auditory cortex

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STRFs in primary auditory cortex emerge from masking-based statistics of natural sounds

STRFs in primary auditory cortex emerge from masking-based statistics of natural sounds

Observe that for frequency, for the inhibition and to a lesser extent the excitation, the tun- ing widths of the MCA model STRFs match relatively well the tuning widths of the STRFs of real neurons. For the temporal dimension we see more strongly diverging properties which may have been expected by considering the statistical modeling approach: Like sparse coding or ICA we do focus on the composition of the data points in terms of structural primitives. Our model itself does not contain statistical dependencies in time unlike hidden Markov mod- els or linear dynamical systems would do. As acoustic data does contain such dependencies on multiple time scales, it is likely that neural processing reflects also these dependencies. The dis- crepancy of temporal modulation in contrast to frequency modulation may therefore be taken as evidence for the auditory cortex capturing the intricate statistical dependencies over time which neither sparse coding, ICA nor the here studied MCA model addresses. The control experiments using BSC support this interpretation. Also for BSC no asymmetry similar to the one of the measured ferret STRFs is observed. Histograms for BSC computed analogously to
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Attentional influences on functional mapping of speech sounds in human auditory cortex

Attentional influences on functional mapping of speech sounds in human auditory cortex

We analyzed the magnetic N100 (N100m) response to two vowels [o] and [ø], both produced by a male and a female speaker. Subject's attention was either on the vowel or on the speaker difference, in a counterbalanced order. How would a controlled shift of attention from spe- cific phonological features of speech to features of speaker identity affect the speech sound mapping in timing and topography of the brain response? Two concurrent out- comes are conceivable here: First, from the numerous par- allels between the auditory and other sensory domains, one might expect a blurring of differences of the phono- logical map in auditory cortex when features such as the speaker identity rather than phonological differences are attended over minutes. Second, phonological processing could be the default process needed in all speech-listening situations and should therefore activate phonological fea- ture maps irrespectively of attentional demands. We would then expect that the separate mapping of DORSAL and CORONAL vowels described previously [15] is unaf- fected by an attentional focus on speaker identity. How- ever, a shift of activational patterns as an entity would reveal more about the staging of parallel processing in the flow of the 'what' stream.
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Sustained Selective Attention to Competing Amplitude-Modulations in Human Auditory Cortex

Sustained Selective Attention to Competing Amplitude-Modulations in Human Auditory Cortex

Abstract Auditory selective attention plays an essential role for identifying sounds of interest in a scene, but the neural underpinnings are still incompletely understood. Recent findings demonstrate that neural activity that is time-locked to a particular amplitude-modulation (AM) is enhanced in the auditory cortex when the modulated stream of sounds is selectively attended to under sensory competition with other streams. However, the target sounds used in the previous studies differed not only in their AM, but also in other sound features, such as carrier frequency or location. Thus, it remains uncertain whether the observed enhancements reflect AM-selective attention. The present study aims at dissociating the effect of AM frequency on response enhancement in auditory cortex by using an ongoing auditory stimulus that contains two competing targets differing exclusively in their AM frequency. Electroencephalography results showed a sustained response enhancement for auditory attention compared to visual attention, but not for AM-selective attention (attended AM frequency vs. ignored AM frequency). In contrast, the response to the ignored AM frequency was enhanced, although a brief trend toward response enhancement occurred during the initial 15 s. Together with the previous findings, these observations indicate that selective enhancement of attended AMs in auditory cortex is adaptive under sustained AM- selective attention. This finding has implications for our understanding of cortical mechanisms for feature-based attentional gain control.
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Processing of acoustic motion in the auditory cortex of the rufous horseshoe bat, Rhinolophus rouxi

Processing of acoustic motion in the auditory cortex of the rufous horseshoe bat, Rhinolophus rouxi

Other aspects of auditory physiology in bats have been less intensively studied so far. Thus, only few authors have tackled the question how a moving sound is represented in the auditory system of bats. For horseshoe bats, Schlegel (1980) and Kleiser & Schuller (1995) found that neurons in the IC responded with shifts of the spatial RF location due to opposite directions of simulated acoustic motion. The same was found for IC neurons in the mustached bat (Pteronotus parnellii) by Wilson & O’Neill (1998). Whether the mechanism underlying these shifts is adaptation of excitation as stated by Ingham et al. (2001) for the guinea pig, or if more complex mechanisms are involved is unclear. Furthermore, how the motion information is processed at higher levels of the auditory pathway, e.g. the auditory cortex of bats is unknown. The auditory cortex of R. rouxi consists of at least five different fields defined by physiological and cytoarcitectural features and thalamocortical connections (Radtke-Schuller, 1997). Several specializations of the different fields have been shown in the past. For example, the dorso-dorsal field (DDF) contains neurons preferentially activated by combinations of time delayed, linearly frequency-modulated stimuli, so-called FM/FM neurons (Schuller et al., 1991). These neurons might serve as target-range encoding neurons. A special feature of the anterior-dorsal field (ADF) was the concentration of neurons responding to the bats own vocalization, whereas in the posterior dorsal field (PDF) many neurons were extremely narrow tuned to frequencies of the FM portion of echolocation calls (Radtke-Schuller & Schuller, 1995) which could be useful for exact temporal encoding of start and/or end of calls and echoes. As studies on other animals mainly investigated the coding properties for moving sounds of neurons in the primary auditory cortex (AI), the detailed knowledge about the properties of different fields additionally to the primary field in the rufous horseshoe bat provides a good basis to investigate if motion processing is uniformly in the whole auditory cortex or if specializations exist.
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Functional segregation of Ferret Auditory Cortex probed with natural and model-matched sounds

Functional segregation of Ferret Auditory Cortex probed with natural and model-matched sounds

We compared fMRI responses in humans and fUS recordings in ferrets to speech/music and their model-matched counterparts. Interestingly, we observed speech selective regions in the ferret auditory cortex. However, and contrary to the real speech- and music-selective response components observed in human non-primary regions (Norman-Haigneré, 2015/2018), model-matched stimuli evoked similar responses in the ferret. Because speech and music are not ecologically relevant sounds for ferrets, we wanted to test whether ferret auditory cortex could discriminate between ferret pup vocalizations and their corresponding model-matched versions. We observed differences in animal motor activity for original vocalizations compared to model-matched stimuli, indicating that the animal is able to perceptually discriminate these two classes of sounds. We are currently investigating the neural correlates of this capability in auditory cortex responses. Follow-up work will test if ferrets can innately discriminate original vs synthetic speech, or whether perceptual learning is necessary to do so.
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Thalamocortical and corticothalamic interactions of the auditory cortex in the Mongolian gerbil (Meriones unguiculatus)

Thalamocortical and corticothalamic interactions of the auditory cortex in the Mongolian gerbil (Meriones unguiculatus)

The auditory cortex (AC) holds a key role in the neuronal bottom-up and top-down processing of auditory as well as of non-auditory information. The medial geniculate body (MGB) of the thalamus is the major source of subcortical input to the AC. Thus, the neuronal spectro-temporal response properties of auditory cortical neurons depend highly on their thalamocortical (TC) connectivities. Thalamic neurons, in turn, are also massively innervated by corticothalamic (CT) neurons. The cortex is thus able to dynamically influence thalamic processing and ultimately adjust its own input via recurrent corticoefferent feedback. In the Mongolian gerbil (Meriones unguiculatus), a frequently used animal model in auditory research, the detailed anatomy of the TC and CT system has not yet been worked out. Furthermore, many questions about how the transthalamic feedbackloop actually contributes to cortical activation patterns in vivo are still unanswered. This thesis therefore had the following objectives: (1) to investigate the anatomy of the TC system by iontophoretic injections of the anterograde tract tracer biocytin into the MGB, (2) to characterize the ultrastructure hitherto unknown “giant” TC terminals arising from the medial (MGm) division [which were discovered during (1)], and (3) to examine the cortico-thalamo-cortical (CTC) interactions by means of current source density (CSD) analysis after a selective photolytic apoptosis of CT neurons.
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Attentional influences on functional mapping of speech sounds in human auditory cortex

Attentional influences on functional mapping of speech sounds in human auditory cortex

We analyzed the magnetic N100 (N100m) response to two vowels [o] and [ø], both produced by a male and a female speaker. Subject's attention was either on the vowel or on the speaker difference, in a counterbalanced order. How would a controlled shift of attention from spe- cific phonological features of speech to features of speaker identity affect the speech sound mapping in timing and topography of the brain response? Two concurrent out- comes are conceivable here: First, from the numerous par- allels between the auditory and other sensory domains, one might expect a blurring of differences of the phono- logical map in auditory cortex when features such as the speaker identity rather than phonological differences are attended over minutes. Second, phonological processing could be the default process needed in all speech-listening situations and should therefore activate phonological fea- ture maps irrespectively of attentional demands. We would then expect that the separate mapping of DORSAL and CORONAL vowels described previously [15] is unaf- fected by an attentional focus on speaker identity. How- ever, a shift of activational patterns as an entity would reveal more about the staging of parallel processing in the flow of the 'what' stream.
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Auditory gating in the ventral striatum and auditory cortex - the role of stimulus-locking and the influence of discrimination learning

Auditory gating in the ventral striatum and auditory cortex - the role of stimulus-locking and the influence of discrimination learning

during FM tone presentation the inter-area phase-locking was significantly decreased (Figure 2.8 ), i.e. the electrical signals within both areas were out of phase, especially in the theta (4-8 Hz) and alpha frequency band (8-12 Hz) during S1 presentation and lower beta frequency band (12-16 Hz) during S2 presentation. After tone offsets, phase-locking appeared to increase again, marginally rising above baseline phase-locking values. The found decreased coherence during single FM tone stimulation (with a duration of 200 ms) represents another indication that acoustical information might primarily reach both areas on different paths (cf. Section 1.4.2 ). It also suggests that during S2 presentation, during which the auditory gating in the striatum is enforced, and during which auditory-cortex – striatum phase-locking was not existent, both areas are subjected to differential mechanisms: while the auditory cortex is destined to exactly follow the acoustical content of the stimuli, striatum-relevant acoustical features were probably already extracted during S1 presentation and then subjected to further local processing. Phase-locking appeared to increase after tone- offsets during both tested ISI conditions. During the short ISI condition, phase-locking in the FM presence was indifferent between S1 and S2 in the beta frequency band but it was higher in the post-stimulus episode after S2 compared to S1.
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Sensory integration in parietal but not auditory cortex mediates multisensory integration and recalibration

Sensory integration in parietal but not auditory cortex mediates multisensory integration and recalibration

We found neural signatures of audio-visual integration (the VE bias) in superior temporal and parietal cortex. Of these, activity in parietal regions mediated the behavioural recalibration of unisensory auditory perception (the VAE bias). This suggests that parietal, but not auditory cortex, integrates audio-visual information and combines this with persistent representations about prior stimuli to guide adaptive multisensory behaviour. Keywords: Multisensory integration, audio-visual perception, sensory recalibration

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Assessing Perinatal Maturation of Human Primary and Nonprimary Auditory Cortex

Assessing Perinatal Maturation of Human Primary and Nonprimary Auditory Cortex

1. Monson BB, Eaton-Rosen Z, Kapur K, Liebenthal E, Brownell A, Smyser CD, Rogers CE, Inder TE, Warfield SK, and Neil JJ. Differential rates of perinatal maturation of human primary and nonprimary auditory cortex. eNeuro. 2018;5(1):e0380-17.2017, 1-12. doi: http://dx.doi.org/10.1523/ENEURO.0380- 17.2017

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Amplitude modulation rate dependent topographic organization of the auditory steady-state response in human auditory cortex

Amplitude modulation rate dependent topographic organization of the auditory steady-state response in human auditory cortex

Our most important finding is the topographic organization of the aSSR depending on AM rate, especially in the anterior-posterior direction auditory cortices in both hemispheres when comparing high vs low AM rates and for the right hemisphere using our nonparametric permutation test of regression coef ficients. A strong topographic organization of AM rates was also identi fied in the medial-lateral direction of both auditory cortices. Overall, faster AM rates lead to aSSRs located in more posterior and medial parts of the STG, whereas slower AM rates peaked at more anterior and lateral locations. The general trend aligns well with a recent monkey study ( Baumann et al., 2015 ), as well as human fMRI studies ( Barton et al., 2012; Herdener et al., 2013 ); however, the spatial resolution in the current study is too limited to make claims for sub fields of the auditory cortex. This is not only due to basic limitations of the technique with regards to localization, but also due to the fact that we decided to use a template anatomy for all participants since structural data was largely missing. This will lead to inaccuracies of the headmodel and by extension the resolution of our localization will suffer to some extent. Despite these methodological limita- tions, when grouping over different AM rates, faster modulation rates lead to maxima more in primary auditory regions (BA 41/42) as compared to slower modulation rates that overall more located in secondary auditory regions (BA22). Based on these results, it is likely that different AM rates engage auditory fields (core and belt regions) of auditory cortex in a differential manner. This finding is in line with animal electrophysiology showing a decreased syn- chronization of more rostral regions of the auditory cortex, in particular, to faster AM rates ( Bendor and Wang, 2008 ). These ef- fects may in part be due to timing advantages of neural responses of more caudal auditory regions as compared to rostral regions, that could belong to dorsal and ventral auditory streams respectively ( Camalier et al., 2012 ). However, to investigate to what extent these animal works re flect similar processes as observed in our study would require high spatially-resolved invasive mapping of the aSSR in animals. One potential aspect that could contribute to the pre- sented findings is that the faster periodicities (>30 Hz) used in the present study could be accompanied by a distinct perception of pitch (or roughness, when individual beats are not anymore perceived), which would be absent for the lower AM rates (when individual beats are still perceived. While this is theoretically possible, it does not seem to fit with current ideas of dedicated pitch processing areas, which would suggest a more lateral
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Effects of different forms of engagement on the neuronal activity in the monkey's primary auditory cortex

Effects of different forms of engagement on the neuronal activity in the monkey's primary auditory cortex

107 Similarly to the present study, some researchers described lower neuronal responses in the auditory cortex to the acoustical stimuli with meaning while animals performed instrumental conditions compared with the same acoustical stimuli presented to the passively listening animals (Lee and Midlebrooks 2011, Otazu et al. 2009). Similar effects was observed in the olfactory (Fontanini and Katz 2006) and visual cortexes (Shuler and Bear 2006) to the meaningful stimuli with corresponding modalities. In contrast, many studies showed that the responses to the acoustical stimuli in the auditory (Atiani et al. 2014, Hubel et al. 1959, Shinba et al. 1995) and other sensory cortexes (Maunsell and Cook 2002) increased with meaning. The study made by Abolafia and colleagues (2011) described both effects that were found in different units, the higher and lower responses to the meaningful acoustical stimuli. We were surprised to find that much more units in the population had lower responses to the acoustical stimuli with meaning. Higher responses to acoustical stimuli with meaning would be much more intuitive. However, it is still unknown what the way of brain is to indicate the meaning of sounds or some other stimuli. After revealing both, the higher and lower responses to the stimuli with meaning, some researchers rather focused their attention on the higher responses to the sounds with meaning (for review read Ohl and Scheich 2005). Nevertheless, it may turn out that the lower responses evoked by a stimulus is a marker of meaning for the brain. For instance, the results of our study showed only the part of the units that responded significantly lower to the sound with meaning. There were also a lot of units that had no differences between the responses to these sounds. Thus, the comparison of the differences in one subgroup of units with no change in another subgroup could be a key factor for indicating the meaning of the acoustical stimuli. Thus, probably, the differences of changes between subpopulations of units indicate importance of acoustical stimuli (Fishman et al. 2001, 2012, 2017, Fritz et al. 2007a, 2007b, Knyazeva et al. 2018, Shamma et al. 2011). An additional bonus to this way of functioning would be the energy saving for an organism (compared to the situation where an important acoustical stimulus leads to even higher responses). A similar reasoning of the lower responses to the acoustical stimuli with higher meaning was also given by other researchers (Ghose 2004, Ghose et al. 2002).
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Mechanisms of inhibition and neuronal integration for signal processing in the primary auditory cortex of the Mongolian gerbil (Meriones unguiculatus)

Mechanisms of inhibition and neuronal integration for signal processing in the primary auditory cortex of the Mongolian gerbil (Meriones unguiculatus)

receptor mediated inhibition completely suppressed their ability to respond to pure tone stimuli. Silent neurons were also reported in the inferior colliculus of horseshoe bats (Vater et al. 1992), in the bird auditory cortex analogue (Müller and Scheich 1987), and in cat somatosensory cortex (Dykes et al. 1984). One could argue that anaesthesia could lead to a change of response pattern and possibly to a complete suppression of neuronal activity of neurons. However, in the case of the anaesthetic used in this study (ketamine/xylazine), a possible change of the response pattern would most probably not be caused by an influence on GABAergic receptors but, if at all, by a blockade of glutaminergic receptors (NMDA receptors). The strongest argument against the possibility that silent neurons are due to a general effect of anaesthesia is the fact that such neurons were almost exclusively found in the deep layers. This property implies a more specific physiological response characteristic inherent to the neurons. Similar to the present data, Dykes et al. (1984) found silent neurons mainly in superficial and deeper layers. Dykes et al. (1984) routinely applied glutamate to isolate neurons in all layers and to detect silent neurons in the somatosensory cortex of the cat. Usually, I did not apply glutamate to search for neurons and, consequently, in the present study silent neurons might be underrepresented. Therefore, the percentage of silent neurons in layer VI might be even higher suggesting that tonic inhibition is remarkably pronounced in this layer. In the present study, most of these neurons were found in layer VI. Neurons in layer VI mainly project to the contralateral cortex. They represent major output neurons of the cortex, and it may be of functional significance that their activity can be completely switched off by appropriate GABAergic inhibition.
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Deafness weakens interareal couplings in the auditory cortex

Deafness weakens interareal couplings in the auditory cortex

The function of the cerebral cortex essentially depends on the ability to form functional assemblies across different cortical areas serving different functions. Here we investigated how developmental hearing experience affects functional and effective interareal connectivity in the auditory cortex in an animal model with years-long and complete auditory deprivation (deafness) from birth, the congenitally deaf cat (CDC). Using intracortical multielectrode arrays, neuronal activity of adult hearing controls and CDCs was registered in the primary auditory cortex and the secondary posterior auditory field (PAF). Ongoing activity as well as responses to acoustic stimulation (in adult hearing controls) and electric stimulation applied via cochlear implants (in adult hearing controls and CDCs) were analyzed. As functional connectivity measures pairwise phase consistency and Granger causality were used. While the number of coupled sites was nearly identical between controls and CDCs, a reduced coupling strength between the primary and the higher order field was found in CDCs under auditory stimulation. Such stimulus-related decoupling was particularly pronounced in the alpha band and in top–down direction. Ongoing connectivity did not show such a decoupling. These findings suggest that developmental experience is essential for functional interareal interactions during sensory processing. The outcomes demonstrate that corticocortical couplings, particularly top-down connectivity, are compromised following congenital sensory deprivation.
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Targeted Neuroplasticity in Rat Primary Auditory Cortex with Vagus Nerve Stimulation and Near-Threshold Tones

Targeted Neuroplasticity in Rat Primary Auditory Cortex with Vagus Nerve Stimulation and Near-Threshold Tones

Vagus nerve stimulation (VNS) is a method for driving therapeutic, targeted neuroplasticity in clinical populations suffering from tinnitus and stroke. VNS facilitates specific cortical changes through the phasic release of plasticity promoting neuromodulators simultaneously paired with delivery of a sensory stimulus, such as tones or speech. Recent clinical evidence and ongoing pre-clinical experiments in rats show that VNS paired with near-threshold somatosensation of the hand/paw can significantly reduce elevated sensory thresholds resulting from neural injuries after only one week of therapy. A possible explanation for this quick and robust recovery is that VNS is more effective at driving neuroplasticity in cortical circuits when paired with stimuli just above the response threshold of neural receptive fields. To date, all auditory VNS therapies have used stimuli considerably above auditory thresholds, potentially diminishing the therapeutic effect of VNS-paired treatments. To test the effectiveness of VNS-paired, near-threshold stimuli in driving auditory neuroplasticity, unimpaired adult rats will receive VNS repeatedly paired with the brief presentation of a 10 dB SPL 9 kHz tone for one week. A cortical map of receptive field properties in primary auditory cortex will be made one day later and compared to the maps of naïve rats.
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Spatial processing in the auditory cortex for stream segregation and localization

Spatial processing in the auditory cortex for stream segregation and localization

The further apart two sounds are along the horizontal azimuth, the more likely they are to be heard as two separate sources. This spatial stream segregation (SSS) function may be dissociable from that of locating sound sources, but most neuroscience research on spatial hearing has focussed on the latter. Such research has uncovered spatial-sensitivity in the posterior auditory cortex, which has correspondingly been characterized as part of the "where" processing pathway for localization. However, other evidence indicates that this spatial sensitivity may be more relevant for SSS than for localization. We tested this hypothesis using 7 tesla functional magnetic resonance imaging. We measured brain activity in ten, normal-hearing adults while they listened to two concurrent auditory streams, spatially-separated along the horizontal azimuth. We applied multivoxel pattern classifiers to decode brain activity patterns associated with changes in location that resulted in either altered or constant SSS. We reasoned that if spatially-sensitive auditory cortex is optimized for SSS, then changes in spatial separation will be better decoded than mere changes in location. Our hypothesis was supported in the hemisphere contralateral to the sound locations. This result supports that spatial sensitivity in the auditory cortex is optimized for scene analysis rather than localization.
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The auditory cortex of the bat Phyllostomus discolor

The auditory cortex of the bat Phyllostomus discolor

organization of the AC in bats has been extensively studied physiologically in several species (e.g. Pteronotus parnellii (O'Neill and Suga 1982; Fitzpatrick et al. 1998b), Rhinolophus spec. (Ostwald 1984; Radtke-Schuller and Schuller 1995), Eptesicus fuscus (Dear et al. 1993; Jen et al. 2003), for review see (O'Neill 1995)). Among the best studied ACs so far are those of the mustached bat P. parnellii and the horseshoe bat, Rhinolophus rouxi, both belonging to the group of the so-called CF/FM-bats whose echolocation pulses consist of a constant frequency (CF) and a frequency modulated (FM) component. As common to all mammals studied so far, their ACs contain a tonotopically organized primary auditory field (AI) with the frequency gradient running from caudal to rostral. However, in both CF/FM-bats frequencies of the CF component of the calls are largely overrepresented in AI while frequencies of the FM component are only weakly represented (Suga and Jen 1976). The AI is surrounded by cortical regions with neurons that show facilitated responses to specific spectral and temporal combinations of the CF and FM parts of the different harmonics of the echolocation pulses. CF/FM-bats are rather specialized echolocators in that they hunt almost exclusively insects on the wings, whereas other bat species display more varied feeding ecology (insects, vertebrates, nectar, and fruits) and very commonly use short downward FM echolocation pulses often with several harmonic components. In these bats the functional specialization of the AC is often not so clearly apparent, but still cortical fields can be segregated based on neurophysiological criteria like best frequency (BF; frequency at which threshold is lowest) representation and response threshold (Wong and Shannon 1988; Dear et al. 1993). In the phyllostomid FM-bat Carollia perspicillata for example, two dorsal fields containing mainly neurons with BFs in the high-frequency range have been reported in addition to the tonotopically organized fields AI and anterior auditory field (AAF) (Esser and Eiermann 1999). In these high-frequency fields some neurons exhibited pulse-echo delay sensitivity as in CF/FM-bats (Hackel and Esser 1998), but without topographical organization.
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Changed temporal processing in the human auditory cortex by transcranial direct current stimulation

Changed temporal processing in the human auditory cortex by transcranial direct current stimulation

perception reported rather inconsistent results. Whereas Mathys et al. (2010) showed a decrement of pitch discrimination induced by cathodal tDCS over the left and right AC, anodal tDCS had no effect on task performance. In contrast, Tang and Hammond (2013) reported that anodal tDCS over the right AC causes diminished frequency discrimination by decreasing sensitivity to temporal fine structure, but did not affect spectral selectivity. Impey & Knott (2015) demonstarted that anodal tDCS over the left AC enhances MMN to spectral deviants only in individuals with low MMN baseline amplitudes. It can be assumed that different stimulation parameter such as stimulation power, electrode size, and electrode placement especially of the reference electrode, as well as the individual auditory stimuli contribute to these varying tDCS-effects. Finally, the auditory evoked MMN does not exclusively originate in temporal regions. The prefrontal cortex has been associated with generation of auditory evoked MMN as well (Doeller et al., 2003; Deouell, 2007; Garrido et al., 2009a; Garrido et al., 2009b). Anodal tDCS over the right frontal cortex exclusively affects MMN to spectral deviants whereas neither anodal nor cathodal tDCS modulate MMN to temporal deviants (Chen et al., 2013). Thus, specifically for spectral processing, varying stimulation locations over the temporo-frontal network seem to influence tDCS induced effects on the MMN measurement considerably. To this date, the asymmetry of the auditory domain for low-level acoustic features is still controversially discussed (Scott & McGettigan, 2013). By directly modulating the reactivity of the underlying neural cortex, HD-tDCS can provide causal evidence for a relationship between the activity of the left and right auditory cortices and its functional specification. Thus studies using HD-tDCS might help to advance our understanding of hemispheric lateralization for low-level acoustic feature processing.
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The Interhemispheric Coupling of Auditory Cortices

The Interhemispheric Coupling of Auditory Cortices

The DL task is the most commonly used paradigm to investigate the relation between interhemispheric interaction, conscious auditory perception, and language lateralisation (Westerhausen et al. 2009). In particular, understanding the neurophysiological underpinning of those three parameters within healthy probands plays a crucial role for the investigation of different patient groups, such as schizophrenia patients who suffer from auditory verbal hallucinations (AVH) (i.e. hearing voices), or patients with tinnitus (i.e. auditory phantom precept) that show alterations in this regard. It has been shown in a meta-analysis of DL studies (Ocklenburg et al. 2013) that reduced left-hemispheric language lateralisation correlates strongly with the occurrence of AVH in patients with schizophrenia (see review by Steinmann et al. 2014b). In addition, Diesch et al. (2012) showed an alteration of CC size and auditory cortex volume within patients suffering from tinnitus compared to healthy controls.
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A speed trap on the auditory pathway: investigation of early auditory evoked brainstem activity / eingereicht von Florian Geyer

A speed trap on the auditory pathway: investigation of early auditory evoked brainstem activity / eingereicht von Florian Geyer

Forte, Etard and Reichenbach investigated 2017 the modulation of attention on early auditory evoked activity. To achieve this, they developed a method to measure early auditory evoked activity in response to running speech instead of repetitive click stimulation. They claimed attention to higher the signal of the overall ABR. On basis of the findings of Hashimoto, Ishiyama, Yoshimoto & Nemoto (1981) they denied the participation of auditory cortex in the first ten ms of ABR. Our results, in line with literature in humans (Brugge et al. 2008, 2009) and monkeys (Steinschneider et al. 1992), however reveal cortical activation already at 9.4 ms after stimulus onset. It may be that their results are biased by the participation of auditory cortex. This puts a question mark behind the attentional modulation of ABR on the level of brainstem or auditory nerve.
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