Biomedical subjects

M Sams

Publications and source records attributed to M Sams.

At least 19 recordsLinked to original sources

PubMed1998

Differential effects of alcohol on the cortical processing of foreign and native language.

The effect of alcohol (ethanol) on cortical processing of Finnish vs. English words in Finnish-speaking subjects was studied by recording auditory event-related potentials in 10 subjects who had started studying English at the age of 9-10 years. At the beginning of the block of 100 words, the subject heard an introductory sentence. Half of the words completed the sentence well and the other half did not. The subject pressed a reaction key immediately after hearing a proper word. After the control condition, the subject ingested alcohol (1 ml/kg). Alcohol attenuated the amplitude of N100 to both Finnish and English words, this attenuation being significantly stronger for English than for Finnish words. The early differential effect of alcohol suggests that language-specific information is extracted in the cortex already approximately 100 ms from the word onset. The results are in line with animal experiments demonstrating that alcohol selectively affects the activity of single units involved in newer forms of behavior.

Acoustic Stimulation↗

PubMed1997

Frequency and periodicity are represented in orthogonal maps in the human auditory cortex: evidence from magnetoencephalography.

Timbre and pitch are two independent perceptual qualities of sounds closely related to the spectral envelope and to the fundamental frequency of periodic temporal envelope fluctuations, respectively. To a first approximation, the spectral and temporal tuning properties of neurons in the auditory midbrain of various animals are independent, with layouts of these tuning properties in approximately orthogonal tonotopic and periodotopic maps. For the first time we demonstrate by means of magnetoencephalography a periodotopic organization of the human auditory cortex and analyse its spatial relationship to the tonotopic organization by using a range of stimuli with different temporal envelope fluctuations and spectra and a magnetometer providing high spatial resolution. We demonstrate an orthogonal arrangement of tonotopic and periodotopic gradients. Our results are in line with the organization of such maps in animals and closely match the perceptual orthogonality of timbre and pitch in humans.

Acoustic Stimulation↗

PubMed1997

Face-specific responses from the human inferior occipito-temporal cortex.

Whole-head neuromagnetic responses were recorded from seven subjects to pictures of faces and to various control stimuli. Four subjects displayed signals specific to faces. The combination of functional information from magnetoencephalography and anatomical data from magnetic resonance images suggests that the face-specific activity was generated in the inferior occipitotemporal cortex. All four subjects showed the face-specific response in the right hemisphere, one of them also in the left. Our results, together with recent position emission tomography and lesion studies, suggest a right-hemisphere preponderance of face processing in the inferior occipitotemporal cortex.

Adult↗

PubMed1997

Disrupting human auditory change detection: Chopin is superior to white noise.

A deviant sound in a sequence of standard sounds elicits a neuromagnetic mismatch field (MMF) reflecting change detection based on the auditory sensory memory trace. To illuminate the nature of this trace, we investigated the effects of white noise and music maskers on the MMF. The stimuli were delivered to the participant's right ear, and the maskers were delivered to the same or contralateral ear. Only maskers containing transients (music) presented to either ear abolished the MMF. In parallel, the ability to discriminate the deviants decreased dramatically, probably because of integration of transient features of the music to the neural representations of standards and deviants. As a result, the similarity of these representations prevents change detection. White noise affected the MMF amplitude only when presented to the same ear to which the stimuli were presented. All maskers decreased the M100 but not the M50 amplitude, suggesting that the neural generators behind these responses are functionally separate.

Acoustic Stimulation↗

PubMed1996

Temporal integration in auditory sensory memory: neuromagnetic evidence.

The cortical mechanisms of auditory sensory memory were investigated by analysis of neuromagnetic evoked responses. The major deflection of the auditory evoked field (N100m) appears to comprise an early posterior component (N100mP) and a late anterior component (N100mA) which is sensitive to temporal factors. When pairs of identical sounds are presented at intervals less that about 250 msec, the second sound evokes N100mA with enhanced amplitude at a latency of about 150 msec. We suggest that N100mA may index the activity of two distinct processes in auditory sensory memory. Its recovery cycle may reflect the activity of a memory trace which, according to previous studies, can retain processed information about an auditory sequence for about 10 sec. The enhancement effect may reflect the activity of a temporal integration process, whose time constant is such that sensation persists for 200-300 msec after stimulus offset, and so serves as a short memory store. Sound sequences falling within this window of integration seem to be coded holistically as unitary events.

Acoustic Stimulation↗

PubMed1995

Auditory evoked magnetic fields to tones and pseudowords in healthy children and adults.

Neuromagnetic responses to tones and pseudowords were measured with a 24-channel magnetometer in nine adults and in 23 children, the latter aged 0.3-15 years. Both stimulus types elicited substantially similar responses in all subjects. At 0.9-s interstimulus interval (ISI), the adult response was a stable P1m-N1m-P2m-N2m sequence peaking at 50, 100, 200, and 250 ms, respectively. A biphasic P1m-N1,2m response with peaks at 100 and 260 ms occurred in children up to 12 years of age. At longer ISIs (1.2-2.4 s), an adult-type N1m response appeared in most children. N1m amplitude suppression at short ISIs was stronger in children than in adults and may reflect a longer refractory period of the N1 generator neurons during early childhood than later in life. Peak latencies of P1m, N1m, and N2m decreased with age, most rapidly < 7 years of age. All deflections originated in nearby cortical areas within the posterior sylvian fissure, and may serve as functional landmarks for that anatomic area.

Adolescent↗

PubMed1994

Dynamics of brain activation during picture naming.

The cerebral representation of language, deduced from observing patients with brain lesions and from stimulations and recordings performed during brain surgery, has been further clarified by recent positron emission tomography and functional magnetic resonance imaging measurements. We now expand this static view into the dynamics of cortical activation using the accurate spatiotemporal resolution of whole-head magnetoencephalography. During picture naming, the conversion from visual to symbolic representation progressed bilaterally from the occipital visual cortex towards temporal and frontal lobes. Overt naming elicited the most widespread cortical activation. Some language-related sites also reacted, though more weakly or after a longer delay, during covert naming and even passive viewing.

Adult↗

PubMed1994

Evidence of sharp frequency tuning in the human auditory cortex.

The frequency tuning of the human auditory cortex was studied by masking 100-ms tones of 1 and 2 kHz by continuous white-noise maskers with frequency notches around the tone frequencies. The subjects ignored the stimuli and concentrated on a reading task. The neuronal activity elicited by the test tones in the auditory cortex was measured with a 24-channel neuromagnetometer. The masker affected the amplitude and latency of the neuromagnetic N100m response, peaking about at 100 ms after stimulus onset, in a systematic way: the wider the notch, the shorter was the latency and the larger the amplitude. The source location of N100m in the auditory cortex did not depend on the notch width. Auditory filters at 1 and 2 kHz were modelled by a single-parameter rounded-exponential [Roex(p)] filter, based on the amplitude changes of N100m. The filters revealed sharp tuning of the auditory cortex, resembling that obtained in psychoacoustical masking studies. The results demonstrate that frequency tuning of the neurons or neuron ensembles in the human auditory cortex can be studied completely noninvasively. Moreover, since the stimuli were ignored by the subjects, the filter shape is not affected by the criterion adopted by the subject in the discrimination task.

Acoustic Stimulation↗

PubMed1993

Phonetic invariance in the human auditory cortex.

Neuromagnetic signals evoked by synthesized syllables (/bae/ and /gae/) were recorded over the left auditory cortex of healthy humans. The fundamental frequencies of the syllables varied as if the same speaker had pronounced them at 16 different pitches. Specific mismatch responses to infrequent syllables among frequent syllables of the other type indicated that phonetically invariant information had been extracted at the level of the auditory cortex from the extensive irrelevant pitch variation. Such a detection mechanism is necessary for perceiving speech sounds in natural situations with a great deal of acoustic variation present.

Acoustic Stimulation↗

PubMed1993

Human auditory cortex responses to rising versus falling glides.

A 24-channel SQUID magnetometer was used to record signals from the right auditory cortex to tone glides with 16 different centre frequencies (ranging from 0.5 to 2 kHz), sweeping over one octave. The stimulus sequence, presented with an interstimulus onset interval of 0.6 s, consisted of infrequent 'deviant' rising (falling) glides and frequent 'standard' falling (rising) glides; the rising glides were identical to the falling glides but presented in the reverse direction. Deviant glides elicited significantly larger responses than standards at a latency of about 100 ms. This amplitude difference presumably arises from a mismatch response to the deviants. These results suggest that the auditory cortex extracts the direction of frequency transition even when the stimuli do not contain same frequencies.

Acoustic Stimulation↗

PubMed1993

Functional organization of the human first and second somatosensory cortices: a neuromagnetic study.

Multichannel neuromagnetic recordings were used to differentiate signals from the human first (SI) and second (SII) somatosensory cortices and to define representations of body surface in them. The responses from contralateral SI, peaking at 20-40 ms, arose mainly from area 3b, where representations of the leg, hand, fingers, lips and tongue agreed with earlier animal studies and with neurosurgical stimulations and recordings on convexial cortex in man. Representations of the five fingers were limited to a cortical strip of approximately 2 cm in length. Responses from SII peaked 100-140 ms after contra- and ipsilateral stimuli and varied considerably from one subject to another. Signs of somatotopical organization were seen also in SII. Responses of SII were not fully recovered at interstimulus intervals of 8 s.

Acoustic Stimulation↗

PubMed1993

Responses of the human auditory cortex to changes in one versus two stimulus features.

Neuromagnetic responses were recorded with a 24-SQUID magnetometer in two "oddball" experiments to determine whether mismatch responses to changes in single stimulus features are additive. In experiment 1, the one-feature deviants differed from standards in interstimulus interval (ISI) or frequency, and the two-feature deviants in both ISI and frequency. In experiment 2, deviants differed in duration, frequency, or both. All deviants evoked a mismatch field (MMF) with sources close to each other in the supratemporal auditory cortex. Except for the ISI deviants, the MMF sources were about 1 cm anterior to the source of the 100-ms response, N100m, to the standards. In the two experiments, MMFs obtained in response to the two-feature deviants resembled closely the sum of MMFs in response to one-feature deviants. The results suggest that the standards leave a multiple neuronal representation in the human auditory cortex. The particular neuronal traces of the representation react independently to changes in different features of sound stimuli.

Acoustic Stimulation↗

PubMed1993

Determinants of the auditory mismatch response.

The auditory mismatch field (MMF) is supposed to reflect a comparison process between an infrequent deviant stimulus and the memory trace left by frequent standard stimuli. Therefore, the MMF amplitude has been thought to depend on the strength of such a trace. We examined this hypothesis in records with a 24-channel planar SQUID magnetometer by varying the number of stimuli preceding each deviant, the interdeviant interval (IDI) and the interstimulus interval (ISI) just preceding the deviant (pISI). When a constant IDI was employed and the number of standards between two deviants varied in different sessions, MMF amplitude increased as the number of standards increased. However, MMF did not depend on the number of standards between two deviants when the number varied within a single session and ISI varied as well. MMF decreased slightly when pISI increased from 0.6 to 3.4 sec. When IDI increased and the ISI remained constant, MMF amplitude increased. Most results can be explained within the framework of the memory-trace hypothesis of MMF generation. However, the strengthening of the trace seems to be a complex process which is also affected by the temporal features of the stimulus sequence.

Adult↗

PubMed1993

Human auditory cortical mechanisms of sound lateralization: I. Interaural time differences within sound.

Neuromagnetic responses to 600-ms binaural click trains, presented once every 1.1 s, were recorded with a 24-channel gradiometer from 6 healthy humans. During the first 300 ms, the left-ear stimulus led the right by 0.7 ms and the sound was lateralized to the left ear. At 300 ms, the interaural time difference (ITD) changed and the lateralization moved to one of 5 different locations between the ears. An N100m response peaked about 110 ms after the sound onset and an N130mc response (c to stress a response to the change) about 135 ms after the ITD change. The source locations of N100m and N130mc agreed with activity in the supratemporal auditory cortex; this was confirmed in one subject by superimposing MEG results on MR images. The sources of N100m and N130mc did not differ statistically significantly from each other, nor were there differences in N130mc sources to various lateralization changes. N130mc grew larger when the ITD change increased, in parallel with the increase in the change of the perceived location. We suggest that N130mc is analogous to N100m, but is delayed due to postmasking induced by the early part of the sound.

Acoustic Stimulation↗

PubMed1993

Human auditory cortical mechanisms of sound lateralization: II. Interaural time differences at sound onset.

Neuromagnetic responses were recorded over the right temporal cortex using a 24-channel gradiometer. Stimuli were binaural click trains, presented with six separate interaural time differences (ITDs). N100m to sound onset was larger and earlier for stimuli presented with left- than with right-leading ITDs. With stimulus lateralization taken into account, monaural and binaural stimuli evoked responses of roughly equal amplitude. In selective adaptation and oddball experiments, stimuli presented with different ITDs excited overlapping neuronal populations, but the amount of overlap decreased as the ITD between the stimuli increased. There were no systematic differences in the cortical source locations of the N100m as a function of ITD, however. Thus it appears that ITD-sensitive neurons in the human auditory cortex are not organized into a large-scale, orderly representation, which could be resolved by MEG.

Acoustic Stimulation↗

PubMed1992

Event-related potentials to repetition and change of auditory stimuli.

The major intent of this study was to compare the role of stimulus repetition and change in the elicitation of the MMN, an ERP component specific to stimulus change, and N2b, usually partially overlapping the MMN when stimuli are attended. Event-related potentials were recorded in one set of conditions where subjects ignored the stimuli and read a book, and in another set of conditions where subjects counted stimuli designated as targets. Stimuli were delivered in 4 ways, the common feature between all these conditions being the occurrence of infrequent events at a probability of 0.20: (1) an oddball paradigm with 1 deviant, (2) an oddball paradigm with 2 deviants, each with a probability of 0.10, (3) a regular alternation of tones of 2 pitches where either of the 2 tones infrequently repeated (P = 0.20), and (4) a random presentation of tones of 5 different pitches, where any of the 5 tones infrequently repeated (P = 0.20). In the count conditions, the infrequent events were designated as targets. It was found that the MMN was elicited by stimulus change and not stimulus repetition in the ignore and count conditions, whereas the N2b was elicited by both stimulus changes and repetitions in the count conditions. It was also possible, in the count conditions, to disentangle the part of the late positive complex which is related to stimulus deviation and the part which is related to stimulus significance (target).

Acoustic Stimulation↗

PubMed1992

Neuromagnetic mismatch fields to single and paired tones.

In 8 subjects we recorded multichannel magnetic responses to pitch changes in single 50 msec tones and in tone pairs (oddball paradigm; interstimulus interval 745 msec). Either "A" (1 kHz) was standard (90%) and "B" (1.2 kHz) deviant (10%), or "AA" was standard and "AB" deviant in pairs with onset asynchrony of 75 msec. Subject did not pay attention to the tones. A mismatch field (MMF) was evident in responses to deviants with an equivalent source in the supratemporal auditory cortex, about 1 cm anterior to that for N100m. The MMF source was 3-fold stronger for tone pairs than for single tones.

Adult↗

PubMed1991

Seeing speech: visual information from lip movements modifies activity in the human auditory cortex.

Neuromagnetic responses were recorded over the left hemisphere to find out in which cortical area the heard and seen speech are integrated. Auditory stimuli were Finnish/pa/syllables presented together with a videotaped face articulating either the concordant syllable/pa/(84% of stimuli, V = A) or the discordant syllable/ka/(16%, V not equal to A). In some subjects the probabilities were reversed. The subjects heard V not equal to A stimuli as/ta/ or ka. The magnetic responses to infrequent perceptions elicited a specific waveform which could be explained by activity in the supratemporal auditory cortex. The results show that visual information from articulatory movements has an entry into the auditory cortex.

Adult↗