Biomedical subjects

Christo Pantev

Publications and source records attributed to Christo Pantev.

At least 19 recordsLinked to original sources

PubMed2006

Enhanced anterior-temporal processing for complex tones in musicians.

OBJECTIVE: To examine how auditory brain responses change with increased spectral complexity of sounds in musicians and non-musicians. METHODS: Event-related potentials (ERPs) and fields (ERFs) to binaural piano tones were measured in musicians and non-musicians. The stimuli were C4 piano tones and a pure sine tone of the C4 fundamental frequency (f0). The first piano tone contained f0 and the first eight harmonics, the second piano tone consisted of f0 and the first two harmonics and the third piano tone consisted of f0. RESULTS: Subtraction of ERPs of the piano tone with only the fundamental from ERPs of the harmonically rich piano tones yielded positive difference waves peaking at 130 ms (DP130) and 300 ms (DP300). The DP130 was larger in musicians than non-musicians and both waves were maximally recorded over the right anterior scalp. ERP source analysis indicated anterior temporal sources with greater strength in the right hemisphere for both waves. Arbitrarily using these anterior sources to analyze the MEG signals showed a DP130m in musicians but not in non-musicians. CONCLUSIONS: Auditory responses in the anterior temporal cortex to complex musical tones are larger in musicians than non-musicians. SIGNIFICANCE: Neural networks in the anterior temporal cortex are activated during the processing of complex sounds. Their greater activation in musicians may index either underlying cortical differences related to musical aptitude or cortical modification by acoustical training.

Acoustic Stimulation↗

PubMed2006

Rhythmic brain activities related to singing in humans.

To investigate the motor control related to sound production, we studied cortical rhythmic changes during continuous vocalization such as singing. Magnetoencephalographic (MEG) responses were recorded while subjects spoke in the usual way (speaking), sang (singing), hummed (humming) and imagined (imagining) a popular song. The power of alpha (8-15 Hz), beta (15-30 Hz) and low-gamma (30-60 Hz) frequency bands was changed during and after vocalization (singing, speaking and humming). In the alpha band, the oscillatory changes for singing were most pronounced in the right premotor, bilateral sensorimotor, right secondary somatosensory and bilateral superior parietal areas. The beta oscillation for the singing was also confirmed in the premotor, primary and secondary sensorimotor and superior parietal areas in the left and right hemispheres where were partly activated even for imagined a song (imaging). These regions have been traditionally described as vocalization-related sites. The cortical rhythmic changes were distinct in the singing condition compared with the other vocalizing conditions (speaking and humming) and thus we considered that more concentrated control of the vocal tract, diaphragm and abdominal muscles is responsible. Furthermore, characteristic oscillation in the high-gamma (60-200 Hz) frequency band was found in Broca's area only in the imaging condition and might occur singing rehearsal and storage process in Broca's area.

Adult↗

PubMed2006

One year of musical training affects development of auditory cortical-evoked fields in young children.

Auditory evoked responses to a violin tone and a noise-burst stimulus were recorded from 4- to 6-year-old children in four repeated measurements over a 1-year period using magnetoencephalography (MEG). Half of the subjects participated in musical lessons throughout the year; the other half had no music lessons. Auditory evoked magnetic fields showed prominent bilateral P100m, N250m, P320m and N450m peaks. Significant change in the peak latencies of all components except P100m was observed over time. Larger P100m and N450m amplitude as well as more rapid change of N250m amplitude and latency was associated with the violin rather than the noise stimuli. Larger P100m and P320m peak amplitudes in the left hemisphere than in the right are consistent with left-lateralized cortical development in this age group. A clear musical training effect was expressed in a larger and earlier N250m peak in the left hemisphere in response to the violin sound in musically trained children compared with untrained children. This difference coincided with pronounced morphological change in a time window between 100 and 400 ms, which was observed in musically trained children in response to violin stimuli only, whereas in untrained children a similar change was present regardless of stimulus type. This transition could be related to establishing a neural network associated with sound categorization and/or involuntary attention, which can be altered by music learning experience.

Acoustic Stimulation↗

PubMed2006

Cortical oscillations related to processing congruent and incongruent grapheme-phoneme pairs.

In this study, we investigated changes in cortical oscillations following congruent and incongruent grapheme-phoneme stimuli. Hiragana graphemes and phonemes were simultaneously presented as congruent or incongruent audiovisual stimuli to native Japanese-speaking participants. The discriminative reaction time was 57 ms shorter for congruent than incongruent stimuli. Analysis of MEG responses using synthetic aperture magnetometry (SAM) revealed that congruent stimuli evoked larger 2-10 Hz activity in the left auditory cortex within the first 250 ms after stimulus onset, and smaller 2-16 Hz activity in bilateral visual cortices between 250 and 500 ms. These results indicate that congruent visual input can modify cortical activity in the left auditory cortex.

Acoustic Stimulation↗

PubMed2005

Modulation of P2 auditory-evoked responses by the spectral complexity of musical sounds.

We investigated whether N1 and P2 auditory-evoked responses are modulated by the spectral complexity of musical sounds in pianists and non-musicians. Study participants were presented with three variants of a C4 piano tone equated for temporal envelope but differing in the number of harmonics contained in the stimulus. A fourth tone was a pure tone matched to the fundamental frequency of the piano tones. A simultaneous electroencephalographic/magnetoencephalographic recording was made. P2 amplitude was larger in musicians and increased with spectral complexity preferentially in this group, but N1 did not. The results suggest that P2 reflects the specific features of acoustic stimuli experienced during musical practice and point to functional differences in P2 and N1 that relate to their underlying mechanisms.

Acoustic Stimulation↗

PubMed2005

Cortical processing of esophageal sensation is related to the representation of swallowing.

The esophagus plays a major role in the act of swallowing. The aim of the present investigation was to apply whole-head magnetoencephalography in order to study the cortical processing of esophageal sensation in healthy humans in whom the cortical representation of swallowing had been established previously. The proximal esophagus was stimulated in nine participants by intermittent 5 ml water infusion. Submental EMG recording was used to identify trials, which were contaminated by subsequent swallowing. Esophageal stimulation led to changes in rhythmic activity of the brain that were localized in the left lateral primary sensorimotor cortex. The pattern of cortical activation showed the same hemispheric lateralization as that of volitional swallowing, however, being localized more lateral. The close anatomical vicinity of these two functions points to an important physiological link between the cortical processing of esophageal sensation and the cortical control of swallowing.

Adult↗

PubMed2005

Effect of bilingualism on cognitive control in the Simon task: evidence from MEG.

The present study used magneto-encephalography (MEG) to determine the neural correlates of the bilingual advantage previously reported for behavioral measures in conflict tasks. Bilingual Cantonese-English, bilingual French-English, and monolingual English speakers, performed the Simon task in the MEG. Reaction times were faster for congruent than for incongruent trials, and the Cantonese group was faster than the other two groups, which did not differ from each other. Analyses of the MEG data using synthetic aperture magnetometry (SAM) and partial last squares (PLS) showed that the same pattern of activity, involving signal changes in left and medial prefrontal areas, characterized all three groups. Correlations between activated regions and reaction times, however, showed that the two bilingual groups demonstrated faster reaction times with greater activity in superior and middle temporal, cingulate, and superior and inferior frontal regions, largely in the left hemisphere. The monolinguals demonstrated faster reaction times with activation in middle frontal regions. The interpretation is that the management of two language systems led to systematic changes in frontal executive functions.

Adult↗

PubMed2005

Automatic encoding of polyphonic melodies in musicians and nonmusicians.

In music, multiple musical objects often overlap in time. Western polyphonic music contains multiple simultaneous melodic lines (referred to as "voices") of equal importance. Previous electrophysiological studies have shown that pitch changes in a single melody are automatically encoded in memory traces, as indexed by mismatch negativity (MMN) and its magnetic counterpart (MMNm), and that this encoding process is enhanced by musical experience. In the present study, we examined whether two simultaneous melodies in polyphonic music are represented as separate entities in the auditory memory trace. Musicians and untrained controls were tested in both magnetoencephalogram and behavioral sessions. Polyphonic stimuli were created by combining two melodies (A and B), each consisting of the same five notes but in a different order. Melody A was in the high voice and Melody B in the low voice in one condition, and this was reversed in the other condition. On 50% of trials, a deviant final (5th) note was played either in the high or in the low voice, and it either went outside the key of the melody or remained within the key. These four deviations occurred with equal probability of 12.5% each. Clear MMNm was obtained for most changes in both groups, despite the 50% deviance level, with a larger amplitude in musicians than in controls. The response pattern was consistent across groups, with larger MMNm for deviants in the high voice than in the low voice, and larger MMNm for in-key than out-of-key changes, despite better behavioral performance for out-of-key changes. The results suggest that melodic information in each voice in polyphonic music is encoded in the sensory memory trace, that the higher voice is more salient than the lower, and that tonality may be processed primarily at cognitive stages subsequent to MMN generation.

Acoustic Stimulation↗

PubMed2004

Responsiveness to repeated speech stimuli persists in left but not right auditory cortex.

Activation of the auditory cortex habituates with repeated stimulation. While behaviorally adaptive in most circumstances, decreasing auditory responsiveness could interfere with speech perception. We therefore tested whether auditory habituation differs for speech and non-speech stimuli and for left and right auditory cortex. We examined seven right-handed subjects in whom we had determined left-hemispheric language dominance by event-related blood flow assessment. We recorded magnetoencephalographic-evoked responses to trains of four sine tones or vowels and measured the decrement from the first to the last stimulus of the response component about 100 ms after stimulus onset (N1). For the sine tones there was a decrement in both hemispheres. Conversely, for vowels there was significant attenuation of the auditory decrement in the left compared with the right hemisphere (p=0.017). This left-hemisphere persistence in auditory responsiveness to vowels demonstrates that the human brain processes speech stimuli differently than non-speech stimuli and that the left-hemisphere plays a dominant role in this speech-specific auditory processing.

Acoustic Stimulation↗

PubMed2004

Sensory mapping of lip representation in brass musicians with embouchure dystonia.

Embouchure dystonia is a focal task-specific disorder involving abnormal non-coordinated movements and involuntary muscle contraction around the mouth. In professional brass players it is often so disabling that patients have to limit or give up their occupation. We examined the somatosensory homuncular representation and measured gap detection sensitivity of the lips in eight former professional musicians affected by embouchure dystonia and eight control subjects. Relative to controls, the patients' digit, and especially the thumb, representations were shifted in a lateral direction towards the lip representational zone. Patients' upper lips showed decreased sensitivity compared to their lower lips (p < 0.01). This asymmetry result was absent in controls. Abnormal somatosensory reorganization may contribute to the disorder.

Adult↗

PubMed2004

N1m recovery from decline after exposure to noise with strong spectral contrasts.

Comb-filtered noise (CFN, derived from white noise by suppressing regularly spaced frequency regions) was presented for 3 s followed by two types of test stimuli. One test stimulus (SB) was comprised of spectra centered in the stop-band regions of the CFN and the other test stimulus (PB) of spectra centered in the band pass regions of the CFN. Magnetoencephalographically recorded N1m responses evoked by SB stimuli were decreased relative to the N1m response evoked by PB stimuli. This effect was maximal when the interval between the CFN and test stimuli was short (0.5 s) but was detected at intervals up to 2 s. The results suggest lateral inhibition in the auditory cortex and point to a decay of inhibition lasting on the order of seconds.

Acoustic Stimulation↗

PubMed2004

An integrative MEG-fMRI study of the primary somatosensory cortex using cross-modal correspondence analysis.

We develop a novel approach of cross-modal correspondence analysis (CMCA) to address whether brain activities observed in magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI) represent a common neuronal subpopulation, and if so, which frequency band obtained by MEG best fits the common brain areas. Fourteen adults were investigated by whole-head MEG using a single equivalent current dipole (ECD) and synthetic aperture magnetometry (SAM) approaches and by fMRI at 1.5 T using linear time-invariant modeling to generate statistical maps. The same somatosensory stimulus sequences consisting of tactile impulses to the right sided: digit 1, digit 4 and lower lip were used in both neuroimaging modalities. To evaluate the reproducibility of MEG and fMRI results, one subject was measured repeatedly. Despite different MEG dipole locations and locations of maximum activation in SAM and fMRI, CMCA revealed a common subpopulation of the primary somatosensory cortex, which displays a clear homuncular organization. MEG activity in the frequency range between 30 and 60 Hz, followed by the ranges of 20-30 and 60-100 Hz, explained best the defined subrepresentation given by both MEG and fMRI. These findings have important implications for improving and understanding of the biophysics underlying both neuroimaging techniques, and for determining the best strategy to combine MEG and fMRI data to study the spatiotemporal nature of brain activity.

Adult↗

PubMed2004

Improving permutation test power for group analysis of spatially filtered MEG data.

Non-parametric statistical methods, such as permutation, are flexible tools to analyze data when the population distribution is not known. With minimal assumptions and better statistical power compared to the parametric tests, permutation tests have recently been applied to the spatially filtered magnetoencephalography (MEG) data for group analysis. To perform permutation tests on neuroimaging data, an empirical maximal null distribution has to be found, which is free from any activated voxels, to determine the threshold to classify the voxels as active at a given probability level. An iterative procedure is used to determine the distribution by computing the null distribution, which is recomputed when a possible activated voxel is found within the current distributions. Besides the high computational costs associated with this approach, there is no guarantee that all activated voxels are excluded when constructing the maximal null distribution, which may reduce the statistical power. In this study, we propose a novel way to construct the maximal null distribution from the data of the resting period. The approach is tested on the MEG data from a somatosensory experiment, and demonstrated that the approach could improve the power of the permutation test while reducing the computational cost at the same time.

Adult↗

PubMed2004

Auditory steady-state responses reveal amplitude modulation gap detection thresholds.

Auditory evoked magnetic fields were recorded from the left hemisphere of healthy subjects using a 37-channel magnetometer while stimulating the right ear with 40-Hz amplitude modulated (AM) tone-bursts with 500-Hz carrier frequency in order to study the time-courses of amplitude and phase of auditory steady-state responses (ASSRs). The stimulus duration of 300 ms and the duration of the silent periods (3-300 ms) between succeeding stimuli were chosen to address the question whether the time-course of the ASSR can reflect both temporal integration and temporal resolution in the central auditory processing. Long lasting perturbations of the ASSR were found after gaps in the AM sound, even for gaps of short duration. These were interpreted as evidences for an auditory reset mechanism. Concomitant psycho-acoustical tests corroborated that gap durations perturbing the ASSR were in the same range as the threshold for AM gap detection. Magnetic source localizations estimated the ASSR sources in the primary auditory cortex, suggesting that the processing of temporal structures in the sound is performed at or below the cortical level.

Acoustic Stimulation↗

PubMed2003

Magnetoencephalographic study of the cortical activity elicited by human voice.

In an attempt to identify voice-specific neural activities in auditory cortex in humans, we recorded cortical magnetic responses. Volunteers were instructed to listen to vocal and instrumental sounds matched in fundamental-frequency, duration, temporal envelope and average root mean square power. The stimuli were sounds produced by four singers and four musical instruments at each of two fundamental frequencies: 220 Hz (musical note A3) and 261.9 Hz (C3). Two components of the evoked responses were analyzed, one at approximately 100 ms (N1m) and the other 400 ms after the stimulus onset (sustained field, SF). The source locations of equivalent current dipoles for both components were estimated around the Heschl's gyrus in both hemispheres. Compared with the instrumental sound, the source strength of the SF component for the voice was significantly larger.

Acoustic Stimulation↗

PubMed2003

Current source density distribution of sleep spindles in humans as found by synthetic aperture magnetometry.

Previous magnetoencephalography (MEG) studies of sleep spindles have identified a complex and widespread distribution in parietal and frontal cortices by fitting a dipolar model to the data. In this study, we used a whole-head 151-channel MEG system with simultaneous electroencephalography (EEG) recording in eight normal subjects. All subjects fell asleep during stage 2 and 3; EEG spindles have been observed in all cases. The current source density distribution of sleep spindles in the 10-15 Hz frequency band was localized by means of synthetic aperture magnetometry, and statistically tested using a permutation analysis. Source locations of the sleep spindles were found primarily in the frontal cortex, including dorsolateral and medial prefrontal areas, as well as the parietal cortex, including the vicinity of the primary sensorimotor areas. These results suggest that sleep spindles are similar in frequency content and spatial location to mu rhythm, and that these two oscillatory activities might also have a common neural basis and physiological meaning.

Adult↗

PubMed2003

Evidence for training-induced crossmodal reorganization of cortical functions in trumpet players.

The aim of this study was to compare multimodal information processing in the somatosensory and auditory cortices and related multimodal areas in musicians (trumpet players) and non-musicians. Magnetoencephalographic activity (MEG) was recorded in response to five stimulus conditions from 10 professional trumpet players and nine musically untrained control subjects. Somatosensory and auditory stimuli were presented alone or in combination. Our data suggest that musicians, in general, process multisensory stimuli differently to the control group. When stimulating the lip in professional trumpet players, a multimodal interaction (expressed as difference between the multimodal response and the sum of unimodal responses) in the corresponding somatosensory cortex showed a positive peak at 33 ms, which was not found in the control group. Conversely, the control group shows a significant interaction of opposite polarity around 60-80 ms. We suggest that training-induced reorganization in musicians leads to a qualitatively different way to process multisensory information. It favors an early stage of cortical processing, which is modified by the connections between multimodal and auditory neurons from thalamus to primary somatosensory area.

Acoustic Stimulation↗

PubMed2003

Learning of tactile frequency discrimination in humans.

Learning is based on the remodeling of neural connections in the brain. The purpose of the present study was to examine the extent to which training-induced improvements in tactile frequency discrimination in humans are correlated with an increase of cortical representations in the primary somatosensory cortex. Healthy male subjects (n = 16) were trained in a tactile frequency discrimination task of the left ring finger. During the first 15 days of training, there was a steep improvement in frequency discrimination, which generalized from the trained finger to its homologue on the opposite hand, and to a lesser extent, to the other fingers on both hands. During the following 15 days of training, there was only a minor improvement in tactile frequency discrimination. Retention of improved performance in frequency discrimination 30 days after training was demonstrated for all digits. Cortical finger representation in the primary somatosensory cortex, as measured by magnetic source imaging, did not change during training. Because of the generalized training effect and the lack of detectable increase in the cortical field evoked from the trained finger, we assume that skill improvement was mediated predominantly by regions outside the primary somatosensory cortex.

Adult↗