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PubMed2002

Functional role of auditory cortex in frequency processing and pitch perception.

Microelectrode studies in nonhuman primates and other mammals have demonstrated that many neurons in auditory cortex are excited by pure tone stimulation only when the tone's frequency lies within a narrow range of the audible spectrum. However, the effects of auditory cortex lesions in animals and humans have been interpreted as evidence against the notion that neuronal frequency selectivity is functionally relevant to frequency discrimination. Here we report psychophysical and anatomical evidence in favor of the hypothesis that fine-grained frequency resolution at the perceptual level relies on neuronal frequency selectivity in auditory cortex. An adaptive procedure was used to measure difference thresholds for pure tone frequency discrimination in five humans with focal brain lesions and eight normal controls. Only the patient with bilateral lesions of primary auditory cortex and surrounding areas showed markedly elevated frequency difference thresholds: Weber fractions for frequency direction discrimination ("higher"-"lower" pitch judgments) were about eightfold higher than Weber fractions measured in patients with unilateral lesions of auditory cortex, auditory midbrain, or dorsolateral frontal cortex; Weber fractions for frequency change discrimination ("same"-"different" pitch judgments) were about seven times higher. In contrast, pure-tone detection thresholds, difference thresholds for pure tone duration discrimination centered at 500 ms, difference thresholds for vibrotactile intensity discrimination, and judgments of visual line orientation were within normal limits or only mildly impaired following bilateral auditory cortex lesions. In light of current knowledge about the physiology and anatomy of primate auditory cortex and a review of previous lesion studies, we interpret the present results as evidence that fine-grained frequency processing at the perceptual level relies on the integrity of finely tuned neurons in auditory cortex.

Acoustic Stimulation↗
PubMed1994

Primary auditory pathway and reticular activating system dysfunction in Alzheimer's disease.

Patients with Alzheimer's disease (AD) have pathologic involvement of several important components of the primary auditory pathway, including the inferior colliculus, medial geniculate body, primary auditory cortex, and secondary auditory cortex. The main components of the brainstem auditory evoked response (BAER) and middle latency response (MLR) reflect the function of portions of the primary auditory pathway, including those affected pathologically in AD. The amplitude of the P1 component of the MLR reflects the degree of neuronal activity of midbrain portions of the ascending reticular activating system (ARAS) with cortical cholinergic projections. To determine whether there is dysfunction of the primary auditory pathway and ARAS in AD, we compared simultaneous BAER and MLR component latency and amplitude measurements in patients with mild-moderate AD (n = 35) and age-matched healthy elderly controls (n = 34). There were significant latency delays in brainstem transmission time (BAER I-V interpeak latency; p < 0.05) and in primary auditory cortex evoked potential generation (MLR Pa latency; p < 0.05) in the AD group compared with controls. In addition, there was a significant reduction in the P1 component amplitude of the MLR in the AD group (p < 0.01). These results indicate dysfunction of the primary auditory pathway and ARAS in patients with mild-moderate AD and support the hypothesis that impairment of auditory function and of arousal are intrinsic features of AD.

Aged↗
PubMedDate not supplied

[Middle and late latency auditory evoked potentials in adults with AIDS].

BACKGROUND: Middle and late latency auditory evoked potentials. AIM: to verify the occurrence of middle and late latency auditory evoked potentials disorders in adults with Acquired Immunodeficiency Syndrome (AIDS). METHOD: Middle and late latency auditory evoked potentials of 8 individuals with AIDS, with ages ranging from 10 to 51 years, with normal hearing, or with sensoryneural hearing losses up to moderate, and normal results in the Auditory Brainstem Response, comparing the results with the responses obtained for a control group which was composed by 25 individuals, with ages ranging from 19 to 24 years, with no hearing complaints and with normal hearing and normal results in the Auditory Brainstem Response. RESULTS: The Pa wave latency and amplitude averages in the C3/A2 and C4/A1 modalities, and the average of the P300 wave were analyzed. No significant differences were observed in the Pa wave amplitude and latency averages between the groups, although a non-statistically significant increase was observed in the latency and a decrease in the amplitude of such wave for the research group in the C3/A2 modality. The latency of the P300 wave was significantly longer to the left for the research group. It was also observed a longer latency to the right, although this was not statistically significant. CONCLUSION: Adult individuals with AIDS do not present alterations in the middle latency auditory evoked potential and do present alterations in the cognitive potential, indicating a disorder in the cortical regions of the auditory pathway and a deficit in the cognitive processing of auditory information for this population. Such findings stress the importance of a careful investigation of the auditory function of individuals with AIDS, thus favoring the therapeutic planning.

Acoustic Stimulation↗
PubMed1998

Concurrent visual task effects on evoked and emitted auditory p300 in adolescents.

Using an oddball stimulus presentation paradigm, the effects of divided attention on auditory P300s were studied. Auditory attention was either divided or focused, depending on the demands placed on subjects during the performance of a concomitantly presented visual task. Two types of auditory tasks were performed under each of the two auditory attention conditions. In one, subjects responded to infrequently presented high pitched tones (oddball stimuli). In the other they responded to the occasional omission of a stimulus in an otherwise rhythmically presented chain of stimuli. P300s and reaction times were recorded to both the rare tones and the omissions. The Sternberg visual memory task was used to manipulate the subject's auditory attention state. Subjects actively performed the Sternberg task during the divided auditory attention condition, whereas during the focused attention condition they were not required to respond to the visual stimuli. During focused auditory attention, evoked auditory P300s were both larger and faster than their emitted counterparts. During divided attention, auditory P300s were reduced in amplitude but latency was unaffected. Evoked auditory P300s showed evidence of containing P300a as well as P300b components, particularly when attention was shared with the visual task.

Adolescent↗
PubMed1995

The effects of visual and auditory models on the learning of a rhythmical synchronization dance skill.

The purpose of this study was to investigate the effect of visual and auditory concurrent models on the acquisition of a rhythmical synchronization task. Subjects attempted to synchronize a series of dance steps to the beat of two auditory rhythms. Subjects performed five trial blocks in one of four practice conditions: (a) audio-visual (auditory rhythms combined with a visual model), (b) audio-auditory (auditory rhythms combined with an auditory model), (c) auditory only (auditory rhythms with no model), and (d) visual only (no auditory rhythms but exposure to a visual model). Rhythmical timing and synchronization accuracy served as the dependent variables. Results revealed no practice condition learning differences for rhythmical timing. For synchronization accuracy, the audio-auditory group produced significantly lower error scores at acquisition, but no differences were found at retention. Apparently, the availability of models created an information dependency that resulted in a decrease of performance and, consequently, no group differences in retention.

Adolescent↗
PubMed1994

Linguistic influences on the auditory processing of speech by children with normal hearing or hearing impairment.

OBJECTIVE: The accurate perception of speech requires the processing of multidimensional information. The aim of this research was to examine linguistic influences on the auditory processing of speech in the presence of childhood hearing impairment. DESIGN: The processing interactions characterizing the linguistic and auditory dimensions were assessed with a pediatric auditory analog of the Pomerantz task (Pomerantz, Pristach, & Carson, 1989). The task yields measures of Stroop interference, the effect of irrelevant semantic content, and of Garner interference, the effect of irrelevant linguistic variability (Stroop, 1935; Garner, 1974a). Subjects were 100 normal-hearing children and 60 hearing-impaired children. Subjects were required to attend selectively to the auditory (voice-gender) dimension and to ignore the linguistic dimension. The logic of the task is that performance for the voice-gender dimension will be unaffected by what is happening on the irrelevant dimension if the dimensions are processed independently. On the other hand, if the dimensions are not processed independently, subjects will not be able to attend selectively and performance for the relevant dimension will be affected by what is happening on the to-be-ignored dimension. RESULTS: Both the normal-hearing and hearing-impaired children showed auditory Stroop and Garner interference effects, indicating that the auditory and linguistic dimensions were not processed independently by either group. However, the linguistic dimension exerted significantly less influence on auditory processing in the presence of childhood hearing impairment. Whereas normal-hearing children had remarkable difficulty ignoring irrelevant word input and focusing exclusively on voice-gender, hearing-impaired children were relatively successful at ignoring the linguistic dimension and attending selectively to the auditory dimension of speech. This result implies that the linguistic dimension of auditory speech input may have a different weight or processing value in the presence of childhood hearing impairment. It may be the case that hearing-impaired children encode spoken speech disproportionately in terms of the auditory dimensions, which offer important supplementary aids to speechreading. Further research is being carried out to address these possibilities. CONCLUSIONS: Both Stroop and Garner interference were significantly reduced in the presence of childhood hearing impairment. This pattern of results suggests that multidimensional speech processing is carried out in a less stimulus-bound manner in the presence of childhood hearing impairment.

Acoustic Stimulation↗
PubMed2002

External auditory canal stenosis after radiation therapy.

OBJECTIVES: To determine whether the risk of external auditory canal stenosis from external-beam radiation therapy is dose dependent. STUDY DESIGN: Retrospective chart review. METHODS: The presence of external auditory canal disease was recorded for patients who received low-dose (e.g., lymphoma [20-40 Gy]), medium-dose (e.g., chemodectoma [40-55 Gy]), or high-dose (e.g., parotid and nasopharyngeal neoplasms [55-75 Gy]) external-beam radiation therapy from 6 months to over 8 years following treatment. The incidence of external auditory canal disease was compared between groups. RESULTS: None of 13 low-dose, none of 19 medium-dose, and 8 of 91 (8.7%) high-dose external-beam radiation therapy subjects developed ipsilateral external auditory canal stenosis. No external auditory canal stenosis developed in patients treated with high-dose external-beam radiation therapy in the absence of parotid surgery. External auditory canal stenosis developed only in patients treated with parotidectomy and high-dose external-beam radiation therapy (P =.0059), and all of these cases of external auditory canal stenosis developed within 3 years of radiation therapy. CONCLUSIONS: High dose external-beam radiation therapy alone does not significantly predispose patients to external auditory canal stenosis. However, combined high-dose external-beam radiation therapy and surgery around the external auditory canal do significantly increase the risk of external auditory canal stenosis.

Constriction, Pathologic↗
PubMed1995

Robust estimation of speech in noisy backgrounds based on aspects of the auditory process.

A new approach to speech enhancement is proposed where constraints based on aspects of the auditory process augment an iterative enhancement framework. The basic enhancement framework is based on a previously developed dual-channel scenario using a two-step iterative Wiener filtering algorithm. Constraints across broad speech sections and over iterations are then experimentally developed on a novel auditory representation derived by transforming the speech magnitude spectrum. The spectral transformations are based on modeling aspects of the human auditory process which include critical band filtering, intensity-to-loudness conversion, and lateral inhibition. The auditory transformations and perceptual based constraints are shown to result in a new set of auditory constrained and enhanced linear prediction (ACE-LP) parameters. The ACE-LP based speech spectrum is then incorporated into the iterative Wiener filtering framework. The improvements due to auditory constraints are demonstrated in several areas. The proposed auditory representation is shown to result in improved spectral characterization in background noise. The auditory constrained iterative enhancement (ACE-II) algorithm is shown to result in improved quality over all sections of enhanced speech. Adaptation of auditory based constraints to changing spectral characteristics over broad classes of speech is another novel aspect of the proposed algorithm. The consistency of speech quality improvement for the ACE-II algorithm is illustrated over time and across all phonemes classified over a large set of phonetically balanced sentences from the TIMIT database. This study demonstrates the application of auditory based perceptual properties of a human listener to speech enhancement in noise, resulting in improved and consistent speech quality over all regions of speech.

Humans↗
PubMedDate not supplied

[Functional activity of auditory cortex studied with SPECT: methodology validation and application in bilateral profound deafness].

To evaluate the differences in the functional activity of the auditory cortex between normal hearing and profound deafness, a perfusion single photon emission tomography (SPECT) study was designed. SPECT stereotaxic localisation of the auditory cortex was previously validated in 2 brains by means of an anatomical study of the macroscopic localisation and cytoarchitecture of the auditory cortex. Additionally, 15 controls with normal hearing and 30 patients with profound bilateral deafness were scanned using external anatomical point sources (glabela, ineon) for stereotaxic location of the auditory cortex. The normal controls were scanned in auditive deprivation and, in 10 cases, during a monoaural tonal stimulation. Cerebral blood flow relative to cerebellum (relCBF) was assessed in the auditory cortex. The anatomical study showed that mean differences between the true auditory cortex size and the measured SPECT value were less than 2.5 mm. Nevertheless, only the caudal aspect of this area corresponded to the primary auditory cortex in the cytoarchitectonic study. During tonal stimulation, control subjects presented a significant increase of relCBF in the auditory cortex bilaterally, with significant differences in the asymmetry index (contralateral to the side of stimulation). The relCBF in the auditory cortex of controls in deprivation conditions was significantly higher than in deaf patients. There were no significant differences between groups of deaf patients, however the highest values were seen after cochlear implant. SPECT is a suitable method for studying changes in auditory cortex activity relative to different functional conditions, with a possible role in cochlear implant candidates in predicting the future benefit of the implantation.

English Abstract↗
PubMed1989

Auditory cortical projection from the anterior ectosylvian sulcus (Field AES) to the superior colliculus in the cat: an anatomical and electrophysiological study.

Sensory activity in the deep layers of the superior colliculus (SC) is strongly influenced by descending cortical inputs. Elimination (permanent or reversible) of specific regions of visual or somatosensory cortex, known to have direct access to the SC, abolishes or dramatically reduces SC responses to stimuli from those modalities. While many SC neurons are also responsive to auditory cues, the origin of auditory corticotectal connections is not clear at present and their affect on activity in the SC is unknown. Therefore, the present study was undertaken to determine the origin, organization, and functional characteristics of auditory corticotectal projections. Of the auditory cortices (AI; AII; Fields A, P, and VP), only the auditory subregion of the banks of the anterior ectosylvian sulcus (Field AES) showed a robust anatomical projection to the SC. These data were confirmed physiologically: auditory neurons in Field AES projected to the SC and auditory SC neurons responded to stimulation of the Field AES. However, neither anatomical nor physiological techniques revealed a clear topographic relationship between the Field AES and the SC but suggested instead a diffuse and extremely divergent/convergent projection. Stimulation and cryoblockade of Field AES demonstrated the excitatory nature of this corticotectal pathway, whose influence was most evident on SC responses to stimuli of reduced intensity. Given the short latency of this ear-cortex-SC circuit and its excitatory influence on unimodal as well as on multisensory auditory neurons, it seems likely that Field AES plays a significant role in facilitating SC responses to auditory stimuli.

Acoustic Stimulation↗
PubMed2003

DMXB, an alpha7 nicotinic agonist, normalizes auditory gating in isolation-reared rats.

RATIONALE: Impaired auditory gating is common in schizophrenic patients. Evidence suggests that this deficit is related to a reduced number of alpha(7) nicotinic receptors and therefore treatment with alpha(7) nicotinic agonists may improve this condition. 3-(2,4)-Dimethoxybenzylidine anabaseine (DMXB; also known as GTS-21) is such an agonist and has shown efficacy in mice both orally and intraperitoneally. OBJECTIVE: Rats reared in social isolation post weaning have demonstrated a deficit in auditory gating similar to that seen in schizophrenia patients. The current study determined the effects of DMXB on auditory gating in awake, freely moving rats, comparing a group born and raised in-house and reared in isolation post-weaning (isolation reared) with a group shipped from the supplier as adults and housed in groups prior to surgery (controls). METHODS: Ten unmedicated, baseline recordings were obtained following surgical implantation of a recording electrode. All control group rats and the isolation-reared rats that showed deficient gating at baseline were treated with 1.0, 3.33, 10 or 33 mg/kg DMXB, IP, to determine the drug's impact on auditory gating. RESULTS: Isolation-reared rats had significantly improved auditory gating at the 3.33, 10 and 33 mg/kg doses, while control rats had a significant impairment in their auditory gating at the 33 mg/kg dose. CONCLUSIONS: DMXB improved the auditory gating deficit seen in isolation-reared rats. As previously observed in another model, the change was produced through a decrease in the test amplitude in isolation-reared animals. Control animals had a significant reduction in conditioning amplitude at the high dose, which produced the loss of auditory gating. The results in the isolation-reared rats are in concert with previous studies which found similar improvement in auditory gating following administration of DMXB to DBA mice, the only differences being in the duration of the effect.

Animals↗
PubMed1986

Frequency sensitivities of auditory neurons in the cerebellum of the cat.

Threshold tuning curves were obtained from neurons in the cerebellar auditory area of the cat. The threshold of the brainstem auditory evoked response was also measured in each animal as a function of sound frequency in order to monitor the overall frequency sensitivity of the auditory periphery. Cerebellar auditory neurons responded to sound stimuli with little discrimination for the sound frequency. The values of Q10dB (a measure of the sharpness of tuning) were less than 2 for most of the neurons in this study. There was no significant difference in the sharpness of tuning for neurons in the various layers of the cerebellar auditory area. Electrophysiological mapping showed that the frequency sensitivity of single neurons did not appear to vary as a function of location within the cerebellar auditory area which includes lobules VI and VII of Larsell. Broad tuning was observed in long-latency (greater than 11 ms) neurons which responded to binaural sound stimuli as well as in short-latency (less than 6 ms) neurons which only responded to monaural sound stimuli. Within each animal, tuning curves of single cerebellar neurons were essentially superimposable onto each other and matched well with the overall frequency sensitivity of the animal as shown by brainstem auditory evoked response. Since the frequency tuning of these neurons appeared to reflect the overall frequency sensitivity of the auditory periphery, auditory neurons in the posterior vermis may receive inputs that involve convergence and integration from the entire length of the cochlea.

Animals↗
PubMed1992

Auditory response properties and spatial response areas of single neurons in the pontine nuclei of the big brown bat, Eptesicus fuscus.

Using free-field acoustic stimulation conditions, we studied the response properties and spatial sensitivity of 146 pontine neurons of the big brown bat, Eptesicus fuscus. The best frequency (BF) and minimum threshold (MT) of a pontine neuron were first determined with a sound broadcast from a loudspeaker placed ahead of the bat. A BF sound was delivered from the loudspeaker as it moved across the frontal auditory space in order to locate the response center at which the neuron had its lowest MT. Then the basic response properties of the neuron to a sound delivered from the response center were studied. As in inferior collicular and auditory cortical neurons, pontine neurons can be characterized as phasic responders, phasic bursters and tonic responders. They have both monotonic and non-monotonic intensity-rate functions. However, most of them are broadly tuned as are cerebellar neurons. Auditory spatial sensitivity was studied for 144 pontine neurons. In 9 neurons, variation of MT with a BF sound delivered from several azimuthal and elevational angles along the horizontal and vertical planes crossing the neuron's response center was measured. In addition, variation in the number of impulses with several stimulus intensities at 10 dB increments above a neuron's MT delivered from each angle was also studied. The auditory spatial sensitivity of other pontine neurons was studied by measuring the response area of each neuron with stimulus intensities at 3, 5, 10, 15 or 40 dB above its lowest MT. The response areas of pontine neurons expanded asymmetrically with stimulus intensity, but the size of the response area was not correlated with either MT or BF. In half of the pontine neurons studied, the response area expanded greatly and eventually covered almost the entire frontal auditory space. The response areas of the other half of the pontine neurons only expanded to a restricted area of frontal auditory space. Two possible neural mechanisms underlying these two types of response areas are hypothesized. The response centers of all 144 neurons were located within a small area of the frontal auditory space. The locations of response centers of these neurons are not correlated with their BFs. The distribution pattern of these response centers is comparable to that of superior collicular and cerebellar neurons but is different from that of inferior collicular and auditory cortical neurons. The results of our study suggest that auditory information is integrated in the pontine nuclei before being further sent into the cerebellum.

Acoustic Stimulation↗
PubMed1990

The nature of selective attention effects on auditory event-related potentials.

The purpose of the research reported here was to examine a number of issues relating to the nature of selective attention effects on auditory event-related potentials (ERPs), namely, to determine the relative contribution of N1 and slow wave (SW) to the early and late components of Nd respectively, where Nd is defined as the negative shift of attended ERPs relative to unattended ERPs; to examine whether individual differences in Nd morphology are related to performance and the strategies that subjects use; and to determine the contribution of changes in the attended and unattended ERPs to Nd. Auditory ERPs were recorded from subjects as they carried out an auditory selective attention task and a visual target detection task. The auditory selective attention task was a multidimensional task in which stimuli varied on location, pitch and duration and in which the subject's task was to pay attention to a particular location/pitch combination and respond whenever they detected a long-duration target tone. In the visual target detection task, subjects were required to respond whenever they detected a colour change in a light-emitting diode which also acted as a fixation point. Auditory ERPs recorded during the visual task were used to provide a measure of exogenous components uncontaminated by differential effects of selective processing of auditory stimuli. The results suggested that early Nd and N1 are independently generated as Nd did not exhibit the contralateral scalp focus typical of N1, and that late Nd is independent of SW. While substantial differences in Nd morphology were observed over subjects, these differences showed no consistent relationships to performance or to task strategies. Comparison of auditory ERPs during active auditory attention with auditory ERPs recorded during the visual control task indicated that there was an early negative shift of the attended ERP, a later negative shift of the attended ERP which had a frontal focus and a later positive shift of the unattended ERP. These results suggest that there are active processes involved in the processing of stimuli from both the attended and unattended source.

Adolescent↗
PubMed1994

Cytochrome oxidase activity in the auditory system of the mouse: a qualitative and quantitative histochemical study.

Detailed qualitative and quantitative determinations of cytochrome oxidase activity in the central auditory system of BALB/cJ mice were obtained at the light microscopic level. Cytochrome oxidase activity was determined using quantitative densitometry calibrated with standards of spectrophotometrically assayed enzymatic activity. This was done together with a cobalt-intensified histochemical procedure using fresh-frozen brains without perfusion-fixation. The resulting method showed improved sensitivity and allowed quantification of histochemical labeling as actual enzyme activity units. Adjacent sections were processed for either Nissl, fiber or Golgi stains to correlate the histochemical labeling with tissue morphology. The more peripheral auditory nuclei showed primarily somatic labeling with specific cell types showing predominant reactivity. However, higher auditory structures, including the inferior colliculus, medial geniculate and auditory cortex, showed predominantly neuropil reactivity. Comparison of mean cytochrome oxidase activities for the 27 auditory regions quantified revealed a trend for decreasing activity from the brainstem to the forebrain in central lemniscal structures. The extra-lemniscal auditory regions at each level showed lower activity than the corresponding lemniscal regions. The regions with the higher activity values showed around 10 times the labeling density of the white matter, indicating the high sensitivity of the method. The darkly labeling auditory structures were clearly delineated from surrounding neural regions, supporting the concept that basal levels of oxidative metabolic capacity are larger for the auditory system. It was concluded that the quantitative approach to cytochrome oxidase histochemistry may be applied successfully to the mouse brain. The normative data presented may be used as a starting point for other investigations of the effects of experimental manipulations on the metabolic activity of the auditory system.

Animals↗
PubMed2006

Electrophysiological and behavioral evidence of auditory processing deficits in children with reading disorder.

OBJECTIVE: The aim of the research was to investigate auditory processing abilities in children with reading disorders using electrophysiological and behavioral tasks. METHODS: Differences in auditory processing between control, compensated (age appropriate reading skills with a history of reading disorder), and reading disordered groups were systematically investigated. RESULTS: The reading disorder group had significantly lower results than control and compensated reader groups for most tests in the reading and auditory processing test battery. All children with a reading disorder did not pass at least one behavioral test of auditory processing, and hence would be diagnosed clinically as having an auditory processing disorder (APD). The reading disorder group also had significantly smaller /ga/-evoked mismatch negativity (MMN) area than the control group. Compensated and control groups had similar results for the electrophysiological and behavioral auditory processing tests. Correlation analyses showed that reading fluency and accuracy and nonword scores (measured using Castle and Coltheart's word/nonword test) correlated significantly with most APD measures. CONCLUSIONS: The general profile of auditory processing deficits in children with reading disorder was a combination of deficits on frequency patterns (i.e. frequency pattern test) and absent or small /ga/-evoked MMN. Significant results from the correlation analyses support the co-morbidity of reading and auditory processing disorders. SIGNIFICANCE: Children with reading disorders are likely to have auditory processing disorders.

Acoustic Stimulation↗
PubMed2005

Cholinergic modulation of preattentive auditory processing in aging.

Auditory event-related potential (ERP) components P50 and N100 are thought to index preattentive auditory processing underlying stimulus detection, whereas a subsequent component termed mismatch negativity (MMN) has been proposed to reflect comparison of incoming stimuli to a short-lived sensory memory trace of preceding sounds. Existing evidence suggests impairment of preattentive auditory processing in aging, which appears to be accompanied by decline of cholinergic activity. Previous studies indicate that scopolamine, which is a centrally acting muscarinic receptor antagonist, modulates preattentive auditory processing in young subjects. It has remained elusive, however, to which extent scopolamine affects preattentive auditory processing in aged subjects. We measured auditory responses simultaneously with electroencephalogram (EEG) and magnetoencephalogram (MEG) from nine non-demented elderly subjects after intravenous injection of scopolamine or glycopyrrolate, the latter being a peripherally acting cholinergic antagonist, using a double blind protocol. Scopolamine significantly delayed electric P50, both electric and magnetic N100 responses, whereas subsequent MMN and P200 responses were not altered by scopolamine. Our results indicate that the cholinergic system modulates auditory processing underlying stimulus detection in aging. In addition, auditory evoked responses appear to have different age-related sensitivity to cholinergic modulation. The combined MEG/EEG measurements using particularly auditory N100 response might offer an objective tool to monitor cholinergic activity in aging and Alzheimer's disease (AD).

Aged↗
PubMed2005

Topography of projections from the primary and non-primary auditory cortical areas to the medial geniculate body and thalamic reticular nucleus in the rat.

The functional significance of parallel and redundant information processing by multiple cortical auditory fields remains elusive. A possible function is that they may exert distinct corticofugal modulations on thalamic information processing through their parallel connections with the medial geniculate body and thalamic reticular nucleus. To reveal the anatomical framework for this function, we examined corticothalamic projections of tonotopically comparable subfields in the primary and non-primary areas in the rat auditory cortex. Biocytin was injected in and around cortical area Te1 after determining best frequency at the injection site on the basis of epicortical field potentials evoked by pure tones. The rostral part of area Te1 (primary auditory area) and area temporal cortex, area 2, dorsal (Te2D) (posterodorsal auditory area) dorsal to the caudal end of area Te1, which both exhibited high best frequencies, projected to the ventral zone of the ventral division of the medial geniculate body. The caudal end of area Te1 (auditory area) and the rostroventral part of area Te1 (a part of anterior auditory field), which both exhibited low best frequencies, projected to the dorsal zone of the ventral division of the medial geniculate body. In contrast to the similar topography in the projections to the ventral division of the medial geniculate body, collateral projections to the thalamic reticular nucleus terminated in the opposite dorsal and ventral zones of the lateral and middle tiers of the nucleus in each pair of the tonotopically comparable cortical subfields. In addition, the projections of the non-primary cortical subfields further arborized in the medial tier of the thalamic reticular nucleus. The results suggest that tonotopically comparable primary and non-primary subfields in the auditory cortex provide corticofugal excitatory effects to the same part of the ventral division of the medial geniculate body. On the other hand, corticofugal inhibition via the thalamic reticular nucleus may operate in different parts of the ventral division of the medial geniculate body or different thalamic nuclei. The primary and non-primary cortical auditory areas are presumed to subserve distinct gating functions for auditory attention.

Acoustic Stimulation↗