Propofol anesthesia-induced spatiotemporal changes in cortical activity with loss of external and internal awareness: An electrocorticography study.

OBJECTIVE: To understand the underlying mechanism of consciousness, investigating spatiotemporal changes in the cortical activity during the induction phase of unconsciousness is important. Loss of consciousness induced by general anesthesia is not necessarily accompanied by a uniform inhibition of all cortical activities. We hypothesized that cortical regions involved in internal awareness would be suppressed after disruption of cortical regions involved in external awareness. Thus, we investigated temporal changes in cortex during induction of unconsciousness. METHODS: We recorded electrocorticography data of 16 epilepsy patients and investigated power spectral changes during induction phase from awake state to unconsciousness. Temporal changes were assessed at 1) the start point and 2) the interval of normalized time between start and end of power change (Δ tnormalized). RESULTS: We found that the power increased at frequencies < 46 Hz, and decreased in range of 62-150 Hz, in global channels. In temporal changes of power change, superior parietal lobule and dorsolateral prefrontal cortex started to change early, but the changes were completed over a prolonged interval, whereas angular gyrus and associative visual cortex showed a delayed change and rapid completion. CONCLUSIONS: Loss of consciousness induced by general anesthesia results first from disrupted communication between self and external world, followed by disrupted communication within self, with decreased activities of superior parietal lobule and dorsolateral prefrontal cortex, and later, attenuated activities of angular gyrus. SIGNIFICANCE: Our findings provided neurophysiological evidence for the temporal changes in consciousness components induced by general anesthesia.

Dissociation of Connectivity for Syntactic Irregularity and Perceptual Ambiguity in Musical Chord Stimuli.

Musical syntax has been studied mainly in terms of "syntactic irregularity" in harmonic/melodic sequences. However, "perceptual ambiguity" referring to the uncertainty of judgment/classification of presented stimuli can in addition be involved in our musical stimuli using three different chord sequences. The present study addresses how "syntactic irregularity" and "perceptual ambiguity" on musical syntax are dissociated, in terms of effective connectivity between the bilateral inferior frontal gyrus (IFGs) and superior temporal gyrus (STGs) by linearized time-delayed mutual information (LTDMI). Three conditions were of five-chord sequences with endings of dominant to tonic, dominant to submediant, and dominant to supertonic. The dominant to supertonic is most irregular, compared with the regular dominant to tonic. The dominant to submediant of the less irregular condition is the most ambiguous condition. In the LTDMI results, connectivity from the right to the left IFG (IFG-LTDMI) was enhanced for the most irregular condition, whereas that from the right to the left STG (STG-LTDMI) was enhanced for the most ambiguous condition (p = 0.024 in IFG-LTDMI, p < 0.001 in STG-LTDMI, false discovery rate (FDR) corrected). Correct rate was negatively correlated with STG-LTDMI, further reflecting perceptual ambiguity (p = 0.026). We found for the first time that syntactic irregularity and perceptual ambiguity coexist in chord stimulus testing musical syntax and that the two processes are dissociated in interhemispheric connectivities in the IFG and STG, respectively.

Increased fronto-temporal connectivity by modified melody in real music.

In real music, the original melody may appear intact, with little elaboration only, or significantly modified. Since a melody is most easily perceived in music, hearing significantly modified melody may change a brain connectivity. Mozart KV 265 is comprised of a theme with an original melody of "Twinkle Twinkle Little Star" and its significant variations. We studied whether effective connectivity changes with significantly modified melody, between bilateral inferior frontal gyri (IFGs) and Heschl's gyri (HGs) using magnetoencephalography (MEG). Among the 12 connectivities, the connectivity from the left IFG to the right HG was consistently increased with significantly modified melody compared to the original melody in 2 separate sets of the same rhythmic pattern with different melody (p = 0.005 and 0.034, Bonferroni corrected). Our findings show that the modification of an original melody in a real music changes the brain connectivity.

An Electrode Configuration for Recording Muscle Motor Evoked Potentials in the Upper Extremities during Intraoperative Neurophysiological Monitoring.

OBJECTIVE: The main aim of the present study is to examine the electrode configurations used to record the muscle motor evoked potential (mMEP) in the upper extremities during surgery with the goal of producing a high and stable mMEP signal, in particular among the abductor pollicis brevis (APB), abductor digiti minimi (ADM), and across the APB-ADM muscles, which have been widely used for the mMEP in the upper extremities. METHODS: Thirty right-handed patients were recruited in this prospective study. No patients showed any adverse events in their mMEP signals of the upper extremities during surgery. The mMEPs were recorded independently from the signals for the APB and ADM and for those across the APB-ADM. RESULTS: The mMEP amplitude from across the APB-ADM was statistically higher than those recorded from the APB and ADM muscles. Moreover, the coefficient of variation of the mMEP amplitude from across the APB-ADM was smaller than those of mMEP amplitude recorded from the APB and ADM muscles. CONCLUSION: The mMEP from across the APB-ADM muscles showed a high yield with high stability compared to those in each case from the APB and ADM muscles. The configuration across the APB-ADM muscles would be best for mMEP recordings from the upper extremities for intraoperative neurophysiological monitoring purposes.

Electrophysiological resting-state biomarker for diagnosing mesial temporal lobe epilepsy with hippocampal sclerosis.

The main aim of the present study was to evaluate whether resting-state functional connectivity of magnetoencephalography (MEG) signals can differentiate patients with mesial temporal lobe epilepsy (MTLE) from healthy controls (HC) and can differentiate between right and left MTLE as a diagnostic biomarker. To this end, a support vector machine (SVM) method among various machine learning algorithms was employed. We compared resting-state functional networks between 46 MTLE (right MTLE=23; left MTLE=23) patients with histologically proven HS who were free of seizure after surgery, and 46 HC. The optimal SVM group classifier distinguished MTLE patients with a mean accuracy of 95.1% (sensitivity=95.8%; specificity=94.3%). Increased connectivity including the right posterior cingulate gyrus and decreased connectivity including at least one sensory-related resting-state network were key features reflecting the differences between MTLE patients and HC. The optimal SVM model distinguished between right and left MTLE patients with a mean accuracy of 76.2% (sensitivity=76.0%; specificity=76.5%). We showed the potential of electrophysiological resting-state functional connectivity, which reflects brain network reorganization in MTLE patients, as a possible diagnostic biomarker to differentiate MTLE patients from HC and differentiate between right and left MTLE patients.

Intraoperative Motor-Evoked Potential Disappearance versus Amplitude-Decrement Alarm Criteria During Cervical Spinal Surgery: A Long-Term Prognosis.

BACKGROUND AND PURPOSE: We studied the clinical significance of amplitude-reduction and disappearance alarm criteria for transcranial electric muscle motor-evoked potentials (MEPs) during cervical spinal surgery according to different lesion locations [intramedullary (IM) vs. nonintramedullary (NIM)] by evaluating the long-term postoperative motor status. METHODS: In total, 723 patients were retrospectively dichotomized into the IM and NIM groups. Each limb was analyzed respectively. One hundred and sixteen limbs from 30 patients with IM tumors and 2,761 limbs from 693 patients without IM tumors were enrolled. Postoperative motor deficits were assessed up to 6 months after surgery. RESULTS: At the end of surgery, 61 limbs (2.2%) in the NIM group and 14 limbs (12.1%) in the IM group showed MEP amplitudes that had decreased to below 50% of baseline, with 13 of the NIM limbs (21.3%) and 2 of the IM limbs (14.3%) showing MEP disappearance. Thirteen NIM limbs (0.5%) and 5 IM limbs (4.3%) showed postoperative motor deficits. The criterion for disappearance showed a lower sensitivity for the immediate motor deficit than did the criterion for amplitude decrement in both the IM and NIM groups. However, the disappearance criterion showed the same sensitivity as the 70%-decrement criterion in IM (100%) and NIM (83%) surgeries for the motor deficit at 6 months after surgery. Moreover, it has the highest specificity for the motor deficits among diverse alarm criteria, from 24 hours to 6 months after surgery, in both the IM and NIM groups. CONCLUSIONS: The MEP disappearance alarm criterion had a high specificity in predicting the long-term prognosis after cervical spinal surgery. However, because it can have a low sensitivity in predicting an immediate postoperative deficit, combining different MEP alarm criteria according to the aim of specific instances of cervical spinal surgery is likely to be useful in practical intraoperative monitoring.

Effect of peripheral nerve tetanic stimulation on the inter-trial variability and accuracy of transcranial motor-evoked potential in brain surgery.

OBJECTIVES: The aim of this study was to evaluate and compare the advantages of post-tetanic motor-evoked potential (p-MEP) and conventional motor-evoked potential (c-MEP) in terms of MEP inter-trial variability and accuracy. METHODS: c-MEP and p-MEP were quantified in subjects who underwent brain surgery. c-MEP was generated by transcranial electrical stimulation (TES). p-MEP was generated using a preconditioning process involving tetanic stimulation at the left tibial nerve followed by TES. The presence of significant MEP deterioration was monitored during major surgical process. An additional 5-8 MEP obtained after major surgical process were used to analyze amplitude parameters such as mean, standard deviation, range, coefficient of variation (CV), and range to mean ratio. RESULTS: When only irreversible MEP deteriorations were considered as positive results, the false-positive rate was identical for p-MEP and c-MEP. When total MEP deteriorations were considered as positive results, the false-positive rate of p-MEP was lower and p-MEP had higher specificity than c-MEP. The mean amplitude of p-MEP was significantly higher than that of c-MEP. The CV and range to mean ratio of p-MEP were less than those of c-MEP. CONCLUSION: The p-MEP technique is useful for augmenting MEP amplitude and reducing inter-trial variability. SIGNIFICANCE: p-MEP has clinical significance as a useful technique for intraoperative monitoring.

Multimodal intraoperative monitoring during intramedullary spinal cord tumor surgery.

BACKGROUND: The aim of this work is to evaluate the utility of multimodal intraoperative monitoring (IOM) during intramedullary spinal cord tumor (IMSCT) surgery in our institution, and to investigate which IOM events are likely to be encountered during critical surgical phases. METHODS: Twenty-five patients who underwent IMSCT surgery with IOM were included in this study. Our multimodal IOM assessment included SSEP, mMEP, and fEMG monitoring. Positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were assessed 24 h and 1 month after surgery. The IOM events during three main surgical phases were also investigated. For mMEP assessment, two warning criteria (>50 % decrease in mMEP amplitude and all-or-none mMEP amplitude presence) were employed. RESULTS: Long-term outcome prediction was better when the all-or-none criterion was applied than when the >50 % amplitude decrease criterion was applied. Based on the all-or-none criterion, the PPV, NPV, sensitivity, and specificity were 60, 100, 100, and 91 %. Frequent IOM events were observed during the three major main surgical phases. Seven (29 %) patients showed SSEP events during opening of the spinal cord. During tumor removal, 21 of 25 patients (84 %) had IOM events, and 13 of 18 (72 %) of the fEMG events occurred prior to the mMEP events. CONCLUSIONS: Based on the association of fEMG events with upcoming mMEP events during tumor removal, we recommend inclusion of fEMG monitoring in IOM. Multimodal IOM provides useful electrophysiological information during IMSCT surgery, especially during the main surgical phases.

Functional substrate for memory function differences between patients with left and right mesial temporal lobe epilepsy associated with hippocampal sclerosis.

OBJECTIVE: Little is known about the functional substrate for memory function differences in patients with left or right mesial temporal lobe epilepsy (mTLE) associated with hippocampal sclerosis (HS) from an electrophysiological perspective. To characterize these differences, we hypothesized that hippocampal theta connectivity in the resting-state might be different between patients with left and right mTLE with HS and be correlated with memory performance. METHODS: Resting-state hippocampal theta connectivity, identified via whole-brain magnetoencephalography, was evaluated. Connectivity and memory function in 41 patients with mTLE with HS (left mTLE=22; right mTLE=19) were compared with those in 46 age-matched healthy controls and 28 patients with focal cortical dysplasia (FCD) but without HS. RESULTS: Connectivity between the right hippocampus and the left middle frontal gyrus was significantly stronger in patients with right mTLE than in patients with left mTLE. Moreover, this connectivity was positively correlated with delayed verbal recall and recognition scores in patients with mTLE. Patients with left mTLE had greater delayed recall impairment than patients with right mTLE and FCD. Similarly, delayed recognition performance was worse in patients with left mTLE than in patients with right mTLE and FCD. No significant differences in memory function between patients with right mTLE and FCD were detected. Patients with right mTLE showed significantly stronger hippocampal theta connectivity between the right hippocampus and left middle frontal gyrus than patients with FCD and left mTLE. CONCLUSION: Our results suggest that right hippocampal-left middle frontal theta connectivity could be a functional substrate that can account for differences in memory function between patients with left and right mTLE. This functional substrate might be related to different compensatory mechanisms against the structural hippocampal lesions in left and right mTLE groups. Given the positive correlation between connectivity and delayed verbal memory function, hemispheric-specific hippocampal-frontal theta connectivity assessment could be useful as an electrophysiological indicator of delayed verbal memory function in patients with mTLE with HS.

Mesial temporal lobe epilepsy with hippocampal sclerosis is a network disorder with altered cortical hubs.

OBJECTIVE: Electrophysiologic hubs within the large-scale functional networks in mesial temporal lobe epilepsy (mTLE) with hippocampal sclerosis (HS) have not been investigated. We hypothesized that mTLE with HS has different resting-state network hubs in their large-scale functional networks compared to the hubs in healthy controls (HC). We also hypothesized that the hippocampus would be a functional hub in mTLE patients with HS. METHODS: Resting-state functional networks, identified by using magnetoencephalography (MEG) signals in the theta, alpha, beta, and gamma frequency bands, were evaluated. Networks in 44 mTLE patients with HS (left mTLE = 22; right mTLE = 22) were compared with those in 46 age-matched HC. We investigated betweenness centrality at the source-level MEG network. RESULTS: The main network hubs were at the pole of the left superior temporal gyrus in the beta band, the pole of the left middle temporal gyrus in the beta and gamma bands, left hippocampus in the theta and alpha bands, and right posterior cingulate gyrus in all four frequency bands in mTLE patients; all of which were different from the main network hubs in HC. Only patients with left mTLE showed profound differences from HC at the left hippocampus in the alpha band. SIGNIFICANCE: Our analysis of resting-state MEG signals shows that altered electrophysiologic functional hubs in mTLE patients reflect pathophysiologic brain network reorganization. Because we detected network hubs in both hippocampal and extrahippocampal areas, it is probable that mTLE is a large-scale network disorder rather than a focal disorder. The hippocampus was a network hub in left mTLE but not in right mTLE patients, which may be due to intrinsic functional and structural asymmetries between left and right mTLE patients. The evaluation of cortical hubs, even in the spike-free resting-state, could be a clinical diagnostic marker of mTLE with HS.

Focal cortical dysplasia alters electrophysiological cortical hubs in the resting-state.

OBJECTIVE: To test the hypothesis that epilepsy patients with focal cortical dysplasia (FCD) have different electrophysiological functional cortical hubs from those of healthy controls. METHODS: Resting-state functional networks in the theta, alpha, beta and gamma frequency bands were evaluated in 35 epilepsy patients with histopathologically verified FCD as a single pathology and in 46 age-matched healthy controls. Using magnetoencephalography (MEG), we investigated the network differences between the two groups by comparing the nodal efficiency (Enodal) and betweenness centrality (BC) values at the source level. RESULTS: The FCD patients had significant Enodal increases in the functional cortical hubs in the left anterior, middle, and posterior cortices and the medial orbital superior frontal cortex in the beta band. The left posterior cingulate cortex showed significant BC increases in the theta, alpha, and beta bands. There was a negative correlation between Enodal and age at seizure onset. CONCLUSIONS: Cortical dysplasia alters whole brain functional cortical hubs compared to healthy controls. The age at seizure onset was negatively correlated with Enodal in the beta band in FCD patients. SIGNIFICANCE: Our study for the first time investigated the functional cortical hubs and their alteration in the resting-state functional network in epilepsy patients with FCD using noninvasive MEG signals.

Abnormal functional brain network in epilepsy patients with focal cortical dysplasia.

PURPOSE: Focal cortical dysplasia (FCD) is the second most common pathological entity in surgically treated neocortical focal epilepsy. Despite the recent increase of interest in network approaches derived from graph theory on epilepsy, resting state network analysis of the FCD brain has not been adequately investigated. In this study, we investigated the difference in the resting state functional network between epilepsy patients with FCD and healthy controls using whole-brain magnetoencephalography (MEG) recordings. METHODS: Global mutual information (MIglob) and global efficiency (Eglob) were calculated for theta (4-7 Hz), alpha (8-12 Hz), beta (13-30 Hz), and gamma (31-45 Hz) bands in 35 epilepsy patients with FCD and 23 healthy controls. RESULTS: Resting state FCD brains had stronger functional connectivity (MIglob) in the beta and gamma bands and higher functional efficiency (Eglob) in the beta and gamma bands than those of the controls (p<0.05). The MIglob and Eglob values of FCD type I and II brains in the beta band were higher than those of healthy control brains (p<0.05). In the gamma band, the values of FCD type II brains were higher than those of control and FCD type I brains (p<0.05). CONCLUSIONS: FCD brains had increased functional connectivity in the beta and gamma frequency bands at the resting state compared with those in healthy controls. In addition, patients exhibited different network characteristics depending on the type of FCD. The resting state network analysis could be useful in a clinical setting because we observed network differences even when there was no prominent interictal spike activity.

Functional connectivity of resting state EEG and symptom severity in patients with post-traumatic stress disorder.

OBJECTIVES: Post-traumatic stress disorder (PTSD) is thought to be a brain network disorder. This study aimed to examine the resting-state functional connectivity (FC) in patients with PTSD. METHODS: Thirty-three PTSD patients and 30 age- and gender-matched healthy controls were recruited. Symptom severity of the PTSD patients was assessed, and 62-channel EEG was measured. EEGs were recorded during the resting state, with the eyes closed. Three nodal network measures to assess nodal centrality [nodal degree (Dnodal; connection strength), nodal efficiency (Enodal; communication efficiency), and betweenness centrality (BC; connection centrality)] were calculated in the delta, theta, alpha, beta, and gamma bands. RESULTS: Dnodal and Enodal of the beta and gamma bands were decreased in PTSD patients compared to healthy controls. These decreased nodal centrality values were observed primarily at the frontocentral electrodes. In addition, Dnodal of the beta and gamma bands was significantly correlated with depressive symptoms and increased arousal symptoms, respectively. Enodal of the beta and gamma bands was significantly correlated with re-experience, increased arousal, and the severity and frequency of general PTSD symptoms. CONCLUSION: Compared to controls, patients with PTSD were found to have decreased resting-state FC, and these FC measures were significantly correlated with PTSD symptom severity. Our results suggest that resting-state FC could be a useful biomarker for PTSD.

Preserved high-centrality hubs but efficient network reorganization during eyes-open state compared with eyes-closed resting state: an MEG study.

A question to be addressed in the present study is how different the eyes-closed (EC) and eyes-open (EO) resting states are across frequency bands in terms of efficiency and centrality of the brain functional network. We investigated both the global and nodal efficiency and betweenness centrality in the EC and EO resting states from 39 volunteers. Mutual information was used to obtain the functional connectivity for each of the four frequency bands (theta, alpha, beta, and gamma). We showed that the cortical hubs with high betweenness centrality were maintained in the EC and EO resting states. We further showed that these hubs were associated with more than three frequency bands, suggesting that these hubs play an important role in the brain functional network at multiple temporal scales in the resting states. Enhanced global efficiency values were found in the theta and alpha bands in the EO state compared with those in the EC state. Moreover, it turned out that in the EO state the functional network was reorganized to enhance nodal efficiency at the nodes related to both the default mode and the dorsal attention networks and sensory-related resting-state networks. This result suggests that in the EO state the brain functional network was efficiently reorganized, facilitating the adaptation of the brain network to the change in state, which could help in understanding brain disorders that have a disturbance in communication with external environments by using the adaptation ability of brain functional networks.

A new measure for monitoring intraoperative somatosensory evoked potentials.

OBJECTIVE: To propose a new measure for effective monitoring of intraoperative somatosensory evoked potentials (SEP) and to validate the feasibility of this measure for evoked potentials (EP) and single trials with a retrospective data analysis study. METHODS: The proposed new measure (hereafter, a slope-measure) was defined as the relative slope of the amplitude and latency at each EP peak compared to the baseline value, which is sensitive to the change in the amplitude and latency simultaneously. We used the slope-measure for EP and single trials and compared the significant change detection time with that of the conventional peak-to-peak method. When applied to single trials, each single trial signal was processed with optimal filters before using the slope-measure. In this retrospective data analysis, 7 patients who underwent cerebral aneurysm clipping surgery for unruptured aneurysm middle cerebral artery (MCA) bifurcation were included. RESULTS: We found that this simple slope-measure has a detection time that is as early or earlier than that of the conventional method; furthermore, using the slope-measure in optimally filtered single trials provides warning signs earlier than that of the conventional method during MCA clipping surgery. CONCLUSION: Our results have confirmed the feasibility of the slope-measure for intraoperative SEP monitoring. This is a novel study that provides a useful measure for either EP or single trials in intraoperative SEP monitoring.

Functional cortical hubs in the eyes-closed resting human brain from an electrophysiological perspective using magnetoencephalography.

It is not clear whether specific brain areas act as hubs in the eyes-closed (EC) resting state, which is an unconstrained state free from any passive or active tasks. Here, we used electrophysiological magnetoencephalography (MEG) signals to study functional cortical hubs in 88 participants. We identified several multispectral cortical hubs. Although cortical hubs vary slightly with different applied measures and frequency bands, the most consistent hubs were observed in the medial and posterior cingulate cortex, the left dorsolateral superior frontal cortex, and the left pole of the middle temporal cortex. Hubs were characterized as connector nodes integrating EC resting state functional networks. Hubs in the gamma band were more likely to include midline structures. Our results confirm the existence of multispectral cortical cores in EC resting state functional networks based on MEG and imply the existence of optimized functional networks in the resting brain.

Information source in multiple MEG spike clusters can be identified by effective connectivity in focal cortical dysplasia.

It has been reported that patients with a single MEG spike cluster have better postoperative outcomes compared to patients with multiple clusters. However, the problem of identifying a genuine source in the multiple MEG spike clusters remains unsolved. The aim of this study was to determine the focus of the epileptic activity in a situation with multiple MEG spike clusters. Five patients with intractable epilepsy with multiple MEG spike clusters were retrospectively investigated. They had pathologically proven type IA focal cortical dysplasia (FCD) with discordant multimodal presurgical evaluations, and showed a favorable postoperative outcome. MEG spikes were localized and clustered using a hierarchical clustering method. Then, effective connectivity (a phase-slope index method) referring to the causal interaction between distant structures in the brain was applied to the source waveforms extracted from the multiple MEG spike clusters. Finally, the information source, that is, the driver region between multiple clusters, could be identified. We found that 4 of the 5 FCD patients exhibited the driver regions were coincident with the resection area, which was also quite consistent at different epochs. Our results suggest that effective connectivity analysis has a potential value as a presurgical evaluation when multiple MEG spike clusters are found.

Messages from the brain connectivity regarding neural correlates of consciousness.

Consciousness has become a legitimate theme of neuroscientific discourse over the last two decades. Neuroscientific investigation seeking neural correlates of consciousness (NCC) has ranged from the neuronal level to the system level. Regarding system level studies, there is a large body of evidence supporting the idea that functional connectivity studies can help in examining NCC. Functional connectivity studies have suggested the involvement of the thalamo-cortical, frontoparietal, and other cortico-cortical connectivity under anesthetic-induced unconsciousness and in disorders of consciousness. Likewise, effective connectivity has been used to investigate the causal interactions among elements of functional connectivity in various consciousness states, and provided a deeper understanding of NCC. Moreover, as an extended version of connectivity studies, complex network methods have also been used for studies on NCC. In this review, we focused on the aspect of the brain system level of NCC including functional and effective connectivity networks from methodological perspectives. In addition, as for states of consciousness, anesthetic-induced unconsciousness and disorders of consciousness are the main subjects. This review discusses what we have learned from recent studies about the exploration of human brain connectivity on consciousness and its neural correlates.

Timing-dependent modulation of the posterior parietal cortex-primary motor cortex pathway by sensorimotor training.

Interplay between posterior parietal cortex (PPC) and ipsilateral primary motor cortex (M1) is crucial during execution of movements. The purpose of the study was to determine whether functional PPC-M1 connectivity in humans can be modulated by sensorimotor training. Seventeen participants performed a sensorimotor training task that involved tapping the index finger in synchrony to a rhythmic sequence. To explore differences in training modality, one group (n = 8) learned by visual and the other (n = 9) by auditory stimuli. Transcranial magnetic stimulation (TMS) was used to assess PPC-M1 connectivity before and after training, whereas electroencephalography (EEG) was used to assess PPC-M1 connectivity during training. Facilitation from PPC to M1 was quantified using paired-pulse TMS at conditioning-test intervals of 2, 4, 6, and 8 ms by measuring motor-evoked potentials (MEPs). TMS was applied at baseline and at four time points (0, 30, 60, and 180 min) after training. For EEG, task-related power and coherence were calculated for early and late training phases. The conditioned MEP was facilitated at a 2-ms conditioning-test interval before training. However, facilitation was abolished immediately following training, but returned to baseline at subsequent time points. Regional EEG activity and interregional connectivity between PPC and M1 showed an initial increase during early training followed by a significant decrease in the late phases. The findings indicate that parietal-motor interactions are activated during early sensorimotor training when sensory information has to be integrated into a coherent movement plan. Once the sequence is encoded and movements become automatized, PPC-M1 connectivity returns to baseline.

Reorganization of brain functional small-world networks during finger movements.

A functional measure of brain organization is the efficiency of functional connectivity. The degree of functional connectivity can differ during a task compared to the rest, and to study this issue, we investigated the functional connectivity networks in healthy subjects during a simple, right-handed, sequential finger-tapping task using graph theoretic measures. EEGs were recorded from 58 channels in 15 healthy subjects at rest and during a motor task. We estimated mutual information values of wavelet coefficients to create an association matrix between EEG electrodes and produced a series of adjacency matrices or graphs, A, by thresholding with network cost. These graphs are called small-world networks, and we assessed their efficiency measures. We found economical small-world properties in brain functional connectivity networks in the alpha and beta band networks. The efficiency of the brain networks was enhanced during the task in the beta band networks, but not in the alpha band networks. A regional efficiency analysis during the task showed that the bilateral primary motor and left sensory areas showed increased nodal efficiency, Enodal, whereas decreased Enodal was found over the posterior parietal areas. The present study provides evidence for the reorganization of brain functional connectivity networks in a motor task with the greatest increase in Enodal in motor executive areas.