Auditory discrimination after left-hemisphere stroke: a mismatch negativity follow-up study

Electrophysiological Changes in Patients with Post-stroke Aphasia: A Systematic Review

Background Magnetoencephalography (MEG) and electroencephalography (EEG) record two main types of data: continuous measurements at rest or during sleep, and event-related potentials/evoked magnetic fields (ERPs/EMFs) that involve specific and repetitive tasks. In this systematic review, we summarized longitudinal studies on recovery from post-stroke aphasia that used continuous or event-related temporal imaging (EEG or MEG). Methods We searched PubMed and Scopus for English articles published from 1950 to May 31, 2022. Results 34 studies were included in this review: 11 were non-interventional studies and 23 were clinical trials that used specific rehabilitation methods, neuromodulation, or drugs. The results of the non-interventional studies suggested that poor language recovery was associated with slow-wave activity persisting over time. The results of some clinical trials indicated that behavioral improvements were correlated with significant modulation of the N400 component. Discussion Compared with continuous EEG, ERP/EMF may more reliably identify biomarkers of therapy-induced effects. Electrophysiology should be used more often to explore language processes that are impaired after a stroke, as it may highlight treatment challenges for patients with post-stroke aphasia.

Structural Changes in the Arcuate Fasciculus and Recovery of Post-stroke Aphasia: A 6-Month Follow-up Study using Diffusion Tensor Imaging

BACKGROUND

Temporal changes in the structural connectivity of major language tracts after stroke and their contribution to aphasia recovery are unclear.

OBJECTIVE

To investigate longitudinal arcuate fasciculus (AF) integrity changes and their relationship with post-stroke aphasia recovery using diffusion tensor imaging (DTI).

METHODS

Thirty-five patients with aphasia due to first-ever left hemispheric stroke underwent the Korean version of the Western Aphasia Battery and DTI at 1- and 6-month post stroke onset. Fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), and axial diffusivity (AD) of both AF tracts were analyzed to evaluate the temporal changes in tract integrity and determine the correlation between changes (Δ; follow-up - initial) in DTI parameters and language scores.

RESULTS

At 6 months post-stroke, the mean FA decreased, and mean MD and RD increased in both hemispheres; however, compared with mean AD observed after 1 month, the mean observed at 6 months increased only in the left hemisphere (P < .05). ΔFA of the left AF and proportional change in the aphasia quotient showed a significant positive correlation (r = 0.365, P = .031). No correlation was found between changes in the right AF parameters and language score. The group with increased FA in the left AF showed more significant language improvement than the group with decreased FA.

CONCLUSIONS

During the subacute stage, the integrity of AF decreased in both hemispheres in patients with aphasia, and the change in structural connectivity of the left AF was associated with language improvement.

Electrophysiologic evidence of reorganization in poststroke aphasia

Electrophysiologic methods have been used to investigate neural changes in individuals with poststroke aphasia. The major types of electrophysiologic measures include the event-related potential (ERP) and spectral power, and aspects of both (including amplitude, topography, and power) have been shown to differ in people with aphasia. Not only that, these measures are sensitive to spontaneous and treatment-induced language change. The purpose of this chapter is to review evidence of poststroke reorganization in the language network that has been identified in the acute and chronic phases of poststroke aphasia. The chapter will begin with a brief introduction to electrophysiologic methods and then focus on evidence from the most commonly studied ERPs and spectral bands in aphasia.

The role and use of event-related potentials in aphasia: A scoping review

Event-related potentials (ERPs) can provide important insights into underlying language processes in both unimpaired and neurologically impaired populations and may be particularly useful in aphasia. This scoping review was conducted to provide a comprehensive summary of how ERPs have been used with people with aphasia (PWA), with the goal of exploring the potential clinical application of ERPs in aphasia assessment and treatment. We identified 117 studies that met inclusionary criteria, reflecting six thematic domains of inquiry that relate to understanding both unimpaired and aphasic language processing and the use of ERPs with PWA. In these studies, a wide variety of ERP components were reported. Inconsistencies in reporting of participant characteristics and study protocols limit our ability to generalize beyond the individual studies and understand implications for clinical applicability. We discuss the potential roles of ERPs in aphasia management and make recommendations for further developing ERPs for clinical utility in PWA.

The Electrophysiological Correlates of Phoneme Perception in Primary Progressive Aphasia: A Preliminary Case Series

Aims: This study aimed to investigate phoneme perception in patients with primary progressive aphasia (PPA) by using the event-related potential (ERP) technique. These ERP components might contribute to the diagnostic process of PPA and its clinical variants (NFV: nonfluent variant, SV: semantic variant, LV: logopenic variant) and reveal insights about phoneme perception processes in these patients.

Method: Phoneme discrimination and categorization processes were investigated by the mismatch negativity (MMN) and P300 in eight persons with early- and late-stage PPA (3 NFV, 2 LV, 2 SV, and 1 PPA-NOS; not otherwise specified) and 30 age-matched healthy adults. The mean amplitude, the onset latency, and the topographic distribution of both components in each patient were compared to the results of the control group.

Results: The MMN was absent or the onset latency of the MMN was delayed in the patients with the NFV, LV, and PPA-NOS in comparison to the control group. In contrast, no differences in mean amplitudes and onset latencies of the MMN were found between the patients with the SV and the control group. Concerning the P300, variable results were found in the patients with the NFV, SV, and PPA-NOS, but the P300 of both patients with the LV was delayed and prolonged with increased mean amplitude in comparison to the control group.

Conclusion: In this preliminary study, phoneme discrimination deficits were found in the patients with the NFV and LV, and variable deficits in phoneme categorization processes were found in all patients with PPA. In clinical practice, the MMN might be valuable to differentiate the SV from the NFV and the LV and the P300 to differentiate the LV from the NFV and the SV. Further research in larger and independent patient groups is required to investigate the applicability of these components in the diagnostic process and to determine the nature of these speech perception deficits in the clinical variants of PPA.

Te.M.P.O., an app for using temporal musical mismatch in post-stroke neurorehabilitation: A preliminary randomized controlled study

BACKGROUND: Recently, the potential rehabilitation value of music has been examined and music-based interventions and techniques such as the Negative Mismatch (MMN) have been increasingly investigated in the neurological rehabilitation context. OBJECTIVE: The aim of this study was to investigate the effectiveness of a negative mismatch-based therapy on the disability and quality of life in patients with stroke in sub-acute phase. METHODS: Thirty patients with a stroke diagnosis in sub-acute phase were randomly assigned to one of two groups: Mismatch (Mg) or Control (CTRLg) group. Both groups used an innovative Android application: Temporal Musical Patterns Organisation (Te.M.P.O). The Disability Rating Scale (DRS), the Modified Barthel Index (MBI) and the Stroke Specific Quality of Life scale (SSQoL) were used at the baseline (T0) and after four weeks of training (T1), in order to assess changes over time. RESULTS: Statistical analysis was performed using the data of 24 (Mg = 12, CTRLg = 12) subjects. The results show a major improvement of the Mg with respect to the CTRLg in all clinical scales score. CONCLUSION: The temporal negative mismatch-based therapy performed with the Te.M.P.O. application could be useful in improving the disability and the quality of life in stroke survivors in a sub-acute phase.

Markers for the central serotonin system correlate to verbal ability and paralinguistic social voice processing in autism spectrum disorder

Impairment in verbal communication abilities has been reported in autism spectrum disorder (ASD). Dysfunction of the serotonergic system has also been reported in ASD. However, it is still unknown how the brain serotonergic system relates to impairment in verbal communication abilities in individuals with ASD. In the present study, we investigated the correlation between brain serotonergic condition and brain sensitivity to paralinguistic stimuli (i.e., amplitude in the human voice prosodic change-evoked mismatch field) measured by magnetoencephalography (MEG) or verbal ability in 10 adults with ASD. To estimate the brain serotonergic condition, we measured the serotonin transporter nondisplaceable binding potential cerebrum-wide using positron emission tomography with [11C]N,N-dimethyl-2-(2-amino-4-cyanophenylthio)benzylamine ([11C] DASB). The results demonstrated a significant positive correlation between brain activity to paralinguistic stimuli and brain serotonin transporter binding potential in the left lingual gyrus, left fusiform gyrus and left calcarine cortex. In addition, there were significant positive correlations between verbal ability and serotonergic condition in the right anterior insula, right putamen and right central operculum. These results suggested that the occipital cortex is implicated in recognition of the prosodic change in ASD, whereas the right insula-involved serotonergic system is important in nurturing verbal function in ASD.Trial registration: UMIN000011077.

The sensitivity of event-related potentials/fields to logopedic interventions in patients with stroke-related aphasia

Recovery of stroke-related aphasia can be affected by language therapy in the early and chronic stage. Objectively monitoring therapy-induced neuroplasticity is possible by several measurement techniques including electro- and magneto-encephalography. The obtained event-related potentials (ERPs) and fields (ERFs) provide insights into the neural basis of intact or deficient language processing with milliseconds precision. In this literature review, we highlight the sensitivity of ERPs and ERFs to logopedic interventions by providing an overview of therapy-induced changes in the amplitude, latency and topography of early and mid-to-late components.

Neurophysiological predictors of aphasia recovery in patients with large left-hemispheric infarction

Background:

Although the rehabilitation of aphasia has been extensively studied, the prediction of language outcome still has not received sufficient attention. The aim of this study was to predict the language outcome using mismatch negativity (MMN) in patients with large left-hemispheric infarction.

Methods:

MMN was elicited by an oddball paradigm in which a standard tone (1000 Hz) and deviant tone (1500 Hz) were presented at 90% and 10% of the number of tones, respectively. The mean amplitudes and laterality indexes (LIs) of MMN were measured over the prefrontal, frontal, central, parietal, temporal, and perisylvian electrodes and both hemispheres during the first 7 days (session 1) and 10 to 20 days (session 2) post-onset. Mixed three-way analysis of variance (ANOVA) was used to investigate differences in these factors between two aphasia groups (the good recovery group and poor recovery group). The predictive value of the most significant LI was also compared with the score of National Institutes of Health Stroke Scale score and low-density volume on computed tomography.

Results:

A total of 18 patients were enrolled in this study. Mixed three-way ANOVA showed no interaction effect of session × region of interest (ROI) × group (F [3.59, 57.38] = 1.301, P = 0.282) and no interaction effect of ROI × group (F [1.81, 29.01] = 0.71, P = 0.487) and session × group (F [1.00, 16.00] = 0.084, P = 0.776) for MMN amplitude. No interaction effect of session × ROI × group (F [1.79, 28.58] = 0.62, P = 0.530), but an interaction effect of session × group (F [1.00, 16.00] = 5.21, P = 0.036) was found for LIs. In the poor recovery group, the LIs of MMN over all the ROIs, except the parietal area, became more negative at session 2 than those at session 1 (P < 0.05), but this effect was not observed in the good recovery group. Additionally, significant differences were observed in the LIs at session 2 between the two groups (P < 0.05). The LI over the perisylvian area at session 2 had the highest predictive value with an area under the curve of 0.963 (95% confidence interval: 0.884–1.000). An LI score >−0.36 over the perisylvian area suggested good recovery, but a score <−0.36 suggested poor recovery. The LI cut-off value of −0.36 had the highest sensitivity (90.0%) and specificity (87.5%) for predicting a good language outcome at 3 months post-stroke.

Conclusion:

LIs of MMN amplitudes at approximately 2 weeks post left-hemisphere stroke serve as more sensitive predictors of language outcome, among which the LI over the perisylvian area exhibits the best predictive value.

Disrupted brain connectivity networks in acute ischemic stroke patients

Neuroimaging studies have shown that local brain lesions could result in abnormal information transfer far from the lesion site in acute ischemic stroke (AIS) patients; yet, little is known about alternations of the topological organization of whole-brain networks in AIS. By using resting state functional magnetic resonance imaging (MRI) and graph theory analysis, we systematically investigated the topological properties of the functional brain networks of 28 healthy controls (HC, age: 56.9 ± 0.45 years) and 29 AIS (age: 57.6 ± 0.21 years) with proximal anterior circulation occlusion within 12 h of symptom onset. In our results, both the AIS and HC groups exhibited small-world network organization, suggesting a functional balance between local specialization and global integration. However, compared with the HC, the AIS patients had a lower shortest path length and higher global efficiency, indicating a tendency of randomization in patients' functional brain networks. The AIS patients had an increased nodal degree in the precuneus (PCUN), middle frontal gyrus (MFG), medial part of the superior frontal gyrus (SFGmed), orbital part of the middle frontal gyrus, and the opercular part of the inferior frontal gyrus, and increased nodal efficiency in the PUCN, MFG, SFGmed, and the angular gyrus. The decreased nodal degree in AIS was found in the heschl gyrus (HES), and no significant decreased nodal efficiency was observed. The dysfunctional connections were mainly concentrated in the HES and prefrontal cortex. Furthermore, the altered nodal centrality of the MFG and abnormal functional connectivity in AIS were associated with patients' Mini-Mental State Examination scores. These results suggested that interrupted functional connectivity in language system organization after focal brain lesions could also result in disruptions in the topological organization of other brain circuits, and this may contribute to disturbances in cognition in AIS patients.

Electrophysiological evidence for pre-attention information processing improvement in patients with central hemiplegic after peripheral nerve rewiring: a pilot study

Central neurologic injury (CNI) causes dysfunctions not only in limbs but also in cognitive ability. We applied a novel peripheral nerve rewiring (PNR) surgical procedure to restore limb function. Here, we conducted a prospective study to develop estimates for the extent of preattentive processes to cognitive function changes in CNI patients after PNR. Auditory mismatch negativity (MMN) was measured in CNI patients who received the PNR surgery plus conventional rehabilitation treatment. During the 2-year follow-up, the MMN was enhanced with increased amplitude in the PNR plus rehabilitation group compared to the rehabilitation-only group as the experiment progressed, and progressive improvement in behavioural examination tests was also observed. Furthermore, we found a significant correlation between the changes in Fugl-Meyer assessment scale scores and in MMN amplitudes. These results suggested that PNR could affect the efficiency of pre-attention information processing synchronously with the recovery of motor function in the paralyzed arm of the in chronic CNI patients. Such electroencephalographic measures might provide a biological approach with which to distinguish patient subgroups after surgery, and the change in MMN may serve as an objective auxiliary index, indicating the degree of motor recovery and brain cognitive function.

Ultra-rapid access to words in chronic aphasia: the effects of intensive language action therapy (ILAT)

Effects of intensive language action therapy (ILAT) on automatic language processing were assessed using Magnetoencephalography (MEG). Auditory magnetic mismatch negativity (MMNm) responses to words and pseudowords were recorded in twelve patients with chronic aphasia before and immediately after two weeks of ILAT. Following therapy, Patients showed significant clinical improvements of auditory comprehension as measured by the Token Test and in word retrieval and naming as measured by the Boston Naming Test. Neuromagnetic responses dissociated between meaningful words and meaningless word-like stimuli ultra-rapidly, approximately 50 ms after acoustic information first allowed for stimulus identification. Over treatment, there was a significant increase in the left-lateralisation of this early word-elicited activation, observed in perilesional fronto-temporal regions. No comparable change was seen for pseudowords. The results may reflect successful, therapy-induced, language restitution in the left hemisphere.

Task instructions modulate the attentional mode affecting the auditory MMN and the semantic N400

Event-related potentials (ERPs) have been proven to be a useful tool to complement clinical assessment and to detect residual cognitive functions in patients with disorders of consciousness. These ERPs are often recorded using passive or unspecific instructions. Patient data obtained this way are then compared to data from healthy participants, which are usually recorded using active instructions. The present study investigates the effect of attentive modulations and particularly the effect of active vs. passive instruction on the ERP components mismatch negativity (MMN) and N400. A sample of 18 healthy participants listened to three auditory paradigms: an oddball, a word priming, and a sentence paradigm. Each paradigm was presented three times with different instructions: ignoring auditory stimuli, passive listening, and focused attention on the auditory stimuli. After each task, the participants indicated their subjective effort. The N400 decreased from the focused task to the passive task, and was extinct in the ignore task. The MMN exhibited higher amplitudes in the focused and passive task compared to the ignore task. The data indicate an effect of attention on the supratemporal component of the MMN. Subjective effort was equally high in the passive and focused tasks but reduced in the ignore task. We conclude that passive listening during EEG recording is stressful and attenuates ERPs, which renders the interpretation of the results obtained in such conditions difficult.

Mismatch negativity (MMN) as an index of cognitive dysfunction

Cognition is often affected in a variety of neuropsychiatric, neurological, and neurodevelopmental disorders. The neural discriminative response, reflected in mismatch negativity (MMN) and its magnetoencephalographic equivalent (MMNm), has been used as a tool to study a variety of disorders involving auditory cognition. MMN/MMNm is an involuntary brain response to auditory change or, more generally, to pattern regularity violation. For a number of disorders, MMN/MMNm amplitude to sound deviance has been shown to be attenuated or the peak-latency of the component prolonged compared to controls. This general finding suggests that while not serving as a specific marker to any particular disorder, MMN may be useful for understanding factors of cognition in various disorders, and has potential to serve as an indicator of risk. This review presents a brief history of the MMN, followed by a description of how MMN has been used to index auditory processing capability in a range of neuropsychiatric, neurological, and neurodevelopmental disorders. Finally, we suggest future directions for research to further enhance our understanding of the neural substrate of deviance detection that could lead to improvements in the use of MMN as a clinical tool.

A stroke patient with impairment of auditory sensory (echoic) memory

A 42-year-old man suffered damage to the left supra-sylvian areas due to a stroke and presented with verbal short-term memory (STM) deficits. He occasionally could not recall even a single syllable that he had heard one second before. A study of mismatch negativity using magnetoencephalography suggested that the duration of auditory sensory (echoic) memory traces was reduced on the affected side of the brain. His maximum digit span was four with auditory presentation (equivalent to the 1st percentile for normal subjects), whereas it was up to six with visual presentation (almost within the normal range). He simply showed partial recall in the digit span task, and there was no self correction or incorrect reproduction. From these findings, reduced echoic memory was thought to have affected his verbal short-term retention. Thus, the impairment of verbal short-term memory observed in this patient was "pure auditory" unlike previously reported patients with deficits of the phonological short-term store (STS), which is the next higher-order memory system. We report this case to present physiological and behavioral data suggesting impaired short-term storage of verbal information, and to demonstrate the influence of deterioration of echoic memory on verbal STM.

The right hemisphere supports but does not replace left hemisphere auditory function in patients with persisting aphasia

In this study, we used magnetoencephalography and a mismatch paradigm to investigate speech processing in stroke patients with auditory comprehension deficits and age-matched control subjects. We probed connectivity within and between the two temporal lobes in response to phonemic (different word) and acoustic (same word) oddballs using dynamic causal modelling. We found stronger modulation of self-connections as a function of phonemic differences for control subjects versus aphasics in left primary auditory cortex and bilateral superior temporal gyrus. The patients showed stronger modulation of connections from right primary auditory cortex to right superior temporal gyrus (feed-forward) and from left primary auditory cortex to right primary auditory cortex (interhemispheric). This differential connectivity can be explained on the basis of a predictive coding theory which suggests increased prediction error and decreased sensitivity to phonemic boundaries in the aphasics' speech network in both hemispheres. Within the aphasics, we also found behavioural correlates with connection strengths: a negative correlation between phonemic perception and an inter-hemispheric connection (left superior temporal gyrus to right superior temporal gyrus), and positive correlation between semantic performance and a feedback connection (right superior temporal gyrus to right primary auditory cortex). Our results suggest that aphasics with impaired speech comprehension have less veridical speech representations in both temporal lobes, and rely more on the right hemisphere auditory regions, particularly right superior temporal gyrus, for processing speech. Despite this presumed compensatory shift in network connectivity, the patients remain significantly impaired.

Music listening after stroke: beneficial effects and potential neural mechanisms

Music is an enjoyable leisure activity that also engages many emotional, cognitive, and motor processes in the brain. Here, we will first review previous literature on the emotional and cognitive effects of music listening in healthy persons and various clinical groups. Then we will present findings about the short- and long-term effects of music listening on the recovery of cognitive function in stroke patients and the underlying neural mechanisms of these music effects. First, our results indicate that listening to pleasant music can have a short-term facilitating effect on visual awareness in patients with visual neglect, which is associated with functional coupling between emotional and attentional brain regions. Second, daily music listening can improve auditory and verbal memory, focused attention, and mood as well as induce structural gray matter changes in the early poststroke stage. The psychological and neural mechanisms potentially underlying the rehabilitating effect of music after stroke are discussed.

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.

Auditory and cognitive deficits associated with acquired amusia after stroke: a magnetoencephalography and neuropsychological follow-up study

Acquired amusia is a common disorder after damage to the middle cerebral artery (MCA) territory. However, its neurocognitive mechanisms, especially the relative contribution of perceptual and cognitive factors, are still unclear. We studied cognitive and auditory processing in the amusic brain by performing neuropsychological testing as well as magnetoencephalography (MEG) measurements of frequency and duration discrimination using magnetic mismatch negativity (MMNm) recordings. Fifty-three patients with a left (n = 24) or right (n = 29) hemisphere MCA stroke (MRI verified) were investigated 1 week, 3 months, and 6 months after the stroke. Amusia was evaluated using the Montreal Battery of Evaluation of Amusia (MBEA). We found that amusia caused by right hemisphere damage (RHD), especially to temporal and frontal areas, was more severe than amusia caused by left hemisphere damage (LHD). Furthermore, the severity of amusia was found to correlate with weaker frequency MMNm responses only in amusic RHD patients. Additionally, within the RHD subgroup, the amusic patients who had damage to the auditory cortex (AC) showed worse recovery on the MBEA as well as weaker MMNm responses throughout the 6-month follow-up than the non-amusic patients or the amusic patients without AC damage. Furthermore, the amusic patients both with and without AC damage performed worse than the non-amusic patients on tests of working memory, attention, and cognitive flexibility. These findings suggest domain-general cognitive deficits to be the primary mechanism underlying amusia without AC damage whereas amusia with AC damage is associated with both auditory and cognitive deficits.

Music and Speech Listening Enhance the Recovery of Early Sensory Processing after Stroke

Our surrounding auditory environment has a dramatic influence on the development of basic auditory and cognitive skills, but little is known about how it influences the recovery of these skills after neural damage. Here, we studied the long-term effects of daily music and speech listening on auditory sensory memory after middle cerebral artery (MCA) stroke. In the acute recovery phase, 60 patients who had middle cerebral artery stroke were randomly assigned to a music listening group, an audio book listening group, or a control group. Auditory sensory memory, as indexed by the magnetic MMN (MMNm) response to changes in sound frequency and duration, was measured 1 week (baseline), 3 months, and 6 months after the stroke with whole-head magnetoencephalography recordings. Fifty-four patients completed the study. Results showed that the amplitude of the frequency MMNm increased significantly more in both music and audio book groups than in the control group during the 6-month poststroke period. In contrast, the duration MMNm amplitude increased more in the audio book group than in the other groups. Moreover, changes in the frequency MMNm amplitude correlated significantly with the behavioral improvement of verbal memory and focused attention induced by music listening. These findings demonstrate that merely listening to music and speech after neural damage can induce long-term plastic changes in early sensory processing, which, in turn, may facilitate the recovery of higher cognitive functions. The neural mechanisms potentially underlying this effect are discussed.

Event-related potentials in clinical research: guidelines for eliciting, recording, and quantifying mismatch negativity, P300, and N400

This paper describes recommended methods for the use of event-related brain potentials (ERPs) in clinical research and reviews applications to a variety of psychiatric and neurological disorders. Techniques are presented for eliciting, recording, and quantifying three major cognitive components with confirmed clinical utility: mismatch negativity (MMN), P300, and N400. Also highlighted are applications of each of the components as methods of investigating central nervous system pathology. The guidelines are intended to assist investigators who use ERPs in clinical research, in an effort to provide clear and concise recommendations and thereby to standardize methodology and facilitate comparability of data across laboratories.

Increased cognitive functioning in symptomatic Huntington's disease as revealed by behavioral and event-related potential indices of auditory sensory memory and attention

Cognitive functions are thought to deteriorate globally in late stages of various neurodegenerative disorders. Here we describe that this general assumption is not justified and fails in Huntington's disease (HD). Presymptomatic gene mutation carriers (pHDs) and healthy controls performed worse compared with symptomatic HDs in an auditory signal detection task. During task performance, behavioral data and event-related potentials (ERPs) [i.e., MMN (mismatch negativity), P3a, and RON (reorienting negativity)] were recorded. Not only behavioral performance but also neurophysiological correlates of auditory sensory memory and attentional reorientation indicate enhanced performance occurring primal in late stages of a neurodegenerative disorder. Increased activity of the NMDA-receptor system, an assumed pathogenic mechanism in HD, might facilitate signal propagation at striatal level that enables more efficient task execution through a winner-take-all process. The results challenge the view that late stage neurodegeneration is necessarily related to a global decline in cognitive abilities in HD. In contrast, selectively enhanced cognitive functioning can emerge together with otherwise impaired cognitive functioning.

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.

Plastic Phase-Locking and Magnetic Mismatch Response to Auditory Deviants in Temporal Lobe Epilepsy

The magnetic equivalent (MMNm) of mismatch negativity may reflect auditory discrimination and sensory memory. To study whether temporal lobe epilepsy (TLE) affects automatic central auditory-change processing, we recorded magnetoencephalographic (MEG) responses to standard and duration-deviant sounds in 12 TLE patients and 12 age-matched controls, and repeated MEG measurement in 8 patients 6-30 months following epilepsy surgery and in 6 controls 3-8 months after their first measurement. We compared the MMNm between patients and controls, and also evaluated intertrial phase coherences as indexed by phase-locking factors (PLF) using wavelet-based analyses. We observed longer MMNm latencies for patients than for controls. Dipole modeling and minimum-current estimates together showed bi-frontotemporal sources for MMNm. The phase locking across trials was dominant at the 4- to 14-Hz band, and the main difference in PLF between deviant- and standard-evoked responses occurred in the time frame of 150-250 ms after stimulus onset. Notably, in the 5 patients who became seizure free after removal of right temporal epileptic focus, the phase-locking phenomena resulting from deviant stimuli were enhanced, and even more distributed in the frontotemporal regions. We conclude that mesial TLE might affect auditory-change detection, and a successful surgery causes a possible plastic change in phase locking of deviant-evoked signals.

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.

Neurophysiological endophenotypes of schizophrenia: the viability of selected candidate measures

In an effort to reveal susceptibility genes, schizophrenia research has turned to the endophenotype strategy. Endophenotypes are characteristics that reflect the actions of genes predisposing an individual to a disorder, even in the absence of diagnosable pathology. Individual endophenotypes are presumably determined by fewer genes than the more complex phenotype of schizophrenia and would, therefore, reduce the complexity of genetic analyses. Unfortunately, despite there being rational criteria to define a viable endophenotype, the term is sometimes applied indiscriminately to characteristics that are deviant in affected individuals. Schizophrenia patients exhibit deficits in several neurophysiological measures of information processing that have been proposed as candidate endophenotypes. Successful processing of sensory inputs requires the ability to inhibit intrinsic responses to redundant stimuli and, reciprocally, to facilitate responses to less frequent salient stimuli. There is evidence to suggest that both these processes are "impaired" in schizophrenia. Measures of inhibitory failure include prepulse inhibition of the startle reflex, P50 auditory evoked potential suppression, and antisaccade eye movements. Measures of impaired deviance detection include mismatch negativity and the P300 event-related potential. The purpose of this review is to systematically evaluate the endophenotype candidacy of these key neurophysiological abilities. For each candidate, we describe typical experimental procedures, the current understanding of the underlying neurobiology, the nature of the abnormality in schizophrenia, the reliability, stability and heritability of the measure, and any reported gene associations. We conclude with a discussion of the few studies thus far that have employed a multivariate approach with these candidates.

The Role of Early Auditory Discrimination Deficits in Language Disorders

Language impairments can have a devastating effect on the individual’s life. Brain damage such as stroke may cause varying degrees of impaired language. Even milder language problems, such as developmental dyslexia or specific language impairment, can have long-lasting detrimental effects on the individual’s life, affecting both success at school as well as motivation and even self-esteem. In recent years, the mismatch negativity (MMN) has been intensively applied to study the neural basis of language impairments. These studies have shown that the MMN, which reflects the early stages of cortical sound discrimination, is abnormal in a large variety of language impairments. Furthermore, a close relationship between the MMN and some language disorders is suggested by significant correlations between the MMN and language test results. Further support is provided by follow-up studies suggesting that the MMN parameters may predict future language problems in children and by investigations indicating that intervention programs with an ameliorating effect also concurrently change the MMN. However, when interpreting the implications of MMN results it is important to acknowledge that this response specifically reflects early stages of auditory discrimination and should, therefore, be combined with measures probing the further steps of auditory processing for a more complete picture of the underlying deficits of language. The current review addresses how the MMN can be used in determining auditory impairments in language disorders such as aphasia, dyslexia, autism spectrum, and specific language impairment.

Mismatch negativity elicited by tones and speech sounds: changed topographical distribution in aphasia

This study used the event-related brain potential mismatch negativity (MMN) to investigate preconscious discrimination of harmonically rich tones (differing in duration) and consonant-vowel syllables (differing in the initial consonant) in aphasia. Eighteen Norwegian aphasic patients, examined on average 3 months after brain injury, were compared to 11 healthy controls. The main finding was a difference in topographic distribution of the MMN: the aphasia group showed a less lateralized and centralized topographic pattern especially to CV syllables, which is consistent with a reduced temporal lobe processing contribution and an increased right hemisphere activation. No correlations between MMN amplitude and aphasia test results were found.

Temporal processing and context dependency of phoneme discrimination in patients with aphasia

Standard diagnostic procedures for assessing temporal-processing abilities of adult patients with aphasia have so far not been developed. In our study, temporal-order measurements were conducted using two different experimental procedures to identify a suitable measure for clinical studies. Additionally, phoneme-discrimination abilities were tested on the word, as well as on the sentence level, as a relationship between temporal processing and phoneme-discrimination abilities is assumed. Patients with aphasia displayed significantly higher temporal-order thresholds than control subjects. The detection of an association between temporal processing and speech processing, however, depended on the stimuli and the phoneme-discrimination tasks used. Our results also suggest top-down feedback on phonemic processing.

The role of P300 in the recovery of post-stroke global aphasia

Seventeen right-handed patients suffering from global aphasia caused by a recent stroke in the left-hemisphere were studied. Passive P300 auditory event related potential paradigm was applied every months for 6 months. Aachen subtests were used for evaluating comprehension. Only a minority of the patients displayed the P300 at the baseline. Those patients had the best outcome at the Aachen comprehension subtest. Latency and amplitude changed over time in an unpredictable way. The number of patients presenting with the P300 also fluctuated, since some patients could regain the potential, whereas some other patients could lose that from month to month. Passive P300 is a monitor of recovery following global aphasia. A single passive P300 recording is useful for prognostic purposes. Repairing mechanisms in the first 6 months have a non-linear trend.

Therapy-related reorganization of language in both hemispheres of patients with chronic aphasia

The brain processes of language recovery after stroke are poorly understood, partly because past research did not allow to differentiate the effects of spontaneous restitution processes from those of learning-related cortical reorganization. Here, we use a new approach offered by recently developed intense neuropsychological therapy methods, which allow for improving language functions within a short time period. Stroke patients with chronic aphasia received intense language therapy for 2 weeks and, over this period, improved their language performance as assessed using clinical tests. Neurophysiological activity elicited by words and pseudowords was measured before and after treatment. Over the therapy interval, early word evoked potentials (latency 250-300 ms) became significantly stronger whereas pseudoword responses did not change. Word-specific changes were documented by analyses of ERP amplitudes and root mean square values, which revealed interactions of the factors Assessment time (before vs. after therapy) and Wordness (word vs. pseudoword). Source localization using Minimum Norm Current Estimates showed that bilateral cortical sources activated by word stimuli contributed to the change, suggesting that neuronal networks distributed over both hemispheres are the substrate of cortical reorganization of language processing in intense aphasia therapy. Word-evoked differences in source strengths were significantly correlated with performance on a clinical language test, demonstrating a link between behavioral and neurophysiological changes. We suggest that the early word-evoked negativity might represent an index of reorganization of language after stroke and thus an aphasia recovery potential.