Inharmonicity detection

Detection of mistuned partials in otherwise harmonic complex tones was investigated in naïve subjects of three different age groups. Signals were presented at constant sensation level to compensate for differences in hearing sensitivity and to specifically examine age-related changes in inharmonicity perception. Performance was measured under two conditions, monaural signal presentation and dichotic signal-noise presentation, with the latter aiming at the influence of contralateral distractor sounds. Stimuli were complex tones with ten harmonics and 125-Hz fundamental frequency. Mistuning detection was measured for the first, second, fourth, and eighth harmonic. In a three-interval, three-alternative forced-choice procedure, subjects were required to distinguish a complex tone containing one mistuned partial from two reference tones, with all partials at their harmonic frequencies. Thresholds were measured as the amount of frequency shift necessary for the mistuning to be detected. Performance deteriorated moderately with age for the two higher partials tested, but not for the lower ones. Thresholds for dichotic signal/noise presentation did not differ significantly from monaural ones in any of the age groups. Results are discussed in relation to hypotheses of harmonicity perception in auditory scene analysis and with respect to the investigation of patients suffering form respective deficits due to acquired brain lesions.     

Stimulus complexity enhances auditory discrimination in patients with extremely severe brain injuries

There is controversy as to what extent the processing of spectrally rich sounds in the human auditory cortex is related to the processing of singular frequencies. An informative index of the function of the auditory cortex, particularly important in neurological patients, is the mismatch negativity (MMN), a component of auditory event-related potentials. In the present study the MMN was recorded in 79 patients with extremely severe diffuse brain injuries, most of them in persistent vegetative state or minimal consciousness state. Both sinusoidal ('pure') and complex musical tones were used. Different statistical approaches converged in that musical tones elicited an MMN significantly more frequently, and of a larger amplitude, than simple sine tones. This implies that using simple stimuli in clinical populations may lead to a severe underestimation of the functional state of a patient's auditory system. The findings are also in line with behavioral and physiological data indicating independent processing of complex sounds in the auditory cortex.     

Spectral response patterns of auditory cortex neurons to harmonic complex tones in alert monkey (Macaca mulatta)

1. The auditory cortex in the superior temporal region of the alert rhesus monkey was explored for neuronal responses to pure and harmonic complex tones and noise. The monkeys had been previously trained to recognize the similarity between harmonic complex tones with and without fundamentals. Because this suggested that they could preceive the pitch of the lacking fundamental similarly to humans, we searched for neuronal responses relevant to this perception. 2. Combination-sensitive neurons that might explain pitch perception were not found in the surveyed cortical regions. Such neurons would exhibit similar responses to stimuli with similar periodicities but differing spectral compositions. The fact that no neuron with responses to a fundamental frequency responded also to a corresponding harmonic complex missing the fundamental indicates that cochlear distortion products at the fundamental may not have been responsible for missing fundamental-pitch perception in these monkeys. 3. Neuronal responses can be expressed as relatively simple filter functions. Neurons with excitatory response areas (tuning curves) displayed various inhibitory sidebands at lower and/or higher frequencies. Thus responses varied along a continuum of combined excitatory and inhibitory filter functions. 4. Five elementary response classes along this continuum are presented to illustrate the range of response patterns. 5. "Filter (F) neurons" had little or no inhibitory sidebands and responded well when any component of a complex tone entered its pure-tone receptive field. Bandwidths increased with intensity. Filter functions of these neurons were thus similar to cochlear nerve-fiber tuning curves. 6. "High-resolution filter (HRF) neurons" displayed narrow tuning curves with narrowband widths that displayed little growth with intensity. Such cells were able to resolve up to the lowest seven components of harmonic complex tones as distinct responses. They also responded well to wideband stimuli. 7. "Fundamental (F0) neurons" displayed similar tuning bandwidths for pure tones and corresponding fundamentals of harmonic complexes. This response pattern was due to lower harmonic complexes. This response pattern was due to lower inhibitory sidebands. Thus these cells cannot respond to missing fundamentals of harmonic complexes. Only physically present components in the pure-tone receptive field would excite such neurons. 8. Cells with no or very weak responses to pure tones or other narrowband stimuli responded well to harmonic complexes or wideband noise.(ABSTRACT TRUNCATED AT 400 WORDS)     

Responses of inferior colliculus neurons to double harmonic tones

The auditory system can segregate sounds that overlap in time and frequency, if the sounds differ in acoustic properties such as fundamental frequency (f0). However, the neural mechanisms that underlie this ability are poorly understood. Responses of neurons in the inferior colliculus (IC) of the anesthetized chinchilla were measured. The stimuli were harmonic tones, presented alone (single harmonic tones) and in the presence of a second harmonic tone with a different f0 (double harmonic tones). Responses to single harmonic tones exhibited no stimulus-related temporal pattern, or in some cases, a simple envelope modulated at f0. Responses to double harmonic tones exhibited complex slowly modulated discharge patterns. The discharge pattern varied with the difference in f0 and with characteristic frequency. The discharge pattern also varied with the relative levels of the two tones; complex temporal patterns were observed when levels were equal, but as the level difference increased, the discharge pattern reverted to that associated with single harmonic tones. The results indicated that IC neurons convey information about simultaneous sounds in their temporal discharge patterns and that the patterns are produced by interactions between adjacent components in the spectrum. The representation is "low-resolution," in that it does not convey information about single resolved components from either individual sound.     

Consonance and dissonance of musical chords: neural correlates in auditory cortex of monkeys and humans.

Some musical chords sound pleasant, or consonant, while others sound unpleasant, or dissonant. Helmholtz's psychoacoustic theory of consonance and dissonance attributes the perception of dissonance to the sensation of "beats" and "roughness" caused by interactions in the auditory periphery between adjacent partials of complex tones comprising a musical chord. Conversely, consonance is characterized by the relative absence of beats and roughness. Physiological studies in monkeys suggest that roughness may be represented in primary auditory cortex (A1) by oscillatory neuronal ensemble responses phase-locked to the amplitude-modulated temporal envelope of complex sounds. However, it remains unknown whether phase-locked responses also underlie the representation of dissonance in auditory cortex. In the present study, responses evoked by musical chords with varying degrees of consonance and dissonance were recorded in A1 of awake macaques and evaluated using auditory-evoked potential (AEP), multiunit activity (MUA), and current-source density (CSD) techniques. In parallel studies, intracranial AEPs evoked by the same musical chords were recorded directly from the auditory cortex of two human subjects undergoing surgical evaluation for medically intractable epilepsy. Chords were composed of two simultaneous harmonic complex tones. The magnitude of oscillatory phase-locked activity in A1 of the monkey correlates with the perceived dissonance of the musical chords. Responses evoked by dissonant chords, such as minor and major seconds, display oscillations phase-locked to the predicted difference frequencies, whereas responses evoked by consonant chords, such as octaves and perfect fifths, display little or no phase-locked activity. AEPs recorded in Heschl's gyrus display strikingly similar oscillatory patterns to those observed in monkey A1, with dissonant chords eliciting greater phase-locked activity than consonant chords. In contrast to recordings in Heschl's gyrus, AEPs recorded in the planum temporale do not display significant phase-locked activity, suggesting functional differentiation of auditory cortical regions in humans. These findings support the relevance of synchronous phase-locked neural ensemble activity in A1 for the physiological representation of sensory dissonance in humans and highlight the merits of complementary monkey/human studies in the investigation of neural substrates underlying auditory perception.     

Scalp potentials to pitch change in rapid tone sequences. A correlate of sequential stream segregation

The object of the study was to look for a neurophysiological substrate of sequential auditory stream segregation. When a sequence of tones alternates rapidly between pitches separated by more than a few semitones, there is a tendency for it to be perceived as two independent "streams". We examined the scalp potentials evoked when the pitch interval abruptly changes, to see whether there are response parameters which might be correlated with sudden stream segregation and/or integration. For 3 s a continuous synthesized tone of "clarinet" timbre oscillated between pitches of F4 and F#4 (one semitone higher) at 16 notes/s, perceived as an integrated stream. The upper note was then raised to E5 (11 semitones above F4, perceived as segregated streams) for a further 3 s and the cycle was repeated 40 times. In a second condition also starting with oscillation between F4 and F#4, the upper note was lowered to E4 (one semitone below F4, still perceived as a single stream). Further conditions examined the changes between oscillations of 1 and 11 semitones down from E5, 1 and 23 semitones up from F4, and 10 and 11 semitones up from F4. Virtually no potentials were detectable during the periods of unchanging oscillation, but an N1/P2 complex was evoked on each change in the pitch interval. The N1 was termed "MN1" on account of its arguable relatedness to the mismatch negativity, recorded in a separate experiment using discontinuous tones at a much slower rate. The mean peak latency of the MN1 varied between 96 and 123 ms, the shortest latencies being recorded, not to the largest changes of pitch interval but to the widest pitch intervals between the new tone and the immediately preceding one. Therefore, although a causal relationship with streaming cannot necessarily be inferred, the MN1 latency appears to mark the degree of pitch contrast between consecutive tones, in correlation with the streaming effect. Electronic Publication     

Spectral integration in A1 of awake primates: neurons with single- and multipeaked tuning characteristics

We investigated modulations by stimulus components placed outside of the classical receptive field in the primary auditory cortex (A1) of awake marmosets. Two classes of neurons were identified using single tone stimuli: neurons with single-peaked frequency tuning characteristics (147/185, 80%) and neurons with multipeaked frequency tuning characteristics (38/185, 20%), referred to as single- and multipeaked units, respectively. Each class of neurons was further studied using two-tone paradigms in which the frequency, intensity, and timing of the second tone were systematically varied while a unit was driven by the first tone placed at a unit's characteristic frequency (CF) if it was single-peaked or at one of multiple spectral peaks if it was multipeaked. The main findings were: 1) excitatory spectral peaks in the frequency tuning of the multipeaked units were often harmonically related. 2) Multipeaked units showed facilitation in their responses to combinations of two harmonically related tones placed at the spectral peaks of their frequency tuning. The two-tone facilitation was strongest for the simultaneously presented tones. 3) In 76 of 113 single-peaked units studied using the two-tone paradigm, facilitatory and/or inhibitory modulations by distant off-CF tones were observed. This distant inhibition differed from flanking (or side-band) inhibitions near CF. 4) In single-peaked units, the distant off-CF inhibitions were dominated by tones at frequencies that were harmonically related to the CF of a unit, whereas the facilitation by off-CF tones was observed for a wide range of frequencies. And 5) in both single- and multipeaked units, sound levels of two interacting tones determined whether the two tones produced excitation or inhibition. The largest facilitation was achieved by using two tones at their corresponding preferred sound levels. Together, these findings suggest that extracting or rejecting harmonically related components embedded in complex sounds may represent fundamental signal processing properties in different classes of A1 neurons.     

Processing of novel sounds and frequency changes in the human auditory cortex: Magnetoencephalographic recordings

Whole-head magnetoencephalographic (MEG) responses to repeating standard tones and to infrequent slightly higher deviant tones and complex novel sounds were recorded together with event-related brain potentials (ERPs). Deviant tones and novel sounds elicited the mismatch negativity (MMN) component of the ERP and its MEG counterpart (MMNm) both when the auditory stimuli were attended to and when they were ignored. MMNm generators were located bilateral to the superior planes of the temporal lobes where preattentive auditory discrimination appears to occur. A subsequent positive P3a component was elicited by deviant tones and with a larger amplitude by novel sounds even when the sounds were to be ignored. Source localization for the MEG counterpart of P3a (P3am) suggested that the auditory cortex in the superior temporal plane is involved in the neural network of involuntary attention switching to changes in the acoustic environment.     

Assessing functioning of the prefrontal cortical subregions with auditory evoked potentials in sleep-wake cycle

Our previously observations showed that the amplitude of cortical evoked potentials to irrelevant auditory stimulus (probe) recorded from several different cerebral areas was differentially modulated by brain states. At present study, we simultaneously recorded auditory evoked potentials (AEPs) from the dorsolateral prefrontal cortex (DLPFC) and the ventromedial prefrontal cortex (VMPFC) in the freely moving rhesus monkey to investigate state-dependent changes of the AEPs in the two subregions of prefrontal cortex. AEPs obtained during passive wakefulness (PW), active wakefulness (AW), slow wave sleep (SWS) and rapid-eye-movement sleep (REM) were compared. Results showed that AEPs from two subregions of prefrontal cortex were modulated by brain states. Moreover, a significantly greater increase of the peak-to-peak amplitude (PPA) of N1-P1 complexes appears in the DLPFC during PW compared to that during AW. During REM, the PPA of N1-P1 complexes presents a contrary change in the two subregions with significant difference: a significant increase in the DLPFC and a slight decrease in the VMPFC compared to that during AW. These results indicate that the modulation of brain states on AEPs from two subregions of the prefrontal cortex investigated is also not uniform, which suggests that different subregions of the prefrontal cortex have differential functional contributions during sleep-wake cycle.     

Frequency and amplitude representations in anterior primary auditory cortex of the mustached bat

The orientation sound emitted by the Panamanian mustached bat, Pteronotus parnellii rubiginosus, consists of four harmonics. The third harmonic is 6-12 dB weaker than the predominant second harmonic and consists of a long constant-frequency component (CF3) at about 92 kHz and a short frequency-modulated component (FM3) sweeping from about 92 to 74 kHz. Our primary aim is to examine how CF3 and FM3 are represented in a region of the primary auditory cortex anterior to the Doppler-shifted constant-frequency (DSCF) area. Extracellular recordings of neuronal responses from the unanesthetized animal were obtained during free-field stimulation of the ears with pure tones. FM sounds, and signals simulating their orientation sounds and echoes. Response properties of neurons and tonotopic and amplitopic representations were examined in the primary and the anteroventral nonprimary auditory cortex. In the anterior primary auditory cortex, neurons responded strongly to single pure tones but showed no facilitative responses to paired stimuli. Neurons with best frequencies from 110 to 90 kHz were tonotopically organized rostrocaudally, with higher frequencies located more rostrally. Neurons tuned to 92-94 kHz were overpresented, whereas neurons tuned to sound between 64 and 91 kHz were rarely found. Consequently a striking discontinuity in frequency representation from 91 to 64 kHz was found across the anterior DSCF border. Most neurons exhibited monotonic impulse-count functions and responded maximally to sound pressure level (SPL). There were also neurons that responded best to weak sounds but unlike the DSCF area, amplitopic representation was not found. Thus, the DSCF area is quite unique not only in its extensive representation of frequencies in the second harmonic CF component but also in its amplitopic representation. The anteroventral nonprimary auditory cortex consisted of neurons broadly tuned to pure tones between 88 and 99 kHz. Neither tonotopic nor amplitopic representation was observed. Caudal to this area and near the anteroventral border of the DSCF area, a small cluster of FM-FM neurons sensitive to particular echo delays was identified. The responses of these neurons fluctuated significantly during repetitive stimulation.     

Immediate changes in tuning of inferior colliculus neurons following acute lesions of cat spiral ganglion.

In previous studies, we demonstrated that acute lesions the spiral ganglion (SG), the cells of origin of the auditory nerve (AN), change the frequency organization of the inferior colliculus central nucleus (ICC) and primary auditory cortex (AI). In those studies, we used a map/re-map approach and recorded the tonotopic organization of neurons before and after restricted SG lesions. In the present study, response areas (RAs) of ICC multi-neuronal clusters were recorded to contralateral and ipsilateral tones after inserting and fixing-in-place tungsten microelectrodes. RAs were recorded from most electrodes before, immediately (within 33-78 min) after, and long (several hours) after restricted mechanical lesions of the ganglion. Each SG lesion produced a "notch" in the tone-evoked compound action potential (CAP) audiogram corresponding to a narrow range of lesion frequencies with elevated thresholds. Responses of contralateral IC neurons, which responded to these lesion frequencies, underwent an elevation in threshold to the lesion frequencies with either no change in sensitivity to other frequencies or with dramatic decreases in threshold to lesion-edge frequencies. These changes in sensitivity produced shifts in characteristic frequency (CF) that could be more than an octave. Thresholds at these new CFs matched the prelesion thresholds of neurons tuned to the lesion-edge frequencies. Responses evoked by ipsilateral tones delivered to the intact ear often underwent complementary changes, i.e., decreased thresholds to lesion frequency tones with little or no change in sensitivity to other frequencies. These results indicate that responses of IC neurons are produced by convergence of auditory information across a wide range of AN fibers and that the acute "plastic" changes reported in our previous studies occur within 1 h of an SG lesion.     

Analysis of auditory evoked potential parameters in the presence of radiofrequency fields using a support vector machines method

The paper presents a study of global system for mobile (GSM) phone radio-frequency effects on human cerebral activity. The work was based on the study of auditory evoked potentials (AEPs) recorded from healthy humans and epileptic patients. The protocol allowed the comparison of AEPs recorded with or without exposure to electrical fields. Ten variables measured from AEPs were employed in the design of a supervised support vector machines classifier. The classification performance measured the classifier′s ability to discriminate features performed with or without radiofrequency exposure. Most significant features were chosen by a backward sequential selection that ranked the variables according to their pertinence for the discrimination. Finally, the most discriminating features were analysed statistically by a Wilcoxon signed rank test. For both populations, the N100 amplitudes were reduced under the influence of GSM radiofrequency (mean attenuation of −0.36μV for healthy subjects and −0.6OμV for epileptic patients). Healthy subjects showed a NIOO latency decrease (−5.23ms in mean), which could be consistent with mild, localised heating. The auditory cortical activity in humans was modified by GSM phone radio-frequencies, but an effect on brain functionality has not been proven. MBEC online number: 20043906     

The effect of species-specific vocalization on the discharge of auditory cortical cells in the awake squirrel monkey (Saimiri sciureus)

Summary Action potentials of single auditory cortical neurons of the squirrel monkey were recorded in a chronic, unanesthetized preparation. The responsiveness of units was tested with various types of simple and complex acoustic stimuli in a free field situation. As simple auditory stimuli, bursts of pure tones, clicks, and white noise were utilized. Species-specific vocalizations served as complex, biologically significant stimuli.The data are based on 48 neurons which showed a discrete response to speciesspecific vocalizations. In 63% the response to calls could be predicted from the units' responses to simple stimuli. Thirty-seven percent of the neurons were classified as unpredictable with respect to their responsiveness to vocalizations. The response of most units was restricted to call stimuli which showed similarities in their frequency-time characteristics. About 7% of the 116 units responding to calls were classified as selective responders because they were not excited by any other stimulus tested. It was not possible to single out the acoustic features to which these units responded.Peter Winter died in an skiing accident in March, 1972.     

Representation of harmonic frequencies in auditory memory: a mismatch negativity study

Most natural sounds are composed of a mixture of frequencies, which activate separate neurons in the tonotopic auditory cortex. Nevertheless, we perceive this mixture as an integrated sound with unique acoustic properties. We used the Mismatch Negativity (MMN), a marker of auditory change detection, to determine whether individual harmonics are represented in sensory memory. The MMN elicited by duration and pitch deviations were compared for harmonic and pure tones. Controlled for acoustic differences between standards and deviants and their relative probabilities, the MMN was larger for harmonic than pure tones for duration but not for pitch deviance. Because the magnitude of the MMN reflects the number of concurrent changes in the acoustic input relative to a preexistent acoustic representation, these results suggest that duration is represented and compared separately for individual frequencies, whereas pitch comparison occurs after integration.     

Feature extraction and tonotopic organization in the avian auditory forebrain

Summary In a neurophysiological study within the auditory centers of the mediocaudal telencephalon of the starling, 601 neurons were tested for auditory responses. 369 of these units responded to pure tones, noise bands, amplitude modulations (AM), or species-specific sounds. Of all the auditory neurons, 16.8% did not respond to pure tones but only to more complex stimuli (tone-unresponsive-, TU-units). The remaining auditory units were classified as tone-responsive (TR-units). In 44.3% of TR-units (i.e. 36.9% of all auditory units) differing responses to tones versus more complex stimuli were observed. Responses as they occur in TU-units and in the differing responses of TR-units can be explained by neuronal extraction of features in the time (108 out of 198 neurons) and in the spectral domain (82 out of 198 neurons). Responses to species-specific sounds usually can be explained in terms of extraction of these features. Among neurons sensitive to temporal features, exclusive responses to a narrow range of AM frequencies were observed. In those TU-units that represent spectral features some restrict their responses to noise bands with distinct bandwidths centered around a specific midfrequency. These units reject both wider and narrower noise bands. A tonotopic arrangement of auditory units is found in field L, the surrounding neostriatum (NCM), and the Hyperstriatum ventrale (HV). Isofrequency lines run as a continuum through NCM, field L, and the caudal part of HV. TU-units are integrated into the tonotopic gradient according to the midfrequency of effective stimuli (e.g. noise bands or AM). The anatomical position of auditory units is correlated to their response properties. Within one isofrequency contour an increase in response selectivity is seen from field L to the postsynaptic areas in the NCM and the HV. The results are discussed in terms of possible mechanisms of feature extraction in the avian auditory system.Part of the program of the Sonderforschungsbereich 114 (BIONACH) funded by the Deutsche Forschungsgemeinschaft     

The Auditory Evoked Response to Stimuli Producing Periodicity Pitch

The cortical evoked response in man to an amplitude modulated complex sound was investigated in order to find out whether the response reflects the acoustic spectrum of the stimulus or its modulation rate. The complex sound consisted of a train of square waves repeated 200 times a second and filtered so that only the acoustic energy confined predominantly to the region of 1000 Hz was delivered to the listener. Perceptually, the pitch of this complex sound is in the neighborhood of 200 Hz. The results from 10 listeners, tested repeatedly, showed that the presence of 1000 Hz tones interposed between successive presentations of the periodic complex stimulus served to habituate the response to the latter; intervening 200 Hz tones exerted relatively little effect on the responsiveness to the periodic stimulus. These data suggest that periodicity differences in stimulation at the periphery are not converted into place differences at the level of the auditory cortex; that a low-pitched sound is not necessarily mediated by those neural units maximally responsive to low frequency sinusoids.     

Passive long-latency event-related potentials in mental retardation.

Long-latency auditory event-related potentials (ERPs) were passively recorded in ten mental retardates and ten age-matched normal controls. Patients were mildly to moderately retarded and had epilepsy controlled with monotherapy, ERPs were recorded from CA-A1+A2, with 1000 and 3000 Hz tones in an "oddball" paradigm. Latency and amplitude of N1, N2, P2, and P3 components were compared in controls and retardates. All ten patients had reproducible AEPs, but these were attenuated in amplitude in four, although amplitudes did not differ significantly from controls. P3 was prolonged in latency in four patients, but patients and controls did not differ significantly. AEP latency and amplitude was not correlated with degree of retardation. These findings suggest that "cognitive" evoked potentials an be recorded passively in persons with impaired cognition, but are not correlated with intellectual ability and may not reflect specific cognitive functions.     

Decrease of functional coupling between left and right auditory cortices during dichotic listening: an electroencephalography study

The present study focused on functional coupling between human bilateral auditory cortices and on possible influence of right over left auditory cortex during dichotic listening of complex non-verbal tones having near (competing) compared with distant non-competing fundamental frequencies. It was hypothesized that dichotic stimulation with competing tones would induce a decline of functional coupling between the two auditory cortices, as revealed by a decrease of electroencephalography coherence and an increase of directed transfer function from right (specialized for the present stimulus material) to left auditory cortex. Electroencephalograph was recorded from T3 and T4 scalp sites, overlying respectively left and right auditory cortices, and from Cz scalp site (vertex) for control purposes. Event-related coherence between T3 and T4 scalp sites was significantly lower for all electroencephalography bands of interest during dichotic listening of competing than non-competing tone pairs. This was a specific effect, since event-related coherence did not differ in a monotic control condition. Furthermore, event-related coherence between T3 and Cz and between T4 and Cz scalp sites showed no significant effects. Conversely, the directed transfer function results showed negligible influence at group level of right over left auditory cortex during dichotic listening. These results suggest a decrease of functional coupling between bilateral auditory cortices during competing dichotic stimuli as a possible neural substrate for the lateralization of auditory stimuli during dichotic listening.     

Prevalence of stereotypical responses to mistuned complex tones in the inferior colliculus

The human auditory system has an exceptional ability to separate competing sounds, but the neural mechanisms that underlie this ability are not understood. Responses of inferior colliculus (IC) neurons to "mistuned" complex tones were measured to investigate possible neural mechanisms for spectral segregation. A mistuned tone is a harmonic complex tone in which the frequency of one component has been changed; that component may be heard as a separate sound source, suggesting that the mistuned tone engages the same mechanisms that contribute to the segregation of natural sounds. In this study, the harmonic tone consisted of eight harmonics of 250 Hz; in the mistuned tone, the frequency of the fourth harmonic was increased by 12% (120 Hz). The mistuned tone elicited a stereotypical discharge pattern, consisting of peaks separated by about 8 ms and a response envelope modulated with a period of 100 ms, which bore little resemblance to the discharge pattern elicited by the harmonic tone or to the stimulus waveform. Similar discharge patterns were elicited from many neurons with a range of characteristic frequencies, especially from neurons that exhibited short-latency sustained responses to pure tones. In contrast, transient and long-latency neurons usually did not exhibit the stereotypical discharge pattern. The discharge pattern was generally stable when the stimulus level or component phase was varied; the major effect of these manipulations was to shift the phase of the response envelope. Simulation of IC responses with a computational model suggested that off-frequency inhibition could produce discharge patterns with these characteristics.     

Hydrogen-rich saline reduces oxidative stress and inflammation by inhibit of JNK and NF-κB activation in a rat model of amyloid-beta-induced Alzheimer's disease

Dyslexia is characterized by deficits in phonological processing abilities. However, it is unclear what the underlying factors for poor phonological abilities or speech sound representations are. One hypothesis suggests that individuals with dyslexia have problems in basic acoustic perception which in turn can also cause problems in speech perception. Here basic auditory processing was assessed by auditory event-related potentials recorded for paired tones presented in an oddball paradigm in 9-year-old children with dyslexia and a familial background of dyslexia, typically reading children at familial risk for dyslexia and control children without risk for dyslexia. The tone pairs elicited a P1-N250 complex with emerging N1-P2 complex. Control children showed larger responses over the left-than-right hemisphere at the P1 and P2 time windows for both short and long within-pair intervals (WPI; 10 and 255ms) whereas children with dyslexia showed this pattern only for the tone pairs with the long WPI. The response for the pairs with the short WPI showed equal amplitudes over both hemispheres in children with dyslexia. The findings indicate that individuals with dyslexia process basic auditory information differently when the tones are within the temporal window of integration.