Association between somatosensory sensitivity and regional gray matter volume in healthy young volunteers: a voxel-based morphometry study.

Two-point discrimination (2PD) test reflects somatosensory spatial discrimination ability, but evidence on the relationship between 2PD and cortical gray matter (GM) volume is limited. This study aimed to analyze the relationship between cortical GM volume and 2PD threshold in young healthy individuals and to clarify the characteristics of brain structure reflecting the individual differences in somatosensory function. 2PD was measured in 42 healthy (20 females) volunteers aged 20-32 years using a custom-made test system that can be controlled by a personal computer. The 2PD of the right index finger measured with this device has been confirmed to show good reproducibility. T1-weighted images were acquired using a 3-T magnetic resonance imaging scanner for voxel-based morphometry analysis. The mean 2PD threshold was 2.58 ± 0.54 mm. Whole-brain multiple regression analysis of the relationship between 2PD and GM volume showed that a lower 2PD threshold (i.e. better somatosensory function) significantly correlated with decreased GM volume from the middle temporal gyrus to the inferior parietal lobule (IPL) in the contralateral hemisphere. In conclusion, a lower GM volume in the middle temporal gyrus and IPL correlates with better somatosensory function. Thus, cortical GM volume may be a biomarker of somatosensory function.

Hippocampal-prefrontal long-term potentiation-like plasticity with transcranial direct current stimulation in rats.

Transcranial direct current stimulation (tDCS) has been explored as a new treatment method for improving cognitive and motor functions. However, the neuronal mechanisms of tDCS in modulating brain functions, especially cognitive and memory functions, are not well understood. In the present study, we assessed whether tDCS could promote neuronal plasticity between the hippocampus and prefrontal cortex in rats. This is important because the hippocampus-prefrontal pathway is a key pathway in cognitive and memory functions and is involved in various psychiatric and neurodegenerative disorders. Specifically, the effect of anodal or cathodal tDCS on the medial prefrontal cortex was investigated in rats by measuring the medial prefrontal cortex response to electrical stimulation applied to the CA1 region of the hippocampus. Following anodal tDCS, the evoked prefrontal response was potentiated compared to that in the pre-tDCS condition. However, the evoked prefrontal response did not show any significant changes following cathodal tDCS. Furthermore, the plastic change of the prefrontal response following anodal tDCS was only induced when hippocampal stimulation was continuously applied during tDCS. Anodal tDCS without hippocampal activation showed little or no changes. These results indicate that combining anodal tDCS of the prefrontal cortex with hippocampal activation induces long-term potentiation (LTP)-like plasticity in the hippocampus-prefrontal pathway. This LTP-like plasticity can facilitate smooth information transmission between the hippocampus and the prefrontal cortex and may lead to improvements in cognitive and memory function.

Gray Matter Volume Variability in Young Healthy Adults: Influence of Gender Difference and Brain-Derived Neurotrophic Factor Genotype.

Although brain gray matter (GM) plastically changes during short-term training, it is still unclear whether brain structures are stable for short periods (several months). Therefore, this study aimed to re-test the short-term variability of GM volumes and to clarify the effect of factors (gender and BDNF-genotype) expected to contribute to such variability. The subjects comprised 41 young healthy adults. T1-weighted images were acquired twice with an interval of approximately 4 months using a 3 T-MRI scanner. Voxel-based morphometry (VBM) was used to calculate GM volumes in 47 regions. The intraclass correlation coefficient (ICC) and Test-retest variability (%TRV) were used as indices of variability. As a result, the ICCs in 43 regions were excellent (ICC > 0.90) and those in 3 regions were good (ICC > 0.80), whereas the ICC in the thalamus was moderate (ICC = 0.694). Women had a higher %TRV than men in 5 regions, and %TRV of the Val66Val group was higher than that of the Met carrier group in 2 regions. Moreover, the Female-Val66Val group had a higher %TRV than the Male-Met carrier group in 3 regions. These results indicate that although the short-term variability of GM volumes is small, it is affected by within-subject factors.

Structural Plastic Changes of Cortical Gray Matter Revealed by Voxel-Based Morphometry and Histological Analyses in a Monkey Model of Central Post-Stroke Pain.

Central post-stroke pain (CPSP) is a chronic pain caused by stroke lesions of somatosensory pathways. Several brain imaging studies among patients with CPSP demonstrate that the pathophysiological mechanism underlying this condition is the maladaptive plasticity of pain-related brain regions. However, the temporal profile of the regional plastic changes, as suggested by brain imaging of CPSP patients, as well as their cellular basis, is unknown. To investigate these issues, we performed voxel-based morphometry (VBM) using T1-weighted magnetic resonance imaging and immunohistochemical analysis with our established CPSP monkey model. From 8 weeks after a hemorrhagic lesion to the unilateral ventral posterolateral nucleus of the thalamus, the monkeys exhibited significant behavioral changes that were interpreted as reflecting allodynia. The present VBM results revealed a decrease in gray matter volume in the pain-related areas after several weeks following the lesion. Furthermore, immunohistochemical staining in the ipsilesional posterior insular cortex (ipsi-PIC) and secondary somatosensory cortex (ipsi-SII), where the significant reduction in gray matter volume was observed in the VBM result, displayed a significant reduction in both excitatory and inhibitory synaptic terminals compared to intact monkeys. Our results suggest that progressive changes in neuronal morphology, including synaptic loss in the ipsi-PIC/SII, are involved in theCPSP.

The intervention of mechanical tactile stimulation modulates somatosensory evoked magnetic fields and cortical oscillations.

The different cortical activity evoked by a mechanical tactile stimulus depends on tactile stimulus patterns, which demonstrates that simple stimuli (i.e., global synchronous stimulation the stimulus area) activate the primary somatosensory cortex alone, whereas complex stimuli (i.e., stimulation while moving in the stimulus area) activate not only the primary somatosensory cortex but also the primary motor area. Here, we investigated whether the effects of a repetitive mechanical tactile stimulation (MS) on somatosensory evoked magnetic fields (SEFs) and cortical oscillations depend on MS patterns. This single-blinded study included 15 healthy participants. Two types interventions of MS lasting 20 min were used: a repetitive global tactile stimulation (RGS) was used to stimulate the finger by using 24 pins installed on a finger pad, whereas a sequential stepwise displacement tactile stimulation (SSDS) was used to stimulate the finger by moving a row of six pins between the left and right sides on the finger pad. Each parameter was measured pre- and post-intervention. The P50m amplitude of the SEF was increased by RGS and decreased by SSDS. The modulation of P50m was correlated with its amplitude before RGS and with the modulation of beta band oscillation at the resting state after SSDS. This study showed that the effects of a 20-min MS on SEFs and cortical oscillations depend on mechanical tactile stimulus patterns. Moreover, our results offer potential for the modulation of tactile functions and selection of stimulation patterns according to cortical states.

Brain function effects of autonomous sensory meridian response (ASMR) video viewing.

Background: Autonomous sensory meridian response (ASMR) is the sensation of tingling from audiovisual stimuli that leads to positive emotions. ASMR is used among young people to relax, induce sleep, reduce stress, and alleviate anxiety. However, even without experiencing tingling, ASMR is used by many young people to seek relaxation. Auditory stimulation in ASMR is thought to play the most important role among its triggers, and previous studies have used a mixture of auditory and visual stimulation and auditory stimulation. This is the first study to approach the differences between the effects of direct audiovisual and auditory stimulation from the perspective of brain function using functional magnetic resonance imaging (fMRI) and to clarify the effects of ASMR, which attracts many young people. Methods: The subjects were 30 healthy subjects over 19 years old or older who had not experienced tingling. Brain function was imaged by fMRI while watching ASMR videos or listening to the sound files only. We administered a questionnaire based on a Likert scale to determine if the participants felt a "relaxed mood" and "tingling mood" during the task. Results: Significant activation was found in the visual cortex for audiovisual stimulation and in the visual and auditory cortex for auditory stimulation. In addition, activation of characteristic sites was observed. The specific sites of activation for audiovisual stimulation were the middle frontal gyrus and the left nucleus accumbens, while the specific sites of activation for auditory stimulation were the bilateral insular cortices. The questionnaire showed no significant differences in either "relaxed mood" or "tingling mood" in response to auditory and visual stimulation or auditory stimulation alone. Conclusion: The results of this study showed that there was a clear difference between auditory and audiovisual stimulation in terms of the areas of activation in the brain, but the questionnaire did not reveal any difference in the subjects' mood. Audiovisual stimulation showed activation of the middle frontal gyrus and the nucleus accumbens, whereas auditory stimulation showed activation of the insular cortex. This difference in brain activation sites suggests a difference in mental health effects between auditory and audiovisual stimulation. However, future research on comparisons between those who experience tingling and those who do not, as well as investigations of physiological indices, and examination of the relationship with activated areas in the brain may show that ASMR is useful for mental health.

The relaxation effect of autonomous sensory meridian response depends on personal preference.

Background: Autonomous sensory meridian response (ASMR) is a sensory response such as tingling and pleasantness from audiovisual stimuli. ASMR videos come in a wide variety of types, and personal preferences are biased. There are many reports of the effects os ASMR on sleep onset, anxiety relief, and other relaxation effects. However, prior task-oriented studies have used ASMR videos provided by the experimenter. We hypothesized that ASMR movies of a personal preference would show significantly increased activity in the nucleus accumbens, frontal cortex, and insular cortex, which are brain areas associated with relaxation. Therefore, the purpose of this study was to elucidate the neuroscientific basis for the relaxation effects of ASMR videos that match someone's personal preferences. Methods: This study included 30 healthy individuals aged ≥18 years. ASMR enthusiasts were included as the target population due to the need to have a clear preference for ASMR videos. A control video (1 type) and ASMR videos (20 types) were used as the stimulus tasks. Among the ASMR videos, those with high and low evaluation scores were considered liked and dislikedASMR videos, respectively. Functional magnetic resonance imaging was performed while the participants viewed a block design with a resting task in between. The data were analyzed using Statistical Parametric Mapping 12 to identify the areas activated by control, disliked, and liked ASMR videos. Results: Emotion-related areas (the amygdala, frontal cortex, and insular cortex) not activated by control and unliked ASMR videos were activated only by liked ASMR videos. Conclusion: The amygdala, frontal cortex, and insular cortex may be involved in the limbic dopamine circuits of the amygdala and middle frontal gyrus and the autonomic balance of the left and right insular cortices. This suggests the potential of positive mood and its use as a treatment for patients with anxiety and depression. These results suggest that the use of ASMR videos to match individual preferences may induce relaxation and have beneficial effects on depression and other disorders, and also support the introduction of ASMR videos in mental health care.

Pharmacological inactivation of the primate posterior insular/secondary somatosensory cortices attenuates thermal hyperalgesia.

BACKGROUND: We previously established a macaque model of central post-stroke pain (CPSP) and confirmed the involvement of increased activity of the posterior insular cortex (PIC) and secondary somatosensory cortex (SII) to somatosensory stimuli in mechanical allodynia by a combination of imaging techniques with local pharmacological inactivation. However, it is unclear whether the same intervention would be effective for thermal hyperalgesia. Therefore, using the macaque model, we examined behavioural responses to thermal stimuli following pharmacological inactivation of the PIC/SII. METHODS: Two CPSP model macaques were established based on collagenase-induced unilateral hemorrhagic lesions in the ventral posterolateral nucleus of the thalamus. To evaluate pain perception, withdrawal latencies to thermal stimuli of 37, 45, 50, 52, and 55 °C to hands were measured. Several weeks after the lesion induction, pharmacological inactivation of the PIC/SII by microinjection of muscimol was performed. The effect of inactivation on withdrawal latency was assessed by comparison with withdrawal latency after vehicle injection. RESULTS: Several weeks after induction of the thalamic lesions, both macaques demonstrated a reduction in withdrawal latencies to thermal stimulation (<50 °C) on the contralesional hand, indicating the occurrence of thermal hyperalgesia. When the PIC/SII were inactivated by muscimol, the withdrawal latencies to thermal stimuli of 50 and 52 °C were significantly increased compared to those after vehicle injection. CONCLUSIONS: Our data emphasize that increased activity in the PIC/SII after appearance of thalamic lesions can contribute to abnormal pain of multiple modalities, and the modulation of PIC/SII activity may be a therapeutic approach for thermal hyperalgesia. SIGNIFICANCE: CPSP is caused by stroke lesions in the sensory system and characterized by mechanical allodynia or thermal hyperalgesia. Inactivation of the PIC/SII has an analgesic effect on mechanical allodynia; however, it is not clear whether the same intervention could reduce thermal hyperalgesia. Here, using the macaque model, we demonstrated that inactivation of these cortices reduces hypersensitivity to thermal stimuli. This result emphasizes that increased PIC/SII activity can contribute to abnormal pain of multiple modalities.

Relationship between Tactile Sensation, Motor Activity, and Differential Brain Activity in Young Individuals.

In this study, we compared the differences in brain activation associated with the different types of objects using functional magnetic resonance imaging (fMRI). Twenty-six participants in their 20s underwent fMRI while grasping four different types of objects. After the experiment, all of the participants completed a questionnaire based on the Likert Scale, which asked them about the sensations they experienced while grasping each object (comfort, hardness, pain, ease in grasping). We investigated the relationship between brain activity and the results of the survey; characteristic brain activity for each object was correlated with the results of the questionnaire, indicating that each object produced a different sensation response in the participants. Additionally, we observed brain activity in the primary somatosensory cortex (postcentral gyrus), the primary motor cortex (precentral gyrus), and the cerebellum exterior during the gripping task. Our study shows that gripping different objects produces activity in specific and distinct brain regions and suggests an "action appraisal" mechanism, which is considered to be the act of integrating multiple different sensory information and connecting it to actual action. To the best of our knowledge, this is the first study to observe brain activity in response to tactile stimuli and motor activity simultaneously.

Structural plasticity of motor cortices assessed by voxel-based morphometry and immunohistochemical analysis following internal capsular infarcts in macaque monkeys.

Compensatory plastic changes in the remaining intact brain regions are supposedly involved in functional recovery following stroke. Previously, a compensatory increase in cortical activation occurred in the ventral premotor cortex (PMv), which contributed to the recovery of dexterous hand movement in a macaque model of unilateral internal capsular infarcts. Herein, we investigated the structural plastic changes underlying functional changes together with voxel-based morphometry (VBM) analysis of magnetic resonance imaging data and immunohistochemical analysis using SMI-32 antibody in a macaque model. Unilateral internal capsular infarcts were pharmacologically induced in 5 macaques, and another 5 macaques were used as intact controls for immunohistochemical analysis. Three months post infarcts, we observed significant increases in the gray matter volume (GMV) and the dendritic arborization of layer V pyramidal neurons in the contralesional rostral PMv (F5) as well as the primary motor cortex (M1). The histological analysis revealed shrinkage of neuronal soma and dendrites in the ipsilesional M1 and several premotor cortices, despite not always detecting GMV reduction by VBM analysis. In conclusion, compensatory structural changes occur in the contralesional F5 and M1 during motor recovery following internal capsular infarcts, and the dendritic growth of pyramidal neurons is partially correlated with GMV increase.

Effect of Transcranial Electrical Stimulation over the Posterior Parietal Cortex on Tactile Spatial Discrimination Performance.

The intraparietal sulcus region, which is part of the posterior parietal cortex (PPC), has been shown to play an important role in discriminating object shapes using the fingers. Transcranial random noise stimulation (tRNS) and anodal transcranial pulsed current stimulation (tPCS) are noninvasive strategies widely used to modulate neural activity in cortical regions. Therefore, we investigated the effects of tRNS and anodal tPCS applied to left or right PPC on the tactile discrimination performance of the right index finger in 20 neurologically healthy subjects. A grating orientation task (GOT) was performed before and immediately after delivering tRNS (stimulus frequency 0.1-640 Hz) in Experiment 1 or anodal tPCS (pulse width 50 ms and inter-pulse interval 5 ms) in Experiment 2. Performing tRNS over the right PPC significantly improved discrimination performance on the GOT. Subjects were classified into low and high baseline performance groups. Conducting tRNS over the left PPC significantly reduced the GOT discrimination performance in the high-performance group. By contrast, anodal tPCS delivered to the PPC of the left and right hemispheres had no significant effect on the tactile GOT discrimination performance of the right hand. We show that transcranial electric stimulation over the PPC may improve tactile perception but the effect depends on stimulus modality, parameters, and on the stimulated hemisphere.

Cortical signature related to psychometric properties of pain vigilance in healthy individuals: A voxel-based morphometric study.

The Pain Vigilance and Awareness Questionnaire (PVAQ) is a questionnaire for non-clinical and clinical cases of patients, such as those suffering from chronic pain. Moreover, it is used for evaluation of two aspects of habitual attention to pain: attention to pain and attention to changes in pain. As the PVAQ assesses two different aspects of attention function, different neural basis may present. However, it remains unclear which brain regions are involved. Here, we performed voxel-based morphometry (VBM) in 30 healthy participants to determine the regional morphology associated with the two attention states. Multiple regression analysis was conducted between each score and the regional grey matter (GM) volume, which revealed that a decreased GM volume in the left anterior insular cortex (AIC) was associated with a higher attention to pain score. In contrast, no brain region was correlated with the attention to changes in pain score. Our VBM results demonstrate that attention to pain scores assessed by PVAQ are associated with morphological features of the left AIC. Moreover, they may contribute to the elucidation of the complex psychological and neurophysiological characteristics of patients with chronic pain.

Changes in excitability and GABAergic neuronal activity of the primary somatosensory cortex after motor learning.

Introduction: It is widely known that motor learning changes the excitability of the primary motor cortex. More recently, it has been shown that the primary somatosensory cortex (S1) also plays an important role in motor learning, but the details have not been fully examined. Therefore, we investigated how motor skill training affects somatosensory evoked potential (SEP) in 30 neurologically healthy subjects. Methods: SEP N20/P25_component and N20/P25 SEP paired-pulse depression (SEP-PPD) were assessed before and immediately after complex or simple visuomotor tasks. Results: Motor learning was induced more efficiently by the complex visuomotor task than by the simple visuomotor task. Both the N20/P25 SEP amplitude and N20/P25 SEP-PPD increased significantly immediately after the complex visuomotor task, but not after the simple visuomotor task. Furthermore, the altered N20/P25 SEP amplitude was associated with an increase in motor learning efficiency. Conclusion: These results suggest that motor learning modulated primary somatosensory cortex excitability.

Lesions of the nucleus basalis magnocellularis (Meynert) induce enhanced somatosensory responses and tactile hypersensitivity in rats.

We used the immunotoxin 192 immunoglobulin G-saporin to produce a selective cholinergic lesion in the nucleus basalis of Meynert (NBM) of rats and investigated whether the NBM lesion led to tactile hypersensitivity in the forepaw. The paw mechanical threshold test showed that the lesioned rats had a decreased threshold compared to the control. Surprisingly, there was a significant positive correlation between mechanical threshold and survival rate of NBM cholinergic neurons. Furthermore, using local field potential (LFP) recordings and voltage-sensitive dye (VSD) imaging, we found that the forepaw-evoked response in the primary somatosensory cortex (S1) was significantly enhanced in both amplitude and spatial extent in the NBM-lesioned rats. The neurophysiological measures of S1 response, such as LFP amplitude and maximal activated cortical area depicted by VSD, were also correlated with withdrawal behavior. Additional pharmacological experiments demonstrated that forepaw-evoked responses were increased in naive rats by blocking S1 cholinergic receptors with mecamylamine and scopolamine, while the response decreased in NBM-lesioned rats with the cholinergic agonist carbachol. In addition, NBM burst stimulation, which facilitates acetylcholine release in the S1, suppressed subsequent sensory responses to forepaw stimulation. Taken together, these results suggest that neuronal loss in the NBM diminishes acetylcholine actions in the S1, thereby enhancing the cortical representation of sensory stimuli, which may in turn lead to behavioral hypersensitivity.

Induction of Relaxation by Autonomous Sensory Meridian Response.

Background: Autonomous sensory meridian response (ASMR) is used by young people to induce relaxation and sleep and to reduce stress and anxiety; it comprises somatosensation caused by audiovisual stimuli (triggers) that lead to positive emotions. Auditory stimuli play the most important role among the triggers involved in ASMR and have been reported to be more triggering than visual stimuli. On the other hand, classical music is also known to have a relaxing effect. This is the first study to clarify the difference in brain activation associated with relaxation effects between ASMR and classical music by limiting ASMR to auditory stimulation alone. Methods: Thirty healthy subjects, all over 20 years of age, underwent fMRI while listening to ASMR and classical music. We compared the differences in brain activation associated with classical music and ASMR stimulation. After the experiment, the subjects were administered a questionnaire on somatosensation and moods. After the experiment, the participants were asked whether they experienced ASMR somatosensation or frisson. They were also asked to rate the intensity of two moods during stimulation: "comfortable mood," and "tingling mood". Result: The results of the questionnaire showed that none of the participants experienced any ASMR somatosensation or frisson. Further, there was no significant difference in the ratings given to comfort mood, but there was a significant difference in those given to tingling mood. In terms of brain function, classical music and ASMR showed significant activation in common areas, while ASMR showed activation in more areas, with the medial prefrontal cortex being the main area of activation during ASMR. Conclusion: Both classical music and the ASMR auditory stimulus produced a pleasant and relaxed state, and ASMR involved more complex brain functions than classical music, especially the activation of the medial prefrontal cortex. Although ASMR was limited to auditory stimulation, the effects were similar to those of listening to classical music, suggesting that ASMR stimulation can produce a pleasant state of relaxation even if it is limited to the auditory component, without the somatic sensation of tingling. ASMR stimulation is easy to use, and appropriate for wellness purposes and a wide range of people.

Influence of Catechol-O-Methyltransferase Gene Polymorphism on the Correlation between Alexithymia and Hypervigilance to Pain.

The psychological characteristic of having difficulty expressing emotions, known as alexithymia, is associated with hypervigilance to pain and is considered one of the risk factors for chronic pain. The correlation between alexithymia and hypervigilance to pain can be observed even in healthy individuals. However, the factors influencing this correlation remain unknown. We explored the dopamine system, which is known to be involved in emotion and pain. The dopamine-degrading enzyme catechol-O-methyltransferase (COMT) has a genetic polymorphism known to influence dopamine metabolism in the prefrontal cortex. COMT polymorphism reportedly affects various aspects of pain and increases pain sensitivity in Met allele carriers. Therefore, we investigated whether the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism in healthy individuals. The results revealed a significant positive correlation between the "difficulty describing feelings" of the 20-item Toronto Alexithymia Scale and the "attention to changes in pain" of the pain vigilance and awareness questionnaire in COMT Met carriers but not in Val/Val individuals. This finding suggests that the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism.

Region-Specific Effects of 10-Hz Transcranial Alternate Current Stimulation Over the Left Posterior Parietal Cortex and Primary Somatosensory Area on Tactile Two-Point Discrimination Threshold.

Changes in α-band cortical oscillatory activity (8-13 Hz) affect perception; however, how these changes in the left posterior parietal cortex (PPC) and primary somatosensory cortex (S1), which play different roles in determining the two-point discrimination (TPD) threshold, affect TPD threshold remains unelucidated. Therefore, to determine TPD threshold, we aimed to investigate the function of the left PPC and S1 by applying α-band transcranial alternating current stimulation (α-tACS; 10 Hz). TPD threshold was examined at the pad of the right index finger, contralateral to the stimulation site, in 17 healthy adults using a custom-made, computer-controlled, two-point tactile stimulation device, with random application of either active or sham α-tACS over the left PPC (Experiment 1) and left S1 (Experiment 2). Then, 50% TPD threshold was obtained in the active and sham conditions via logistic regression analysis. Afterward, we compared the difference between the active and sham conditions at 50% TPD threshold in each region and found that α-tACS reduced TPD threshold when applied over the left PPC (P = 0.010); however, its effect was insignificant when applied over the left S1 (P = 0.74). Moreover, a comparison of the change in 50% TPD threshold among the regions revealed that α-tACS applied over the left PPC significantly reduced TPD threshold compared with that applied over the left S1 (P = 0.003). Although we did not reveal the actual changes in cortical activity induced by α-tACS, this is the first empirical evidence that α-tACS applied over the left PPC and left S1 exerts region-specific effects on determining TPD threshold assessed in the contralateral index finger pad by stimulation.

Brain activity changes in a monkey model of central post-stroke pain.

Central post-stroke pain (CPSP) can occur after stroke in the somatosensory pathway that includes the posterolateral region of the thalamus. Tactile allodynia, in which innocuous tactile stimuli are perceived as painful, is common in patients with CPSP. Previous brain imaging studies have reported plastic changes in brain activity in patients with tactile allodynia after stroke, but a causal relationship between such changes and the symptoms has not been established. We recently developed a non-human primate (macaque) model of CPSP based on thalamic lesions, in which the animals show behavioral changes consistent with the occurrence of tactile allodynia. Here we performed functional magnetic resonance imaging under propofol anesthesia to investigate the changes in brain activation associated with the allodynia in this CPSP model. Before the lesion, innocuous tactile stimuli significantly activated the contralateral sensorimotor cortex. When behavioral changes were observed after the thalamic lesion, equivalent stimuli significantly activated pain-related brain areas, including the posterior insular cortex (PIC), secondary somatosensory cortex (SII), anterior cingulate cortex (ACC), and amygdala. Moreover, when either PIC/SII or ACC was pharmacologically inactivated, the signs of tactile allodynia were dampened. Our results show that increased cortical activity plays a role in CPSP-induced allodynia.

Brain Temperature Alters Contributions of Excitatory and Inhibitory Inputs to Evoked Field Potentials in the Rat Frontal Cortex.

Changes in brain temperature have been reported to affect various brain functions. However, little is known about the effects of temperature on the neural activity at the network level, where multiple inputs are integrated. In this study, we recorded cortical evoked potentials while altering the local brain temperature in anesthetized rats. We delivered electrical stimulations to the midbrain dopamine area and measured the evoked potentials in the frontal cortex, the temperature of which was locally altered using a thermal control device. We focused on the maximum negative peaks, which was presumed to result mainly from polysynaptic responses, to examine the effect of local temperature on network activity. We showed that focal cortical cooling increased the amplitude of evoked potentials (negative correlation, >17°C); further cooling decreased their amplitude. This relationship would be graphically represented as an inverted-U-shaped curve. The pharmacological blockade of GABAergic inhibitory inputs eliminated the negative correlation (>17°C) and even showed a positive correlation when the concentration of GABAA receptor antagonist was sufficiently high. Blocking the glutamatergic excitatory inputs decreased the amplitude but did not cause such inversion. Our results suggest that the negative correlation between the amplitude of evoked potentials and the near-physiological local temperature is caused by the alteration of the balance of contribution between excitatory and inhibitory inputs to the evoked potentials, possibly due to higher temperature sensitivity of inhibitory inputs.

The after-effect of noisy galvanic vestibular stimulation on postural control in young people: A randomized controlled trial.

Noisy galvanic vestibular stimulation (nGVS) enhances the vestibular system. The center of pressure (COP) sway has been shown to decrease during nGVS, but the after-effect of nGVS remains unclear. The aim of this study is to elucidate the after-effect of nGVS on COP sway. We randomly assigned 26 participants to either control (sham stimulation) or nGVS groups. All participants were measured for COP sway while standing with open eyes at baseline, during stimulation, and after stimulation. In the nGVS group, sway path length, mediolateral mean velocity, and anteroposterior mean velocity decreased both during stimulation and after stimulation compared with baseline. Conversely, no significant difference in COP sway was detected in the control group. There was a correlation between the stimulation effect and the after-effect in the nGVS group, indicating that nGVS is effective for people with high baseline COP sway.