Ichiro Shimoyama

The synchronization between brain areas under motor inhibition process in humans estimated by event-related EEG coherence.

To investigate the functional connection of brain areas under motor inhibition, the event-related coherence (ERCoh) of the electroencephalogram (EEG) was calculated for 10 subjects who were asked to perform a visual discrimination (GO/NO-GO) task. The subjects were instructed to push (GO) or not to push (NO-GO) a micro-switch according to different visual stimuli. Twenty-one-channel scalp EEGs were recorded and the surface Laplacians were calculated at F3, F4, C3, C4, P3 and P4 using the source derivation method. The time-courses of the inter- and intra-hemispheric coherence were calculated using the fast Fourier transform for each condition (GO or NO-GO), and were compared statistically between the two conditions. The results suggest that the ERCoh under the NO-GO condition consisted of two components; alpha band synchronization between bilateral frontal areas and theta band synchronization among bilateral frontal, central and parietal areas. It is likely that the former is related directly to the decision not to move, and the latter is related to the motor inhibition process.

EVENT-RELATED DYNAMICS OF THE GAMMA-BAND OSCILLATION IN THE HUMAN BRAIN : INFORMATION PROCESSING DURING A GO/NOGO HAND MOVEMENT TASK

To investigate the gamma band activity relating to the discrimination process and motor behavior in the human brain, the event-related dynamics of the EEG spectrum was calculated during the visual GO/NOGO hand movement task and a control task (the visual element of the GO/NOGO task only) in eight subjects. The subjects were instructed to push (GO) or not to push (NOGO) a microswitch according to different visual stimuli and 21-channel scalp EEGs were recorded. The time courses of the power spectra after the stimuli were calculated using the fast Fourier transform for each condition (GO, NOGO and the control task), and were compared statistically between the conditions. The results suggested that a high gamma band oscillation, occurring at the frontal and left parieto-occipital areas at around 90 ms after the stimuli, relates to the discrimination process. Under the GO condition, this oscillation continued until 140 ms, and a subsequent oscillation occurred over the motor areas at around 200 ms, which seemed to be related to the motor action. On the other hand, under the NOGO condition, a low gamma band oscillation occurred in the central area at around 230 ms, which seemed to be related to the inhibition process.

Synaptic origin of the respiratory-modulated activity of laryngeal motoneurons.

To determine the synaptic source of the respiratory-related activity of laryngeal motoneurons, spike-triggered averaging of the membrane potentials of laryngeal motoneurons was conducted using spikes of respiratory neurons located between the Bötzinger complex and the rostral ventral respiratory group as triggers in decerebrate, paralyzed cats. We identified one excitatory and two inhibitory sources for inspiratory laryngeal motoneurons, and two inhibitory sources for expiratory laryngeal motoneurons. In inspiratory laryngeal motoneurons, monosynaptic excitatory postsynaptic potentials were evoked by spikes of inspiratory neurons with augmenting firing patterns, and monosynaptic inhibitory postsynaptic potentials (IPSPs) were evoked by spikes of expiratory neurons with decrementing firing patterns and by spikes of inspiratory neurons with decrementing firing patterns. In expiratory laryngeal motoneurons, monosynaptic IPSPs were evoked by spikes of inspiratory neurons with decrementing firing patterns and by spikes of expiratory neurons with augmenting firing patterns. We conclude that various synaptic inputs from respiratory neurons contribute to shaping the respiratory-related trajectory of membrane potential of laryngeal motoneurons.

The time course of interhemispheric EEG coherence during a GO/NO-GO task in humans

Event-related coherence of the EEG was calculated for 10 subjects performing a visual discrimination GO/NO-GO task. The subjects were instructed to push (GO) or not to push (NO-GO) a button according to visual stimuli. Twenty-one-channel scalp EEGs were recorded and the surface Laplacian was calculated using the source derivation method. The time courses of the coherence between F3 and F4, C3 and C4, and P3 and P4 were calculated using the fast Fourier transform for each task and were compared between conditions. Statistical analysis showed that coherence in the NO-GO condition became significantly higher than that in the GO condition between F3 and F4. The synchronization between bilateral dorsolateral frontal areas might therefore play an important role in the motor inhibition process.

Gastric and non-gastric signals in electrogastrography

Electrogastrography (EGG) is the cutaneous recording of gastric myoelectrical activity, and the dominant frequency reflects the rhythm of the gastric slow wave. Ambulatory EGG is contaminated with a large amount of motion artifacts, and it is unclear how much of the signals comprising the dominant frequency originates from non-gastric sources. The aim of the present study was to evaluate the pattern of gastric and non-gastric signals in the dominant frequency histogram (DFH) obtained from long-term ambulatory EGG recordings. Ten normal controls and five post-gastrectomy patients participated in the present study. Twenty-four hour ambulatory EGG was recorded under normal daily conditions. The DFH of normal controls showed two distinctive peaks, and that of the post-gastrectomy patients, a single peak. The common peak at approximately 1.5 cpm was seen in both DFHs, and the peak at 3 cpm was seen only in the DFH of normal controls. Thus, the common peak was thought to be a product of non-gastric origin. In conclusion, the dominant frequency consists of gastric and non-gastric components which have a specific distribution pattern in the DFH. These findings quantified the contribution of gastric and non-gastric signals to the dominant frequencies in long-term ambulatory EGG.

Visual evoked potentials relating to imagery: words for concrete objects versus absolute concepts.

SummaryWe recorded visual evoked potentials (VEPs) elicited with high or low imaginable Chinese characters (HIC or LIC), representing concrete objects or absolute concepts, respectively. A closed circle (CC) acts as control stimulus. These were displayed (at 1.6° visual angle) for 35 ms on a TV monitor. Twenty-one channel VEPs (band-pas filter: 0.05–60 Hz), using balanced non-cephalic electrodes, were recorded from −100 to 924 ms for 11 right-handed male volunteers. The VEPs were analyzed by multivariate analysis of variance (MANOVA) and comparison of topographies at four remarkable peaks (P110, N160, P230 and N320). MANOVA showed significant differences (p< 0.001) for both conditions of channel and stimuli (HIC, LIC or CC). P100 for the CC-VEPs, N160 for the HIC-and LIC-VEPs, P230 for the CC-VEPs, and N320 for the HIC-VEPs were remarkable in the posterior scalp regions. Topographies at P100 and N160 showed no difference between the HIC-and LIC-stimuli. However, those at N320 showed difference between the HIC-and LIC-stimuli over the occipital and posterior temporal areas. Those results suggest that the responses at P100 and N160 might segregate Chinese characters from non Chinese characters. N320 suggested certain processes in imagery on recognizing Chinese characters over the occipital and posterior temporal areas.

Effect of pinealectomy on cortically kindled rats

Cortical kindling in pinealectomized rats was studied to observe the effect of pinealectomy on local afterdischarge thresholds and seizure development. Although the local afterdischarge thresholds were not affected by pinealectomy, the kindling process itself was hastened. These results suggest that the anticonvulsive function of the pineal body is due not to a decrease in local afterdischarge thresholds, but to retardation of secondary generalization.

Quantitative measurement of changes in calcium channel activity in vivo utilizing dynamic manganese-enhanced MRI (dMEMRI)

The ability of manganese ions (Mn(2+)) to enter cells through calcium ion (Ca(2+)) channels has been used for depolarization dependent brain functional imaging with manganese-enhanced MRI (MEMRI). The purpose of this study was to quantify changes to Mn(2+) uptake in rat brain using a dynamic manganese-enhanced MRI (dMEMRI) scanning protocol with the Patlak and Logan graphical analysis methods. The graphical analysis was based on a three-compartment model describing the tissue and plasma concentration of Mn. Mn(2+) uptake was characterized by the total distribution volume of manganese (Mn) inside tissue (V(T)) and the unidirectional influx constant of Mn(2+) from plasma to tissue (K(i)). The measurements were performed on the anterior (APit) and posterior (PPit) parts of the pituitary gland, a region with an incomplete blood brain barrier. Modulation of Ca(2+) channel activity was performed by administration of the stimulant glutamate and the inhibitor verapamil. It was found that the APit and PPit showed different Mn(2+) uptake characteristics. While the influx of Mn(2+) into the PPit was reversible, Mn(2+) was found to be irreversibly trapped in the APit during the course of the experiment. In the PPit, an increase of Mn(2+) uptake led to an increase in V(T) (from 2.8±0.3 ml/cm(3) to 4.6±1.2 ml/cm(3)) while a decrease of Mn(2+) uptake corresponded to a decrease in V(T) (from 2.8±0.3 ml/cm(3) to 1.4±0.3 ml/cm(3)). In the APit, an increase of Mn(2+) uptake led to an increase in K(i) (from 0.034±0.009 min(-1) to 0.049±0.012 min(-1)) while a decrease of Mn(2+) uptake corresponded to a decrease in K(i) (from 0.034±0.009 min(-1) to 0.019±0.003 min(-1)). This work demonstrates that graphical analysis applied to dMEMRI data can quantitatively measure changes to Mn(2+) uptake following modulation of neural activity.

DIFFERENCES IN AUDITORY SCALP POTENTIALS EVOKED BY MEANINGFUL WORDS AND NONLINGUISTIC STIMULI

Differences in auditory evoked potentials with meaningful words and their reverse playback may reflect different neural processes in recognizing auditory Stimuli. Auditory evoked potentials with the words and their reverse playback were analyzed for eight volunteers, and a maximal difference was observed at a latency around 400 msec. over the left middle temporal central area.

Visual evoked potentials to a faint light: signal propagation analyzed with peak latency and topographic mapping.

SummaryAccurate localization for the process of recognition of a light stimulus is yet to be determined. We studied 19-channel VEP from nine healthy volunteers, evoked by physiologically faint light less than 200 Cd/m2, using a light emitting diode (5 mm ø,0.3°, energized for 5 msec). VEP was bandpass filtered from 0.16 to 120 Hz, and analyzed from 20 msec pre-stimulus to 184.2 msec post-stimulus. The grand average VEP suggested an initial positive peak at 115.8 msec at the frontal poles and at 136 msec over the occipital areas. An initial negative peak was noted at 156 msec a the frontal poles and at 179.2 msec over the occipital areas. This might suggest that the potentials evoked had propagated from the frontal poles to the occipital areas, taking about 20 msec. However, the topographic maps contained little evidence for such a propagation, but rather indicated the waxing and waning of positive or negative extremes.