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M Huotilainen

Publications and source records attributed to M Huotilainen.

34 records · Page 2Linked to original sources
PubMed1997

Language-specific phoneme representations revealed by electric and magnetic brain responses.

There is considerable debate about whether the early processing of sounds depends on whether they form part of speech. Proponents of such speech specificity postulate the existence of language-dependent memory traces, which are activated in the processing of speech but not when equally complex, acoustic non-speech stimuli are processed. Here we report the existence of these traces in the human brain. We presented to Finnish subjects the Finnish phoneme prototype /e/ as the frequent stimulus, and other Finnish phoneme prototypes or a non-prototype (the Estonian prototype /õ/) as the infrequent stimulus. We found that the brain's automatic change-detection response, reflected electrically as the mismatch negativity (MMN), was enhanced when the infrequent, deviant stimulus was a prototype (the Finnish /ö/) relative to when it was a non-prototype (the Estonian /õ/). These phonemic traces, revealed by MMN, are language-specific, as /õ/ caused enhancement of MMN in Estonians. Whole-head magnetic recordings located the source of this native-language, phoneme-related response enhancement, and thus the language-specific memory traces, in the auditory cortex of the left hemisphere.

Acoustic Stimulation↗
PubMed1997

Electrophysiological evidence for cross-modal plasticity in humans with early- and late-onset blindness.

It is commonly believed that sensory deprivation can lead to cross-modal reorganization in an immature but not in a mature brain. The results of the present study suggest, however, that plasticity between sensory modalities is possible even in adults: activity indicating involvement of parietal or occipital brain areas in pitch-change discrimination was found in individuals blinded after childhood. Event-related brain potentials of early blinded (before the age of 2 years), late-blinded (12-28 years of age), and sighted adults were recorded to stimulus sequences consisting of standard tones occasionally replaced by deviant tones. Even when participants were not attending to auditory stimuli, the deviant tones elicited the mismatch negativity (MMN) in each group. There were no significant MMN front-back scalp distribution differences among the groups. However, when participants were detecting deviant stimuli, these stimuli elicited N2 and P3 waves that were posterior in distribution in both groups of blind participants relative to those of the sighted participants. These results suggest that cross-modal reorganization may occur even in the mature human brain.

Adult↗
PubMed1996

Optimal resource allocation for novelty detection in a human auditory memory.

A theory of resource allocation for neuronal low-level filtering is presented, based on an analysis of optimal resource allocation in simple environments. A quantitative prediction of the theory was verified in measurements of the magnetic mismatch response (MMR), an auditory event-related magnetic response of the human brain. The amplitude of the MMR was found to be directly proportional to the information conveyed by the stimulus. To the extent that the amplitude of the MMR can be used to measure resource usage by the auditory cortex, this finding supports our theory that, at least for early auditory processing, energy resources are used in proportion to the information content of incoming stimulus flow.

Acoustic Stimulation↗
PubMed1996

Alzheimer's disease affects parallel processing between the auditory cortices.

Auditory evoked magnetic fields (AEFs) were recorded from 11 patients with Alzheimer's disease (AD) and 11 age-matched controls using the 122-channel whole-head magnetometer. Auditory stimuli were monaurally presented with interstimulus intervals (ISI) of 0.5 and 2.5 s in different blocks. The peak latencies of P50m and N100m responses were significantly longer in AD patients than in controls over the ipsilateral but not over the contralateral auditory cortex with respect to the ear stimulated. This finding suggests that parallel auditory processing is impaired between the auditory cortices in AD patients. The present MEG measurement might provide an objective index to evaluate auditory dysfunction in AD.

Acoustic Stimulation↗
PubMed1996

Processing of complex sounds in the human auditory cortex as revealed by magnetic brain responses.

Processing of simple and complex sounds in the human brain was compared by recording extracranial magnetic mismatch responses (MMNm; the magnetic counterpart of the mismatch negativity, or MMN) to frequency changes in these sounds. Generator sources, modeled as equivalent current dipoles (ECDs), of MMNm responses to a change in one frequency element of complex sounds (a chord and a serial tone pattern) were located in supratemporal auditory cortex, on average, 10 mm medially to the source of an MMNm elicited by an identical frequency change in a simple tone. These results suggest that at least partially different supratemporal neuron populations are involved in processing changes in simple and complex sounds and that sensory-memory representations for these sounds may be located in different fields of the auditory cortex.

Adult↗
PubMed1995

From objective to subjective: pitch representation in the human auditory cortex.

Magnetic brain responses to infrequent changes in the pitch of complex sounds were recorded. The composition of the test sounds required that pitch-deviant stimuli elicited the mismatch response only if perceived pitch was represented in auditory sensory memory. Results revealed that subjective features, such as pitch, are formed from objective stimulus parameters (i.e. the spectral contents of a sound) before storing acoustic information in memory. The origin of the magnetic response to pitch change showed that pitch deviation was detected in the auditory cortex. Pitch memory might also be located in the auditory cortex, as previous evidence suggests that storage for an auditory feature lies in the vicinity of the neuronal elements activated by deviations in that feature.

Acoustic Stimulation↗
PubMed1995

Age-related functional differences between auditory cortices: a whole-head MEG study.

Auditory evoked magnetic fields (AEFs) were recorded from 10 healthy younger and 10 older subjects using a whole-head magnetometer. Two blocks of tone pips were presented to the left ear with constant inter-stimulus intervals (ISIs) of 0.5 and 2.5 s. The amplitude of P50m, unlike that of N100m, was larger in the older subjects. In both groups, the peak latencies of P50m and N100m responses were significantly shorter over the contralateral than ipsilateral cortex. The interhemispheric latency difference of N100m was significantly increased with age. These findings suggest that ageing delays signal processing in the ipsilateral auditory cortex and that ageing affects consecutive AEFs in a different manner.

Acoustic Stimulation↗
PubMed1995

Sustained fields of tones and glides reflect tonotopy of the auditory cortex.

Cortical activation in response to two types of auditory stimuli, constant-frequency tones and frequency glides, was studied by measuring the magnetic field outside the head using a whole-head 122-channel magnetometer. Both the magnetic N1m and sustained responses were located in the supratemporal plane of the primary auditory cortex. The sustained responses both to constant-frequency tones and frequency glides reflect tonotopic organization of the auditory cortex both in depth and direction, thus revealing the underlying neuroanatomical structure of the auditory cortex.

Acoustic Stimulation↗
PubMed1995

Visual cortex activation in blind humans during sound discrimination.

We used a whole-scalp magnetometer with 122 planar gradiometers to study the activity of the visual cortex of five blind humans deprived of visual input since early infancy. Magnetic responses were recorded to pitch changes in a sound sequence when the subjects were either counting these changes or ignoring the stimuli. In two of the blind subjects, magnetic resonance images were also obtained, showing normal visual cortex macroanatomy. In these subjects, the magnetic responses to counted pitch changes were located at visual and temporal cortices whereas ignored pitch changes activated the temporal cortices almost exclusively. Also in two of the other three blind, the visual-cortex activation was detectable in the auditory counting task. Our results suggest that the visual cortex of blind humans can participate in auditory discrimination.

Acoustic Stimulation↗
PubMed1995

Pitch change of a continuous tone activates two distinct processes in human auditory cortex: a study with whole-head magnetometer.

Previous studies have shown that a frequency change in a continuous tone elicits an NI type of ERP (event-related potential) component. It remained unclear, however, whether this response is a "genuine" N1 (onset detector response) or the mismatch negativity (MMN), a change-detector type of ERP response, elicited in previous studies by an infrequent change in a sequence of homogeneous stimuli. A further possibility is a nearly perfect overlap of the two types of ERP components. The advent of modern, high-resolution magnetometers has opened a new, powerful way to tackle such component-overlap problems. Subjects were presented with a continuous tone of 988 Hz which was occasionally increased to 1108 Hz for a period of 100 msec. The magnetic responses to this change consisted of two partially overlapping components with peaks separated by 30 msec. The earlier component was probably generated by neuronal populations of the auditory cortex corresponding to the supratemporal N1, whereas the later one, generated anteriorly and inferiorly to the first, probably reflects a mismatch process causing the magnetic equivalent of the electrical MMN.

Acoustic Stimulation↗
PubMed1995

Signal-space projections of MEG data characterize both distributed and well-localized neuronal sources.

We describe the use of signal-space projection (SSP) for the detection and characterization of simultaneous and/or sequential activation of neuronal source distributions. In this analysis, a common signal space is used to represent both the signals measured by an array of detectors and the underlying brain sources. This presents distinct advantages for the analysis of EEG and MEG data. Both highly localized and distributed sources are characterized by the components of the field patterns which are measured by the detectors. As a result, a unified description of arbitrary source configurations is obtained which permits the consistent implementation of a variety of analysis techniques. The method is illustrated by the application of SSP to auditory, visual and somatosensory evoked-response MEG data. Single-trace evoked responses obtained by SSP of spontaneous activity demonstrate that a considerable discrimination against both system noise and uncorrelated brain activity may be achieved. Application of signal-space projections determined in the frequency domain to spontaneous activity illustrates the possibility of including temporal relationships into the analysis. Finally, we demonstrate that SSP is particularly useful for the description of multiple sources of distributed activity and for the comparison of the strengths of specific neuronal sources under a variety of different paradigms or subject conditions.

Brain↗
PubMed1994

Auditory stimuli activate parietal brain regions: a whole-head MEG study.

Previous studies using magnetoencephalographic (MEG) recordings have revealed neuronal populations responding to discrete auditory stimuli in the supratemporal cortex of the human brain. We used the novel whole-head magnetometer (Neuromag-122) to determine whether regions outside the auditory cortex are activated by auditory stimulation as well. In the present study we report evidence for activation of the parietal cortex of the human brain in response to auditory stimuli.

Acoustic Stimulation↗
PubMed1993

Interaction between representations of different features of auditory sensory memory.

The neurophysiological basis of sensory memory was studied by measuring the magnetic counterpart (MMNm) of the mismatch negativity (MMN) with a whole-head 122-channel magnetometer. The MMNm is a response to a difference in the presented stimulus and a neuronal memory trace formed by repeated standard stimuli. This trace must contain information about the feature differing in the deviant. Keeping one feature (frequency) constant, we studied how other stimulus features affect the strength of the MMNm. The MMNm to a frequency change was weaker when the other features varied than when they were constant. This suggests that the MMNm to a frequency change is not independent of other stimulus features.

Acoustic Stimulation↗
PubMed1993

Memory-related processing of complex sound patterns in human auditory cortex: a MEG study.

Responses of the human brain to a complex sound pattern were recorded with a 24 channel magnetometer. The sound pattern consisted of 9 successive 50 ms segments, each with a different frequency. An infrequent change in the frequency of one of the segments elicited a magnetic mismatch response (MMNm) which peaked at about 200 ms after the deviant segment onset and resembled the electrical mismatch negativity (MMN). The equivalent current dipole which best explained the MMNm was located in the supratemporal auditory cortex, suggesting that a memory trace for the sound pattern was stored in that region.

Adult↗
PubMed1993

Tonotopic auditory cortex and the magnetoencephalographic (MEG) equivalent of the mismatch negativity.

Two tone stimuli, one frequent (standard) and the other infrequent (a slightly higher, deviant tone), were presented in random order and at short intervals to subjects reading texts they had selected. In different blocks, standards were either 250, 1,000, or 4,000 Hz, with the deviants always being 10% higher in frequency than the standards of the same blocks. Magnetic responses elicited by the standard and deviant tones included N1m, the magnetoencephalographic equivalent of the electrical N1 (its supratemporal component). In addition, deviant stimuli elicited MMNm, the magnetic equivalent of the electrical mismatch negativity, MMN. The equivalent dipole sources of the two responses were located in supratemporal auditory cortex, with the MMNm source being anterior to that of N1m. The dipole orientations of both sources in teh sagittal plane depended on stimulus frequency, suggesting that the responses are generated by tonotopically organized neuronal populations. The tonotopy reflected by the frequency dependence of the MMNm source might be that of the neural trace system underlying frequency representation of auditory stimuli in sensory memory.

Acoustic Stimulation↗