Kiwako Sakamoto

Somato-motor inhibitory processing in humans: An event-related functional MRI study

Inhibiting inappropriate behavior and thoughts is an essential ability for humans, but the regions responsible for inhibitory processing are a matter of continuous debate. This is the first study of somatosensory go/nogo tasks using event-related functional magnetic resonance imaging (fMRI). Fifteen subjects preformed two different types of go/nogo task, i.e. (1) Movement and (2) Count, to compare with previous studies using visual go/nogo tasks, and confirm whether the inhibitory processing is dependent on sensory modalities. Go and nogo stimuli were presented with an even probability. Our data indicated that the response inhibition network involved the dorsolateral (DLPFC) and ventrolateral (VLPFC) prefrontal cortices, pre-supplementary motor area (pre-SMA), anterior cingulate cortex (ACC), inferior parietal lobule (IPL), insula, and temporoparietal junction (TPJ), which were consistent with previous results obtained using visual go/nogo tasks. These activities existed in both Movement and Count Nogo trials. Therefore, our results suggest that the network for inhibitory processing is not dependent on sensory modalities but reflects common neural activities. In addition, there were differences of activation intensity between Movement and Count Nogo trials in the prefrontal cortex, temporal lobe, and ACC. Thus, inhibitory processing would involve two neural networks, common and uncommon regions, depending on the required response mode.

Somatosensory evoked magnetic fields following stimulation of the tongue in humans

OBJECTIVE To clarify the characteristics relating to the temporal dynamics of the tongue primary somatosensory cortex (SI). METHODS We fabricated individual intraoral devices and recorded somatosensory-evoked magnetic fields (SEFs) from 10 normal subjects. The tongue was stimulated with a concentrated bipolar electrode in four areas: the right and left antero-lateral margins, and the right and left postero-lateral margins. RESULTS The primary component was recorded about 19 ms post-stimulation. Six components, termed 1M, 2M, 3M, 4M, 5M, and 6M, respectively, were found within 130 ms of the stimulation. These activities were detected in hemispheres both contralateral and ipsilateral to the stimulation, and were estimated to be located around the tongue SI. In addition, the latency of the contralateral hemisphere was significantly shorter than that of the ipsilateral hemisphere for all components, independent of the area stimulated. CONCLUSIONS Tactile stimulation of the tongue-elicited activity in the tongue SI in both hemispheres. SIGNIFICANCE This is the first study to investigate the brain responses evoked by stimulating different areas of the tongue, using magnetoencephalography.

The effect of mastication on human cognitive processing: a study using event-related potentials.

OBJECTIVE The purpose of the present study was to clarify the effect of mastication on cognitive processing using reaction time (RT) and event-related potentials (ERPs). METHODS The two experiments consisted of two conditions, Mastication (chewing gum) and Control (relaxing without chewing gum) in Experiment 1, and Jaw Movement (opening and closing the jaw) and Finger Tapping (tapping the right index finger) in Experiment 2. The subjects performed four sessions of an auditory oddball paradigm. RT and ERPs were recorded in these four sessions, Pre (before chewing), and Post 1, Post 2 and Post 3 (after chewing). RESULTS In Mastication for RT and the peak latencies of P300 and N100, the values were significantly longer in Pre than in Post 2 or Post 3. By contrast, in Control, Jaw Movement, and Finger Tapping, they were almost identical among sessions or significantly shorter in Pre than in Post 2 or Post 3. CONCLUSIONS Mastication influences cognitive processing time as reflected by RT and the latency of ERP waveforms. SIGNIFICANCE This is the first study investigating the effect of mastication on the central nervous system using event-related potentials.

Evoked magnetic fields following noxious laser stimulation of the thigh in humans

Primary somatosensory cortex (SI) and posterior parietal cortex (PPC) are activated by noxious stimulation. In neurophysiological studies using magnetoencephalography (MEG), however, it has been difficult to separate the activity in SI from that in PPC following stimulation of the upper limb, since the hand area of SI is very close to PPC. Therefore, we investigated human pain processing using MEG following the application of a thulium-YAG laser to the left thigh to separate the activation of SI and PPC, and to clarify the time course of the activities involved. The results indicated that cortical activities were recorded around SI, contralateral secondary somatosensory cortex (cSII), ipsilateral secondary somatosensory cortex (iSII), and PPC between 150-185 ms. The precise location of PPC was indicated to be the inferior parietal lobule (IPL), corresponding to Brodmanns area 40. The mean peak latencies of SI, cSII, iSII and IPL were 152, 170, 181, and 183 ms, respectively. This is the first study to clarify the time course of the activities of SI, SII, and PPC in human pain processing using MEG.

Diffuse central hypomyelination presenting as 4H syndrome caused by compound heterozygous mutations in POLR3A encoding the catalytic subunit of polymerase III

We describe a 33-year-old male patient with mental retardation and cerebellar ataxia whose brain magnetic resonance imaging (MRI) showed diffuse central hypomyelination. The associated hypogonadotropic hypogonadism and hypodontia were consistent with the clinical diagnosis of 4H syndrome. Two compound heterozygous mutations in POLR3A were found: p.Met852Val and p.Asn1249His. MRI of the brain showed cerebellar atrophy, atrophy of the corpus callosum, and diffuse hypomyelination extending as far as the U-fibers, with preservation of the basal ganglia. T2 hyperintensity was observed in the bilateral middle cerebellar peduncles. The patient showed almost normal development until 4-5years of age. After 25years of age, the patient showed a gradual but consistent motor and cognitive deterioration. We demonstrated the involvement of the corticospinal tract electrophysiologically, but peripheral nerve conduction was normal. Although this disease may start very early in life, the clinical course in the present case suggests that brains that initially appear to have developed normally may show dysfunction later in life, although the pathophysiological bases for this dysfunction may not be evident on MRIs.

Meditation reduces pain-related neural activity in the anterior cingulate cortex, insula, secondary somatosensory cortex, and thalamus.

Recent studies have shown that meditation inhibits or relieves pain perception. To clarify the underlying mechanisms for this phenomenon, neuroimaging methods, such as functional magnetic resonance imaging, and neurophysiological methods, such as magnetoencephalography and electroencephalography, have been used. However, it has been difficult to interpret the results, because there is some paradoxical evidence. For example, some studies reported increased neural responses to pain stimulation during meditation in the anterior cingulate cortex (ACC) and insula, whereas others showed a decrease in these regions. There have been inconsistent findings to date. Moreover, in general, since the activities of the ACC and insula are correlated with pain perception, the increase in neural activities during meditation would be related to the enhancement of pain perception rather than its reduction. These contradictions might directly contribute to the ‘mystery of meditation.’ In this review, we presented previous findings for brain regions during meditation and the anatomical changes that occurred in the brain with long-term meditation training. We then discussed the findings of previous studies that examined pain-related neural activity during meditation. We also described the brain mechanisms responsible for pain relief during meditation, and possible reasons for paradoxical evidence among previous studies. By thoroughly overviewing previous findings, we hypothesized that meditation reduces pain-related neural activity in the ACC, insula, secondary somatosensory cortex, and thalamus. We suggest that the characteristics of the modulation of this activity may depend on the kind of meditation and/or number of years of experience of meditation, which were associated with paradoxical findings among previous studies that investigated pain-related neural activities during meditation.

Centrifugal modulation of human LEP components to a task-relevant noxious stimulation triggering voluntary movement

In the present study, we investigate the top-down centrifugal modulation of neural responses to a task-relevant noxious stimulation triggering voluntary movement by recording magnetoencephalography (MEG) and electroencephalography (EEG) simultaneously. An auditory warning signal was followed 2-3 s later by a noxious YAG laser stimulation as an imperative signal delivered to the left hand dorsum. Ten normal subjects performed three different conditions, Control, Movement, and Count. In Control, the subjects were asked to relax and rest quietly with no task. In Movement, the subjects extended the left index finger after imperative stimuli. In Count, the subjects counted the number of imperative stimuli silently. The amplitude of the N2 component recorded by EEG, which peaked about 220 ms after noxious stimulation, was significantly attenuated in Movement, but not in Count, compared to Control. The root-mean-square (RMS) from both hemispheres, and areal mean signal (AMS) amplitudes and the equivalent current dipole (ECD) strengths from SI/PPC and bilateral SII recorded at around 170 ms by MEG were not significantly different among the three conditions. In contrast, ECD strengths and AMS amplitudes from the anterior cingulate cortex (ACC), which showed a similar peak to the N2 component, were smaller in Movement than Control and Count. We therefore suspect that neural activities related to generator mechanisms of N2, especially including ACC, are inhibited by movement-related neural activities during the preparatory period. The present findings indicate a characteristic of pain-motor integration in a movement preparatory period.

Executive functions with different motor outputs in somatosensory Go/Nogo tasks: An event-related functional MRI study

The aim of this event-related functional magnetic resonance imaging (fMRI) study was to investigate and compare executive functions with different motor outputs in somatosensory Go/Nogo tasks: (1) Button press and (2) Count. Go and Nogo stimuli were presented with an even probability. We observed a common network for Movement and Count Go trials in several regions of the brain including the dorsolateral (DLPFC) and ventrolateral prefrontal cortices (VLPFC), supplementary motor area (SMA), posterior parietal cortex (PPC), inferior parietal lobule (IPL), Insula, and superior temporal gyrus (STG). Direct comparison revealed that primary sensorimotor area (SMI), premotor area (PM), and anterior cingulate cortex (ACC) were more activated during Movement than Count Go trials. In contrast, the VLPFC was more activated during Count than Movement Go trials. Our results suggest that there were two neural networks for the supramodal executive function, common and uncommon, depending on the required response mode.

The characteristics of no-go potentials with intraepidermal stimulation

The objective of this study was to investigate whether no-go potentials during go/no-go tasks were observed after painful stimulation using intraepidermal electrical stimulation. Event-related potentials were recorded by stimulating the medial or lateral side of the left-hand dorsum. Peak amplitudes of N2 and P3 were significantly larger in no-go trials than in go trials at frontocentral electrodes during go/no-go task, but the differences were not found during rest control and choice reaction time tasks. These characteristics of no-go-related potentials were very similar to event-related potential waveforms during visual, auditory, and somatosensory go/no-go tasks. We suggest that cortical activities relating to response inhibitory processing are not dependent on the sensory modality used.

The relationship between reaction time and response variability and somatosensory No-go potentials.

We investigated the relationship between reaction time (RT) and response variability and somatosensory Go/No-go potentials. Event-related potentials following electrical stimulation of the second (Go stimulus) or fifth (No-go stimulus) digit of the left hand were recorded from 16 subjects, and Go and No-go stimuli were presented at an even probability. The subjects were instructed to respond to the Go stimuli by pushing a button with their right thumb. We analyzed the correlation between RT and the N140 and P300 components, and between the standard deviation (SD) of RT and the N140 and P300. Neither the amplitude nor latency of the No-go-N140 (N140 evoked by No-go stimuli) or the Go-N140 (N140 evoked by Go stimuli) related significantly with RT and the SD of RT. There was a significant negative correlation between RT and the amplitude of the No-go-P300 (P300 evoked by No-go stimuli) at Fz and C3, indicating that subjects with a shorter RT had a No-go-P300 of larger amplitude. The latency of the Go-P300 (P300 evoked by Go stimuli) at Pz and C3 showed a significant correlation with RT. The SD of RT was significantly correlated with the amplitudes of the No-go-P300 at C3 and Go-P300 at Pz and C4, and the latency of the No-go-P300 at Cz and Go-P300 at Fz, Cz, Pz, C3, and C4. Our results suggest that response speed and variability for the Go stimulus in Go/No-go paradigms affect No-go-related neural activity for the No-go stimulus.