Biomedical subjects

Tuan Diep Tran

Publications and source records attributed to Tuan Diep Tran.

13 recordsLinked to original sources

PubMed2004

Effects of distraction on magnetoencephalographic responses ascending through C-fibers in humans.

OBJECTIVE: Using magnetoencephalography (MEG), we evaluated the cerebral regions relating to second pain perception ascending through C-fibers and investigated the effect of distraction on each region. METHODS: Thirteen normal subjects participated in this study. CO2 laser pulses were delivered to the dorsum of the left hand to selectively activate C-fibers. The MEG responses were analyzed using a multi-dipole model. RESULTS: (1) primary somatosensory cortex (SI), and (2) secondary somatosensory cortex (SII)--insula were the main generators for the primary component, 1M, whose mean peak latency was 744 ms. In addition to (1) and (2), (3) cingulate cortex and (4) medial temporal area (MT) were also activated for the subsequent component, 2M, whose mean peak latency was 947 ms. During a mental calculation task (Distraction), all 6 sources were significantly reduced in amplitude, but the SII-insula (P < 0.01) and cingulate cortex (P < 0.001) were more sensitive than the SI (P < 0.05) and MT (P < 0.05). CONCLUSIONS: We confirmed that SI in the contralateral hemisphere and SII-insula, cingulate cortex and MT in bilateral hemispheres play a major role in second pain perception, and all sites were much affected by a change of attention, indicating that these regions are related to the cognitive aspect of second pain perception. SIGNIFICANCE: The SI, SII, cingulate and MT were activated during the C-fiber-related MEG response, and responses in these regions were significantly diminished during mental distraction.

Adult↗

PubMed2004

Movements modulate cortical activities evoked by noxious stimulation.

To evaluate the effects of movement on cortical activities evoked by noxious stimulation, we recorded magnetoencephalography following noxious YAG laser stimulation applied to the dorsum of the left hand in normal volunteers. Results of the present study can be summarized as follows: (1) active movement of the hand ipsilateral to the side of noxious stimulation resulted in significant attenuation of both primary and secondary somatosensory cortices (SI and SII) in the hemisphere contralateral to the stimulated hand (cSI and cSII). Activity in the hemisphere ipsilateral to the side of stimulation (iSII) was not affected. (2) Active movement of the hand contralateral to the side of noxious stimulation resulted in significant attenuation of cSII. Activity in cSI and iSII was not affected. (3) Passive movement of the hand ipsilateral to the side of noxious stimulation resulted in significant attenuation of cSI. Activity in cSII and iSII was not affected. (4) Visual analogue scale (VAS) changes showed a similar pattern to the amplitude changes of cSII. These results suggest that activities in three regions are modulated by movements differently. Inhibition in cSI was considered to be mainly due to an interaction in SI by the signals ascending from the stimulated and movement hand. Inhibition in cSII was considered to be mainly due to particular brain activities relating to motor execution and/or movement execution associated with a specific attention effect. In addition, since VAS changes showed a similar relationship with the amplitude changes of cSII, cSII may play a role in pain perception.

Adult↗

PubMed2004

Patients with benign rolandic epilepsy have a longer duration of somatosensory evoked high-frequency oscillations.

BACKGROUND: High-frequency oscillations (HFO) ranging between 300-900 Hz have been shown to be superimposed on an early component of somatosensory evoked potentials (SEP) to median nerve stimulation in humans. Although the HFO are speculated to be a localized activity of the GABAergic inhibitory interneurons, the significance in the epileptogenicity remains unclear. The authors of this study analyzed HFO using magnetoencephalography in patients with benign rolandic epilepsy (BRE) to clarify the neurophysio-logical basis of rolandic discharges (RD). METHODS: Nine patients with BRE and six patients with other epileptic syndrome (non-BRE) participated in the study. Somatosensory evoked fields (SEF) including HFO to median nerve stimulation were measured in a magnetically shielded room with a 37-channel neuromagnetometer. RESULTS: Two kinds of HFO, 300 Hz- and 600 Hz-HFO, were identified and the duration of the HFO in patients with BRE was significantly longer than that in patients with non-BRE. CONCLUSIONS: The results suggest that the longer part of HFO (P30m-related) is closely related to the pathogenesis of RD and that the longer HFO in patients with BRE might be mediated by altered GABAergic inhibition modulated by the cholinergic system.

Adolescent↗

PubMed2003

Microneurographic study of C fiber discharges induced by CO2 laser stimulation in humans.

We investigated C-fiber discharges and cerebral potentials evoked by weak CO(2) laser beams applied to a tiny skin area in five healthy subjects. Microneurography was performed from the peroneal nerve in the right popliteal area. Cerebral potentials were recorded from the Cz electrode referred to linked earlobes. The mean conduction velocity of five stable single units was 1.1+/-0.3 m/s. The mean latency of the positive peak of cerebral potentials was 1327.4+/-46.2 ms. These findings indicated that this new stimulation method selectively activated C-fiber nociceptors of the skin.

Adult↗

PubMed2003

Effects of sleep on pain-related somatosensory evoked potentials in humans.

We investigated effects of sleep on pain-related somatosensory evoked potentials (SEP) following painful electrical stimulation of the left index finger. The biggest advantage of this method is that signals ascending through both A-beta fibers relating to touch and A-delta fibers relating to pain can be recorded simultaneously. While the subject was awake, non-painful stimulation evoked early- and middle latency components, N20, P30 and N60, at the C4 electrode, and painful stimulation evoked not only early- and middle latency components at the C4 but also later pain-specific components, N130 and P240, at the Cz electrode. During sleep, N20 and P30 did not show a significant change in amplitude, N60 showed a slight but significant amplitude reduction, and N130 and P240 significantly decreased in amplitude or disappeared, as compared with those while awake. Therefore, we speculate on the mechanisms generating each component as follows; (1) N20 and P30 are the primary components generated in SI ascending through A-beta fibers. (2) N60 is the secondary component generated in SI involving cognitive function to some degree. (3) N130-P240 are the pain-specific components ascending through A-delta fibers, and closely related to cognitive function, because they were much affected by consciousness, different from the components ascending through A-beta fibers.

Adult↗

PubMed2003

Cerebral responses following stimulation of unmyelinated C-fibers in humans: electro- and magneto-encephalographic study.

There are two kinds of pain, a sharp pain ascending through Adelta fibers (first pain) and a second burning pain ascending though C fibers (second pain). By using a novel method, the application of a low intensity CO(2) laser beam to a tiny area of skin using a very thin aluminum plate with numerous tiny holes as a spatial filter, we succeeded in selectively stimulating unmyelinated C fibers of the skin in humans, and could record consistent and clear brain responses using electroencephalography (EEG) and magnetoencephalography (MEG). The conduction velocity (CV) of the C fibers of the peripheral nerve and spinal cord, probably spinothalamic tract (STT), is approximately 1-4 m/s, which is significantly slower than that of Adelta (approximately 10-15 m/s) and Abeta fibers (approximately 50-70 m/s). This method should be very useful for clinical application. Following C fiber stimulation, primary and secondary somatosensory cortices (SI and SII) are simultaneously activated in the cerebral hemisphere contralateral to the stimulation, and then, SII in the hemisphere ipsilateral to the stimulation is activated. These early responses are easily detected by MEG. Then, probably limbic systems such as insula and cingulate cortex are activated, and those activities reflected in EEG components. Investigations of the cortical processing in pain perception including both first and second pain should provide a better understanding of pain perception and, therefore, contribute to pain relief in clinical medicine.

Animals↗

PubMed2003

Effects of sleep on pain-related somatosensory evoked magnetic fields in humans.

We investigated the effects of sleep on pain-related somatosensory evoked magnetic fields (SEFs) following painful electrical stimulation to identify the mechanisms generating them in both fast A-beta fibers relating to touch and slow A-delta fibers relating to pain. While the subjects were awake, non-painful and painful electrical stimulations were applied, and while asleep, painful stimulation was applied to the left index finger. During awake, five components (1M-5M) were identified following both non-painful and painful stimulation, but the 4M and 5M at around 70-100 ms and 140-180 ms, respectively, were significantly enhanced following painful stimulation. During sleep, 1M and 2M generated in the primary somatosensory cortex (SI) did not show a significant change, 3M in SI showed a slight but significant amplitude reduction, and 4M and 5M generated in both SI and the secondary somatosensory cortex (SII) were significantly decreased in amplitude or disappeared. The 4M and 5M are complicated components generated in SI and SII ascending through both A-beta fibers and A-delta fibers. They are specifically enhanced by painful stimulation due to an increase of signals ascending through A-delta fibers, and are markedly decreased during sleep, because they much involve cognitive function.

Adult↗

PubMed2003

Sensory perception during sleep in humans: a magnetoencephalograhic study.

We reported the changes of brain responses during sleep following auditory, visual, somatosensory and painful somatosensory stimulation by using magnetoencephalography (MEG). Surprisingly, very large changes were found under all conditions, although the changes in each were not the same. However, there are some common findings. Short-latency components, reflecting the primary cortical activities generated in the primary sensory cortex for each stimulus kind, show no significant change, or are slightly prolonged in latency and decreased in amplitude. These findings indicate that the neuronal activities in the primary sensory cortex are not affected or are only slightly inhibited during sleep. By contrast, middle- and long-latency components, probably reflecting secondary activities, are much affected during sleep. Since the dipole location is changed (auditory stimulation), unchanged (somatosensory stimulation) or vague (visual stimulation) between the state of being awake and asleep, different regions responsible for such changes of activity may be one explanation, although the activated regions are very close to each other. The enhancement of activities probably indicates two possibilities, an increase in the activity of excitatory systems during sleep, or a decrease in the activity of some inhibitory systems, which are active in the awake state. We have no evidence to support either, but we prefer the latter, since it is difficult to consider why neuronal activities would be increased during sleep.

Adult↗

PubMed2003

Pain processing within the primary somatosensory cortex in humans.

To investigate the processing of noxious stimuli within the primary somatosensory cortex (SI), we recorded magnetoencephalography following noxious epidermal electrical stimulation (ES) and innocuous transcutaneous electrical stimulation (TS) applied to the dorsum of the left hand. TS activated two sources sequentially within SI: one in the posterior bank of the central sulcus and another in the crown of the postcentral gyrus, corresponding to Brodmann's areas 3b and 1, respectively. Activities from area 3b consisted of 20- and 30-ms responses. Activities from area 1 consisted of three components peaking at 26, 36 and 49 ms. ES activated one source within SI whose location and orientation were similar to those of the TS-activated area 1 source. Activities from this source consisted of three components peaking at 88, 98 and 109 ms, later by 60 ms than the corresponding TS responses. ES and TS subsequently activated a similar region in the upper bank of the sylvian fissure, corresponding to the secondary somatosensory cortex (SII). The onset latency of the SII activity following ES (109 ms) was later by 29 ms than that of the first SI response (80 ms). Likewise, the onset latency of SII activity following TS (52 ms) was later by 35 ms than that of area 1 of SI (17 ms). Therefore, our results showed that the processing of noxious and innocuous stimuli is similar with respect to the source locations and activation timings within SI and SII except that there were no detectable activations within area 3b following noxious stimulation.

Adult↗

PubMed2002

Conduction velocity of the spinothalamic tract following CO2 laser stimulation of C-fibers in humans.

Pain-related somatosensory-evoked potential following CO(2) laser stimulation (laser-evoked potential (LEP)) is now used not only for research objectives, but also for clinical applications. Estimating the conduction velocity (CV) of the spinothalamic tract (STT) by analyzing LEP following activation of Adelta-fibers (Adelta-CVSTT) by CO(2) laser stimulation has been performed previously, but estimating the CV of STT following activation of C-fibers (C-CVSTT) has not. This is the first report to estimate the C-CVSTT in humans; by using the novel method of CO(2) laser stimulation applied to tiny skin areas. The calculation method was based on that of Kakigi and Shibasaki (Electroenceph clin Neurophysiol 80 (1991) 39) who measured Adelta-CVSTT by conventional CO(2) laser stimulation. The C-CVSTT ranged between 1.4 and 4.0 m/s, and its mean+/-SD was 2.9+/-0.8 m/s. This C-CVSTT was significantly slower than the Adelta-CVSTT, which ranged approximately from 10 to 21 m/s. The nociceptive signal of the C-fibers in STT is probably conveyed by unmyelinated axons of projection neurons to reach the thalamus. Our findings provide the first physiological evidence of the signals ascending through unmyelinated axons in the spinal cord in humans. In addition, estimating C-CVSTT and Adelta-CVSTT combined with conventional methods to measure the CV of the posterior column using electrical stimulation should be useful and have important clinical applications, particularly in patients with spinal cord lesions showing various kinds of sensory disturbances.

Adult↗

PubMed2002

Preferential stimulation of Adelta fibers by intra-epidermal needle electrode in humans.

We recorded evoked potentials (EPs) induced by conventional transcutaneous electrical stimulation (TS), laser stimulation (LS) and epidermal electrical stimulation (ES) using a specially made needle electrode. We evaluated the activated fibers by epidermal stimulation by assessing the conduction velocity (CV) of the peripheral nerves. The EPs were recorded from Cz electrode (vertex) of the International 10-20 system in 12 healthy subjects. For the ES, the tip of a stainless steel needle electrode was inserted in the epidermis of the skin (0.2 mm in depth). Distal and proximal sites of the upper limb were stimulated by the LS and ES with an intensity which induced a definite pain sensation. Similar sites were stimulated by TS with an intensity of two times the sensory threshold. A major EP positive response (P1) was obtained by stimulation by all three types of stimuli. The P1 latency for the TS (245+/-22 ms) was significantly shorter than that for the ES (302+/-17 ms, P<0.0001) and LS (341+/-21 ms, P<0.0001) and the peak latency P1 by the LS was also significantly longer, approximately 40 ms, than that by the ES (P<0.0001). The CVs were 15.1, 15.3 and 44.1 m/s obtained by ES, LS and TS, respectively. The CV indicated that the fibers activated by the ES were mainly A fibers, which corresponded to the fibers stimulated by the LS. We considered that the ES with our newly developed needle electrode was a very convenient method for the selective stimulation of the A fibers, since it was very simple, not requiring any special apparatus, did not cause bleeding or burns and caused minimum uncomfortable feeling.

Adult↗

PubMed2002

Pain-related magnetic fields evoked by intra-epidermal electrical stimulation in humans.

OBJECTIVES: We recently developed a new method for the preferential stimulation of Adelta fibers in humans. The aim of the present study was to examine whether this method can serve as an appropriate stimulus in a magnetoencephalographic study. METHODS: We recorded somatosensory-evoked magnetic fields (SEFs) following intra-epidermal electrical stimulation applied to the hand and elbow. Superficial parts of the skin were electrically stimulated through a needle electrode whose tip was inserted in the epidermis. RESULTS: In all 13 subjects, the equivalent current dipole was estimated in the secondary somatosensory cortices (SII). In 5 out of 13 subjects, simultaneous activation of the primary somatosensory cortex (SI) in the hemisphere contralateral to the stimulation was identified. The mean peak latencies of magnetic fields corresponding to contralateral SI, SII and ipsilateral SII activation following hand stimulation were 162, 158 and 171 ms, respectively. The respective latency following elbow stimulation was 137, 139 and 157 ms, respectively. Estimated peripheral conduction velocity was 15.6m/s. CONCLUSIONS: All the results were consistent with previous findings in pain SEF studies. We concluded that our novel intra-epidermal electrical stimulation is useful for pain SEF studies since it does not need special equipment and is easy to control.

Adult↗

PubMed2002

Effects of attention, distraction and sleep on CO(2) laser evoked potentials related to C-fibers in humans.

OBJECTIVES: The objective of this study is to evaluate the effects of attention, distraction and sleep on CO(2) laser-evoked potentials (LEP) relating to C-fibers (ultra-late LEP). METHODS: Non-painful CO(2) laser pulses were delivered to a tiny skin area of the dorsum of the right hand. Ultra-late LEP were recorded from 10 normal subjects in 5 different conditions: control (wakefulness), attention, distraction, drowsiness and sleep (stage 2). RESULTS: The amplitude of ultra-late LEP was slightly increased during attention and significantly decreased during distraction, relative to the control. The ultra-late LEP decreased much in amplitude or almost disappeared during sleep. However, significant differences in latency among the conditions were not found. CONCLUSIONS: We confirmed that the brain responses relating to signals ascending through C-fibers were much affected by the level of consciousness, being consistent with the findings of late LEP relating to Adelta-fibers. This is the first study to indicate the important characteristics of ultra-late LEP relating to consciousness, suggesting that they include cognitive function and also that one has to be careful of the change in alertness when recording.

Adult↗