Christo Pantev

Increased Cortical Representation of the Fingers of the Left Hand in String Players

Magnetic source imaging revealed that the cortical representation of the digits of the left hand of string players was larger than that in controls. The effect was smallest for the left thumb, and no such differences were observed for the representations of the right hand digits. The amount of cortical reorganization in the representation of the fingering digits was correlated with the age at which the person had begun to play. These results suggest that the representation of different parts of the body in the primary somatosensory cortex of humans depends on use and changes to conform to the current needs and experiences of the individual.

Specific tonotopic organizations of different areas of the human auditory cortex revealed by simultaneous magnetic and electric recordings

This paper presents data concerning auditory evoked responses in the middle latency range (wave Pam/Pa) and slow latency range (wave N1m/N1) recorded from 12 subjects. It is the first group study to report multi-channel data of both MEG and EEG recordings from the human auditory cortex. The experimental procedure involved potential and current density topographical brain mapping as well as magnetic and electric source analysis. Responses were compared for the following 3 stimulus frequencies: 500, 1000 and 4000 Hz. It was found that two areas of the auditory cortex showed mirrored tonotopic organization; one area, the source of N1m/N1 wave, exhibited higher frequencies at progressively deeper locations, while the second area, the source of the Pam/Pa wave, exhibited higher frequencies at progressively more superficial locations. The Pa tonotopic map was located in the primary auditory cortex anterior to the N1m/N1 mirror map. It is likely that N1m/N1 results from activation of secondary auditory areas. The location of the Pa map in A1, and its N1 mirror image in secondary auditory areas is in agreement with observations from animal studies.

Alteration of digital representations in somatosensory cortex in focal hand dystonia

FOCAL hand dystonia involves a loss of motor control of one or more digits; it is associated with the repetitive, synchronous movements of the digits made by musicians over periods of many years. Magnetic source imaging revealed that there is a er distance (fusion) between the representations of the digits in somatosensory cortex for the affected hand of dystonic musicians than for the hands of non-musician control subjects. The data suggest that use-dependent susceptibility to digital representation fusion in cortex may be involved in the etiology of focal dystonia. A successful therapy for the condition has been developed based on this consideration.

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 representa- tions 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.

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.

Musical Training Enhances Automatic Encoding of Melodic Contour and Interval Structure

In music, melodic information is thought to be encoded in two forms, a contour code (up/down pattern of pitch changes) and an interval code (pitch distances between successive notes). A recent study recording the mismatch negativity (MMN) evoked by pitch contour and interval deviations in simple melodies demonstrated that people with no formal music education process both contour and interval information in the auditory cortex automatically. However, it is still unclear whether musical experience enhances both strategies of melodic encoding. We designed stimuli to examine contour and interval information separately. In the contour condition there were eight different standard melodies (presented on 80 of trials), each consisting of five notes all ascending in pitch, and the corresponding deviant melodies (20) were altered to descending on their final note. The interval condition used one five-note standard melody transposed to eight keys from trial to trial, and on deviant trials the last note was raised by one whole tone without changing the pitch contour. There was also a control condition, in which a standard tone (990.7 Hz) and a deviant tone (1111.0 Hz) were presented. The magnetic counterpart of the MMN (MMNm) from musicians and nonmusicians was obtained as the difference between the dipole moment in response to the standard and deviant trials recorded by magnetoencephalography. Significantly larger MMNm was present in musicians in both contour and interval conditions than in nonmusicians, whereas MMNm in the control condition was similar for both groups. The interval MMNm was larger than the contour MMNm in musicians. No hemispheric difference was found in either group. The results suggest that musical training enhances the ability to automatically register abstract changes in the relative pitch structure of melodies.

A high-precision magnetoencephalographic study of human auditory steady-state responses to amplitude-modulated tones

The cerebral magnetic field of the auditory steady-state response (SSR) to sinusoidal amplitude-modulated (SAM) tones was recorded in healthy humans. The waveforms of underlying cortical source activity were calculated at multiples of the modulation frequency using the method of source space projection, which improved the signal-to-noise ratio (SNR) by a factor of 2 to 4. Since the complex amplitudes of the cortical source activity were independent of the sensor position in relation to the subjects head, a comparison of the results across experimental sessions was possible. The effect of modulation frequency on the amplitude and phase of the SSR was investigated at 30 different values between 10 and 98 Hz. At modulation frequencies between 10 and 20 Hz the SNR of harmonics near 40 Hz were predominant over the fundamental SSR. Above 30 Hz the SSR showed an almost sinusoidal waveform with an amplitude maximum at 40 Hz. The amplitude decreased with increasing modulation frequency but was significantly different from the magnetoencephalographic (MEG) background activity up to 98 Hz. Phase response at the fundamental and first harmonic decreased monotonically with increasing modulation frequency. The group delay (apparent latency) showed peaks of 72 ms at 20 Hz, 48 ms at 40 Hz, and 26 ms at 80 Hz. The effects of stimulus intensity, modulation depth, and carrier frequency on amplitude and phase of the SSR were also investigated. The SSR amplitude decreased linearly when stimulus intensity or the modulation depth were decreased in logarithmic steps. SSR amplitude decreased by a factor of 3 when carrier frequency increased from 250 to 4000 Hz. From the phase characteristics, time delays were found in the range of 0 to 6 ms for stimulus intensity, modulation depth, and carrier frequency, which were maximal at low frequencies, low intensities, or maximal modulation depth.

Plastic changes in the auditory cortex induced by intensive frequency discrimination training

The slow auditory evoked (wave Nlm) and mismatch field (MMF) elicited by sequences of pure tones of 1000 Hz and deviant tones of 1050, 1010 and 1005 Hz were measured before, during and 3 weeks after subjects were trained at frequency discrimination for 15 sessions (over 3 weeks) using an odd-ball procedure. The task of the subject was to detect deviants differing by progressively smaller frequency shifts from the standard stimulus. Frequency discrimination improved rapidly in the first week and was followed by small but constant improvements thereafter. Nlm and MMF responses to the deviant stimuli increased in amplitude during training. This enhancement persisted until training was finished, but decreased 3 weeks later. The results suggest a plastic reorganization of the cortical representation for the trained frequencies.

Cortical Plasticity Induced by Short-Term Unimodal and Multimodal Musical Training

Learning to play a musical instrument requires complex multimodal skills involving simultaneous perception of several sensory modalities: auditory, visual, somatosensory, as well as the motor system. Therefore, musical training provides a good and adequate neuroscientific model to study multimodal brain plasticity effects in humans. Here, we investigated the impact of short-term unimodal and multimodal musical training on brain plasticity. Two groups of nonmusicians were musically trained over the course of 2 weeks. One group [sensorimotor-auditory (SA)] learned to play a musical sequence on the piano, whereas the other group [auditory (A)] listened to and made judgments about the music that had been played by participants of the sensorimotor-auditory group. Training-induced cortical plasticity was assessed by recording the musically elicited mismatch negativity (MMNm) from magnetoencephalographic measurements before and after training. SA and A groups showed significantly different cortical responses after training. Specifically, the SA group showed significant enlargement of MMNm after training compared with the A group, reflecting greater enhancement of musical representations in auditory cortex after sensorimotor-auditory training compared with after mere auditory training. Thus, we have experimentally demonstrated that not only are sensorimotor and auditory systems connected, but also that sensorimotor-auditory training causes plastic reorganizational changes in the auditory cortex over and above changes introduced by auditory training alone.

Evoked and induced gamma-band activity of the human cortex

SummaryThe evoked gamma-band activity is an event related rhythmic response which persists within the first 100ms after the stimulus onset. It shows spectral peaks between 30 and 40 Hz in the auditory, between 45 and 55 Hz in the somatosensory and between 100 and 110 Hz in the visual system. After separation of the wide-band activity in slow and gamma-band activity, a moving single equivalent current dipole model accounts for each activity almost completely. The induced gamma-band activity is not phase-locked to the stimulus or it is strongly gittering and thus it cannot be extracted in time domain. In this case we are using signal analysis methods in frequency domain. The evaluation of the induced brain gamma-band activity around 30 Hz shows differences to word and nonword stimuli. It was supposed that the induced gamma-band activity represents the synchronized activity of Hebbian cell assemblies correlated to words.