Hirooki Yabe

Temporal window of integration revealed by MMN to sound omission

THE central auditory system for event perception involves the integrating mechanism of sequential information addressed by the present study. The mismatch negativity (MMN) component of the event-related potentials (ERP) reflects the automatic detection of sound change. ERPs to occasionally omitted stimuli were measured when sequences with constant stimulus onset asynchronies (SOAs) were presented. In separate blocks, the SOA was from 100 to 350 ms. A clear MMN was elicited by a stimulus omission in a sequence of regularly spaced tone pips only when the SOA was shorter than 150 ms, yielding an estimate for the duration of the temporal window of integration used the perceptual segregation of auditory events.

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.

Deviant Matters: Duration, Frequency, and Intensity Deviants Reveal Different Patterns of Mismatch Negativity Reduction in Early and Late Schizophrenia

BACKGROUND A reduction in the size of the auditory event-related potential component known as mismatch negativity (MMN) is a consistent finding in schizophrenia. This study was designed to test the hypothesis that sound intensity and duration might be more sensitive to MMN reduction early in the development of schizophrenia because of the computational complexity in extracting these two sound dimensions. METHODS The MMN elicited to sounds deviating in duration, frequency, or intensity was measured in participants with a short (n = 14, mean 2.6 years) and longer length of illness (n = 29, mean 18.9 years) relative to healthy age-matched control subjects. RESULTS For participants early in the illness, a clear reduction was evident in MMN to duration and intensity but not frequency deviants. A different pattern was observed in patients with a longer length of illness--that is, a reduction in frequency and in duration to a lesser degree but not intensity MMN. CONCLUSIONS The results indicate a pronounced age-related decline in duration and intensity MMN in control subjects that might reduce the sensitivity of these indices in schizophrenia when measured later in the course of the illness. The MMN elicited to changes in different sound properties provides potentially complementary information on the onset and progression of neuropathological changes that underlie the reduction in MMN in schizophrenia.

Organizing sound sequences in the human brain: the interplay of auditory streaming and temporal integration

The present study examined the relationship between two of the early brain processes of sound organization: auditory streaming and the temporal window of integration (TWI). Presented at a fast stimulus delivery rate, two tones alternating in frequency are perceived as separate streams of high and low sounds. However, when two sounds are presented within a ca. 200 ms temporal window, they are often processed as a single auditory event. Both stream segregation and temporal integration occur even in the absence of focused attention as was shown by their effect on the mismatch negativity (MMN) event-related potential. The goal of the present study was to determine the precedence between these two sound organization processes by using the stimulus-omission MMN paradigm. Infrequently omitting one stimulus from a homogeneous tone sequence only elicits an MMN when the stimulus onset asynchrony separating successive tones is shorter than 170 ms. This demonstrates the effect of the TWI. Magnetic brain responses elicited by infrequent stimulus omissions appearing in a sequence of two alternating tones were recorded. The magnetic MMN was elicited by tone omission when the alternating tones formed a single stream (with no or only small frequency separation between the two tones) but not when separate high and low streams emerged in perception (large frequency separation between the two alternating tones). This result shows that auditory streaming takes precedence over the processes of temporal integration.

Health effects of radiation and other health problems in the aftermath of nuclear accidents, with an emphasis on Fukushima

437 nuclear power plants are in operation at present around the world to meet increasing energy demands. Unfortunately, five major nuclear accidents have occurred in the past--ie, at Kyshtym (Russia [then USSR], 1957), Windscale Piles (UK, 1957), Three Mile Island (USA, 1979), Chernobyl (Ukraine [then USSR], 1986), and Fukushima (Japan, 2011). The effects of these accidents on individuals and societies are diverse and enduring. Accumulated evidence about radiation health effects on atomic bomb survivors and other radiation-exposed people has formed the basis for national and international regulations about radiation protection. However, past experiences suggest that common issues were not necessarily physical health problems directly attributable to radiation exposure, but rather psychological and social effects. Additionally, evacuation and long-term displacement created severe health-care problems for the most vulnerable people, such as hospital inpatients and elderly people.

Impairment in activation of a frontal attention-switch mechanism in schizophrenic patients.

The present study addresses the difference in activities of frontal and temporal mismatch negativity (MMN) generators between healthy controls and schizophrenic patients. Auditory MMNs were measured from 13 medicated schizophrenic patients in a post-acute phase and 12 healthy controls. The probabilities of the standard stimuli were, in different experimental blocks, 95, 90, 80 or 70%. The mean amplitude of the MMN recorded at Fz was significantly smaller in schizophrenic patients than healthy controls only in the conditions with high probability of standard stimuli, while that recorded at mastoid sites was not different in any condition. The present study suggested that schizophrenic patients might fail to cause involuntary attention switch to stimulus change reflected in the lowered MMN amplitude recorded at Fz; whereas the patients might index an adequate detection of the deviant event reflected by the similar amplitude of MMN recorded at mastoid sites.

Somatosensory automatic responses to deviant stimuli

We studied event-related potentials (ERPs) produced in response to deviant stimuli in a sequence of somatosensory stimuli which were measured under stimulus-ignoring conditions. A change in the repetitive somatosensory input elicited not only a frontal negativity which was similar to the somatosensory mismatch negativity very recently reported by Kekoni et al. [J. Kekoni, H. Hämäläinen, M. Saarinen, J. Gröhn, K. Reinikainen, A. Lehtokoski, R. Näätänen, Rate effect and mismatch responses in the somatosensory system: ERP-recordings in humans, Biol. Psychol. 46 (1997) 125-142] but also a positive deflection ranging in latency from 100 to 200 ms. This somatosensory change-related positivity was reduced with prolongation of the interstimulus interval (ISI) and was different from the responses to the deviant stimuli when they were presented alone. These findings suggest that the somatosensory change-related positivity is probably generated not by activation of new afferent elements but by a detection of change in a process of comparison with sensory memory.

The effect of deviant stimulus probability on the human mismatch process

The present study addresses the separate activities of frontal and temporal MMN generators which might be differentially affected by a change in the probability of standard stimuli. As the probability of standard stimuli was increased, the frontal MMN component significantly increased in amplitude, while the temporal one was not affected. Correspondingly, the scalp current density (SCD) maps showed that the temporal MMN generator was activated even at low probability of standard stimuli, suggesting that even the weak memory trace could start the automatic mismatch process, whereas the frontal MMN generator was activated only with increased probabilities of standard stimuli, suggesting that the stronger the memory trace is, the easier it might trigger the involuntary switching of attention to stimulus change.

Psychological distress and the perception of radiation risks: the Fukushima health management survey.

Abstract Objective To assess relationships between the perception of radiation risks and psychological distress among evacuees from the Fukushima nuclear power plant disaster. Methods We analysed cross-sectional data from a survey of evacuees conducted in 2012. Psychological distress was classified as present or absent based on the K6 scale. Respondents recorded their views about the health risks of exposure to ionizing radiation, including immediate, delayed and genetic (inherited) health effects, on a four-point Likert scale. We examined associations between psychological distress and risk perception in logistic regression models. Age, gender, educational attainment, history of mental illness and the consequences of the disaster for employment and living conditions were potential confounders. Findings Out of the 180 604 people who received the questionnaire, we included 59 807 responses in our sample. There were 8717 respondents reporting psychological distress. Respondents who believed that radiation exposure was very likely to cause health effects were significantly more likely to be psychologically distressed than other respondents: odds ratio (OR) 1.64 (99.9% confidence interval, CI: 1.42–1.89) for immediate effects; OR: 1.48 (99.9% CI: 1.32–1.67) for delayed effects and OR: 2.17 (99.9% CI: 1.94–2.42) for genetic (inherited) effects. Similar results were obtained after controlling for individual characteristics and disaster-related stressors. Conclusion Among evacuees of the Fukushima nuclear disaster, concern about radiation risks was associated with psychological distress.

The difference in Mismatch negativity between the acute and post-acute phase of schizophrenia

In order to investigate the trait and state aspects of Mismatch negativity (MMN) amplitude reduction in schizophrenia, auditory MMNs were measured from 13 schizophrenic patients on two occasions, initially when they showed acute exacerbation and later when their symptoms improved. Patients exhibited reduced mean amplitude of the MMN recorded at Fz. There were no significant changes in the amplitude of MMN at Fz between the acute patients and the post-acute patients, despite significant improvement in symptomatology. However, the acute patients showed a significant attenuation of MMN recorded at both mastoids as compared with the post-acute patients. Although the findings of the MMN at Fz support the overall longitudinal stability of MMN deficits in schizophrenia, the acute phase patients showed a modestly altered MMN activity compared with the post-acute phase patients, suggesting that there is some state-dependent modulation of these deficits.