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Biomedical subjects

K Alho

Publications and source records attributed to K Alho.

At least 55 records · Page 3Linked to original sources
PubMed1997

Effects of involuntary auditory attention on visual task performance and brain activity.

Involuntary attention to auditory stimulus changes during a visual discrimination task was studied with event-related potentials (ERPs) recorded from the human scalp. A repetitive standard tone or an infrequent, slightly higher deviant tone preceded each visual target stimulus. Deviant tones elicited the mismatch negativity and P3a ERP components and caused increases in reaction time and error rate in the visual task indicating involuntary attention to an auditory stimulus change. These effects were observed even when the tones occurred simultaneously with a visual warning stimulus introduced to keep attention focused on the visual task. In the latter condition, involuntary switching of attention away from the visual task also attenuated the N1 ERP component to visual target stimuli preceded by the deviant tone.

Acoustic Stimulation↗
PubMed1997

Preattentive processing of complex sounds in the human brain.

Processing of complex sounds in the human brain was studied with event-related potentials (ERPs) recorded from the scalp. In random stimulus sequences, one serial tone pattern, consisting of nine consecutive tones of different frequencies, was repeatedly presented to the left ear and another pattern to the right ear. Subjects attended either to the left-ear or right-ear patterns in order to detect in the attended ear occasional deviant patterns differing from the repeating standard pattern in the 3rd or 7th tone. Even undetected deviant patterns of the attended ear and deviant patterns of the unattended ear elicited the mismatch negativity component of the ERP. These results indicate preattentive processing of complex sounds in the human brain.

Auditory Perception↗
PubMed1997

The first neurophysiological evidence for cognitive brain dysfunctions in children with CATCH.

CATCH syndrome, caused by a microdelection in chromosome 22, is characterized by cleft palate and cardiac anomalies. The majority of these children also have learning difficulties or speech and language deficits. These problems are often due to the dysmorphology of the articulatory system. In the present study, the duration of auditory sensory memory, which is of central importance to speech perception and understanding, was investigated. As a research method we used mismatch negativity (MMN), an attention independent event-related potential, which provides an objective electrical index of auditory sensory memory. The present data suggest that the duration of this memory span is considerably shorter in 6-10-year-old children with CATCH than in healthy controls. Thus, the language-related problems encountered in children suffering from CATCH syndrome are likely to be caused also by CNS dysfunctions.

Abnormalities, Multiple↗
PubMed1997

The musical brain: brain waves reveal the neurophysiological basis of musicality in human subjects.

To reveal neurophysiological prerequisites of musicality, auditory event-related potentials (ERPs) were recorded from musical and non-musical subjects, musicality being here defined as the ability to temporally structure auditory information. Instructed to read a book and to ignore sounds, subjects were presented with a repetitive sound pattern with occasional changes in its temporal structure. The mismatch negativity (MMN) component of ERPs, indexing the cortical preattentive detection of change in these stimulus patterns, was larger in amplitude in musical than non-musical subjects. This amplitude enhancement, indicating more accurate sensory memory function in musical subjects, suggests that even the cognitive component of musicality, traditionally regarded as depending on attention-related brain processes, in fact, is based on neural mechanisms present already at the preattentive level.

Adolescent↗
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

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↗
PubMed1996

The ontogenetically earliest discriminative response of the human brain.

Speech sounds elicited electric brain responses in healthy premature infants born 30-35 weeks after conception, demonstrating that the human brain is able to discriminate speech sounds even at this early age, well before term, and supporting previous results suggesting that the human fetus may learn to discriminate sounds while still in the womb. We presented preterm infants with stimulus sequences consisting of a repetitive vowel that was occasionally replaced by a different vowel. This infrequent vowel elicited a response resembling the adult mismatch negativity, which is known to reflect the brain's automatic detection of stimulus change. The present results constitute the ontogenetically earliest discriminative response of the human brain ever recorded.

Brain↗
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

Auditory and somatosensory event-related brain potentials in early blind humans.

Previous event-related potential (ERP) studies have suggested a possible participation of the visual cortex of the blind in auditory processing. In the present study, somatosensory and auditory ERPs of blind and sighted subjects were recorded when subjects were instructed to attend to stimuli of one modality and to ignore those of the other. Both modalities were stimulated with frequent ("standard") and infrequent ("deviant") stimuli, which differed from one another in their spatial locus of origin. In the sighted, deviant stimuli of the attended modality elicited N2 type of deflections (auditory N2b and somatosensory N250) over the lateral scalp areas. In contrast, in the blind, these ERP components were centroposteriorly distributed, suggesting an involvement of posterior brain areas in auditory and somatosensory stimulus discrimination. In addition, the mismatch negativity, elicited by deviant auditory stimuli even when the somatosensory stimuli were attended, was larger in the blind than in the sighted. This appears to indicate enhanced automatic processing of auditory stimulus changes in the blind. Thus, the present data suggest several compensatory changes in both auditory and somatosensory modalities after the onset of early visual deprivation.

Adult↗
PubMed1995

Generators of electrical and magnetic mismatch responses in humans.

Studies bearing on generators of the electric and magnetic mismatch responses in humans to change in a repetitive sound are reviewed. It was concluded that the main contribution of the mismatch negativity (MMN) and of its magnetic equivalent MMNm, elicited even in the absence of attention, originates from auditory cortex on the supratemporal plane. In addition, those responses probably have one or two sources on the right lateral temporal cortex and, at least the MMN, a source also in the right frontal cortex. The activation caused by stimulus change in the sensory-specific cortex is, presumably, a manifestation of preperceptual change detection, whereas the frontal activation might be associated with conscious perception of, attention switch to, stimulus change.

Acoustic Stimulation↗
PubMed1995

Mismatch negativity indicates vowel discrimination in newborns.

The present study shows that an infrequent vowel ('deviant') presented among frequent vowels ('standard') elicits in sleeping human newborns a negativity in the auditory event-related potential (ERP) resembling the mismatch negativity (MMN) recorded in adults. Thus, the MMN appears to provide means to investigate brain mechanisms of vowel perception in infants.

Acoustic Stimulation↗
PubMed1995

Cerebral generators of mismatch negativity (MMN) and its magnetic counterpart (MMNm) elicited by sound changes.

Infrequent ("deviant") sounds occurring in a sequence of repetitive ("standard") sounds elicit an event-related brain potential (ERP) response called the mismatch negativity (MMN) even in the absence of attention to these sounds. MMN appears to be caused by a neuronal mismatch between the deviant auditory input and a sensory-memory trace representing the standard stimuli. This automatic mismatch process has presumably a central role in discrimination of changes in the acoustic environment outside the focus of attention. Thus, localizing cerebral generators of MMN might help identify brain mechanisms of auditory sensory memory and involuntary attention. This review summarizes results from studies aimed at localizing MMN generators on the basis of (1) scalp-distribution, (2) magnetoencephalographic (MEG), (3) intracranial, and (4) brain-lesion data. These studies indicate that a major MMN source is located in the auditory cortex. However, the exact location of this MMN generator appears to depend on which feature of a sound is changed (e.g., frequency, intensity, or duration), as well as on the complexity of the sound (e.g., a simple tone versus complex sound). Consequently, memory traces for different acoustic features, as well as for sounds of different complexity, might be located in different regions of auditory cortex. However, MMN appears to have generators in other brain structures, too. There is some evidence for contribution of frontal-lobe activity to the MMN, which might be related to the involuntary switching of attention to a stimulus change occurring outside the focus of attention. In addition, intracranial MMN recordings in animals suggest that at least in some species, MMN subcomponents also may be generated in the thalamus and hippocampus.

Acoustic Stimulation↗
PubMed1995

Mismatch negativity to auditory stimulus change recorded directly from the human temporal cortex.

Mismatch negativity (MMN) is an event-related potential (ERP) component elicited by any discernible change in a repetitive sound even in the absence of attention. Previous studies have established that MMN is generated by change detection in a process comparing the deviant sensory input with the neural memory trace encoding the physical features of the repetitive sound. In the present study, we recorded MMNs to tonal frequency changes directly from the human temporal cortex of patients with electrodes implanted in the brain for diagnosis and therapy. The intracranially recorded MMN was found to be attention independent and modality specific. It was confined to a rather small area in temporal cortex, which was different from the structures where attention-dependent N2 and P3 responses to the frequency change could be recorded.

Acoustic Stimulation↗
PubMed1995

Low dose of ethanol suppresses mismatch negativity of auditory event-related potentials.

The acute effect of a low dose of ethanol (0.5 g/kg) on attention and auditory event-related potentials (ERPs) was investigated in 10 social drinkers using a single-blind, placebo-controlled cross-over design. A dichotic listening task, in which the subjects were instructed to attend selectively to stimuli to one ear while ignoring stimuli to the other, was used. The amplitudes of N1, P2, and the mismatch negativity (MMN) were significantly diminished by alcohol. The latencies of the MMN and N2b were also significantly increased after alcohol ingestion. The novel finding of the significant (> 60% reduction in amplitude) suppression of the MMN can be interpreted as indicating disturbed preconscious detection of acoustic changes outside the scope of attention. Because this is a prerequisite to an attentional shift, the MMN suppression may be related to increased risk for accidents after alcohol ingestion. The same dose of alcohol that suppressed the MMN left intact selective attention and conscious "target" detection, as reflected by the processing negativity and P3 deflections, thus suggesting that the automatic functions of human information processing are more sensitive to alcohol than the controlled, attentional functions.

Adult↗
PubMed1995

Mismatch negativity--a unique measure of sensory processing in audition.

Physically deviant auditory stimuli occurring among frequent ("standard") stimuli (e.g., tones or phonetic stimuli) elicit the mismatch negativity (MMN) of the auditory event-related potential (ERP). The MMN is presumably generated by a mismatch process between the sensory input from a deviant stimulus and a neural sensory-memory trace representing the physical features of the standard stimulus. This process, as well as sensory analysis of auditory input and its encoding into the memory trace, appear to be automatic since the MMN is elicited even by changes in unattended auditory stimuli. Therefore the MMN indirectly provides a unique, objective measure of the central representation of a sound. This opens new possibilities for basic research as well as clinical and other applications.

Adolescent↗