Biomedical subjects

C Pantev

Publications and source records attributed to C Pantev.

At least 37 records · Page 2Linked to original sources

PubMed2001

Cortical reorganization in patients with high frequency cochlear hearing loss.

Animal research has shown that tonotopic representation in the auditory cortex is not statically fixed in the adult organism but can be altered after deafferentation. The present study examines the plasticity of the human auditory cortex in patients with high frequency cochlear hearing loss by means of magnetoencephalographic measurements. The data show that the cortical map can reorganize such that cortical neurons deprived of their usual most sensitive afferent input now respond to tone frequencies adjacent to the frequency range of the partial hearing loss. The results suggest that deafferentation due to cochlear damage in adults may lead to functional reorganization of auditory cortical structures.

Acoustic Stimulation↗

PubMed2001

Human auditory middle latency responses: influence of stimulus type and intensity.

Human auditory middle latency responses (MLR) to click and tone pip stimuli of different intensities were recorded by means of magnetoencephalography (MEG) and electroencephalography (EEG). Clicks elicited larger responses with significantly shorter latencies than the tone pips at the same intensity in dB sensation level (SL). Most MLR amplitudes increased and their latencies decreased with increasing stimulus intensity for both types of stimulation. Pa and Nb amplitudes saturated at intensities of 60 dB SL in the case of click stimulation. The shorter latencies of MLR evoked by the click were explained by its short rise time and the high frequency content of its spectrum. MEG source analysis yielded MLR sources which were clearly different from those of the slow cortical wave N1. They seem to be located in primary auditory areas along Heschl's gyrus.

Acoustic Stimulation↗

PubMed2001

Multiple supratemporal sources of magnetic and electric auditory evoked middle latency components in humans.

The supratemporal sources of the earliest auditory cortical responses (20-80 ms) were identified using simultaneously recorded electroencephalographic (EEG) and magnetoencephalographic (MEG) data. Both hemispheres of six subjects were recorded two or three times in different sessions in response to 8000 right-ear 1 kHz pure tones stimuli. Four components were identified: Pa (28 ms), Nb (40 ms), and two subcomponents of the Pb complex, termed Pb1 (52 ms) and Pb2 (74 ms). Based on MEG data, the corresponding sources were localized on the anatomy using individual realistic head models: Pa in the medial portion of Heschl's gyri (H1/H2); Nb/Pb1 in the lateral aspect of the supratemporal gyrus (STG); and Pb2 in the antero-lateral portion of Heschl's gyri. All sources were oriented antero-superiorly. This pattern was clearest in the contralateral hemisphere, where these three activities could be statistically dissociated. Results agree with previous invasive human intracerebral recordings, with animal studies reporting secondary areas involved in the generation of middle latency auditory-evoked components, and with positron emission tomography and functional magnetic resonance imaging studies often reporting these three active areas although without temporal information. The early STG activity may be attributed to parallel thalamo-cortical connections, or to cortico-cortical connections between the primary auditory cortex and the STG, as recently described in humans.

Acoustic Stimulation↗

PubMed2001

Representational cortex in musicians. Plastic alterations in response to musical practice.

The lifelong ability to adapt to environmental needs is based on the capacity of the central nervous system for plastic alterations. In a series of neurophysiological experiments, we studied the impact of music and musical training in musicians on the specific functional organization in auditory and somatosensory representational cortex. In one such study, subjects listened to music from which one specific spectral frequency was removed. This led to rapid and reversible adaptation of neuronal responses in auditory cortex. Further experimental evidence demonstrated that long years of practice and training by professional musicians to enable them to reach their capacity is associated with enlarged cortical representations in the somatosensory and auditory domains. This tuning of neuronal representations was specifically observed for musical tones and was absent when pure sinusoidal tones were used as stimuli. In the somatosensory cortex, plastic changes proved to be specific for the fingers frequently used and stimulated. These changes were not detected in the fingers of the hand that were not involved in playing the particular instrument. Neuroplastic alterations also may be driven into a domain where they may become maladaptive. The clinical syndrome of focal hand dystonia that may occur in musicians who engage in forceful practice may be one such consequence. We will discuss the possibilities of reversing maladaptive responses leading to the successful treatment of focal hand dystonia, which relies on basic research about cortical reorganization. This example elucidates how neuroscientific progress can guide the development of practice guidelines and therapeutic measures for the benefit of professional musicians.

Auditory Cortex↗

PubMed2000

Brain stem auditory evoked fields in response to clicks.

Magnetoencephalographic correlates of brain stem auditory evoked potentials (BAEP) have been identified by applying the model of a current dipole with invariant location and orientation (fixed dipole) to data recorded with a 37-channel first-order gradiometer system. In all three subjects studied, the dominating wave of the recorded brain stem auditory evoked field (BAEF) coincided exactly with wave V in the contralateral BAEP (maximal field amplitude of the order of 2-3 fT). In one subject, also a wave preceding wave V was observed, which was associated with basically the same spatial pattern as wave V itself, but had an opposite polarity. The study suggests that the supplementary information provided by BAEF measurements could be decisive for a better understanding of human auditory evoked brain stem activity.

Acoustic Stimulation↗

PubMed2000

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

The slow auditory evoked (wave N1m) 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. N1m 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.

Adult↗

PubMed2000

Atypical organisation of the auditory cortex in dyslexia as revealed by MEG.

Neuroanatomical and -radiological studies have converged to suggest an atypical organisation in the temporal bank of the left-hemispheric Sylvian fissure for dyslexia. Against the background of this finding, we applied high temporal resolution magnetoencephalography (MEG) to investigate functional aspects of the left-hemispheric auditory cortex in 11 right-handed dyslexic children (aged 8-13 years) and nine matched normal subjects (aged 8-14 years). Event-related field components during a passive oddball paradigm with pure tones and consonant-vowel syllables were evaluated. The first major peak of the auditory evoked response, the M80, showed identical topographical distributions in both groups. In contrast, the generating brain structures of the later M210 component were located more anterior to the earlier response in children with dyslexia only. Control children exhibited the expected activation of more posterior source locations of the component that appeared later in the processing stream. Since the group difference in the relative location of the M210 source seemed to be independent of stimulus category, it is concluded that dyslexics and normally literate children differ as to the organisation of their left-hemispheric auditory cortex.

Adolescent↗

PubMed2000

The perception of coherent and non-coherent auditory objects: a signature in gamma frequency band.

The pertinence of gamma band activity in magnetoencephalographic and electroencephalographic recordings for the performance of a gestalt recognition process is a question at issue. We investigated the functional relevance of gamma band activity for the perception of auditory objects. An auditory experiment was performed as an analog to the Kanizsa experiment in the visual modality, comprising four different coherent and non-coherent stimuli. For the first time functional differences of evoked gamma band activity due to the perception of these stimuli were demonstrated by various methods (localization of sources, wavelet analysis and independent component analysis, ICA). Responses to coherent stimuli were found to have more features in common compared to non-coherent stimuli (e.g. closer located sources and smaller number of ICA components). The results point to the existence of a pitch processor in the auditory pathway.

Acoustic Stimulation↗

PubMed2000

A combined functional in vivo measure for primary and secondary auditory cortices.

Auditory evoked magnetic fields are reliable physiological in vivo markers of activity generated in auditory cortices. In recent years, several components of auditory evoked fields have been demonstrated with specific topographies within the auditory cortex in man. Their differential elicitation and analyses has rendered the discrimination of neural activities in primary vs. secondary auditory cortical fields possible. This in vivo measure may be of interest in a number of (neuro)psychiatric and neuropsychological disorders with central auditory deficits, in which in vivo anatomical measures do not allow a clear distinction of primary vs. secondary auditory cortex involvement. To help better understand the pathophysiology of such disorders, we developed and introduce a combined measure of steady-state field (SSR) and the N1 component of the transient evoked field. The acoustic stimulus for this paradigm consists of a 500-ms tone burst with 39-Hz amplitude modulation of the carrier frequency. This combined stimulation allows assessment of both auditory cortex components in one brief examination to be well tolerated by patients. We examined the source locations of SSR and N1 component with separate classical stimulation and combined stimulation within-session in healthy volunteer subjects. We demonstrate here that the distinct sources of steady-state (primary auditory cortex) and N1 (secondary auditory cortex) responses can be reliably measured without significant spatial distortion with this combined stimulation paradigm.

Acoustic Stimulation↗

PubMed2000

Magnetoencephalographic studies of functional organization and plasticity of the human auditory cortex.

Magnetoencephalography has proven to be a powerful noninvasive tool for investigating the functional organization of the human auditory cortex and its plastic changes. The first part of this review summarizes some recent experiments on the tonotopic organization, which can be observed not only in the slow auditory evoked fields, but also in the middle-latency and the steady-state fields. In the second part of this review, recent studies on plasticity of the auditory cortex are outlined. These studies showed that the cortical representation of tones may change within hours after a reversible "functional deafferentation" (short-term plasticity) and that early musical training leads to an expansion in the cortical representation of complex harmonic sounds (long-term plasticity).

Acoustic Stimulation↗

PubMed2000

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 subject's 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.

Adult↗

PubMed2000

Magnetic brain activity evoked and induced by visually presented words and nonverbal stimuli.

Evoked and induced magnetic brain activity measured over the left hemisphere were tested for their specificity to language-related processing. Induced activity refers to oscillatory alterations time locked but not phase locked to the stimulus. Words, false font stimuli, and two types of nonverbal patterns were presented visually while subjects performed a nonlinguistic visual feature detection task. The comparison of evoked and induced brain activity around 200 ms after stimulus onset revealed differential sensitivity to the stimuli. The M180 component of the evoked magnetic field was larger at the processing of words and false font stimuli compared with nonverbal stimuli. The induced magnetic brain activity in the 60-Hz band at a compatible latency range was correlated with the familiarity of the visual Gestalt. Sensitivity to language-specific information processing can be concluded if a parameter differentiates the word condition from the nonlexical conditions. Such a difference was observed at sensors located over the frontal-temporal scalp regions for induced but not evoked magnetic brain activity. Thus, evoked and induced magnetic brain activity revealed a differential sensitivity to elements of cognitive processing during the given task.

Adult↗

PubMed1999

Short-term plasticity of the human auditory cortex.

Magnetoencephalographic measurements (MEG) were used to examine the effect on the human auditory cortex of removing specific frequencies from the acoustic environment. Subjects listened for 3 h on three consecutive days to music "notched" by removal of a narrow frequency band centered on 1 kHz. Immediately after listening to the notched music, the neural representation for a 1-kHz test stimulus centered on the notch was found to be significantly diminished compared to the neural representation for a 0.5-kHz control stimulus centered one octave below the region of notching. The diminished neural representation for 1 kHz reversed to baseline between the successive listening sessions. These results suggest that rapid changes can occur in the tuning of neurons in the adult human auditory cortex following manipulation of the acoustic environment. A dynamic form of neural plasticity may underlie the phenomenon observed here.

Acoustic Stimulation↗

PubMed1999

Musicians with absolute pitch show distinct neural activities in the auditory cortex.

Meg responses from musicians who had absolute pitch and from non-musicians were measured while they received different auditory stimuli. The parameters of single equivalent current dipoles (ECDs) were calculated for the N1m responses occurring in the auditory cortex. The location of the ECD for the noise burst was significantly posterior to the ECDs for the tones in the two hemispheres of the musicians, but not for those of the non-musicians. Further, in the left hemisphere the ECDs for the musicians were significantly posterior to those for the non-musicians. These results suggest distinct neural activities in the auditory cortex of musicians, which may be the result of cortical plasticity produced by training and/or an inherent cortical structural specificity.

Acoustic Stimulation↗

PubMed1998

Failure of dominant left-hemispheric activation to right-ear stimulation in schizophrenia.

Schizophrenia is associated with an absence of the lateralizations that typify the human brain. Previous evidence emphasized structural changes, particularly reduced asymmetry in extension and surface of the planum temporale, although gross structural deviations occur only in a minority of patients. The present study describes an absence of lateralization on a robust functional measure that characterized schizophrenia patients: healthy subjects but not schizophrenics displayed a contralateral left-hemispheric dominance of the auditory evoked magnetic field to right-ear auditory stimulation. Absence of contralateral dominance in response to auditory stimuli among schizophrenia patients may indicate a failure to establish unequivocal left-hemispheric dominance of the phonological loop as hypothesized by Crow.

Acoustic Stimulation↗

PubMed1998

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 smaller 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.

Adult↗

PubMed1998

Perceptual correlates of changes in cortical representation of fingers in blind multifinger Braille readers.

The mature mammalian nervous system alters its functional organization in a use-dependent manner. Enhanced stimulation of a body part enlarges its cortical representational zones and may change its topographic order. Little is known about the perceptual and behavioral relevance of these plastic alterations in cortical organization. We used blind Braille readers who use several fingers on each hand and who do so for many hours each day as a model to investigate this issue. Magnetic source imaging indicated that the cortical somatosensory representation of the fingers was frequently topographically disordered in these subjects; in addition, they frequently misperceived which of these fingers was being touched by a light tactile stimulus. In contrast, neither the disordered representation nor mislocalizations were observed in sighted controls. Blind non-teacher Braille readers who used only one finger for reading were not significantly different from the sighted controls. Thus, use-dependent cortical reorganization can be associated with functionally relevant changes in the perceptual and behavioral capacities of the individual.

Adult↗

PubMed1998

Increased auditory cortical representation in musicians.

Acoustic stimuli are processed throughout the auditory projection pathway, including the neocortex, by neurons that are aggregated into 'tonotopic' maps according to their specific frequency tunings. Research on animals has shown that tonotopic representations are not statically fixed in the adult organism but can reorganize after damage to the cochlea or after training the intact subject to discriminate between auditory stimuli. Here we used functional magnetic source imaging (single dipole model) to measure cortical representations in highly skilled musicians. Dipole moments for piano tones, but not for pure tones of similar fundamental frequency (matched in loudness), were found to be enlarged by about 25% in musicians compared with control subjects who had never played an instrument. Enlargement was correlated with the age at which musicians began to practise and did not differ between musicians with absolute or relative pitch. These results, when interpreted with evidence for modified somatosensory representations of the fingering digits in skilled violinists, suggest that use-dependent functional reorganization extends across the sensory cortices to reflect the pattern of sensory input processed by the subject during development of musical skill.

Adult↗