Biomedical subjects

M Huotilainen

Publications and source records attributed to M Huotilainen.

At least 19 recordsLinked to original sources

PubMed2001

Preserved stimulus deviance detection in Alzheimer's disease.

Aging attenuates automatic auditory discrimination to duration change, whereas frequency change detection is relatively unimpaired in aging and in Alzheimer's disease (AD). Here we studied with a whole-head magnetometer whether cortical auditory discrimination to duration change as shown by magnetic mismatch negativity (MMNm) response is impaired in AD. Twenty AD patients with mild to moderate cognitive impairment and 18 age-matched healthy subjects were monaurally presented a sequence of frequent standard tones embedded with occasional deviants with shorter duration. MMNm was significantly delayed in the left hemisphere ipsilaterally to the ear stimulated in the patient group, whereas the MMNm amplitudes over both hemispheres were quite similar in both groups. This suggests that although MMNm is delayed in the left hemisphere, the automatic discrimination to duration change in the auditory cortex is not attenuated in the early stages of AD.

Acoustic Stimulation↗

PubMed2001

Changes in acoustic features and their conjunctions are processed by separate neuronal populations.

We investigated the relationship between the neuronal populations involved in detecting change in two acoustic features and their conjunction. Equivalent current dipole (ECD) models of the magnetic mismatch negativity (MMNm) generators were calculated for infrequent changes in pitch, perceived sound source location, and the conjunction of these two features. All of these three changes elicited MMNms that were generated in the vicinity of auditory cortex. The location of the ECD best describing the MMNm to the conjunction deviant was anterior to those for the MMNm responses elicited by either one of the constituent features. The present data thus suggest that at least partially separate neuronal populations are involved in detecting change in acoustic features and feature conjunctions.

Adult↗

PubMed2000

Harmonic partials facilitate pitch discrimination in humans: electrophysiological and behavioral evidence.

The effect of the spectral tone structure on pre-attentive and attentive pitch discrimination was investigated. The mismatch negativity (MMN) component was recorded from reading subjects to pitch changes of identical magnitude in pure tones with only one sinusoidal frequency component and in spectrally rich tones with two additional harmonic partials. In a separate condition, subjects were asked to indicate detection of pitch change by a button press. The MMN was elicited with a larger amplitude and shorter latency by change in spectrally rich tones than by change in pure tones. Furthermore, the subjects' behavioral responses were more accurate for spectrally rich tones than for sinusoidal tones. Together these data indicate that pre-attentive and attentive pitch discrimination is facilitated with spectrally rich sounds in comparison to pure sinusoidal tones.

Adolescent↗

PubMed1999

Impaired preconscious auditory processing and cognitive functions in Alzheimer's disease.

OBJECTIVE: To study whether preconscious auditory processing is deteriorated in patients with Alzheimer's disease (AD) having mild to moderate cognitive symptoms. To investigate whether auditory processing correlates with the impairment of the higher cortical functions. METHODS: P50m and N100m responses elicited by a sequence of repetitive tones were recorded with a whole-head magnetometer from 22 patients with probable AD and from 18 healthy age-matched controls. In addition, an extensive neuropsychological test battery assessing main cognitive domains was administered to all subjects. RESULTS: The patients with AD had significantly delayed N100m responses in the left hemisphere that correlated with the impairment of the language functions. CONCLUSIONS: N100m auditory responses measured with magnetoencephalography may be useful in evaluating the severity and progression of the cortical dysfunction in dementia.

Aged↗

PubMed1999

Altered parallel auditory processing in schizophrenia patients.

Patients with schizophrenia have impaired auditory processing that has been demonstrated by diminished P50 response to paired auditory stimuli in event-related potential (ERP) studies. Cerebral processing can also be studied with magnetoencephalography (MEG). With a whole-head MEG, which enables one to simultaneously measure brain activity in both hemispheres, we investigated whether early parallel auditory processing is impaired in schizophrenia. Sequences of tones were monaurally presented to schizophrenia patients and healthy controls in a passive condition, and the event-related magnetic fields were recorded simultaneously over both auditory cortices. The interhemispheric latency difference of the P50m, but not that of the N100m, was significantly shorter in the patient group in the right-ear but not in the left-ear stimulus condition. Further, the ipsilateral P50m was significantly earlier in schizophrenia patients in the right-ear condition. This result suggests that schizophrenia affects the consecutive preconscious auditory processing in a different manner.

Adult↗

PubMed1999

Spatiotemporal activity of a cortical network for processing visual motion revealed by MEG and fMRI.

A sudden change in the direction of motion is a particularly salient and relevant feature of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to different features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophysiological data from animals and functional imaging data from humans suggest a number of brain areas responsive to motion, presumably working as a network. Temporal patterns of activity allow the same network to process information in different ways. The present study in humans sought to determine which motion-sensitive areas are involved in processing changes in the direction of motion and to characterize the temporal patterns of processing within this network of brain regions. To accomplish this, we used both magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). The fMRI data were used as supplementary information in the localization of MEG sources. The change in the direction of visual motion was found to activate a number of areas, each displaying a different temporal behavior. The fMRI revealed motion-related activity in areas MT+ (the human homologue of monkey middle temporal area and possibly also other motion sensitive areas next to MT), a region near the posterior end of the superior temporal sulcus (pSTS), V3A, and V1/V2. The MEG data suggested additional frontal sources. An equivalent dipole model for the generators of MEG signals indicated activity in MT+, starting at 130 ms and peaking at 170 ms after the reversal of the direction of motion, and then again at approximately 260 ms. Frontal activity began 0-20 ms later than in MT+, and peaked approximately 180 ms. Both pSTS and FEF+ showed long-duration activity continuing over the latency range of 200-400 ms. MEG responses in the region of V3A and V1/V2 were relatively small, and peaked at longer latencies than the initial peak in MT+. These data revealed characteristic patterns of activity in this cortical network for processing sudden changes in the direction of visual motion.

Adult↗

PubMed1998

Hemispheric lateralization in preattentive processing of speech sounds.

Event-related magnetoencephalographic (MEG) responses to infrequently presented spoken deviant syllables [di] and [ba] among repetitive standard [da)]syllables were recorded in subjects who either attended to these stimuli in order to discriminate the [ba] syllables or ignored them while attending a silent movie. In both conditions, the deviant syllables elicited a mismatch response (MMNm, the magnetic counterpart of mismatch negativity), which was stronger in the left than in the right auditory cortex, indicating left-hemispheric dominance in speech processing already at a preattentive processing level.

Acoustic Stimulation↗

PubMed1998

Reversal of cerebral asymmetry in schizophrenia measured with magnetoencephalography.

It has been suggested that schizophrenic patients fail to develop left-hemisphere dominance because of an early disturbance in neuronal development. This hypothesis has been supported by some post-mortem. CT and magnetic resonance imaging (MRI) studies, while other in-vivo studies have given contradicting results. We used 122-channel whole-head magnetoencephalography and MRI to locate the sources of auditory evoked responses in 19 schizophrenic patients and in 20 healthy controls. Auditory evoked responses were detected in all subjects. The left-right hemisphere asymmetry of cerebral sources for auditory evoked responses was markedly dispersed among patients when compared with controls. The source locations for left auditory cortex were clearly anterior with respect to the right hemisphere in 32% of the patients, while the corresponding prevalence of this abnormal asymmetry was 0% in controls (p = 0.008. Fisher's exact test). The reversed asymmetry appeared to be associated with a shorter anterior-posterior distance between the auditory cortex and the anterior tip of the temporal lobe in the left side when compared with the right side. The reversed asymmetry was associated with higher PANSS general psychopathological score, and especially with higher guilt feelings and motor retardation scores. The large 2.5-fold standard deviation in the inter-hemispheric anterior posterior difference in the location of the auditory cortex among patients (p 0.001 for the difference in the magnitude of variance between controls and patients) clearly reflects the dispersion of the left right asymmetry into both direction, and three of the patients with 'normal asymmetry' had a greater left-right asymmetry than any of the controls. Markedly greater reversal of hemispheric asymmetry among patients implies that regulation of the development of brain asymmetry is disturbed among schizophrenic patients. Abnormality in the cerebral asymmetry may be a crucial factor in the development of schizophrenic disorder in a substantial proportion of patients. The results suggest that the reversed asymmetry is associated with the higher severity of general psychopathological symptoms.

Adult↗

PubMed1998

The mismatch negativity for duration decrement of auditory stimuli in healthy subjects.

The amplitude and latency of the mismatch negativity (MMN) elicited by occasional shorter-duration tones (25 and 50 ms) in a sequence of 75 ms standard tones were studied in 40 healthy subjects (9-84 years). The replicability and age dependence of the MMN-responses were determined. The 25 ms deviant tone evoked a clear response in 39 of the subjects, while the 50 ms deviant tone evoked an observable MMN only in 32 of the subjects. The MMN peak amplitude for the 25 ms deviants was significantly larger than for the 50 ms deviants. There was no significant difference in the peak latencies (measured from stimulus offset). For the 25 ms deviant, the amplitude diminished with increasing age. The MMN curves for the 25 ms deviant, measured on separate days in 14 subjects, looked very replicable. As a result of noise and filtering effect, the product-moment correlations were poor. The results indicate that the signal-to-noise ratio for the MMN to 25 ms deviants, obtained even in a 25 min recording session, is large enough for clinical use and individual diagnostics when undetectable (or very low amplitude) MMN is used as a sign of pathology. However, judged from the low correlation coefficients, despite the good replicability in visual evaluation, better methods for MMN quantification have to be used for clinical follow-up.

Acoustic Stimulation↗

PubMed1998

Combined mapping of human auditory EEG and MEG responses.

Auditory electric and magnetic P50(m), N1(m) and MMN(m) responses to standard, deviant and novel sounds were studied by recording brain electrical activity with 25 EEG electrodes simultaneously with the corresponding magnetic signals measured with 122 MEG gradiometer coils. The sources of these responses were located on the basis of the MEG responses; all were found to be in the supratemporal plane. The goal of the present paper was to investigate to what degree the source locations and orientations determined from the magnetic data account for the measured EEG signals. It was found that the electric P50, N1 and MMN responses can to a considerable degree be explained by the sources of the corresponding magnetic responses. In addition, source-current components not detectable by MEG were shown to contribute to the measured EEG signals.

Acoustic Stimulation↗

PubMed1998

Temporal window of integration of auditory information in the human brain.

A deviation in the acoustic environment activates an automatic change-detection system based on a memory mechanism that builds a neural trace representing the preceding sounds. The present study revealed that the auditory-cortex mechanisms underlying this sensory memory integrate acoustic events over time, producing a perception of a unitary auditory event. We recorded magnetic responses (MMNm) to occasional stimulus omissions in trains of stimuli presented at a constant stimulus-onset asynchrony (SOA) that was, in different blocks, either shorter or longer in duration than the assumed length of the temporal window of integration. A definite MMNm was elicited by stimulus omission only with the three shortest SOAs used: 100, 125, and 150 ms, but not with 175 ms. Thus, 160-170 ms was estimated as the length of the temporal window used by the central auditory system in integrating successive auditory input into auditory event percepts.

Acoustic Stimulation↗

PubMed1998

Processing of novel sounds and frequency changes in the human auditory cortex: magnetoencephalographic recordings.

Whole-head magnetoencephalographic (MEG) responses to repeating standard tones and to infrequent slightly higher deviant tones and complex novel sounds were recorded together with event-related brain potentials (ERPs). Deviant tones and novel sounds elicited the mismatch negativity (MMN) component of the ERP and its MEG counterpart (MMNm) both when the auditory stimuli were attended to and when they were ignored. MMNm generators were located bilateral to the superior planes of the temporal lobes where preattentive auditory discrimination appears to occur. A subsequent positive P3a component was elicited by deviant tones and with a larger amplitude by novel sounds even when the sounds were to be ignored. Source localization for the MEG counterpart of P3a (P3am) suggested that the auditory cortex in the superior temporal plane is involved in the neural network of involuntary attention switching to changes in the acoustic environment.

Acoustic Stimulation↗

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↗