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At least 1,567 records · Page 87Linked to original sources
PubMed1987

Neuromagnetic responses of the human auditory cortex to on- and offsets of noise bursts.

Cortical sources of neuromagnetic responses to noise bursts were compared in 7 healthy humans. The earliest response, P40m, peaking about 40 ms after the stimulus onset, was followed by a prominent deflection in the opposite direction at about 100 ms (N100m) and by another peak at 200 ms (P200m). A sustained field, seen near the end of the 400- to 550-ms stimuli, ended with an off-response of the same polarity as N100m. All deflections could be explained by cortical activity within the Sylvian fissure. The source of P200m was anterior to other sources of the on-response, except P40m. When noise bursts, or pauses of equal duration in a continuous noise were presented to the subject, striking similarities were found between the 100-ms deflections of the on- and off-responses: both peaked at about the same latency; their estimated sources were closed to each other in the supratemporal plane and their amplitudes depended in a similar way on the interstimulus interval (1.1-8.8 s). However, only the on-response was preceded by P40m, suggesting that P40m and N100m are not causally linked. N100m seems to reflect cortical activity related to any abrupt change in the auditory environment.

Auditory Cortex↗
PubMed1992

Peculiarities of inhibition in cat auditory cortex neurons evoked by tonal stimuli of various durations.

The extra- and intracellular responses of 262 neurons in A1 to tones of best frequency with durations ranging from 10 ms to 1.2 min were studied acute experiments on ketamine-anesthetized cats. Following the generation of action potentials in response to the tone stimulus, inhibition of both the background and the auditory stimulus-evoked spike activity were observed in 91% of the investigated neurons. The duration of this inhibition corresponded to the stimulus duration. For the remaining neurons (9%) an inhibition of the stimulus-evoked spike activity alone was seen, also corresponding to the stimulus duration. Maximal inhibition of the spike activity occurred for the first 100-200 ms of the inhibitory response (the period which equalled the time of development of an IPSP in a cell). During this period of IPSP development, the membrane resistance of the neuron was reduced to 60-90% of its initial value. Varying the duration of the acoustic signal within a range of 10-200 ms was accompanied by a change in the IPSP duration and inhibition of the spike activity of the neuron. Whenever the tone lasted more than 200 ms, the membrane potential of the neuron was restored to the resting potential. However, during this period, the responsiveness of the neuron was lower than that initially observed. Measurement of the membrane resistance during the inhibitory pause that was not accompanied by hyperpolarization produced an index with an average 17% lower than the initial value for 87% of the neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed2003

Determination of activation areas in the human auditory cortex by means of synthetic aperture magnetometry.

In this study we applied synthetic aperture magnetometry (SAM) to investigate active cortical areas associated with magnetically recorded transient and steady-state auditory evoked responses. For transient evoked responses, SAM images reveal an activated volume of cortical tissue within the lateral aspect of the superior temporal plane. The volume of cortical activation for steady-state responses was located more medially than that for transient evoked responses. Additionally, SAM also reveals a small overlap of activated areas between transient and steady-state evoked responses, which has not be demonstrated when using equivalent current dipole (ECD) source modeling. Source waveforms from SAM and ECD analyses show comparable temporal information. Results from this study suggest that SAM is a useful technique for imaging cortical structures involved in processing perceptual information.

Acoustic Stimulation↗
PubMedDate not supplied

Noninvasive direct stimulation of the cochlear nerve for functional MR imaging of the auditory cortex.

We herein present our preliminary experience with functional MR imaging of the direct electrical stimulation of the cochlear nerve using an MR imaging-compatible electrode placed in the external auditory meatus of five patients with binaural sensorineural hearing loss. The stimulator was placed outside the imager's bore, and the electrode produced virtually no susceptibility artifacts. In three of five patients, it was possible to activate the superior temporal gyrus during functional MR imaging. No side effects were observed.

Auditory Cortex↗
PubMedDate not supplied

Tinnitus and event-related activity of the auditory cortex.

A neuromagnetic study in tinnitus patients and normal-hearing controls was performed with a modified contingent negative variation (CNV) paradigm. While the warning stimulus S1 was a tone burst at an intensity well above threshold, the imperative stimulus S2 was presented at a near threshold intensity because, in the majority of cases, the perceived loudness of tinnitus is very close to the threshold for a pure tone of the same frequency. Subjects had to respond to S2 by pressing a button until its offset was detected. In this case, instead of the usual sudden cut-off of the CNV after the perception of S2, a slow negative deflection develops, the post-imperative negative variation (PINV). Its initial portion probably indicates the development of a second initial CNV because the subject had to attend also to the offset of S2. The neuromagnetic data were analysed both in the time domain and in the frequency domain (short-time spectral analysis of the classical EEG bands). The time domain waveform as well as the spectrotemporal patterns of the MEG bands exhibited deviations from the normal pattern in several tinnitus subgroups, depending on the characteristics of tinnitus (tonal vs. noisiform, monaural vs. binaural) and on the stimulation conditions (tinnitus side vs. non-tinnitus side).

Adolescent↗