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PubMed2004

Dynamic plasticity in coupled avian midbrain maps.

Internal mapping of the external environment is carried out using the receptive fields of topographic neurons in the brain, and in a normal barn owl the aural and visual subcortical maps are aligned from early experiences. However, instantaneous misalignment of the aural and visual stimuli has been observed to result in adaptive behavior, manifested by functional and anatomical changes of the auditory processing system. Using methods of information theory and statistical mechanics a model of the adaptive dynamics of the aural receptive field is presented and analyzed. The dynamics is determined by maximizing the mutual information between the neural output and the weighted sensory neural inputs, admixed with noise, subject to biophysical constraints. The reduced costs of neural rewiring, as in the case of young barn owls, reveal two qualitatively different types of receptive field adaptation depending on the magnitude of the audiovisual misalignment. By letting the misalignment increase with time, it is shown that the ability to adapt can be increased even when neural rewiring costs are high, in agreement with recent experimental reports of the increased plasticity of the auditory space map in adult barn owls due to incremental learning. Finally, a critical speed of misalignment is identified, demarcating the crossover from adaptive to nonadaptive behavior.

Adaptation, Physiological↗
PubMed2001

The sensory basis of reading problems.

Learning to read is much more difficult than learning to speak. Most children teach themselves to speak with little or no difficulty. Yet a few years later when they come to learn to read they have to be taught how to do it; they do not pick up reading by themselves. This is because we speak in words and syllables, but we write in phonemes. Syllables do not naturally break down into the sounds of letters and letter units (i.e., phonemes) because these do not correspond to physiologically distinct articulatory gestures (Liberman, Shankweiler, & Studdert-Kennedy, 1967). Alphabetic writing was only invented when people realized that syllables could be artificially divided into smaller acoustically distinguishable phonemes that could be represented by a small number of letters. But these distinctions are arbitrary cultural artifacts, and their mastery was originally confined to a select social class. And until about 100 years ago it did not matter much if the majority of people could not read; the acquisition of reading probably had no serious disadvantages. Reading requires the integration of at least two kinds of analysis (Castles & Coltheart, 1993; Ellis, 1984; Manis, Seidenberg, Doi, McBride-Chang, & Petersen, 1996; Morton, 1969; Seidenburg, 1993). First, the visual form of words, the shape of letters, their order in words, and common spelling patterns, which is termed their orthography, has to be processed visually. Their orthography yields the meaning of familiar words very rapidly without needing to sound them out. But for unfamiliar words, and all words are fairly unfamiliar to the beginning reader, the letters have to be translated into the speech sounds (i.e., phonemes) that they stand for, and then those sounds have to be melded together in inner speech to yield the word and its meaning. Reading exclusively by the phonological route is more time consuming than if words can be accessed directly without requiring phonological mediation.

Auditory Pathways↗
PubMed1983

[Study of the response of caudate nucleus neurons to direct electric stimulation of the medial geniculate body in the cat].

Extracellular activity of 124 caudate nucleus neurons during stimulation of parvo- and magnocellular parts of the medial geniculate body by rectangular electrical stimuli were investigated in chronic experiments on cats. Reactions were observed in 54 neurons (43%). Main types of responses were: phasic activation in the form of a single spike or spike discharge, initial activation followed by inhibition and pure inhibition. Excitatory responses prevailed (81% of the reacting neurons). The latent periods in different units fluctuated from 2.7 to 64 ms. In the same unit the latent periods were also very variable, which permits considering them as orthodromic. The mode of the histogram of the latent periods of the excitatory responses was in the range of 9-12 ms. The latent periods of the inhibitory responses varied from 12 to 130 ms and were in most neurons in a range of 40-60 ms. The increase in stimulus intensity led to an increase in response regularity, an increase in the number of spikes, reduced latent periods. In the same neuron the character and the structure of responses to stimulation of the relay nucleus and to sound clicks were usually identical. The latent period of responses to clicks was larger. Peculiarities of functional connection of the medial geniculate body with the caudate nucleus as a forebrain polymodal unspecific structure are discussed.

Animals↗
PubMed2006

A quantitative analysis of psychometric functions for different auditory tasks in gerbils.

The psychometric function relates the probability of a correct response to the variation of a physical stimulus parameter. In many perceptual tasks one point on this function is defined by a more or less arbitrary threshold criterion and threshold is used to study the effects of various treatments or age. Besides threshold, the shape of the psychometric function provides additional information. The variability of internal (neural) noise and the sensorineural transduction function will affect the shape of the psychometric function and may, therefore, reveal important features in the processing of stimulus characteristics. Here we analyze the effect of age on psychometric functions from gerbils: (A) for the detection of a tone or noise pulse in silence which is generally regarded as a measure of cochlear function and (B) for a gap detection task, investigating aspects of temporal processing that involve the ascending auditory pathway. Our data show that the slope of the psychometric function for the detection of tone and noise pulses in silence is independent of age and threshold. In contrast, the steepness of the psychometric function is decreased in gerbils with impaired temporal resolution. We discuss these observations in the context of physiological data from young and old animals.

Acoustic Stimulation↗
PubMedDate not supplied

[Verbal auditory agnosia: SPECT study of the brain].

Verbal auditory agnosia are rare in clinical practice. Clinically, it characterized by impairment of comprehension and repetition of speech but reading, writing, and spontaneous speech are preserved. So it is distinguished from generalized auditory agnosia by the preserved ability to recognize non verbal sounds. We present the clinical picture of a forty-years-old, right handed woman who developed verbal auditory agnosic after an bilateral temporal ischemic infarcts due to atrial fibrillation by dilated cardiomyopathie. Neurophysiological studies by pure tone threshold audiometry: brainstem auditory evoked potentials and cortical auditory evoked potentials showed sparing of peripheral hearing and intact auditory pathway in brainstem but impaired cortical responses. Cranial CT-SCAN revealed two large hypodenses area involving both cortico-subcortical temporal lobes. Cerebral SPECT using 99mTc-HMPAO as radiotracer showed hypoperfusion just posterior in both frontal lobes nect to Roland's fissure and at level of bitemporal lobes just anterior to Sylvian's fissure.

Adult↗
PubMed1996

Topography of auditory evoked cortical potentials in children with severe language impairment: the N1 component.

Topographic maps of late auditory evoked potentials (AEPs) were obtained in a group of 20 children, aged 9-15 years, with severe language impairment (LI) and an age-matched control (C) group of 20 normal children. The study was focused on differences in the latency, amplitude and topography of the N1 component between the two groups and the potential diagnostic value of these variables. The stimulus was a pure tone at 500 Hz with a duration of 100 msec and a rise and fall time of 20 msec. The intensity was 75 dB HL. Six test sequences of 50 stimuli at an interval of 1.0 sec were presented to the left and right ear separately. The AEPs were recorded and analyzed with the Bio-Logic Brain Atlas III program. In the topographic maps a focus corresponding to N1 (FN1) was seen in 15 subjects after left-ear stimulation and in 17 subjects after right-ear stimulation in the LI group. In the C group FN1 was identified in all 20 subjects after left-ear stimulation and in 19 subjects after right-ear stimulation. The position of FN1 was in front of the interaural line and with a dominance on the side contralateral to the ear stimulated in both groups. Among the subjects with an FN1, 6 in the LI group and 4 in the C group had deviating topography. Non-focal maps were seen in 5 LI subjects and 1 C subject. The latencies of N1 were longer in the LI group and there was no decrease in latency with age. There were no differences in FN1 amplitudes between groups. The prolonged latencies in the LI subjects compared to the C subjects may be explained by a slower processing in central auditory pathways and the lack of decrease in latencies with age in the LI subjects might indicate that the disturbance persists and is not a pure delay of maturation. The diagnostic sensitivity of N1 latency, amplitude and topography, in selecting the LI subjects, was 40% with a specificity of 90%. Statistical mapping of a time epoch of 70-140 msec and corresponding to FN1 in the map showed regions of > or = 3 S.D. in 10 LI and 2 C subjects, which corresponds to a sensitivity of 50% and a specificity of 90%. The variability of results within the LI group may reflect different pathophysiological factors underlying the language impairment. In conclusion, topographic evaluation of auditory long-latency potentials may become a diagnostic tool in speech and language disorders.

Adolescent↗
PubMed2003

A whole head MEG study of the amplitude-modulation-following response: phase coherence, group delay and dipole source analysis.

OBJECTIVE: The amplitude-modulation-following response (AMFR) is the frequency component detectable in the electroencephalogram (EEG) or magnetoencephalography (MEG) corresponding to the modulation frequency of an amplitude modulated tone used as a continuous acoustic stimulus. Various properties of the AMFR depend on modulation frequency, suggesting that different generators along the auditory pathway are involved. The present study addresses these issues on the basis of a whole head MEG experiment. METHODS: AM tones with modulators in the 40 Hz and 80 Hz range were presented unilaterally to 10 normal hearing subjects. Biomagnetic responses were recorded with a 151 channel MEG system. The data analysis concentrated on the phase coherence of the responses, group delays and the estimated location of underlying equivalent dipole sources. RESULTS: MEG AMFR is more reliably detected in the 40 Hz than in the 80 Hz range. Both response amplitude and phase coherence indicate clear bilateral activation over the parietal/temporal region. Dipole source analysis confirms that sources are located in or near the auditory cortex. Group delays at 80 Hz are shorter than at 40 Hz. CONCLUSIONS: In both modulation frequency ranges MEG responses are dominated by activity in the auditory cortex, in apparent contrast with EEG data in the literature, pointing to dominant contributions of thalamic sources to the 80 Hz AMFR.

Adolescent↗
PubMed1990

Brainstem acoustic evoked responses: maturational aspects from cochlea to midbrain.

BAEPs were recorded from 92 healthy children with a gestational age of 35 weeks up to 16 years. The maturation kinetic of I-III and I-V interpeak latency can well be approximated by the exponential regressions I-V : y = 0.9588 x e -0.9215 x x + 3.9728; r = 0.87; I-III : y = 0.6182 x e -1.1737 x x + 2.1759; r = 0.81; Adult values are reached by about two years of life. In contrast to this immaturity of the central auditory pathways the slopes of latency--intensity functions of waves I and V show no significant differences between premature infants and neonates versus older children over three years. Caused by the prolonged I-V IPL wave V latency is about 1 ms longer in the first group, whereas wave I is only slightly prolonged (0.2 ms) within the first three months of life.

Acoustic Stimulation↗
PubMed1996

Topography of auditory evoked long-latency potentials in children with severe language impairment: the P2 and N2 components.

OBJECTIVE: To establish objective neurophysiological correlates of a central auditory processing disorder in impaired language development. The study focused on the differences in latency, amplitude, and topography of the auditory evoked long-latency components, P2 and N2, and the potential diagnostic value of these parameters. DESIGN: Topographic maps of the late auditory evoked potentials (AEPs) were obtained in a group of 20 children, aged 9 to 15 yr, with severe language impairment (LI) and in a control (C) group of 20 normal children. Stimulus was a pure tone at 500 Hz with a duration of 100 msec and a rise and fall time of 20 msec. The intensity was 75 dB HL. Six test sequences of 50 stimuli an interval of 1.0 sec were presented to the left and to the right ear separately. The AEPs were recorded and analyzed with the Bio-Logic Brain Atlas III program. RESULTS: In the topographic maps, a focus of positive potential corresponding to P2 (FP2) and a focus of negative potential corresponding to N2 (FN2) were seen in the majority of children, with a similar distribution in the two groups. The latencies of P2 and N2 were significantly longer in the LI group than in the C group, P2 showing the most pronounced difference. The amplitudes of FP2 and FN2 were lower in the LI group. The diagnostic value of the P2 and N2 latency, amplitude, and topography in identifying the LI subjects, was estimated by means of a scoring system. With all three parameters together, the sensitivity was calculated to be 80% and the specificity 80%. Statistical mapping of the latency interval of 135 to 305 msec showed z maps with regions of > or = 3 SD in 14 subjects in the LI group and eight subjects in the C group. CONCLUSIONS: The deviations in the LI group indicate slower processing in central auditory pathways rather than differences in location and orientation of generators. The deviating topography seen in some LI subjects may reflect the various sites and extent of cerebral dysfunction. The results also support the idea of different generators for the P2 and N2 components. Topographic evaluation of long-latency AEPs may become a diagnostic tool in language disorders. The scoring system is a potential model in the establishment of individual diagnostic variables.

Adolescent↗
PubMed1993

Auditory brain-stem responses in blepharospasm.

The auditory brain-stem response (ABR) has been reported to detect abnormalities in both the auditory pathways and in adjacent structures. Ten of 35 consecutive patients with blepharospasm were found to have abnormal ABRs involving poor form and delayed peak latency of positive components III or V. Abnormal ABRs in approximately 30% of patients with essential blepharospasm suggest pathology in the brain-stem of a substantial proportion of patients with this form of cranial-cervical dystonia.

Acoustic Stimulation↗
PubMed1992

The effect of preterm birth on brainstem, middle latency and cortical auditory evoked responses (BMC AERs).

Recent studies on the maturation of auditory brainstem evoked responses (ABRs) present conflicting results, whereas only sparse reports exist with respect to the maturation of middle latency auditory evoked responses (MLRs) and auditory cortical evoked responses (ACRs). The present study reports the effect of preterm birth on the maturation of auditory evoked responses in low risk preterm infants (27-34 weeks conceptional age). The ABRs indicate a consistent trend towards longer latencies for all individual ABR components and towards longer interpeak latencies in preterm infants. The MLR shows longer latencies for early component P0 in preterm infants. The ACRs show a remarkable difference between preterm and term infants. At 40 weeks CA the latencies of ACR components Na and P2 are significantly longer in term infants, whereas at 52 weeks CA the latencies of the same ACR components are shorter in term infants. The results support the hypothesis that retarded myelination of the central auditory pathway is partially responsible for differences found between preterm infants and term infants with respect to late ABR components and early MLR component P0. Furthermore, mild conductive hearing loss in preterm infants may also play its role. A more complex mechanism is implicated to account for the findings noted with respect to MLR component Na and ACR components Na and P2.

Evoked Potentials, Auditory↗
PubMed1986

Auditory response properties of neurons in the anterior ectosylvian sulcus of the cat.

The auditory response properties of single neurons in the fundus and banks of the anterior ectosylvian sulcus (AES) were studied with simple dichotic stimuli (viz. noise- and tone-bursts) in cats anaesthetized with alpha-chloralose. Neurons within AES showed simple onset responses, were most commonly excited by stimulation of both ears, and showed either broad tuning or multiple high best frequencies. Some neurons were also tested for visual responsiveness and it was found that auditory cells and visual cells were intermingled within the sulcus. A small percentage of cells responded to both auditory and visual stimulation. Overall, the response properties of AES neurons differed from those of nearby auditory cortical fields. The region of AES studied appears to be outside the recently defined fourth somatosensory area (SIV), but overlaps para-SIV found deeper in the sulcus. It appears that deep within the sulcus and along most of its length there is a population of auditory, somatosensory and visual cells; to delineate this auditory population from the surrounding auditory cortical fields this region has been designated Field AES.

Animals↗
PubMed2002

Functional MRI of auditory cortex activated by multisite electrical stimulation of the cochlea.

Electrical stimulation of the ear of deaf patients via cochlear implants offers a unique occasion to study activity of central auditory pathways with fMRI, without bias due to scanner noise. Such measurements, however, require one to control the possible interference between fMRI acquisition and the implanted electrodes. A series of measurements on a customized phantom designed to characterize the level of induced currents during MRI acquisition is presented. These experiments demonstrate that the major artifactual contribution is due to radiofrequency interaction and that safe experimental conditions can be obtained with proper shielding of the stimulation cables. The induced currents could be reduced to low levels (<50 microA for a duration <2 ms), below the acoustic perceptual threshold of cochlear implant subjects. Subsequent fMRI experiments on a patient using an Ineraid cochlear implant were conducted. Results revealed bilateral localized activation of the primary auditory cortex. Stimulation of two different intracochlear electrodes elicited activity in two neighboring, but different, regions, in agreement with the known tonotopical organization of the auditory cortex. This work paves the way for fMRI studies of a broad selection of auditory paradigms without interference from unwanted noise.

Artifacts↗
PubMed2004

Auditory neuropathy: a potentially under-recognized neonatal intensive care unit sequela.

Auditory neuropathy (AN) is a hearing disorder that affects newborns. Those with high-risk neonatal histories, family history of childhood hearing loss, and hyperbilirubinemia are at greatest risk. Current neonatal intensive care unit (NICU) hearing screening methods that rely only on otoacoustic emissions will fail to detect this disorder. Auditory neuropathy differs from conductive hearing loss and sensorineural hearing loss; a specific constellation of findings on audiologic evaluation are diagnostic of this disorder. The pathophysiology of AN is unclear; however, it may be caused by demyelinization or degeneration at points along the auditory pathway. The actual incidence of AN is unknown; it is more prevalent in high-risk infants. The course of AN varies widely among patients. Current management ranges from close monitoring of the child's development to cochlear implantation. Neonatal intensive care unit nurses need to be aware of this disorder to help support and educate at-risk families and to alert them of the need to monitor hearing and language development in their infants.

Auditory Diseases, Central↗
PubMed1983

Electrocochleography and brainstem potentials in the diagnosis of the deaf child.

The deaf child must receive sound amplification before he reaches the age of two years. At this age the hearing threshold is best measured objectively by electrocochleography (ECochG) and auditory brainstem response (ABR) audiometry. When used correctly, both methods allow an exact threshold estimation which is informative enough for adequate hearing aid prescription. Both methods have advantages and disadvantages when used in children. The advantages of ECochG are: (a) a more exact threshold estimation and (b) strictly monaural evaluation. The advantages of ABR are: (a) ease of performance; it is not invasive and does not require general anaesthesia and (b) allows for exploration of higher levels in the auditory pathway up to the midbrain. We believe that ECochG and ABR are compatible and complementary in the diagnosis of childhood deafness. ABR could be used in first instance, while ECochG could be reserved for doubtful cases and for those who cannot be adequately sedated. Extra-audiological factors such as the availability of anaesthetists and varying hospital facilities, play a further role in determining the choice of electric response technique.

Audiometry↗
PubMed2004

The octave illusion revisited again.

The octave illusion (D. Deutsch, 1974) occurs when 2 tones separated by an octave are alternated repeatedly, such that when the right ear receives the high tone, the left ear receives the low tone, and vice versa. Most subjects in the original study reported hearing a single tone that alternated from ear to ear, whose pitch also alternated from octave to octave, and D. Deutsch (1975a) proposed an explanation in terms of separate what and where auditory pathways. C. D. Chambers, J. B. Mattingley, and S. A. Moss (2002) argued that the perceived pitch difference generally corresponds more to a semitone and proposed an alternative explanation in terms of diplacusis. This article argues that Chambers et al. used problematic procedures and reports a new experiment on the octave illusion. The findings confirm that an octave difference is generally perceived, and they agree with the model of Deutsch (1975a) but are at variance with the diplacusis hypothesis.

Adolescent↗