Biomedical subjects

Tsunehiro Takeda

Publications and source records attributed to Tsunehiro Takeda.

10 recordsLinked to original sources

PubMed2006

A comparison of stimulus synchronous activity in the primary motor cortices of athletes and non-athletes.

In this study, we measured primary motor cortex (MI) activity during a reaction time task to examine the appearance of MI activity that synchronized with the stimulus presentation (stimulus synchronous MI activity, SSMA). Because brain activity was expected to be enhanced by the repetitive/extensive activation, we hypothesized that the SSMA would be more clearly observable in athletes who were trained to perform reactive movements than in non-athletes. MI activity was measured in ten athletes and ten non-athletes by magnetoencephalography. The tasks were a simple reaction task and a Go/Nogo reaction task in which the subjects were asked to abduct their right index fingers in response to a visual stimulus. The Go/Nogo reaction time task was adopted to confirm the presence of the SSMA, because the MI activity in response to a Nogo stimulus did not overlap with the MI activity that was synchronous with the execution of the movement. The results show that the SSMA was clearly apparent in the athlete group (9/10). In the non-athlete group, however, only three subjects showed the SSMA (3/10). Moreover, the MI activity of the athletes tended to be larger than that of the non-athletes, even though the athletes did not specifically practice these index finger movements during their daily training. We concluded that long-term physical training promotes MI activity and the effects of reactive task repetition were more clearly apparent in the MI activity of the athletes.

Adult↗

PubMed2006

Estimation of the timing of human visual perception from magnetoencephalography.

To explore the timing and the underlying neural dynamics of visual perception, we analyzed the relationship between the manual reaction time (RT) to the onset of a visual stimulus and the time course of the evoked neural response simultaneously measured by magnetoencephalography (MEG). The visual stimuli were a transition from incoherent to coherent motion of random dots and an onset of a chromatic grating from a uniform field, which evoke neural responses in different cortical sites. For both stimuli, changes in median RT with changing stimulus strength (motion coherence or chromatic contrast) were accurately predicted, with a stimulus-independent postdetection delay, from the time that the temporally integrated MEG response crossed a threshold (integrator model). In comparison, the prediction of RT was less accurate from the peak MEG latency, or from the time that the nonintegrated MEG response crossed a threshold (level detector model). The integrator model could also account for, at least partially, intertrial changes in RT or in perception (hit/miss) to identical stimuli. Although we examined MEG-RT relationships mainly for data averaged over trials, the integrator model could show some correlations even for single-trial data. The model predictions deteriorated when only early visual responses presumably originating from the striate cortex were used as the input to the integrator model. Our results suggest that the perceptions for visual stimulus appearances are established in extrastriate areas [around MT (middle temporal visual area) for motion and around V4 (fourth visual area) for color] approximately 150-200 ms before subjects manually react to the stimulus.

Adult↗

PubMed2005

Modulation of early auditory processing by visually based sound prediction.

Brain activity was measured by magnetoencephalography (MEG) to investigate whether the early auditory system can detect changes in audio-visual patterns when the visual part is presented earlier. We hypothesized that a template underlying the mismatch field (MMF) phenomenon, which is usually formed by past sound regularities, is also used in visually based sound prediction. Activity similar to the MMF may be elicited by comparing an incoming sound with the template. The stimulus was modeled after a keyboard: an animation in which one of two keys was depressed was accompanied by either a lower or higher tone. Congruent audio-visual pairs were designed to be frequent and incongruent pairs to be infrequent. Subjects were instructed to predict an incoming sound based on key movement in two sets of trials (prediction condition), whereas they were instructed not to do so in the other two sets (non-prediction condition). For each condition, the movement took 50 ms in one set (Delta = 50 ms) and 300 ms in the other (Delta = 300 ms) to reach the bottom, at which time a tone was delivered. As a result, only under the prediction condition with Delta = 300 ms was additional activity for incongruent pairs observed bilaterally in the supratemporal area within 100-200 ms of the auditory stimulus onset; this activity had spatio-temporal properties similar to those of MMF. We concluded that a template is created by the visually based sound prediction only after the visual discriminative and sound prediction processes have already been performed.

Acoustic Stimulation↗

PubMed2005

MEG responses correlated with the visual perception of velocity change.

Magnetoencephalography (MEG) was used to find neural activities, in the human brain, involved in perception of velocity changes in visual motion. We recorded MEG responses evoked by the stimuli whose velocity increased by 40% or 80% of baseline velocities of 1.0, 2.0, 3.0, and 4.0 deg/s. The velocity increment threshold and the manual reaction time (RT) were also measured under similar stimulus conditions. To manipulate observer's sensitivity to velocity increments, the MEG responses and the psychophysical performances were measured after adaptation to motion in one direction (adapted condition) or alternating directions (control condition). MEG responses evoked by velocity increments peaked at 200-290 ms (M1), and the M1 amplitudes, especially those obtained for 40% increments, were correlated with the sensitivities, which are the reciprocal of velocity increment thresholds. Furthermore, motion adaptation enhanced sensitivity to velocity increments and increased the M1 amplitudes. These results suggest a close correlation between the perceptual velocity increment and the evoked MEG response. In other words, the results suggest that velocity increments are detectable when there is a constant increment in magnetic neural response. As for latencies, nearly constant value of M1 latency did not quantitatively match a large decrease in manual RT with the increase in the baseline velocity. Motion adaptation reduced neither the peak MEG latency nor the manual RT.

Adaptation, Psychological↗

PubMed2005

Direction-specific adaptation of magnetic responses to motion onset.

We investigated the direction-specificity of motion adaptation, by recording magnetic responses evoked by motion onsets under both adapted and control conditions. The inter-stimulus interval was equated between the conditions to precisely evaluate the effect of motion adaptation itself. The onset stimuli at 1.5, 3.0 or 6.0 deg/s moved in the same direction or in the opposite direction to an adaptation stimulus at 3.0 deg/s. The perceived velocity of each test stimulus was measured in separate sessions. The most prominent peak (M2) of evoked responses appeared around 200-300 ms after motion onsets, and the dipoles were mainly estimated in the temporo-occipital area. Adaptation largely affected both perceived velocities and the M2 amplitudes. The M2 amplitudes were decreased by adaptation for both directions of test stimuli, and the decreases were significantly larger for the test stimuli in the adapted direction (49-63% of control condition) than for the test stimuli in the opposite direction (17-27% of control condition). The present study, for the first time, found that magnetic responses evoked by motion onsets reflect the activities of neurons that have direction-specificity.

Adaptation, Physiological↗

PubMed2005

The effect of 1/f fluctuation in inter-stimulus intervals on auditory evoked mismatch field.

This study focused on the effect of regularity of environmental stimuli on the informational order extracting function of human brain. The regularity of environmental stimuli can be described with the exponent n of the fluctuation 1/f(n). We studied the effect of the exponent of the fluctuation in the inter-stimulus interval (ISI) on the elicitation of auditory evoked mismatch fields (MMF) with two sounds with alternating frequency. ISI times were given by three types of fluctuation, 1/f(0), 1/f(1), 1/f(2), and with a fixed interval (1/f(infinity)). The root mean square (RMS) value of the MMF increased significantly (F(3/9)=4.95, p=0.027) with increases in the exponent of the fluctuation. Increments in the regularity of the fluctuation provoked enhancement of the MMF, which reflected the production of a memory trace, based on the anticipation of the stimulus timing. The gradient of the curve, indicating the ratio of increments between the MMF and the exponent of fluctuation, can express a subject's capability to extract regularity from fluctuating stimuli.

Acoustic Stimulation↗

PubMed2004

Bilateral cerebral activity for unilateral foot movement revealed by whole-head magnetoencephalography.

The primary motor cortices controlling foot movement are located on opposite sides of the longitudinal fissure. As a separation of closely located activity sources is not successful, the possibility of bilateral activation for lower limb movement remains undetermined. We therefore examined cerebral activity during unilateral foot movement to investigate the possibility of bilateral activation of primary foot motor cortices. Self-paced foot movement and finger movement (for comparison) were performed on ten subjects. Brain magnetic fields were recorded using a 64-channel whole-cortex magnetoencephalography (MEG) system. Brain activities were identified using 1- to 3-dipole models. Results evaluating finger movement were similar to previous reports. Equivalent current dipoles (ECDs) for foot movements were estimated in the primary foot motor and sensory regions. Sensory activity was always localized to the contralateral hemisphere. Motor activity was estimated by one ECD, but the laterality differed between subjects. Additional activity was discovered together with the primary motor activity, localized around the precentral sulcus. In contrast to consistent results of primary sensory activity, the variation of laterality of the foot primary motor ECD can be explained with a cancellation model, in which the magnetic fields generated from two closely spaced ECDs overlap to cancel each other out. Consequently, activation of the primary foot motor cortices was determined to be bilateral. Furthermore, it was estimated that additional activity may occur in the premotor area. This work suggests not only the bilateral activation of the primary foot motor cortices but also the possibility of a contribution of the premotor area.

Adult↗

PubMed2003

A delayed class of BOLD waveforms associated with spreading depression in the feline cerebral cortex can be detected and characterised using independent component analysis (ICA).

An application of independent component analysis to blood oxygenation level- dependent MRI (BOLD-MRI) results was used to detect cerebrovascular changes that followed the initiation of cortical spreading depression (CSD) in feline brain. The cortical images were obtained from a horizontal plane at 28 s intervals before, and for 1.4-1.75 h after, KCl dissolved in agar (KCl/agar) had been directly applied to the left suprasylvian gyrus of 13 anesthetized cats for 10 min. It successfully resolved, for the first time, a novel class of prolonged, and delayed, biphasic BOLD waveforms. These were larger in amplitude ( approximately 20%), longer lasting and more delayed in onset (13-33 min) than the brief propagating (90 s) BOLD increase ( approximately 4%) already known to be associated with CSD on earlier occasions. Furthermore, such changes occurred in localized regions on the hemisphere ipsilateral to the site of stimulus application in 4 out of 5 control subjects rather than themselves generating propagating waves. Finally, the biphasic waveforms were consistently abolished in the 4 experimental animals studied following the i.v. administration of sumatriptan (0.3 mg kg(-1)), an antimigraine 5-HT(1B/1D) agonist, 15 min before the application of the transient stimulus. They were abolished in 2 out of 4 animals following the intraperitoneal (i.p.) administration of SB-220453 (tonabersat: 10 mg kg(-1), 90 min before stimulus application), a novel anticonvulsant that has recently been reported to inhibit CSD. ICA has thus been successful in detecting a novel localized, as opposed to propagating, signal of potential physiological significance hidden in complex BOLD- MRI data, whose sensitivity to sumatriptan may relate it to the cerebrovascular changes reported in the headache phase of migraine.

Animals↗

PubMed2002

Magnetoencephalographic study of speed-dependent responses in apparent motion.

OBJECTIVES: There have been only few studies of visually-evoked cortical responses to apparent motion as a function of stimulus speed. Most earlier findings on evoked peak magnitudes and latencies, utilizing various types of smooth and apparent motion stimuli, have demonstrated that greater spatial separation/speed resulted in enhanced peak magnitudes, decreasing onset latencies in individual extrastriate neurons and in shorter motor reaction times in subjects. However, some reports using partial-coverage magnetoencephalography stated that increasing the stimulus displacement actually triggered a substantial reduction of the evoked main peak latency while the magnitude showed no clear change. METHODS: To resolve the issue of the dependency of evoked responses on stimulus speed in apparent motion, we presented moving bar stimuli to 6 subjects at velocities within a 100 fold range and investigated the ensuing evoked visual cortical activity using a whole-cortex magnetoencephalograph. The magnitude and the latency of the first major evoked peak M1 was measured and compared for 6 discrete bar-stimuli displacements in all subjects. RESULTS: Our results showed clearly that the M1 peak response magnitudes increased in a nonlinear way with higher apparent speeds (larger displacements), in compliance with the logarithmic Fechner law. We observed also that the fluctuations of the mean evoked M1 peak latency (140+/-10.6 ms) did not reach significance over the tested range of stimulus velocities. CONCLUSIONS: These findings probably reflect global motion processing mechanisms which rely on nonlinear speed-dependent feedback connectivity between striate and extrastriate visual cortex areas.

Adult↗

PubMedDate not supplied

MEG recording from the human ventro-occipital cortex in response to isoluminant color stimulation.

In contrast to PET and fMRI studies, color-selective responses from the ventro-occipital area have rarely been reported in MEG studies. We tried to minimize the stimulation to all areas in the visual system except the color-processing ones by using a color space based on psychophysical and physiological knowledge in order to maximize the signal-to-noise ratio for MEG responses from the ventro-occipital area. MEG obtained from long intermittent reversals (2.0-3.5 s) of isoluminant chromatic gratings showed two major peaks at the latencies of approximately 100 and 150 ms. The estimated location of the equivalent-current dipole for response at 100-ms latency was in the calcarine sulcus and that of the dipole for the response at 150 ms was in the collateral sulcus in the ventro-occipital area. The response around 150 ms was uniquely observed in MEG elicited by chromatic reversals. The average of lags between MEG responses from the calcarine sulcus and ventro-occipital area was 43 ms, which suggests sequential processing of color information across the visual cortices.

Adult↗