161 research outputs found
Acoustic Oddball during NREM Sleep: A Combined EEG/fMRI Study
Background: A condition vital for the consolidation and maintenance of sleep is generally reduced responsiveness to external stimuli. Despite this, the sleeper maintains a level of stimulus processing that allows to respond to potentially dangerous environmental signals. The mechanisms that subserve these contradictory functions are only incompletely understood. Methodology/Principal Findings: Using combined EEG/fMRI we investigated the neural substrate of sleep protection by applying an acoustic oddball paradigm during light NREM sleep. Further, we studied the role of evoked K-complexes (KCs), an electroencephalographic hallmark of NREM sleep with a still unknown role for sleep protection. Our main results were: (1) Other than in wakefulness, rare tones did not induce a blood oxygenation level dependent (BOLD) signal increase in the auditory pathway but a strong negative BOLD response in motor areas and the amygdala. (2) Stratification of rare tones by the presence of evoked KCs detected activation of the auditory cortex, hippocampus, superior and middle frontal gyri and posterior cingulate only for rare tones followed by a KC. (3) The typical high frontocentral EEG deflections of KCs were not paralleled by a BOLD equivalent. Conclusions/Significance: We observed that rare tones lead to transient disengagement of motor and amygdala responses during light NREM sleep. We interpret this as a sleep protective mechanism to delimit motor responses and to reduce the sensitivity of the amygdala towards further incoming stimuli. Evoked KCs are suggested to originate from a brain state wit
Auditory target and novelty processing in patients with unilateral hippocampal sclerosis: A current-source density study
The capacity to respond to novel events is crucial for adapting to the constantly changing environment. Here, we recorded 29-channel Event Related Brain Potentials (ERPs) during an active auditory novelty oddball paradigm and used for the first time Current Source Density-transformed Event Related Brain Potentials and associated time-frequency spectra to study target and novelty processing in a group of epileptic patients with unilateral damage of the hippocampus (N = 18) and in healthy matched control participants (N = 18). Importantly, we used Voxel-Based Morphometry to ensure that our group of patients had a focal unilateral damage restricted to the hippocampus and especially its medial part. We found a clear deficit for target processing at the behavioral level. In addition, compared to controls, our group of patients presented (i) a reduction of theta event-related synchronization (ERS) for targets and (ii) a reduction and delayed P3a source accompanied by reduced theta and low-beta ERS and alpha event-related synchronization (ERD) for novel stimuli. These results suggest that the integrity of the hippocampus might be crucial for the functioning of the complex cortico-subcortical network involved in the detection of novel and target stimuli
Towards Optimal Testing of Auditory Memory : Methodological development of recording of the mismatch negativity (MMN) of the auditory event-related potential (ERP)
The overlapping sound pressure waves that enter our brain via the ears and auditory nerves must be organized into a coherent percept. Modelling the regularities of the auditory environment and detecting unexpected changes in these regularities, even in the absence of attention, is a necessary prerequisite for orientating towards significant information as well as speech perception and communication, for instance. The processing of auditory information, in particular the detection of changes in the regularities of the auditory input, gives rise to neural activity in the brain that is seen as a mismatch negativity (MMN) response of the event-related potential (ERP) recorded by electroencephalography (EEG). --- As the recording of MMN requires neither a subject s behavioural response nor attention towards the sounds, it can be done even with subjects with problems in communicating or difficulties in performing a discrimination task, for example, from aphasic and comatose patients, newborns, and even fetuses. Thus with MMN one can follow the evolution of central auditory processing from the very early, often critical stages of development, and also in subjects who cannot be examined with the more traditional behavioural measures of auditory discrimination. Indeed, recent studies show that central auditory processing, as indicated by MMN, is affected in different clinical populations, such as schizophrenics, as well as during normal aging and abnormal childhood development. Moreover, the processing of auditory information can be selectively impaired for certain auditory attributes (e.g., sound duration, frequency) and can also depend on the context of the sound changes (e.g., speech or non-speech).
Although its advantages over behavioral measures are undeniable, a major obstacle to the larger-scale routine use of the MMN method, especially in clinical settings, is the relatively long duration of its measurement. Typically, approximately 15 minutes of recording time is needed for measuring the MMN for a single auditory attribute. Recording a complete central auditory processing profile consisting of several auditory attributes would thus require from one hour to several hours. In this research, I have contributed to the development of new fast multi-attribute MMN recording paradigms in which several types and magnitudes of sound changes are presented in both speech and non-speech contexts in order to obtain a comprehensive profile of auditory sensory memory and discrimination accuracy in a short measurement time (altogether approximately 15 min for 5 auditory attributes). The speed of the paradigms makes them highly attractive for clinical research, their reliability brings fidelity to longitudinal studies, and the language context is especially suitable for studies on language impairments such as dyslexia and aphasia. In addition I have presented an even more ecological paradigm, and more importantly, an interesting result in view of the theory of MMN where the MMN responses are recorded entirely without a repetitive standard tone. All in all, these paradigms contribute to the development of the theory of auditory perception, and increase the feasibility of MMN recordings in both basic and clinical research. Moreover, they have already proven useful in studying for instance dyslexia, Asperger syndrome and schizophrenia.Tarkoituksenmukainen ääniympäristössä toimiminen, kuten ääniympäristön merkityksellisiin tapahtumiin suuntautuminen ja kielellinen kommunikointi edellyttävät ääniympäristön säännömukaisuuksien, ja näistä poikkeavien tapahtumien tarkkaavuudesta riippumatonta mallintamista ja jäsentämistä yhtenäiseksi havaintokokonaisuudeksi. Tällaisen esitietoisen kuuloinformaation käsittelyn, erityisesti ääniympäristöstä poikkeavien äänien havaitsemisesta syntyvä hermosolujen aktivoituminen näkyy aivosähkökäyrässä tapahtumasidonnaisena MMN-jännitevasteena. --- Koska MMN:n rekisteröiminen ei edellytä tutkittavalta tehtävän tekemistä tai ärsykkeiden aktiivista kuuntelemista, sen avulla voidaan tutkia sensorisen kuulomuistin toimintaa jo vauvaiästä vanhuuteen saakka. Perustutkimuksen lisäksi MMN:ää voidaan hyödyntää erilaisten aivoperäisten ja aivoihin vaikuttavien sairauksien ja tilojen, kuten lukihäiriön, ikääntymisen ja skitsofrenian tutkimuksessa. Viimeaikaiset tutkimukset osoittavatkin, että kuuloinformaation prosessointi MMN:llä tutkittuna on poikkeavaa erilaisissa aivosairauksissa kuten skitsofreniassa, mutta muuttuu myös kehityksen ja normaalin ikääntymisen myötä. Edelleen on osoitettu, että nämä kuuloinformaation prosessoinnin muutokset voivat ilmetä valikoivasti joillekin äänen piirteille (esim. äänen kesto tai taajuus) sekä vain joissakin yhteyksissä (esim. vain puheäänissä).
Vaikka MMN-tutkimuksella onkin huomattavia etuja verrattuna behavioraalisiin menetelmiin, sen yleistymistä laajempaan käyttöön, erityisesti kliiniseen tutkimukseen ja diagnostiikkaan, jarruttaa MMN-rekisteröinnin suhteellinen hitaus. Tavallisesti MMN-rekisteröinti yhdelle äänen piirteelle vaatii n. 15 minuuttia, joten useamman äänen piirteen erottelun profiilin rekisteröiminen vie helposti tunnista useaankin tuntiin. Tässä väitöskirjatutkimuksessa tavoitteena oli kehittää MMN-rekisteröinnissä käytettävää koeasetelmaa siten, että rekisteröinti voitaisiin tehdä aiempaa nopeammin, mutta yhtä luotettavasti. Väitöskirjatutkimuksessa kehitettiin koeasetelmia, joilla voidaan rekisteröidä lyhyessä ajassa (noin 15 minuuttia viidelle eri äänen piirteelle) useiden äänten piirteiden ja erikokoisten äänimuutosten prosessoinnin profiilit sekä puheäänille että ei-puheäänille. Koska näillä koeasetelmilla saadaan tietoa kuuloinformaation prosessoinnista huomattavasti aikaisempaa lyhyemmässä ajassa, ne parantavat MMN:n käytettävyyttä erityisesti kliinisissä tutkimuksissa. Edelleen, lyhyt rekisteröintiaika mahdollistaa entistä kattavamman ja monipuolisemman kuvan muodostamisen tutkittavien erottelukyystä eri äänen piirteiden välillä. Korkea reliabiliteetti puolestaan tuo luotettavuutta erityisesti pitkittäistutkimuksiin ja puhekonteksti soveltuu erityisesti kielen ja sen häiriöiden kuten dysfasian ja afasian tutkimukseen. Kehitimme myös vielä näitäkin taloudellisemman koeasetelman, jossa MMN vaste rekisteröitiin uudella tavalla, ilman toistuvaa ääntä ja tämän osatutkimuksen tulos on merkittävä myös MMN:n ja kuuloinformaation prosessoinnin teorian kannalta. Kaiken kaikkiaan nämä väitöskirjatyössä kehitetyt koeasetelmat tuovat uutta tietoa kuuloinformaation käsittelystä, ja parantavat huomattavasti MMN-menetelmän käytettävyyttä sekä perus- että kliinisessä tutkimuksessa. On myös huomionarvoista, että näiden koeasetelmien on jo osoitettu olevan hyödyllisiä mm. lukihäiriön, Aspergerin syndrooman ja skitsofrenian tutkimuksessa
Low-frequency oscillatory correlates of auditory predictive processing in cortical-subcortical networks: a MEG-study
Emerging evidence supports the role of neural oscillations as a mechanism for predictive information processing across large-scale networks. However, the oscillatory signatures underlying auditory mismatch detection and information flow between brain regions remain unclear. To address this issue, we examined the contribution of oscillatory activity at theta/alpha-bands (4–8/8–13 Hz) and assessed directed connectivity in magnetoencephalographic data while 17 human participants were presented with sound sequences containing predictable repetitions and order manipulations that elicited prediction-error responses. We characterized the spectro-temporal properties of neural generators using a minimum-norm approach and assessed directed connectivity using Granger Causality analysis. Mismatching sequences elicited increased theta power and phase-locking in auditory, hippocampal and prefrontal cortices, suggesting that theta-band oscillations underlie prediction-error generation in cortical-subcortical networks. Furthermore, enhanced feedforward theta/alpha-band connectivity was observed in auditory-prefrontal networks during mismatching sequences, while increased feedback connectivity in the alpha-band was observed between hippocampus and auditory regions during predictable sounds. Our findings highlight the involvement of hippocampal theta/alpha-band oscillations towards auditory prediction-error generation and suggest a spectral dissociation between inter-areal feedforward vs. feedback signalling, thus providing novel insights into the oscillatory mechanisms underlying auditory predictive processing
Direct brain recordings reveal continuous encoding of structure in random stimuli
The brain excels at processing sensory input, even in rich or chaotic environments. Mounting evidence attributes this to the creation of sophisticated internal models of the environment that draw on statistical structures in the unfolding sensory input. Understanding how and where this modeling takes place is a core question in statistical learning and predictive processing. In this context, we address the role of transitional probabilities as an implicit structure supporting the encoding of a random auditory stream. Leveraging information-theoretical principles and the high spatiotemporal resolution of intracranial electroencephalography, we analyzed the trial-by-trial high-frequency activity representation of transitional probabilities. This unique approach enabled us to demonstrate how the brain continuously encodes structure in random stimuli and revealed the involvement of a network outside of the auditory system, including hippocampal, frontal, and temporal regions. Linking the frame-works of statistical learning and predictive processing, our work illuminates an implicit process that can be crucial for the swift detection of patterns and unexpected events in the environment.Fil: Fuhrer, Julian. University of Oslo; NoruegaFil: Kyrre, Glette. University of Oslo; NoruegaFil: Ivanovic, Jugoslav. University of Oslo; NoruegaFil: Gunnar Larsson, Pål. University of Oslo; NoruegaFil: Bekinschtein, Tristán Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Cambridge; Reino UnidoFil: Kochen, Sara Silvia. Universidad Nacional Arturo Jauretche. Unidad Ejecutora de Estudios en Neurociencias y Sistemas Complejos. Provincia de Buenos Aires. Ministerio de Salud. Hospital Alta Complejidad en Red El Cruce Dr. Néstor Carlos Kirchner Samic. Unidad Ejecutora de Estudios en Neurociencias y Sistemas Complejos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Unidad Ejecutora de Estudios en Neurociencias y Sistemas Complejos; ArgentinaFil: Knight, Robert T.. University of California at Berkeley; Estados UnidosFil: Tørresen, Jim. University of Oslo; NoruegaFil: Solbakk, Anne Kristin. University of Oslo; Noruega. Helgeland Hospital; NoruegaFil: Endestad, Tor. University of Oslo; Noruega. Helgeland Hospital; NoruegaFil: Blenkmann, Alejandro Omar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. University of Oslo; Norueg
Deviance detection in auditory subcortical structures: what can we learn from neurochemistry and neural connectivity?
[EN] A remarkable ability of animals that is critical for survival is to detect and respond to to unexpected stimuli in an ever-changing world. Auditory neurons that show stimulusspecific adaptation (SSA), i.e., a decrease in their response to frequently occurring stimuli while maintaining responsiveness when different stimuli are presented, might participate in the coding of deviance occurrence. Traditionally, deviance detection is measured by the mismatch negativity (MMN) potential in studies of evoked local field potentials.We present a review of the state-of-the-art of SSA in auditory subcortical nuclei, i.e., the inferior colliculus and medial geniculate body of the thalamus, and link the differential receptor distribution
and neural connectivity of those regions in which extreme SSA has been found. Furthermore, we review both SSA and MMN-like responses in auditory and non-auditory areas that exhibit multimodal sensitivities that we suggest conform to a distributed network encoding for deviance detection. The understanding
of the neurochemistry and response similarities across these different regions will contribute to a better understanding of the neural mechanism underlying deviance detection
Electrophysiological Investigation of Auditory Mismatch Negativity: A Brain-Based Biomarker of N-Methyl-D-Aspartate Signalling
Inconsistent reports on the therapeutic efficacy of increasing synaptic glycine concentration have raised doubt as to the benefit of N-methyl-D-aspartate receptor (NMDAr) mediated treatments for schizophrenia. Categorising individuals based on broad diagnostic criteria does not appear to adequately identify individuals who will benefit from such treatments. Mismatch negativity (MMN) may be a suitable biomarker of NMDAr function, to help clarify the neurobiological relationship between pharmacological intervention and clinical treatment efficacy. MMN is an auditory event-related potential elicited following the presentation of a deviant stimulus, when it violates an established sequence stored in echoic memory. MMN is a robust deficit in schizophrenia and is categorised as a physiological element in the Cognitive Systems domain of the Research Domain Criteria framework. However, few studies have examined direct pharmacological modulation of MMN in schizophrenia patients. The aim of this thesis was to determine the nature of the relationship between MMN and NMDAr function, to inform the relative utility of MMN as a biomarker of NMDAr-mediated improvements in clinical symptoms in schizophrenia. To achieve this aim, three separate empirical studies were performed..
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