Lars Haab

Corticothalamic Feedback Dynamics for Neural Correlates of Auditory Selective Attention

Auditory evoked cortical potentials (AECPs) have been consolidated as a diagnostic tool in audiology. Further applications of this technique are in experimental neuropsychology, neuroscience, and psychiatry, e.g., for the attention deficit disorder, schizophrenia, or for studying the tinnitus decompensation. In particular, numerous psychophysiological studies have emphasized their dynamic characteristics in relation to exogenous and endogenous attention. However, the effect of corticothalamic feedback dynamics to neural correlates of focal and nonfocal attention and its large-scale effect reflected in AECPs is far from being understood. To address this issue, we model neural correlates of auditory selective attention reflected in AECPs by using corticothalamic feedback dynamics. In our framework, we make use of a well-known multiscale model of evoked potentials, for which we define for the first time a neurofunctional map of relevant corticothalamic loops to the hearing path. Such loops are in turn are coupled to our proposed probabilistic scheme of auditory selective attention. It is concluded that our model represents a promising approach to gain a deeper understanding of the neurodynamics of auditory attention and might be used as an efficient forward model to support hypotheses that are obtained in experimental paradigms involving AECPs.

Neurofunctional model of large-scale correlates of selective attention governed by stimulus-novelty

Multiple studies demonstrate the influence of the limbic system on the processing of sensory events and attentional guidance. But the mechanisms involved therein are yet not entirely clear. The close connection of handling incoming sensory information and memory retrieval, like in the case of habituation towards insignificant stimuli, suggests a crucial impact of the hippocampus on the direction of attention. In this paper we thus present a neurofunctional forward model of a hippocampal comparator function based on the theory of theta-regulated attention. Subsequently we integrated this comparator model into a multiscale framework for the simulation of evoked responses. The results of our simulations were compared to experimental data on electroencephalographic (EEG) correlates of habituation towards familiar stimuli using time-scale analysis. In consequence we are able to present additional evidence for limbic influences on the direction of attention driven by stimulus novelty and a systems neuroscience framework for the statements given in the theta-regulated attention hypothesis.

Modeling limbic influences on habituation deficits in chronic tinnitus aurium

About 93% of healthy subjects suffer from tinnituslike symptoms when deprived of auditory stimuli, e.g., in a sound-proof chamber. This suggests an underlying physiological mechanism causing auditory sensations during absence of an external sound source. Grossberg suggested a mechanism by which hallucinations arise from mechanisms of learning, attention and volition. According to this mechanism notch-like hearing deficits are sufficient for experiencing auditory hallucinations, while their chronification is attributed to reorganization processes. In tinnitus sufferers the auditory sensation is accompanied by the inability to habituate to this endogenous sound. This disability might originate from a coactivation of brain areas that are only indirectly involved in cognitive processing such as areas belonging to the limbic system. Moreover subjective loudness of the tinnitus sensation is likely to depend on the amount of selective attention assigned to the tinnitus stream. Here we propose a functional model of pure–tone tinnitus in which exogenous and endogenous input into processing modules is represented as streams. We model the selection of the tinnitus stream at the subthalamic level according to its weighting. Then we propose a mechanism for the inability to habituate to this stream due to limbic coactivation and amplification by mechanisms of attentional guidance, and by the influence corticofugal projections on lower auditory processing stages. The model is able to replicate the phase stability of auditory evoked potentials as seen in tinnitus sufferers and controls

Assessment of aversive stimuli dependent attentional binding by the N170 VEP component

For social species nonverbal communication by assessment of emotion expression is crucial for building up and maintaining social structures. In humans, body language not only includes gestures but also a variety of facial expressions. Negative associated facial expressions, e.g. disgust, fear, anger call for a higher attentional binding due their evolutionary background, denoting directly personal dangers for the receptive individual. In a number of psychiatric disorders such as schizophrenia or autism spectrum diseases, the assessment of emotions in faces is disturbed, leading to even more pronounced social cuts. In this article we present a new methodology for monitoring the attentional binding to emotion–tinged stimuli in a face recognition task. We were able to demonstrate a significant difference in habituation behavior to neutral and negative associated faces respectively. In future, this methodology might provide a fast and reliable scheme for the detection of psychiatric disorders comprising dysfunction of limbic structures.

Biocybernetics of attention in the tinnitus decompensation: An integrative multiscale modeling approach

Tinnitus is one of the most common symptoms affecting people all over the world. In the absence of an established cure many individuals are not only faced with the need to adjust to the sensation of the tinnitus noise, but also with psychological comorbidities. In recent years, different studies have been directed to elucidate the psychophysiological mechanisms that are involved in the tinnitus decompensation. From these, special emphasis has been placed on studies related to attention and habituation, which accordingly play a crucial role in current tinnitus therapy approaches. In spite of such progress, the relationship between selective attention and the tinnitus decompensation with respect to large-scale neural correlates is still not well understood. In order to address this issue, we propose an integrative multiscale modeling approach for studying neural correlates of auditory selective attention in the tinnitus decompensation. Computational simulations based on our model confirmed electroencephalographic human data of both auditory selective attention and the tinnitus decompensation. It is concluded that the proposed methodology represents a promising approach to give insight into the neurodynamics of auditory selective attention in the tinnitus decompensation.

Modeling Neural Correlates of Auditory Attention in Evoked Potentials using Corticothalamic Feedback Dynamics

Auditory evoked cortical potentials (AECP) are well established as diagnostic tool in audiology and gain more and more impact in experimental neuropsychology, neuro- science, and psychiatry, e.g., for the attention deficit disorder, schizophrenia, or for studying the tinnitus decompensation. The modulation of AECP due to exogenous and endogenous attention plays a major role in many clinical applications and has experimentally been studied in neuropsychology. However the relation of corticothalamic feedback dynamics to focal and non-focal attention and its large-scale effect reflected in AECPs is far from being understood. In this paper, we model neural correlates of auditory attention reflected in AECPs using corticothalamic feedback dynamics. We present a mapping of a recently developed multiscale model of evoked potentials to the hearing path and discuss for the first time its neurofunctionality in terms of corticothalamic feedback loops related to focal and non-focal attention. Our model reinforced recent experimental results related to online attention monitoring using AECPs with application as objective tinnitus decompensation measure. It is concluded that our model presents a promising approach to gain a deeper understanding of the neurodynamics of auditory attention and might be use as an efficient forward model to reinforce hypotheses that are obtained from experimental paradigms involving AECPs.

Support of a patient-specific therapeutical acoustic stimulation in tinnitus by numerical modeling

The pathogenesis of tinnitus involves multiple hierarchical levels of auditory processing and appraisal of sensory saliency. Early tinnitus onset is most likely attributed to homeostatic plasticity in the periphery, while the chronification and decompensation are tightly linked to brain areas for the allocation of attentional resources, such as e.g., the thalamocortical feedback loops and the limbic system. Increased spontaneous firing after sensory deafferentation might be sufficient to generate a phantom perception, yet the question why not every peripheral hearing loss automatically elicits a tinnitus sensation is still to be addressed. Utilizing quantitative modeling of multiple hierarchical levels in the auditory pathway, we demonstrate the effects of lateral inhibition on increased spontaneous firing and the resulting elevation of firing regularity and synchronization of neural activity. The presented therapeutical approach is based on the idea of disrupting the heightened regularity of the neural population response in the tinnitus frequency range. This neural activity regularity depends on lateral dispersion of common noise and thus is susceptible for edge effects and might be influenced by a change in neural activity in bordering frequency ranges by fitted acoustical stimulation. We propose the use of patient specifically adapted tailor-made notched acoustic stimulation, utilizing modeling results for the optimal adjustment of the stimulation frequencies to archive a therapeutical edge-effect.

Motion invariant contrast enhancement of optical imaging data in the gradient domain

Functional optical imaging (OI) of intrinsic signals (like blood oxygenation coupled reflection changes) and of extrinsic properties of voltage sensitive probes (like voltage-sensitive dyes (VSD)) forms a group of neuroimaging techniques that possess up to date highest temporal and spatial resolution on a meso-to macroscopic scale. An inherent problem of OI is a very low signal to noise ratio (SNR), which restricts the recordings to be completely motionless and requires detailed knowledge of the properties of the different noise sources. In our experiments we performed a durectomy and did not use an imaging chamber to allow us future joint electroencephalography-optical imaging (EEG-OI) measures, which resulted in movement artifacts. With the goal of motion compensation in OI recordings and magnification of signal changes, we present a novel processing pipeline, which is based on optic flow guided denoising and gradient domain tone mapping for spatiotemporal contrast enhancement.

Compensation of pulsation artifacts during optical imaging with and without cranial chamber

Functional Optical Imaging (OI) through the opened skull forms a group of Neuroimaging techniques characterized by a high temporal and spatial resolution on a meso-to macroscopic scale. State of the art OI experiments are generally difficult to execute, with a very timely surgical preparation preceding the experiment, that requires a skilled surgeon to mount a sealed imaging chamber onto the skull. The chamber reduces brain pulsation artifacts and swelling of the brain through movement restriction. In this work, we present preliminary results of a novel approach that does not rely on the usage of an imaging chamber with the goal to facilitate heavily the surgical animal preparation and to allow straightforward joint Electroencephalography - Optical Imaging recordings in the future. We carried out experiments to compare the movement restricting properties of the imaging chamber with the movement in a recording of an unconstrained and periodically irrigated brain. We used high-level image processing techniques to reduce brain pulsation artifacts and did a quantitative movement analysis of the recordings. Our results suggest that while recordings with imaging chamber show less sagittal movement, both with and without imaging chamber comprise the same lateral movements.

Notched Environmental Sounds: A New Hearing Aid Supported Tinnitus Treatment Evaluated in 20 Patients.

There is converging evidence that the genesis of tinnitus is related to deterioration of inhibition and/or upregulation of gain for deprived frequency bands in the afferent auditory pathway including the auditory cortex. There is also evidence that the organisation of the auditory scene may benefit from spectral edges because of such inhibitory mechanisms. Using such spectral edges in terms of notch filtering, tailor-made notchedmusic training (TMNMT) has been suggested to reduce tinnitus loudness and tinnitusrelated auditory cortex activity and positively evaluated using subjective and objective criteria subsequently. The TMNMT is designed for patients with tonal tinnitus. They have to listen to enjoyablemusic which has a notch centred at their tinnitus frequency. It was proposed that the acoustic stimulation provided by joyfulmusic plays an important role in the reversion of the maladaptive reorganisation processes induced by the deprived frequency bands. However, apart from possibly limbically trigged reorganisation processes, a key concept of this promising TMNMT might be the suppression of the neural hyperactivity in deprived frequency bands by lateral inhibition using the notch-induced sharp spectral edge. In other words, a localised damage in the lower auditory system results – due to the tonotopic organisation of hearing path – in the bandspecific neural hyperactivity mentioned before. The tailormade notch is adjusted to the tinnitus frequency and deprived frequency band, respectively, so that the spectral edges of the deprived frequency band are enhanced. In this way, the hyperactivity within the band is suppressed by lateral inhibition. The success of this approach depends of course on the careful determination of the tinnitus sound using subjective matching procedures. Up to now, the exact range of the asymmetric lateral inhibition in human is unknown, reducing the theoretical framework of this approach to tonal, small band tinnitus sounds.