Biomedical subjects

Takashi Nagamine

Publications and source records attributed to Takashi Nagamine.

At least 19 recordsLinked to original sources

PubMed2007

Amino acid mediated intramolecular asymmetric aldol reaction to construct a new chiral bicyclic enedione containing a seven-membered ring: remarkable inversion of enantioselectivity compared to the six-membered ring example.

A detailed study to assess the enantioselectivity of the amino acid mediated intramolecular asymmetric aldol reaction of 1,3-cycloheptanedione bearing a C-2 methyl substituent has been undertaken. The cyclizations were mediated by a series of l-amino acids in the presence of an acid cocatalyst. Strikingly, the process is characterized by an inversion of enantioselectivity when compared to a similar reaction involving the 1,3-cyclohexanedione counterpart.

Amino Acids↗

PubMed2006

Transient functional suppression and facilitation of Japanese ideogram writing induced by repetitive transcranial magnetic stimulation of posterior inferior temporal cortex.

The Japanese writing system is unique in that it is composed of two different orthographies: kanji (morphograms) and kana (syllabograms). The retrieval of the visual orthographic representations of Japanese kanji is crucial to the process of writing in Japanese. We used low-frequency repetitive transcranial magnetic stimulation (rTMS) to clarify the functional relevance of the left and right posterior inferior temporal cortex (PITC) to this process in native Japanese speakers. The experimental paradigms included the mental recall of kanji, kana-to-kanji transcription, semantic judgment, oral reading, and copying of kana and kanji. The first two tasks require the visualization of the kanji image of the word. We applied 0.9 Hz rTMS (600 total pulses) over individually determined left or right PITC to suppress cortical activity and measured subsequent task performance. In the mental recall of kanji and kana-to-kanji transcription, rTMS over the left PITC prolonged reaction times (RTs), whereas rTMS over the right PITC reduced RTs. In the other tasks, which do not involve the mental visualization of kanji, rTMS over the left or right PITC had no effect on performance. These results suggest that the left PITC is crucial for the retrieval of the visual graphic representation of kanji. Furthermore, the right PITC may work to suppress the dominant left PITC in the neural network for kanji writing, which involves visual word recognition.

Adult↗

PubMed2006

Ipsilateral facial sensory and motor responses to basal fronto-temporal cortical stimulation: evidence suggesting direct activation of cranial nerves.

To clarify the generator mechanism of sensory and motor facial responses ipsilateral to electrical stimulation of the inferior fronto-temporal cortex in epilepsy patients. Out of 30 patients who have been evaluated with chronically implanted subdural electrodes for medically intractable partial seizure or brain tumor involving the basal frontal or temporal cortex, 4 patients (age ranging 24-57 years) showed sensory and motor responses in the ipsilateral face to high frequency electrical cortical stimulation of the inferior fronto-temporal cortex. We investigated motor evoked potentials (MEPs) in the facial muscle by single pulse stimulation in 2 out of 4 patients. Three patients showed both sensory symptoms and muscle contraction in the ipsilateral lower face when the orbitofrontal or basal temporal cortex was stimulated with 50 Hz electric current. One patient had only sensory symptoms in the lower face when ipsilateral basal temporal area was stimulated. MEPs at the left orbicularis oris muscle were constantly elicited with the onset latency of 7 ms throughout the stimulus rate of 2-30 Hz in 1 patient out of 2 patients was tested. In another patient, MEP onset latency was 3.0 ms with 11 Hz stimulation. With electrical stimulation of the basal fronto-temporal cortex, the ipsilateral facial twitch might occur through either the direct activation of the facial nerve by the current spread in the middle cranial fossa or through the mechanism similar to blink reflex.

Adult↗

PubMed2006

Generators and temporal succession of giant somatosensory evoked potentials in cortical reflex myoclonus: epicortical recording from sensorimotor cortex.

OBJECTIVE: To clarify the generator mechanism of giant somatosensory evoked potentials (giant SEPs) and the hyperexcitability of primary somatosensory and motor cortices (SI and MI). METHODS: In a patient with intractable focal seizures manifesting cortical reflex myoclonus of the left foot, giant SEPs to left tibial nerve stimulation were epicortically recorded as a part of presurgical evaluation with subdural electrodes. RESULTS: In the single pulse SEPs, enlarged P1-N1 components were observed at the foot area of the SI and MI (86.5-258.8 microV, respectively), and the peak latencies were always shorter at SI than at MI by 6 ms. Similar findings were obtained for peroneal and sural nerve stimulation. In the paired pulse SEPs, the second response was less suppressed, as compared to other interstimulus intervals (ISIs), with ISIs of 40 and 200 ms both at SI and MI. CONCLUSIONS: In this particular patient, cortical hyperexcitability to somatosensory stimuli seems to originate from SI but subsequently both SI and MI are responsible for the generation of giant SEPs and cortical reflex myoclonus. SIGNIFICANCE: Somatosensory and primary motor cortices both generated enhanced early cortical components of SEPs, most likely by enhancing the latter by the former.

Adult↗

PubMed2006

Somatosensory evoked magnetic fields to air-puff stimulation on the soft palate.

Impairment of sensory input to the soft palate has been reported in patients with obstructive sleep apnea syndrome. To investigate the reaction in the central nervous system related to soft palate perception, we measured the somatosensory evoked magnetic fields following air-puff stimulation in seven healthy volunteers by using a helmet-shaped 122-channel neuromagnetometer. The air-puffs were produced using compressed nitrogen and directed to the middle of the soft palate with an intraoral device. To evaluate the laterality of responses we used another appliance in which the air-puffs were directed to the middle and right side of the soft palate. In all the subjects, responses were identified symmetrically in the bilateral parietotemporal regions with a mean latency of about 130 ms from the soft palate stimulation. Prior to this peak, no distinct early responses were observed. There was no significant difference in the responses between the middle and right side stimulation. Corresponding equivalent current dipoles were estimated around the Sylvian fissures. These results suggested that the responses were derived from the second somatosensory areas. In conclusion, we could record long-latency responses to air-puff stimulation of the soft palate in the bilateral second somatosensory areas.

Adult↗

PubMed2006

Effects of continuous masking noise on tone-evoked magnetic fields in humans.

Two different types of steep loudness growth have been reported in detail in psychoacoustical studies but have rarely been evaluated by objective methods in humans. One occurs in inner-ear hearing-impaired patients and is known as loudness recruitment. Another similar phenomenon is observed in healthy subjects with concurrent presence of background noise. Concerning the first type, our previous study using magnetoencephalography (MEG) showed that enhancement of the dipole moment of N100m with increase in stimulus intensity was greater in patients than in normal individuals. However, it is unclear whether the enhancement of activity in auditory cortex will also be detected with background noise in healthy subjects. To elucidate the effects of continuous background noise on tone-evoked cortical activity, we measured auditory-evoked magnetic fields (AEFs) from 7 normal-hearing subjects in two different conditions, with and without 55 dB SPL continuous masking white noise (noise/quiet conditions). The stimuli were 200 ms 1-kHz tones delivered monaurally and randomly at 4 different intensities (40-70 dB SPL) with constant 1-s interstimulus intervals. The N100m increased in amplitude and decreased in latency as a function of stimulus intensity in both noise and quiet conditions. The dipole moment of N100m was significantly smaller in the noise than in the quiet condition, showing that continuous background noise suppresses the strength of tone-evoked cortical responses. The mechanisms underlying these two psychoacoustically similar phenomena of rapid loudness growth thus differ.

Acoustic Stimulation↗

PubMed2006

Clinical outcome of patients with SREDA (subclinical rhythmic EEG discharge of adults).

OBJECTIVE: To clarify the clinical significance of subclinical rhythmic EEG discharge of adults' (SREDA) by analyzing characteristics of SREDA and the outcome of patients based on retrospective analysis of EEG data base. METHODS: EEGs were recorded soon after the onset of patient's initial symptoms and repeatedly recorded at various intervals of 2-3 months in all 4 patients. Neurological findings, MRI and SPECT were also investigated. SUBJECTS: Out of 340 consecutive inpatient population who had EEGs, 4 patients (1.2%) showed SREDA. They had a diagnosis of syncope, transient global amnesia, generalized tonic-clonic seizure and right temporal lobe epilepsy for each. RESULTS: There was no consistent abnormality in the brain MRI, CT or SPECT among the 4 patients. The acute and transient symptoms disappeared and did not recur within the follow-up period of 28 months in any patient. In 2 patients SREDA disappeared in the follow-up EEG taken 7-14 days after the first EEG showing SREDA. In the other 2 patients, the follow-up EEGs taken 5 days after the first EEG with SREDA when clinical symptoms disappeared showed less frequent occurrence of SREDA. CONCLUSION: Being different from the previous reports suggesting the relation with cardiogenic insults or persistent ischemic abnormality, SREDA can occur in patients with various acute brain dysfunctions followed by a favorable clinical outcome.

Adolescent↗

PubMed2006

Altered plasticity of the human motor cortex in Parkinson's disease.

Interventional paired associative stimulation (IPAS) to the contralateral peripheral nerve and cerebral cortex can enhance the primary motor cortex (M1) excitability with two synchronously arriving inputs. This study investigated whether dopamine contributed to the associative long-term potentiation-like effect in the M1 in Parkinson's disease (PD) patients. Eighteen right-handed PD patients and 11 right-handed age-matched healthy volunteers were studied. All patients were studied after 12 hours off medication with levodopa replacement (PD-off). Ten patients were also evaluated after medication (PD-on). The IPAS comprised a single electric stimulus to the right median nerve at the wrist and subsequent transcranial magnetic stimulation of the left M1 with an interstimulus interval of 25 milliseconds (240 paired stimuli every 5 seconds for 20 minutes). The motor-evoked potential amplitude in the right abductor pollicis brevis muscle was increased by IPAS in healthy volunteers, but not in PD patients. IPAS did not affect the motor-evoked potential amplitude in the left abductor pollicis brevis. The ratio of the motor-evoked potential amplitude before and after IPAS in PD-off patients increased after dopamine replacement. Thus, dopamine might modulate cortical plasticity in the human M1, which could be related to higher order motor control, including motor learning.

Aged↗

PubMed2005

Cortical mechanisms of unilateral voluntary motor inhibition in humans.

While motor control is very often a goal-oriented event, little is known about the mechanisms underlying the termination of motor performance. To investigate what type of cortical activation underlies the muscle relaxation required to terminate the act, we performed single- and double-pulse transcranial magnetic stimulation (TMS) studies during voluntary muscle relaxation in nine normal volunteers. Subjects maintained a weak isometric contraction of the right first dorsal interosseous muscle (FDI), and either increased the level of contraction (Contraction), terminated the contraction (Relaxation), or maintained it (No-go) depending on a visual cue. Motor evoked potentials (MEP) and the silent period (SP) were recorded from the FDI during motor activity. To measure intra-cortical inhibition (ICI), we also performed double-pulse TMS, applying subthreshold conditioning stimuli at interstimulus intervals of 2 ms. When single-pulse TMS was given just prior to muscle relaxation (-21 to -70 ms), the MEP was reduced while the SP was unchanged. Intra-cortical inhibition was smaller just prior to the muscle relaxation. Unilateral voluntary muscle relaxation may not be associated with activation of the intracortical inhibitory system, but rather with the possible excitation of the corticospinal system, which can inhibit motoneurons disynaptically. These findings suggest that multiple inhibitory mechanisms act in diverse ways to achieve motor inhibition.

Adult↗

PubMed2005

Processing of Japanese morphogram and syllabogram in the left basal temporal area: electrical cortical stimulation studies.

Language functions in the left basal temporal area (LBTA) were investigated using electrical cortical stimulation during functional mapping in six Japanese patients with refractory epilepsy. This study provides the first direct evidence that kana (Japanese syllabogram) is processed in the LBTA. Electrical stimulation of some areas within LBTA induced disturbance in overt reading of kana words only in the first trials, with no errors in the subsequent trials. By contrast, stimulation of the same area caused obvious disturbance in kana non-word reading in all trials. Since a kana word carries both meaning and sound while a kana non-word carries only sounds of a letter string, the contrasting results of partial and complete disturbance imply a possibility that there are two distinct pathways for kana reading: one dealing with both phonological and semantic aspects of the words and the other dealing only with phonological aspect. Kanji words (Japanese morphogram) and objects/pictures were found to be processed in an area different from the area for the kana non-word processing. Furthermore, the present study also identified the common area for processing kanji reading and object/picture naming. There were no errors in matching pictures with kanji words, indicating that concepts of pictures and meanings of kanji words were not interfered by the electrical stimulation of that area. The new insight provides a clue for partial description of processing pathways for language-related visual information in LBTA. Three types of information (morphological, phonological, and semantic) are conveyed together at some stages and are separated into different routes at some other stages.

Acoustic Stimulation↗

PubMed2005

Effect of spatial attention on human sensorimotor integration studied by transcranial magnetic stimulation.

OBJECTIVE: Recent transcranial magnetic stimulation (TMS) studies showed that the sensory input can decrease the motor cortex excitability (afferent inhibition). To clarify the effect of attention on sensorimotor integration, we investigated the effect of spatial attention on afferent inhibition. METHODS: Right median nerve electrical stimulation followed, at variable delays (10-300 ms), by TMS over the left motor cortex was applied to 9 subjects, during 3 conditions; spatial attention to the right and left hand, and control (no attention) tasks. RESULTS: Inhibition of the motor evoked potential occurred at inter-stimulus interval of 20 and 100 ms, which was more was marked during spatial attention to the right than to the left hand. CONCLUSIONS: Enhancement of the afferent inhibition induced by spatial attention to the stimulated side is likely to reflect the interaction between attention and sensorimotor integration. SIGNIFICANCE: The spatial attention may modulate the sensorimotor integration studied by afferent inhibition of the MEP.

Adult↗

PubMed2005

Right hemispheric predominance in the segregation of mistuned partials.

To elucidate the central mechanisms of sound segregation, we compared responses to a harmonic sound and a mistuned sound using a whole-head magnetoencephalography system. The harmonic sound was composed of a 200-Hz tone and its 2nd to 12th harmonics. The mistuned sound had, instead of the 600-Hz harmonic, a 696-Hz tone. In the right hemisphere, the amplitude of N100m responses evoked by the mistuned sound was significantly larger and the peak latency significantly longer than that evoked by the harmonic sound, suggesting that the right hemisphere plays a more important role than the left in detecting mistuned partials.

Acoustic Stimulation↗

PubMed2004

Short-term high-frequency transcutaneous electrical nerve stimulation decreases human motor cortex excitability.

Several previous studies have shown that periods of changed sensory input can have after effects on the excitability of the corticospinal system. Here we test whether the parameters of peripheral stimulation conventionally used to treat pain with transcutaneous electrical nerve stimulation (TENS: 90 Hz) also have modulatory effects on the motor system. We measured the amplitude of motor evoked potentials (MEPs) elicited by the focal transcranial magnetic stimulation in the right abductor pollicis brevis and first dorsal interosseous muscles before and after 30 min TENS over the right thenar eminence. In addition, we evaluated tactile and 2-point discrimination thresholds at the same site. TENS transiently reduced MEPs and increased sensory thresholds. This suggests that short-term TENS might have an inhibitory effect on both the sensory and motor systems.

Adult↗

PubMed2004

Multisensory convergence at human temporo-parietal junction - epicortical recording of evoked responses.

OBJECTIVE: Previous lesion studies in patients and functional imaging studies in normal subjects have led to the notion that the temporo-parietal junction (TPJ) has an integrative function for multisensory inputs. However, its electrophysiological properties such as response latencies and distributions of responses to various stimulus modalities in humans have not been fully investigated. The aim of the study is to clarify this issue. METHODS: We recorded evoked potentials to different kinds of sensory stimuli including somatosensory, auditory and visual modalities in 6 patients with intractable partial epilepsy, who underwent chronic implantation of subdural electrodes in TPJ for presurgical evaluation. RESULTS: In 5 out of 6 subjects, at least one electrode located in TPJ for each subject showed a maximum somatosensory evoked response commonly to electric, passive joint motion and pain stimuli. These electrodes showed the maximum responses also to tone stimuli in all of 4 subjects studied, and to visual motion stimuli in 3 out of 5 subjects studied. The polarity was consistent regardless of the stimulus modality within each individual subject, although the anatomical location, polarity and latency varied among subjects. CONCLUSIONS: A small area in TPJ for each individual subject receives sensory information of multiple modalities possibly coming from different receptive sites, although the electrophysiological properties of the responses may vary among subjects. SIGNIFICANCE: We confirmed the convergence of somatosensory, auditory and visual evoked responses at human TPJ.

Adolescent↗

PubMed2004

Propagation of tonic posturing in supplementary motor area (SMA) seizures.

We analyzed ictal motor symptoms in 10 patients diagnosed to have supplementary motor area (SMA) seizures based on ictal encephalographic (EEG) findings and ictal clinical semiology. Inclusion criteria were (1) EEG seizure pattern in the vertex for the scalp recording or in the area over and/or adjacent to SMA for epicortical recording and (2) ictal motor semiology characterized, as previously reported, by sudden and a brief tonic posturing of extremities and trunk mainly occurring during sleep without loss of consciousness. In 50% (5/10) of the patients, tonic posturing began in one part of the body and moved to other part(s) in 5-10s. Unlike Jacksonian march seen in seizures involving the primary sensorimotor area (S1-M1), it spread in no accordance with the somatotopy in S1-M1. The sequential propagation of tonic posturing may represent the somatotopic organization within the SMA proper.

Adolescent↗

PubMed2003

Role of primary sensorimotor cortex and supplementary motor area in volitional swallowing: a movement-related cortical potential study.

We investigated the role of the cerebral cortex, particularly the face/tongue area of the primary sensorimotor (SMI) cortex (face/tongue) and supplementary motor area (SMA), in volitional swallowing by recording movement-related cortical potentials (MRCPs). MRCPs with swallowing and tongue protrusion were recorded from scalp electrodes in eight normal right-handed subjects and from implanted subdural electrodes in six epilepsy patients. The experiment by scalp EEG in normal subjects revealed that premovement Bereitschaftspotentials (BP) activity for swallowing was largest at the vertex and lateralized to either hemisphere in the central area. The experiment by epicortical EEG in patients confirmed that face/tongue SMI and SMA were commonly involved in swallowing and tongue protrusion with overlapping distribution and interindividual variability. BP amplitude showed no difference between swallowing and tongue movements, either at face/tongue SMI or at SMA, whereas postmovement potential (PMP) was significantly larger in tongue protrusion than in swallowing only at face/tongue SMI. BP occurred earlier in swallowing than in tongue protrusion. Comparison between face/tongue SMI and SMA did not show any difference with regard to BP and PMP amplitude or BP onset time in either task. The preparatory role of the cerebral cortex in swallowing was similar to that in tongue movement, except for earlier activation in swallowing. Postmovement processing of swallowing was lesser than that of tongue movement in face/tongue SMI; probably suggesting that the cerebral cortex does not play a significant role in postmovement processing of swallowing. SMA plays a supplementary role to face/tongue SMI both in swallowing and tongue movements.

Adult↗

PubMed2003

Human V5 demonstrated by magnetoencephalography using random dot kinematograms of different coherence levels.

To investigate the cortical mechanisms for motion perception in human V5, we measured visual evoked magnetic fields in response to random dot kinematograms (RDKs) of three different coherence levels (50, 70 and 100%) using a 122-channel whole-head magnetometer. As the coherence level increased, the peak amplitude measured by the root mean square (RMS) of the local response increased significantly (7.4+/-1.0, 9.5+/-1.5 and 15.5+/-3.2 fT/cm on the right, 6.4+/-0.3, 7.8+/-0.7 and 12.5+/-0.9 fT/cm on the left; for the coherence level of 50, 70 and 100%, respectively). There was no significant difference between the hemispheres. As for the peak latency, there was no significant difference in terms of coherence levels or hemispheres. The response was localized posterior to the junction of the ascending limb of the inferior temporal and lateral occipital sulci (human V5). These findings indicate that processing of global motion in terms of the synchronized portion correlates well with the response amplitude but not with its latency. Thus, we could estimate the magnetic responses of human V5 non-invasively by presenting different coherence levels of the visual motion stimuli. Hemispheric laterality was recognized, although the dominant side varied among subjects.

Adult↗

PubMed2003

Transcranial magnetic stimulation (TMS) of the sensorimotor cortex and medial frontal cortex modifies human pain perception.

OBJECTIVE: Although recent neuroimaging studies have shown that painful stimuli can produce activity in multiple cortical areas, the question remains as to the role of each area in particular aspects of human pain perception. To solve this problem we used transcranial magnetic stimulation (TMS) as an 'interference approach' tool to test the consequence on pain perception of disrupting activity in several areas of cortex known to be activated by painful input. METHODS: Weak CO(2) laser stimuli at an intensity around the threshold for pain were given to the dorsum of the left hand in 9 normal subjects. At variable delays (50, 150, 250, 350 ms) after the onset of the laser stimulus, pairs of TMS pulses (dTMS: interpulse interval of 50 ms, and stimulus intensity of 120% resting motor threshold) were applied in separate blocks of trials over either the right sensorimotor cortex (SMI), midline occipital cortex (OCC), second somatosensory cortex (SII), or medial frontal cortex (MFC). Subjects were instructed to judge whether or not the stimulus was painful and to point to the stimulated spot on a drawing of subject's hand. RESULTS: Subjects judged that the stimulus was painful on more trials than control when dTMS was delivered over SMI at 150-200 ms after the laser stimulus; the opposite occurred when dTMS was delivered over MFC at 50-100 ms. dTMS over the SII or OCC failed to alter the pain threshold. CONCLUSIONS: These results suggest that TMS to SMI can facilitate whereas stimulation over MFC suppresses central processing of pain perception. Since there was no effect of dTMS at any of the scalp sites on the localization task, the cortical locus for point localization of pain may be different from that for perception of pain intensity or may involve a more complex mechanism than the latter. SIGNIFICANCE: This is the first report that TMS of SMI facilitates while that of MFC suppresses the central processing of pain perception. This raises the possibility of using TMS as a therapeutic device to control pain.

Adult↗