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PubMed2003

Aging and the processing of sound duration in human auditory cortex.

Age-related declines in coding the fine temporal structure of acoustic signals is proposed to play a critical role in the speech perception difficulties commonly observed in older individuals. This hypothesis was tested by measuring auditory evoked potentials elicited by sounds of various durations in young, middle-aged and older adults. All stimuli generated N1 and P2 waves that peaked at about 104 and 200 ms post-stimulus onset. The N1 amplitude increased linearly with increases in the tonal duration in young, middle-aged, and older adults. The P2 amplitude also increased linearly with signal duration, but only in young and middle-aged adults. The results demonstrate that the N1 and P2 waves can resolve duration differences as short as 2-4 ms and that normal aging decreases the temporal resolving power for processing small differences in sound duration.

Adult↗
PubMed2005

Reactive blue prevented caffeine-induced neurotoxicity by an independent mechanism from intracellular calcium currents in cell culture from auditory cortex of rats.

Neurotoxicity induced by caffeine in auditory-neuron cultures was studied in rat pups. For possible protective effect, reactive blue (RB) alone and in combination with dantrolene were tested in subsequent doses. RB was found to have a U-shape neuroprotective effect in caffeine neurotoxicity. Dantrolene was also tested in combined application in caffeine neurotoxicity. Despite the existing neuroprotection, no additional protection was obtained with various doses of dantrolene. In conclusion, RB may exert neuroprotective effect by increasing intracellular ATP levels in caffeine toxicity. High ATP levels may postpone the toxic cascade. Dantrolene as an endoplasmic reticulum calcium release blocker had no additional protective effect, suggesting that the increased intracellular calcium levels may be involved in later states of the toxic cascade, occurring after the compensatory phase of the cell death.

Animals↗
PubMedDate not supplied

Normal variation in the frequency and location of human auditory cortex landmarks. Heschl's gyrus: where is it?

Interpersonal communication via the auditory modality is fundamental to normal human development. One of the prominent anatomical specializations supporting this communication is the transverse gyrus of Heschl on the superior surface of the temporal lobe. This gyrus frequently appears duplicated, either by a sulcus indenting the crown of an initially single gyrus (common stem), or by a complete posterior duplication. The frequency of these duplications has been reported to be elevated in populations with learning disabilities and genetic anomalies. The significance of this observation is unclear, however, due to conflicting reports of the base rate of duplication and the location of relevant sulcal landmarks. In this study we report the variation in frequency and location of the sulcal boundaries of Heschl's gyrus in volumetric magnetic resonance imaging scans of 105 normal controls aged 5-65. The major results were as follows: (i) duplications were unstable--the frequency of duplication ranged from 20 to 60% depending on distance from the midline; (ii) common stem duplications were more frequent than posterior duplications, particularly in the right hemisphere. Intra- and interindividual instability in sulcal landmarks pose serious obstacles to the attempt to map behavioral function onto the brain. Novel methods for dealing with structural variation are needed to facilitate the development of valid mapping techniques.

Adolescent↗
PubMed1998

Functional organization of the auditory cortex is different in stutterers and fluent speakers.

Impaired auditory feedback has been suggested to cause stuttering, and subtle irregularities of audition have been reported in behavioural studies. To characterize processing at the auditory cortical level, we recorded neuromagnetic responses to monaural tones in nine stutterers and 10 fluent speakers while the subjects were reading silently, with mouth movements only, aloud, and in chorus with another person. The basic functional organization of the auditory cortices was found to be different in stutterers and controls. The altered interhemispheric balance in stutterers was affected by speech production, due to changes in the left auditory cortical representation, and more severely by self-paced than accompanied speech. This may lead to transient non-optimal interpretation of the auditory input and affect speech fluency.

Adult↗
PubMed2004

Central auditory deficits associated with compromise of the primary auditory cortex.

The subject of this study was a 46-year-old female who had suffered a cerebrovascular accident (CVA). Magnetic resonance imaging revealed damage in the area of the distribution of the middle cerebral artery involving most, if not all, of the primary auditory area of the left hemisphere. No auditory problems were noted prior to the CVA; however, following the CVA, the subject reported a number of auditory difficulties. Pure-tone thresholds were normal post-CVA, and performance on speech recognition testing was good in both ears if ample time was provided between a response and the presentation of the next test item. Duration pattern, intensity discrimination, and middle latency response test results were abnormal for both ears, and right ear deficits were evident on an auditory fusion test and two dichotic speech tests (digits and rhymes). This case is significant in that it demonstrates a good correlation between damage to known key auditory regions and central auditory test results.

Audiometry, Pure-Tone↗
PubMed1984

[Responses of neurons of a chronically isolated strip of cat auditory cortex to intracortical stimulation during paroxysmal electrical activity].

Responses of 155 neurons to single intracortical stimulation during paroxysmal electrical activity caused by series of frequent stimuli (10-20/c) by means of the electrical current were investigated extracellularly in the three-week isolated auditory cortex slab from non-anaesthetized tubocurarin immobilized cats. Depending on the behaviour of neurons during paroxysmal electrical activity and preservation of the ability to respond to intracortical stimulation all investigated neurons of the isolated slab were divided into four groups. Their distribution according to layers and duration of latent periods were investigated. It was shown that 2/3 of the investigated neurons generated impulse activity at the time of paroxysmal discharges, the rest did not manifest such activity.

Animals↗
PubMed1998

Processing of twitter-call fundamental frequencies in insula and auditory cortex of squirrel monkeys.

Amplitude-modulated (AM) and frequency-modulated (FM) elements are prominent periodic sound features of squirrel monkeys' twitter calls. To investigate how the periodic FM elements are represented in the spike activity of cortical neurons, single units in the insula, primary auditory field (AI) and rostral auditory field (R) were recorded. In five monkeys, 566 units (insula, n = 181; AI, n = 221; R, n = 164) were exposed to synthesized fundamental frequencies and one natural twitter call. Neuronal encoding of periodic FM elements takes place by phase-locking to either the up- or the down-directed FM sweeps. The phase-locking was strongly influenced by the FM-period repetition rate. The ability of neurons in both auditory fields and the insula to encode all periodic FM elements showed a marked reduction at 16 Hz FM-period repetition rate. The neurons' best frequency (BF) influenced the quality of periodicity encoding, but neurons with BFs outside the frequency range of the fundamentals also responded with periodic discharge rates. Even neurons in AI (6.8%) and the insula (22.6%) that did not respond to pure tones showed clear periodic FM encoding. The percentage of neurons able to encode all periodic FM elements within the twitter fundamental was significantly higher in field R than in AI and the insula. From 58 simultaneously recorded pairs of units in AI and the insula that had positive cross-correlation coefficients of spontaneous activity, the influence of the FM-period repetition rate on neuronal correlation was investigated. Correlated firing of AI and insula neurons seems limited to low-period repetition rates. The cross-correlation coefficients obtained for spontaneous activity and six different periodic FM sounds showed a band-pass characteristic. The natural twitter call evoked stronger neuronal responses in all fields than the synthesized fundamental frequencies with corresponding bi-directional FM sweeps. The better encoding of the transient features in the natural call can be attributed to the amplitude modulation added to the FM elements in the natural call. These amplitude modulations divide the FM elements of twitter calls into syllable-like sound elements. It is probable that encoding the complex pattern in the time and frequency domains of a call must undergo some integration at a cortical level. Additionally, these data provide the first evidence that insula neurons contribute to the encoding of complex FM signals.

Acoustic Stimulation↗
PubMed2005

Sound processing in the auditory-cortex homologue of songbirds: functional organization and developmental issues.

Recent literature on the Field L of songbirds, showing that some neurons present a clear selectivity towards complex sounds, especially conspecific songs, is reviewed. Furthermore, studies on European starlings have revealed a complex functional organization in this central auditory area, with subareas exhibiting different response features. Interestingly, both the functional organization and the neuronal specialization can be drastically affected by early deprivation, clearly showing the existence of a developmental plasticity. Some recovery seems to remain possible at later stages, and social factors may be involved.

Acoustic Stimulation↗
PubMed1996

Sensitivity to interaural intensity differences of neurons in primary auditory cortex of the cat. I. types of sensitivity and effects of variations in sound pressure level.

1. Interaural intensity differences (IIDs) provide the major cue to the azimuthal location of high-frequency narrowband sounds. In recent studies of the azimuthal sensitivity of high-frequency neurons in the primary auditory cortex (field AI) of the cat, a number of different types of azimuthal sensitivity have been described and the azimuthal sensitivity of many neurons was found to vary as a function of changes in stimulus intensity. The extent to which the shape and the intensity dependence of the azimuthal sensitivity of AI neurons reflects features of their IID sensitivity was investigated by obtaining data on IID sensitivity from a large sample of neurons with a characteristic frequency (CF) > 5.5 kHz in AI of anesthetized cats. IID sensitivity functions were classified in a manner that facilitated comparison with previously obtained data on azimuthal sensitivity, and the effects of changes in the base intensity at which IIDs were introduced were examined. 2. IID sensitivity functions for CF tonal stimuli were obtained at one or more intensities for a total of 294 neurons, in most cases by a method of generating IIDs that kept the average binaural intensity (ABI) of the stimuli at the two ears constant. In the standard ABI range at which a function was obtained for each unit, five types of IID sensitivity were distinguished. Contra-max neurons (50% of the sample) had maximum response (a peak or a plateau) at IIDs corresponding to contralateral azimuths, whereas ipsi-max neurons (17%) had the mirror-image form of sensitivity. Near-zero-max neurons (18%) had a clearly defined maximum response (peak) in the range of +/- 10 dB IID, whereas a small group of tough neurons (2%) had a restricted range of minimal responsiveness with near-maximal responses at IIDs on either side. A final 18% of AI neurons were classified as insensitive to IIDs. The proportions of neurons exhibiting the various types of sensitivity corresponded closely to the proportions found to exhibit corresponding types of azimuthal sensitivity in a previous study. 3. There was a strong correlation between a neuron's binaural interaction characteristics and the form of its IID sensitivity function. Thus, neurons excited by monaural stimulation of only one ear but with either inhibitory, facilitatory, or mixed facilitatory-inhibitory effects of stimulation of the other ear had predominantly contra-max IID sensitivity (if contralateral monaural stimulation was excitatory) or ipsi-max sensitivity (if ipsilateral monaural stimulation was excitatory). Neurons driven weakly or not at all by monaural stimulation but facilitated binaurally almost all exhibited near-zero-max IID sensitivity. The exception to this tight association between binaural input and IID sensitivity was provided by neurons excited by monaural stimulation of either ear (EE neurons). Although EE neurons have frequently been considered to be insensitive to IIDs, our data were in agreement with two recent reports indicating that they can exhibit various forms of IID sensitivity: only 23 of 75 EE neurons were classified as insensitive and the remainder exhibited diverse types of sensitivity. 4. IID sensitivity was examined at two or more intensities (3-5 in most cases) for 84 neurons. The form of the IID sensitivity function (defined in terms of both shape and position along the IID axis) was invariant with changes in ABI for only a small proportion of IID-sensitive neurons (approximately 15% if a strict criterion of invariance was employed), and for many of these neurons the spike counts associated with a given IID varied with ABI, particularly at near-threshold levels. When the patterns of variation in the form of IID sensitivity produced by changes in ABI were classified in a manner equivalent to that used previously to classify the effects of intensity on azimuthal sensitivity, there was a close correspondence between the effects of intensity on corresponding types of azimuthal and IID sensitivity

Animals↗
PubMed2005

Opposite effects of tetanic stimulation of the auditory thalamus or auditory cortex on the acoustic startle reflex in awake rats.

The amygdala mediates both emotional learning and fear potentiation of startle. The lateral amygdala nucleus (LA) receives auditory inputs from both the auditory thalamus (medial geniculate nucleus; MGN) and auditory association cortex (AAC), and is critical for auditory fear conditioning. The central amygdala nucleus, which has intra-amygdaloid connections with LA, enhances startle magnitude via midbrain connections to the startle circuits. Tetanic stimulation of either MGN or AAC in vitro or in vivo can induce long-term potentiation in LA. In the present study, behavioural consequences of tetanization of these auditory afferents were investigated in awake rats. The acoustic startle reflex of rats was enhanced by tetanic stimulation of MGN, but suppressed by that of AAC. All the tetanization-induced changes of startle diminished within 24 h. Blockade of GABAB receptors in the LA area reversed the suppressive effect of tetanic stimulation of AAC on startle but did not change the enhancing effect of tetanic stimulation of MGN. Moreover, transient electrical stimulation of MGN enhanced the acoustic startle reflex when it lagged behind acoustic stimulation, but inhibited the acoustic startle reflex when it preceded acoustic stimulation. The results of the present study indicate that MGN and AAC afferents to LA play different roles in emotional modulation of startle, and AAC afferents are more influenced by inhibitory GABAB transmission in LA.

Acoustic Stimulation↗
PubMed1987

Maps of auditory cortex in cats reared after unilateral cochlear ablation in the neonatal period.

The responses of many neurons recorded in the high best-frequency region of primary auditory cortical field, AI, of the normal adult cat depend upon intensity differences of the sounds arriving at the two ears. These binaural interactions are exhibited early in postnatal life, well before structural maturation of the auditory pathways from the ear to the cortex is complete. The aim of the present work was to study certain aspects of the functional development of the auditory cortex in adult cats unilaterally deaf from birth. In adult animals reared with a neonatal cochlear ablation, field AI ipsilateral to the non-operated ear showed a normal tonotopic map, which was derived from single neurons and neuron clusters driven securely by best-frequency tonal stimulation in virtually every electrode penetration. The acoustic thresholds at many recording sites were as low as those obtained in AI contralateral to the non-operated ear. These findings are in marked contrast to those from control experiments on normal adult cats where only about 65% of AI neurons were excited by a sound delivered to the ipsilateral ear and where thresholds to ipsilateral ear stimulation were significantly higher than contralateral thresholds. The spatial distribution of cortical neurons based on acoustic thresholds also appeared to be different in cats unilaterally deaf from birth when compared to control cats. Closely spaced electrode penetrations in AI ipsilateral to the non-operated ear suggested that neurons were separated into low-threshold regions and high-threshold regions. There was no evidence for this type of non-random segregation in control experiments.

Animals↗
PubMed2000

Dysfunction of the auditory cortex persists in infants with certain cleft types.

Language and learning disabilities occur in almost half of individuals with oral clefts. The characteristics of these cognitive dysfunctions vary according to the cleft type, and the mechanisms underlying the relation between cleft type, cognitive dysfunction, and cleft-caused middle-ear disease are unknown. This study investigates preattentive auditory discrimination, which plays a significant role in language acquisition and usage, in infants with different cleft types. A mismatch negativity (MMN) component of brain evoked potentials, which indexes preconscious sound discrimination, and brain responses to rare sine-wave tones were recorded in 12 healthy infants and 32 infants with oral clefts at the ages of 0 and 6 months. Infants with clefts were subdivided into two categories: those with cleft lip and palate (CLP) (n=11 at birth, n=6 at the age of 6 months) and those with cleft palate only (CPO) (n=17 at birth, n=8 at the age of 6 months). At both ages, brain responses to rare sounds tended to be smaller in both cleft subgroups than in healthy peers. However, in the latency range of 300 to 500 ms, the MMN was significantly smaller in infants with CPO. In infants with CLP, the MMN was comparable to that of healthy infants. Differences in auditory discrimination between infants with CLP and CPO, as reflected by MMN, were detectable at birth and persisted into later infancy. This pattern parallels known behavioural differences between children with these cleft types. Brain responses to rare sounds, in contrast, had no differentiative power with respect to the cleft type.

Auditory Cortex↗
PubMed1978

Response variability of auditory cortex cells in the squirrel monkey to constant acoustic stimuli.

Sixty-three cells in the superior temporal gyrus of awake squirrel monkeys were tested with 8 species-specific vocalizations plus noise, clicks and tones. Identical series of stimuli were repeatedly presented over 1-5 hour intervals. The responses elicited by both vocalizations and artificial stimuli in primary and secondary cortical neurons often varied over time. In several cases the selectivity of a cell to specific vocalizations appeared to change, i.e., a vocalization which was effective in eliciting a response at one point in the experiment, later became ineffective. In the primary cortex 50% of the cells gave variable responses to one or more of the vocalizations. Twenty percent of the primary cortical cells appeared to change the selectivity of their responses to specific vocalizations. In the secondary cortex 62% of the cells varied in their responses to vocalizations; 42% showing apparent changes in selectivity.

Acoustic Stimulation↗
PubMed1995

Subdivisions of macaque monkey auditory cortex revealed by calcium-binding protein immunoreactivity.

The aim of this investigation was to characterize auditory areas of the primate cerebral cortex on the basis of chemoarchitecture. Cortical areas of the supratemporal plane were delineated in Macaca fuscata (M. fuscata) by immunocytochemical staining for parvalbumin, staining for cytochrome oxidase, examination of cyto- and myeloarchitecture, and retrograde tracing of corticocortical connections. Comparative observations were made on Macaca fascicularis (M. fascicularis). Differential staining of fiber plexuses, probably of thalamic origin, identifies a central core zone of dense immunostaining and a surrounding zone of moderate-to-dense immunostaining composed of anteromedial, lateral, and posteromedial fields. Outside the second zone, there is a third anterolateral zone of weaker immunoreactivity, and, outside that zone, there is a fourth zone in which immunoreactivity is virtually absent. Differences in parvalbumin immunostaining in the auditory fields may reflect differences in relative contributions of thalamic inputs from parvalbumin-immunoreactive cells in the medial geniculate complex. The central core zone and the surrounding three fields can be correlated with major auditory fields previously defined by multiunit mapping and thalamocortical connectivity. The core zone contains a large principal field and an anterior extension. The pattern of corticocortical connections between these and adjoining fields suggests that the anteromedial, lateral, and posteromedial fields represent first steps in three streams of connections passing outward from auditory into association cortex. M. fuscata has an unusually large auditory cortex that is more deeply placed in the lateral sulcus in comparison to that of M. fascicularis. A small annectant gyrus provides a guide to the position of the primary auditory area.

Animals↗