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Biomedical subjects

C Pantev

Publications and source records attributed to C Pantev.

At least 19 recordsLinked to original sources
PubMed2005

Stimulus induced desynchronization of human auditory 40-Hz steady-state responses.

The hypothesis that gamma-band oscillations are related to the representation of an environmental scene in the cerebral cortex after binding of corresponding perceptual elements is currently under discussion. One question is how the sensory system reacts to a fast change in the scene if perceptual elements are rigidly bound together. A reset of the gamma-band oscillation forced by a change in sensory input may dissolve the binding, which then would be re-established for the new sensation. We studied the reset of gamma-band oscillations on the 40-Hz auditory steady-state responses (ASSR) by means of whole-head magnetoencephalography (MEG). The rhythm of 40-Hz AM of a 500-Hz tone evoked the ASSR, and a short noise burst served as a concurrent stimulus. Possible direct interactions of the auditory stimuli were excluded by presenting the noise impulse in a different frequency channel (2,000-3,000 Hz) to the contralateral ear. The concurrent stimulus induced a considerable decrement in the amplitude of ASSR, which was localized in primary auditory cortices. This decrement lasted 250 ms and was significantly longer than the duration of the transient gamma-band response evoked by the noise burst. Thus it could not be explained by any linear superimposition of the responses. The time courses of ASSR amplitude and phase during recovery from the decrement resembled those after stimulus onset, indicating that a new ASSR was built up after the resetting stimulus. The results are discussed as reset of oscillations in human thalamocortical networks.

Acoustic Stimulation↗
PubMed2005

Dynamics of auditory plasticity after cochlear implantation: a longitudinal study.

Human representational cortex may fundamentally alter its organization and (re)gain the capacity for auditory processing even when it is deprived of its input for more than two decades. Stimulus-evoked brain activity was recorded in post-lingual deaf patients after implantation of a cochlear prosthesis, which partly restored their hearing. During a 2 year follow-up study this activity revealed almost normal component configuration and was localized in the auditory cortex, demonstrating adequacy of the cochlear implant stimulation. Evoked brain activity increased over several months after the cochlear implant was turned on. This is taken as a measure of the temporal dynamics of plasticity of the human auditory system after implantation of cochlear prosthesis.

Acoustic Stimulation↗
PubMed2005

Right hemispheric laterality of human 40 Hz auditory steady-state responses.

Hemispheric asymmetries during auditory sensory processing were examined using whole-head magnetoencephalographic recordings of auditory evoked responses to monaurally and binaurally presented amplitude-modulated sounds. Laterality indices were calculated for the transient onset responses (P1m and N1m), the transient gamma-band response, the sustained field (SF) and the 40 Hz auditory steady-state response (ASSR). All response components showed laterality toward the hemisphere contralateral to the stimulated ear. In addition, the SF and ASSR showed right hemispheric (RH) dominance. Thus, laterality of sustained response components (SF and ASSR) was distinct from that of transient responses. ASSR and SF are sensitive to stimulus periodicity. Consequently, ASSR and SF likely reflect periodic stimulus attributes and might be relevant for pitch processing based on temporal stimulus regularities. In summary, the results of the present studies demonstrate that asymmetric organization in the cerebral auditory cortex is already established on the level of sensory processing.

Acoustic Stimulation↗
PubMed2005

The dependence of the auditory evoked N1m decrement on the bandwidth of preceding notch-filtered noise.

The auditory evoked response is known to be changed by a preceding sound. In this study we investigated by means of magnetoencephalography how a preceding notch-filtered noise (NFN) with different bandwidths influences the human auditory evoked response elicited by the following test stimulus. We prepared white noise (WN) and four NFNs which were derived from WN by suppressing frequency regions around 1 kHz with 1/8-, 1/4-, 1/2- and 1-octave bandwidths. Stimulation for 3 s with this set of noises resulted in differences in responsiveness to a 1-kHz test tone presented 500 ms after the offset of the noises. The N1m response to the 1-kHz test tone stimulus was at a minimum when the preceding NFN had 1/4-octave stop-band frequencies as compared with 1/8-, 1/2- and 1-octave NFN and WN. This N1m decrement is explained by the imbalanced neural activities caused by habituation and lateral inhibition in the auditory system. The results contribute to understanding of the inhibitory system in the human auditory cortex.

Acoustic Stimulation↗
PubMed2004

The effect of attention on the auditory steady-state response.

40-Hz auditory steady state responses to amplitude modulated tones were recorded with magnetoencephalography to investigate the effect of focused attention. A modulation discrimination task and a destructive visual task established the attended and the non-attended experimental conditions. A strong contrast between these conditions was demonstrated by largely enhanced sustained responses under the attention condition. A significant attentional effect on the ASSR amplitude was observed mostly in the left hemisphere between 200 to 500 ms after stimulus onset. In contrast, transient gamma-band and N1 responses were not affected by the different states of attention.

Acoustic Stimulation↗
PubMed2004

Stimulus induced reset of 40-Hz auditory steady-state responses.

Auditory steady-state responses (ASSR) were evoked with 40-Hz amplitude modulated 500-Hz tones. An additional impulse-like noise stimulus (2,000 +/- 500 Hz) with spectrum clearly distinct from the one of the AM sound, induced pronounced perturbations in the ASSR. The effect of the interfering noise was interpreted as (1) reset of the ASSR because of a sudden loss in phase coherence, (2) a decrease in signal power immediately after presentation of the noise impulse, and (3) a modulation of ASSR amplitude and phase resembling the time course of the ASSR onset. The time-course of the ASSR onset was interpreted as reflecting temporal integration over several 100 ms. The reset of the ASSR was discussed as a powerful mechanism, which allows for fast reaction to a short stimulus change that overcomes the disadvantage of the ASSR's long integration time constant.

Acoustic Stimulation↗
PubMed2004

MEG analysis of "theory of mind" in emotional vignettes comprehension.

OBJECTIVE: Several studies suggested that an impaired "theory of mind" might play a key role in psychiatric disorders, such as autism and schizophrenia. Medial frontal lobe lesions of the right frontal lobe were reported to impair this ability. The aim of our study was to locate areas of the brain associated with the process of "theory of mind" in normal subjects. METHODS: In order to index the activity of brain areas related to "theory of mind" reasoning in sixteen normal adults, we administered an emotional ("happy", "sad", "angry" and "neutral") vignettes comprehension task during magnetoencephalography (MEG) recordings and analyzed these data by using SAM (synthetic aperture magnetometry), SPM99 and the permutation method. Subjects were presented with eight different videotaped social situations (each emotion has two vignettes) and were asked to indicate which emotion they represented. RESULTS: Statistically significant activation in the comparison of "happy"-"sad" and "angry"-"sad" was observed in the bilateral medial prefrontal cortices in the alpha frequency band. There were no significant differences in comparisons of each type of emotional vignette to the neutral vignettes, "happy"-"angry" comparison, and male-female comparisons. There was no significant difference in other frequency bands. CONCLUSION: This result suggests that bilateral medial prefrontal cortex are involved in the comprehension of emotional states of others.

Adult↗
PubMed2004

Cortical oscillations modulated by congruent and incongruent audiovisual stimuli.

Congruent or incongruent grapheme-phoneme stimuli are easily perceived as one or two linguistic objects. The main objective of this study was to investigate the changes in cortical oscillations that reflect the processing of congruent and incongruent audiovisual stimuli. Graphemes were Japanese Hiragana characters for four different vowels (/a/, /o/, /u/, and /i/). They were presented simultaneously with their corresponding phonemes (congruent) or non-corresponding phonemes (incongruent) to native-speaking Japanese participants. Participants' reaction times to the congruent audiovisual stimuli were significantly faster by 57 ms as compared to reaction times to incongruent stimuli. We recorded the brain responses for each condition using a whole-head magnetoencephalograph (MEG). A novel approach to analysing MEG data, called synthetic aperture magnetometry (SAM), was used to identify event-related changes in cortical oscillations involved in audiovisual processing. The SAM contrast between congruent and incongruent responses revealed greater event-related desynchonization (8-16 Hz) bilaterally in the occipital lobes and greater event-related synchronization (4-8 Hz) in the left transverse temporal gyrus. Results from this study further support the concept of interactions between the auditory and visual sensory cortices in multi-sensory processing of audiovisual objects.

Acoustic Stimulation↗
PubMed2004

Auditory cortex responses to the transition from monophonic to pseudo-stereo sound.

Human cortical responses to the change in spaciousness of sound were recorded with the method of magnetoencephalography (MEG). The phases of dichotically presented 500-Hz tones were shifted so that the sound was perceived as originating either from a point-like source centered in the head or from separated sources in space. The phase shift was embedded in 40-Hz amplitude modulation. Thus, the phase shift could not be detected from a monaural signal. The transition between 'mono' and 'pseudo-stereo' quality of the sound elicited a P1-N1-P2 response similar to the onset response as well as a decrement in the steady-state response. The responses were discussed as reflecting binaural processing in the central auditory system.

Acoustic Stimulation↗
PubMed2004

Lateral inhibition and habituation of the human auditory cortex.

The goal of this study was to compare the lateral inhibition and the habituation in the human auditory cortex, two important physiological effects during auditory processing that can be reliably measured by means of magnetoencephalography when recording auditory evoked fields. Applying 40-Hz amplitude-modulated stimuli allowed us to record simultaneously the slow transient evoked and the steady-state fields and thus to characterize the lateral inhibition and the habituation effect in primary and non-primary auditory cortical structures. The main finding of the study is that the lateral inhibition effect of non-primary auditory areas as measured on the major component of the slow transient auditory evoked field (N1) is significantly stronger than the corresponding habituation effect. By contrast, this effect was not observed for the 40-Hz steady-state fields, characterizing the activation of the primary auditory cortex in humans. The results might be interpreted as (i) evidence that the inhibition mediated by lateral connections is stronger than the habituation of excitatory neurons in the non-primary auditory cortex and (ii) the processing hierarchy in the human auditory cortex is demonstrated by the different behaviour of lateral inhibition and habituation in primary and non-primary auditory cortical structures.

Acoustic Stimulation↗
PubMed2003

Neuroimaging evidence for cortical involvement in the preparation and in the act of swallowing.

This study employed whole head magnetoencephalography and synthetic aperture magnetometry to investigate the cortical topography of the preparation and the execution of volitional and reflexive water swallowing and of a simple tongue movement. Concerning movement execution, activation of the mid-lateral primary sensorimotor cortex was strongly lateralized to the left during volitional water swallowing, less strongly lateralized to the left during reflexive water swallowing, and not lateralized at all during tongue movement. In contrast, the preparation for both volitional water swallowing and tongue movement showed a bilateral activation of the primary sensorimotor cortex. No activation was seen prior to reflexive water swallowing. Activation of the left insula and frontal operculum was observed only during both the preparation and the execution of volitional water swallowing. These new findings suggest a left hemispheric dominance for the cortical control of swallowing in humans.

Adult↗
PubMed2002

Acoustically and electrically evoked responses of the human cortex before and after cochlear implantation.

Multi-channel auditory evoked potentials (AEP) were recorded before and after cochlear implantation (CI) from a patient suffering from severe high frequency hearing loss with residual, but highly fluctuating hearing around 250 Hz. Immediately after CI activation early components of the N1 were present. Later N1 components developed during the use of CI. The unique result of this single case study is the concordance of the cortical AEP pattern obtained by native and artificial peripheral stimulation, which can be regarded as an indicator for the adequate function of the CI.

Acoustic Stimulation↗
PubMed2001

Functional reorganization of the human primary somatosensory cortex after acute pain demonstrated by magnetoencephalography.

The somatosensory system is capable of functional reorganization following peripheral denervation or training. Studies on human amputees with phantom limb pain provided evidence that these reorganizational changes are modulated through nociceptive input. In the present study we used magnetoencephalographic recordings of six healthy volunteers to assess whether acute pain by itself causes a reorganization of the primary somatosensory cortex. After the induction of an intense experimental pain at the thenar of the left hand by intradermal injection of capsaicin, the extent of the cortical hand representation and the distance between the hand representation and the localization of the lip decreased. A likely mechanism for this acute reorganization is that pain induced hyperresponsiveness of the left thenar to tactile input from neighboring body sites.

Acute Disease↗
PubMed2001

Timbre-specific enhancement of auditory cortical representations in musicians.

Neural imaging studies have shown that the brains of skilled musicians respond differently to musical stimuli than do the brains of non-musicians, particularly for musicians who commenced practice at an early age. Whether brain attributes related to musical skill are attributable to musical practice or are hereditary traits that influence the decision to train musically is a subject of controversy, owing to its pedagogic implications. Here we report that auditory cortical representations measured neuromagnetically for tones of different timbre (violin and trumpet) are enhanced compared to sine tones in violinists and trumpeters, preferentially for timbres of the instrument of training. Timbre specificity is predicted by a principle of use-dependent plasticity and imposes new requirements on nativistic accounts of brain attributes associated with musical skill.

Acoustic Stimulation↗