, and their deficits. Thereafter, issues which need to be taken into account in MMN investigations as well as new improved recording paradigms are discussed.

Auditory processing that leads to conscious perception: A unique window to central auditory processing opened by the mismatch negativity and related responses

In this review, we will present a model of brain events leading to conscious perception in audition. This represents an updated version of Näätänens previous model of automatic and attentive central auditory processing. This revised model is mainly based on the mismatch negativity (MMN) and N1 indices of automatic processing, the processing negativity (PN) index of selective attention, and their magnetoencephalographic (MEG) and functional magnetic resonance imaging (fMRI) equivalents. Special attention is paid to determining the neural processes that might underlie conscious perception and the borderline between automatic and attention-dependent processes in audition.

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.

Plastic neural changes and reading improvement caused by audiovisual training in reading-impaired children

This study aimed at determining whether audiovisual training without linguistic material has a remediating effect on reading skills and central auditory processing in dyslexic children. It was found that this training resulted in plastic changes in the auditory cortex, indexed by enhanced electrophysiological mismatch negativity and faster reaction times to sound changes. Importantly, these changes were accompanied by improvement in reading skills. The results indicate that reading difficulties can be ameliorated by special training programs and, further, that the training effects can be observed in brain activity. Moreover, the fact that the present training effects were obtained by using a program including no linguistic material indicates that dyslexia is at least partly based on a general auditory perceptual deficit.

Memory traces for words as revealed by the Mismatch Negativity

Brain responses to the same spoken syllable completing a Finnish word or a pseudo-word were studied. Native Finnish-speaking subjects were instructed to ignore the sound stimuli and watch a silent movie while the mismatch negativity (MMN), an automatic index of experience-dependent auditory memory traces, was recorded. The MMN to each syllable was larger when it completed a word than when it completed a pseudo-word. This enhancement, reaching its maximum amplitude at about 150 ms after the words recognition point, did not occur in foreign subjects who did not know any Finnish. These results provide the first demonstration of the presence of memory traces for individual spoken words in the human brain. Using whole-head magnetoencephalography, the major intracranial source of this word-related MMN was found in the left superior temporal lobe.

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.

The discrimination of and orienting to speech and non-speech sounds in children with autism.

The present study aimed to find out how different stages of cortical auditory processing (sound encoding, discrimination, and orienting) are affected in children with autism. To this end, auditory event-related potentials (ERP) were studied in 15 children with autism and their controls. Their responses were recorded for pitch, duration, and vowel changes in speech stimuli, and for corresponding changes in the non-speech counterparts of the stimuli, while the children watched silent videos and ignored the stimuli. The responses to sound repetition were diminished in amplitude in the children with autism, reflecting impaired sound encoding. The mismatch negativity (MMN), an ERP indexing sound discrimination, was enhanced in the children with autism as far as pitch changes were concerned. This is consistent with earlier studies reporting auditory hypersensitivity and good pitch-processing abilities, as well as with theories proposing enhanced perception of local stimulus features in individuals with autism. The discrimination of duration changes was impaired in these children, however. Finally, involuntary orienting to sound changes, as reflected by the P3a ERP, was more impaired for speech than non-speech sounds in the children with autism, suggesting deficits particularly in social orienting. This has been proposed to be one of the earliest symptoms to emerge, with pervasive effects on later development.

Cross-modal reorganization of human cortical functions

Recent technological development has opened fascinating opportunities in research on cognitive functions of the human brain. For example, cortical representations of sensory functions and their reorganization, which have been studied thoroughly in animals, are far better understood in humans now than they were only a decade ago. Hemodynamic and electromagnetic studies have demonstrated that a modality-specific brain area that is totally deprived of its normal sensory input becomes responsive to stimulation of other modalities. The functional significance of this cross-modal activation was recently indicated by, for example, studies showing that the occipital cortex of the blind is activated by sound changes, when the task is to detect these changes. Moreover, trans-cranial magnetic stimulation applied to the occipital cortex of blind individuals results in distortions and omissions of letters in Braille text being read by the subject. Contrary to prevailing views, cross-modal neural reorganization might, as shown by recent results, take place even in the mature human brain.

Visual cortex activation in blind humans during sound discrimination

We used a whole-scalp magnetometer with 122 planar gradiometers to study the activity of the visual cortex of five blind humans deprived of visual input since early infancy. Magnetic responses were recorded to pitch changes in a sound sequence when the subjects were either counting these changes or ignoring the stimuli. In two of the blind subjects, magnetic resonance images were also obtained, showing normal visual cortex macroanatomy. In these subjects, the magnetic responses to counted pitch changes were located at visual and temporal cortices whereas ignored pitch changes activated the temporal cortices almost exclusively. Also in two of the other three blind, the visual-cortex activation was detectable in the auditory counting task. Our results suggest that the visual cortex of blind humans can participate in auditory discrimination.

Basic auditory dysfunction in dyslexia as demonstrated by brain activity measurements

Although the generality of dyslexia and its devastating effects on the individuals life are widely acknowledged, its precursors and associated neural mechanisms are poorly understood. One of the two major competing views maintains that dyslexia is based primarily on a deficit in linguistic processing, whereas the other view suggests a more general processing deficit, one involving the perception of temporal information. Here we present evidence in favor of the latter view by showing that the neural discrimination of temporal information within complex tone patterns fails in dyslexic adults. This failure can be traced to early cortical mechanisms that process auditory information independently of attention.