Resting BOLD fluctuations in the primary somatosensory cortex correlate with tactile acuity

The extraordinary enigma of ordinary tickle behavior: Why gargalesis still puzzles neuroscience

Gargalesis, or tickle, is one of the most trivial yet enigmatic human behaviors. We do not know how a touch becomes ticklish or why we respond to other people's tickles but not our own. No theory satisfactorily explains why touch on some body areas feels more ticklish than on others or why some people are highly sensitive while others remain unresponsive. Gargalesis is likely the earliest trigger for laughter in life, but it is unclear whether we laugh because we enjoy it. Socrates, Aristotle, Bacon, Galileo, Descartes, and Darwin theorized about tickling, but after two millennia of intense philosophical interest, experimentation remains scarce. This review argues that gargalesis is an exhilarating scientific puzzle with far-reaching implications for developmental, sensorimotor, social, affective, clinical, and evolutionary neuroscience. We reflect on the challenges in defining and eliciting ticklish sensations in the lab and unraveling their neural mechanism, discuss five classic yet unanswered questions about tickle, and suggest directions for future research.

Temporal lobe dysfunction for comorbid depressive symptoms in postherpetic neuralgia patients

Depression often occurs concurrently with postherpetic neuralgia (PHN), yet the neural mechanism underlying pain-depression comorbidity remains poorly understood. For this observational study, we recruited 17 depressed PHN patients, 19 non-depressed PHN patients, and 34 healthy controls (HCs) for resting-state functional MRI scans. We firstly investigated the differences in fractional amplitude of low-frequency fluctuation and regional homogeneity values among the three groups to identify a characteristic brain signal of pain-depression comorbidity. Abnormal voxel-wised functional connectivity was then compared across groups and correlated with clinical variables in each group. One-way analysis of covariance results revealed the fractional amplitude of low-frequency fluctuation values differences in the right temporal lobe (TL) and its voxel-wised connectivity with the inferior frontal gyrus (IFG) among three groups. Furthermore, the TL-IFG connectivity was positively associated with the positive emotional scores and life quality scores among depressed PHN patients, but not non-depressed PHN patients and HCs. In summary, these findings highlighted the TL dysfunction in pain-depression comorbidity among PHN population and may offer heuristic cues for central therapeutic targets that could disrupt the pain-depression vicious circle.

Differential cortical activation patterns: pioneering sub-classification of tinnitus with and without hyperacusis by combining audiometry, gamma oscillations, and hemodynamics

The ongoing controversies about the neural basis of tinnitus, whether linked with central neural gain or not, may hamper efforts to develop therapies. We asked to what extent measurable audiometric characteristics of tinnitus without (T) or with co-occurrence of hyperacusis (TH) are distinguishable on the level of cortical responses. To accomplish this, electroencephalography (EEG) and concurrent functional near-infrared spectroscopy (fNIRS) were measured while patients performed an attentionally demanding auditory discrimination task using stimuli within the individual tinnitus frequency (fTin) and a reference frequency (fRef). Resting-state-fMRI-based functional connectivity (rs-fMRI-bfc) in ascending auditory nuclei (AAN), the primary auditory cortex (AC-I), and four other regions relevant for directing attention or regulating distress in temporal, parietal, and prefrontal cortex was compiled and compared to EEG and concurrent fNIRS activity in the same brain areas. We observed no group differences in pure-tone audiometry (PTA) between 10 and 16 kHz. However, the PTA threshold around the tinnitus pitch was positively correlated with the self-rated tinnitus loudness and also correlated with distress in T-groups, while TH experienced their tinnitus loudness at minimal loudness levels already with maximal suffering scores. The T-group exhibited prolonged auditory brain stem (ABR) wave I latency and reduced ABR wave V amplitudes (indicating reduced neural synchrony in the brainstem), which were associated with lower rs-fMRI-bfc between AAN and the AC-I, as observed in previous studies. In T-subjects, these features were linked with elevated spontaneous and reduced evoked gamma oscillations and with reduced deoxygenated hemoglobin (deoxy-Hb) concentrations in response to stimulation with lower frequencies in temporal cortex (Brodmann area (BA) 41, 42, 22), implying less synchronous auditory responses during active auditory discrimination of reference frequencies. In contrast, in the TH-group gamma oscillations and hemodynamic responses in temporoparietal regions were reversed during active discrimination of tinnitus frequencies. Our findings suggest that T and TH differ in auditory discrimination and memory-dependent directed attention during active discrimination at either tinnitus or reference frequencies, offering a test paradigm that may allow for more precise sub-classification of tinnitus and future improved treatment approaches.

Evidence- and data-driven classification of low back pain via artificial intelligence: Protocol of the PREDICT-LBP study

In patients presenting with low back pain (LBP), once specific causes are excluded (fracture, infection, inflammatory arthritis, cancer, cauda equina and radiculopathy) many clinicians pose a diagnosis of non-specific LBP. Accordingly, current management of non-specific LBP is generic. There is a need for a classification of non-specific LBP that is both data- and evidence-based assessing multi-dimensional pain-related factors in a large sample size. The "PRedictive Evidence Driven Intelligent Classification Tool for Low Back Pain" (PREDICT-LBP) project is a prospective cross-sectional study which will compare 300 women and men with non-specific LBP (aged 18-55 years) with 100 matched referents without a history of LBP. Participants will be recruited from the general public and local medical facilities. Data will be collected on spinal tissue (intervertebral disc composition and morphology, vertebral fat fraction and paraspinal muscle size and composition via magnetic resonance imaging [MRI]), central nervous system adaptation (pain thresholds, temporal summation of pain, brain resting state functional connectivity, structural connectivity and regional volumes via MRI), psychosocial factors (e.g. depression, anxiety) and other musculoskeletal pain symptoms. Dimensionality reduction, cluster validation and fuzzy c-means clustering methods, classification models, and relevant sensitivity analyses, will classify non-specific LBP patients into sub-groups. This project represents a first personalised diagnostic approach to non-specific LBP, with potential for widespread uptake in clinical practice. This project will provide evidence to support clinical trials assessing specific treatments approaches for potential subgroups of patients with non-specific LBP. The classification tool may lead to better patient outcomes and reduction in economic costs.

Intrinsic excitability of human right parietal cortex shapes the experienced visual size illusions

Converging evidence has found that the perceived visual size illusions are heritable, raising the possibility that visual size illusions might be predicted by intrinsic brain activity without external stimuli. Here we measured resting-state brain activity and 2 classic visual size illusions (i.e. the Ebbinghaus and the Ponzo illusions) in succession, and conducted spectral dynamic causal modeling analysis among relevant cortical regions. Results revealed that forward connection from right V1 to superior parietal lobule (SPL) was predictive of the Ebbinghaus illusion, and self-connection in the right SPL predicted the Ponzo illusion. Moreover, disruption of intrinsic activity in the right SPL by repetitive transcranial magnetic stimulation (TMS) temporally increased the Ebbinghaus rather than the Ponzo illusion. These findings provide a better mechanistic understanding of visual size illusions by showing the causal and distinct contributions of right parietal cortex to them, and suggest that spontaneous fluctuations in intrinsic brain activity are relevant to individual difference in behavior.

Somatosensory Deficits After Stroke: Insights From MRI Studies

Somatosensory deficits after stroke are a major health problem, which can impair patients' health status and quality of life. With the developments in human brain mapping techniques, particularly magnetic resonance imaging (MRI), many studies have applied those techniques to unravel neural substrates linked to apoplexy sequelae. Multi-parametric MRI is a vital method for the measurement of stroke and has been applied to diagnose stroke severity, predict outcome and visualize changes in activation patterns during stroke recovery. However, relatively little is known about the somatosensory deficits after stroke and their recovery. This review aims to highlight the utility and importance of MRI techniques in the field of somatosensory deficits and synthesizes corresponding articles to elucidate the mechanisms underlying the occurrence and recovery of somatosensory symptoms. Here, we start by reviewing the anatomic and functional features of the somatosensory system. And then, we provide a discussion of MRI techniques and analysis methods. Meanwhile, we present the application of those techniques and methods in clinical studies, focusing on recent research advances and the potential for clinical translation. Finally, we identify some limitations and open questions of current imaging studies that need to be addressed in future research.

Limits of Cross-modal Plasticity? Short-term Visual Deprivation Does Not Enhance Cardiac Interoception, Thermosensation, or Tactile Spatial Acuity

In the present study, we investigated the effect of short-term visual deprivation on discriminative touch, cardiac interoception, and thermosensation by asking 64 healthy volunteers to perform four behavioral tasks. The experimental group contained 32 subjects who were blindfolded and kept in complete darkness for 110minutes, while the control group consisted of 32 volunteers who were not blindfolded but were otherwise kept under identical experimental conditions. Both groups performed the required tasks three times: before and directly after deprivation (or control) and after an additional washout period of 40minutes, in which all participants were exposed to normal light conditions. Our results showed that short-term visual deprivation had no effect on any of the senses tested. This finding suggests that short-term visual deprivation does not modulate basic bodily senses and extends this principle beyond tactile processing to the interoceptive modalities of cardiac and thermal sensations.

Behavioral and neural correlates of social network size: The unique and common contributions of face recognition and extraversion

OBJECTIVES

Humans are inherently social creatures and can gain advantages from larger network size. Researches have shown that different cognitive and personality factors may result in individual differences of social network size (SNS). Here, we focused on whether face recognition ability and extraversion were related to SNS and the neural basis underlying the relations.

METHODS

Behaviorally, we adopted the face-inversion task, NEO personality inventory, and computerized SNS test to explore the relationships between face recognition, extraversion, and SNS. Neurally, we used resting state functional magnetic resonance imaging and fractional amplitude of low-frequency fluctuation (fALFF) analysis method to investigate the neural correlates of SNS and then revealed whether face recognition and extraversion were related to SNS relevant brain regions.

RESULTS

We found that individuals with better face recognition ability and more extraverted personality had larger size of social network. In addition, we found that SNS was positively associated with the fALFF in the ventromedial prefrontal cortex (vmPFC), right superior temporal sulcus, and precuneus. Interestingly, the fALFF in the vmPFC significantly correlated with face recognition ability.

CONCLUSIONS

Our study suggests that both face recognition and extraversion may be important correlates of SNS, and the underlying spontaneous neural substrates are partially dissociable.

Investigating the effects of transcranial alternating current stimulation on primary somatosensory cortex

Near-threshold tactile stimuli perception and somatosensory temporal discrimination threshold (STDT) are encoded in the primary somatosensory cortex (S1) and largely depend on alpha and beta S1 rhythm. Transcranial alternating current stimulation (tACS) is a non-invasive neurophysiological technique that allows cortical rhythm modulation. We investigated the effects of tACS delivered over S1 at alpha, beta, and gamma frequencies on near-threshold tactile stimuli perception and STDT, as well as phase-dependent tACS effects on near-threshold tactile stimuli perception in healthy subjects. In separate sessions, we tested the effects of different tACS montages, and tACS at the individualised S1 μ-alpha frequency peak, on STDT and near-threshold tactile stimuli perception. We found that tACS applied over S1 at alpha, beta, and gamma frequencies did not modify STDT or near-threshold tactile stimuli perception. Moreover, we did not detect effects of tACS phase or montage. Finally, tACS did not modify near-threshold tactile stimuli perception and STDT even when delivered at the individualised μ-alpha frequency peak. Our study showed that tACS does not alter near-threshold tactile stimuli or STDT, possibly due to the inability of tACS to activate deep S1 layers. Future investigations may clarify tACS effects over S1 in patients with focal dystonia, whose pathophysiology implicates increased STDT.

Functional and Structural Changes in Postherpetic Neuralgia Brain Before and Six Months After Pain Relieving

Objective

Multimodal magnetic resonance imaging (MRI) was used to detect whether 6 months after pain relieving, the structural and functional abnormalities in the brain of postherpetic neuralgia (PHN) patients are changeable.

Methods

Fifteen successfully treated PHN patients were enrolled; the brain activity and structural abnormalities were detected and compared before and 6 months after treatment. The functional parameters were evaluated with resting-state functional MRI technique, i.e., the regional homogeneity (ReHo) and fractional amplitude of low-frequency fluctuation (fALFF). Structural changes were detected with voxel-based morphometry (VBM) and diffusion kurtosis imaging (DKI).

Results

Six months after pain relieving, PHN brain showed different ReHo and fALFF values in the frontal lobe, caudate, supramarginal gyrus, anterior cingulate cortex (ACC), cuneus, middle temporal gyrus, and cerebellum. In addition, VBM intensity in the cerebellum increased; DKI values decreased in the thalamus and increased in the temporal lobe after successful treatment.

Conclusion

Six months after pain relieving, functional and structural changes exist in PHN brain. Changes in some differential areas in PHN brain, such as ACC, frontal lobe, thalamus, and temporal lobe indicate that the central plasticity may be reversible after chronic pain relieving.

Cause or effect: Altered brain and network activity in cervical dystonia is partially normalized by botulinum toxin treatment

Background

Idiopathic cervical dystonia (CD) is a chronic movement disorder characterized by impressive clinical symptoms and the lack of clear pathological findings in clinical diagnostics and imaging. At present, the injection of botulinum toxin (BNT) in dystonic muscles is an effective therapy to control motor symptoms and pain in CD.

Objectives

We hypothesized that, although it is locally injected to dystonic muscles, BNT application leads to changes in brain and network activity towards normal brain function.

Methods

Using 3 T functional MR imaging along with advanced analysis techniques (functional connectivity, Granger causality, and regional homogeneity), we aimed to characterize brain activity in CD (17 CD patients vs. 17 controls) and to uncover the effects of BNT treatment (at 6 months).

Results

In CD, we observed an increased information flow within the basal ganglia, the thalamus, and the sensorimotor cortex. In parallel, some of these structures became less responsive to regulating inputs. Furthermore, our results suggested an altered somatosensory integration. Following BNT administration, we noted a shift towards normal brain function in the CD patients, especially within the motor cortex, the somatosensory cortex, and the basal ganglia.

Conclusion

The changes in brain function and network activity in CD can be interpreted as related to the underlying cause, the effort to compensate or a mixture of both. Although BNT is applied in the last stage of the cortico-neuromuscular pathway, brain patterns are shifted towards those of healthy controls.

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we characterized brain activity in CD and the effects of BNT using 3T fMR imaging and network analysis techniques

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following treatment with botulinum toxin (BNT), abnormal brain activity patterns in primary dystonia are attenuated

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critical key regions for both the pathophysiology and BNT-induced improvement in cervical dystonia are the BG

Enhanced Central Neural Gain Compensates Acoustic Trauma-induced Cochlear Impairment, but Unlikely Correlates with Tinnitus and Hyperacusis

For successful future therapeutic strategies for tinnitus and hyperacusis, a subcategorization of both conditions on the basis of differentiated neural correlates would be of invaluable advantage. In the present study, we used our refined operant conditioning animal model to divide equally noise-exposed rats into groups with either tinnitus or hyperacusis, with neither condition, or with both conditions co-occurring simultaneously. Using click stimulus and noise burst-evoked Auditory Brainstem Responses (ABR) and Distortion Product Otoacoustic Emissions, no hearing threshold difference was observed between any of the groups. However, animals with neither tinnitus nor hyperacusis responded to noise trauma with shortened ABR wave I and IV latencies and elevated central neuronal gain (increased ABR wave IV/I amplitude ratio), which was previously assumed in most of the literature to be a neural correlate for tinnitus. In contrast, animals with tinnitus had reduced neural response gain and delayed ABR wave I and IV latencies, while animals with hyperacusis showed none of these changes. Preliminary studies, aimed at establishing comparable non-invasive objective tools for identifying tinnitus in humans and animals, confirmed reduced central gain and delayed response latency in human and animals. Moreover, the first ever resting state functional Magnetic Resonance Imaging (rs-fMRI) analyses comparing humans and rats with and without tinnitus showed reduced rs-fMRI activities in the auditory cortex in both patients and animals with tinnitus. These findings encourage further efforts to establish non-invasive diagnostic tools that can be used in humans and animals alike and give hope for differentiated classification of tinnitus and hyperacusis.

Functional network connectivity is altered in patients with upper limb somatosensory impairments in the acute phase post stroke: A cross-sectional study

Background

Aberrant functional connectivity in brain networks associated with motor impairment after stroke is well described, but little is known about the association with somatosensory impairments.

Aim

The objective of this cross-sectional observational study was to investigate the relationship between brain functional connectivity and severity of somatosensory impairments in the upper limb in the acute phase post stroke.

Methods

Nineteen first-ever stroke patients underwent resting-state functional magnetic resonance imaging (rs-fMRI) and a standardized clinical somatosensory profile assessment (exteroception and higher cortical somatosensation) in the first week post stroke. Integrity of inter- and intrahemispheric (ipsilesional and contralesional) functional connectivity of the somatosensory network was assessed between patients with severe (Em-NSA< 13/32) and mild to moderate (Em-NSA> 13/32) somatosensory impairments.

Results

Patients with severe somatosensory impairments displayed significantly lower functional connectivity indices in terms of interhemispheric (p = 0.001) and ipsilesional intrahemispheric (p = 0.035) connectivity compared to mildly to moderately impaired patients. Significant associations were found between the perceptual threshold of touch assessment and interhemispheric (r = -0.63) and ipsilesional (r = -0.51) network indices. Additional significant associations were found between the index of interhemispheric connectivity and light touch (r = 0.55) and stereognosis (r = 0.64) evaluation.

Conclusion

Patients with more severe somatosensory impairments have lower inter- and ipsilesional intrahemispheric connectivity of the somatosensory network. Lower connectivity indices are related to more impaired exteroception and higher cortical somatosensation. This study highlights the importance of network integrity in terms of inter- and ipsilesional intrahemispheric connectivity for somatosensory function. Further research is needed investigating the effect of therapy on the re-establishment of these networks.

Reduced sound-evoked and resting-state BOLD fMRI connectivity in tinnitus

The exact neurophysiological basis of chronic tinnitus, which affects 10-15% of the population, remains unknown and is controversial at many levels. It is an open question whether phantom sound perception results from increased central neural gain or not, a crucial question for any future therapeutic intervention strategies for tinnitus. We performed a comprehensive study of mild hearing-impaired participants with and without tinnitus, excluding participants with co-occurrences of hyperacusis. A right-hemisphere correlation between tinnitus loudness and auditory perceptual difficulty was observed in the tinnitus group, independent of differences in hearing thresholds. This correlation was linked to reduced and delayed sound-induced suprathreshold auditory brain responses (ABR wave V) in the tinnitus group, suggesting subsided rather than exaggerated central neural responsiveness. When anatomically predefined auditory regions of interest were analysed for altered sound-evoked BOLD fMRI activity, it became evident that subcortical and cortical auditory regions and regions involved in sound detection (posterior insula, hippocampus), responded with reduced BOLD activity in the tinnitus group, emphasizing reduced, rather than increased, central neural gain. Regarding previous findings of evoked BOLD activity being linked to positive connectivities at rest, we additionally analysed r-fcMRI responses in anatomically predefined auditory regions and regions associated with sound detection. A profound reduction in positive interhemispheric connections of homologous auditory brain regions and a decline in the positive connectivities between lower auditory brainstem regions and regions involved in sound detection (hippocampus, posterior insula) were observed in the tinnitus group. The finding went hand-in-hand with the emotional (amygdala, anterior insula) and temporofrontal/stress-regulating regions (prefrontal cortex, inferior frontal gyrus) that were no longer positively connected with auditory cortex regions in the tinnitus group but were instead positively connected to lower-level auditory brainstem regions. Delayed sound processing, reduced sound-evoked BOLD fMRI activity and altered r-fcMRI in the auditory midbrain correlated in the tinnitus group and showed right hemisphere dominance as did tinnitus loudness and perceptual difficulty. The findings suggest that reduced central neural gain in the auditory stream may lead to phantom perception through a failure to energize attentional/stress-regulating networks for contextualization of auditory-specific information. Reduced auditory-specific information flow in tinnitus has until now escaped detection in humans, as low-level auditory brain regions were previously omitted from neuroimaging studies.

TRIAL REGISTRATION

German Clinical Trials Register DRKS0006332.

Functional MRI signal fluctuations highlight altered resting brain activity in Huntington's disease

The fractional Amplitude of Low Frequency Fluctuations (fALFF) and the degree of local synchronization (Regional Homogeneity - ReHo) of resting-state BOLD signal have been suggested to map spontaneous neuronal activity and local functional connectivity, respectively. We compared voxelwise, independent of atrophy, the fALFF and ReHo patterns of 11 presymptomatic (ps-HD) and 28 symptomatic (sHD) Huntington's disease mutation carriers, with those of 40 normal volunteers, and tested their possible correlations with the motor and cognitive subscores of the Unified Huntington's Disease Rating Scale. In sHD patients, fALFF was mainly reduced bilaterally in parietal lobes (right precuneus being already affected in psHD), and in superior frontal gyri, and increased bilaterally in cerebellar lobules VI, VIII and IX, as well as in the right inferior temporal gyrus. In sHD, and to a lesser extent in psHD, ReHo was bilaterally reduced in putamina, cerebellar lobules III to VI, and superior medial frontal gyri, and increased in both psHD and sHD in fronto-basal cortices, and in the right temporal lobe. fALFF correlated inversely with cognitive scores in lobule IX of the cerebellum (mainly with total Stroop score, p < 0.0001), and in the medial portions of both thalami. These results are consistent with a reduced neuronal activity in the cortical components of the executive networks, known to be affected in Huntington's Disease, and with reduced local functional integration in subcortical and cerebellar components of the sensori-motor network. Cerebellar clusters of significant correlation of fALFF with executive function scores may be related to compensatory mechanisms.

Herpes zoster chronification to postherpetic neuralgia induces brain activity and grey matter volume change

OBJECTIVE

Herpes zoster (HZ) can develop into postherpetic neuralgia (PHN), which is a chronic neuropathic pain (NP). Whether the chronification from HZ to PHN induced brain functional or structural change is unknown and no study compared the changes of the same brains of patients who transited from HZ to PHN. We minimized individual differences and observed whether the chronification of HZ to PHN induces functional and pain duration dependent grey matter volume (GMV) change in HZ-PHN patients.

METHODS

To minimize individual differences induced error, we enrolled 12 patients with a transition from HZ to PHN. The functional and structural changes of their brains between the two states were identified with resting-state functional MRI (rs-fMRI) technique (i.e., the regional homogeneity (ReHo) and fractional aptitude of low-frequency fluctuation (fALFF) method) and the voxel based morphometry (VBM) technology respectively. The correlations between MRI parameters (i.e., ΔReHo, ΔfALFF and ΔVBM) and Δpain duration were analyzed too.

RESULTS

Compared with HZ brains, PHN brains exhibited abnormal ReHo, fALFF and VBM values in pain matrix (the frontal lobe, parietal lobe, thalamus, limbic lobe and cerebellum) as well as the occipital lobe and temporal lobe. Nevertheless, the activity of vast area of cerebellum and frontal lobe significantly increased while that of occipital lobe and limbic lobe showed apparent decrease when HZ developed to PHN. In addition, PHN brain showed decreased GMV in the frontal lobe, the parietal lobe and the occipital lobe but increased in the cerebellum and the temporal lobe. Correlation analyses showed that some of the ReHo, fALFF and VBM differential areas (such as the cerebellum posterior lobe, the thalamus extra-nuclear and the middle temporal gyrus) correlated well with Δpain duration.

CONCLUSIONS

HZ chronification induced functional and structural change in cerebellum, occipital lobe, temporal lobe, parietal lobe and limbic lobe. These changes may be correlated with HZ-PHN chronification. In addition, these changes could be reasons of refractory chronic pain of PHN.

Regionally Specific Regulation of Sensorimotor Network Connectivity Following Tactile Improvement

Correlations between inherent, task-free low-frequency fluctuations in the blood oxygenation level-dependent (BOLD) signals of the brain provide a potent tool to delineate its functional architecture in terms of intrinsic functional connectivity (iFC). Still, it remains unclear how iFC is modulated during learning. We employed whole-brain resting-state magnetic resonance imaging prior to and after training-independent repetitive sensory stimulation (rSS), which is known to induce somatosensory cortical reorganization. We investigated which areas in the sensorimotor network are susceptible to neural plasticity (i.e., where changes in functional connectivity occurred) and where iFC might be indicative of enhanced tactile performance. We hypothesized iFC to increase in those brain regions primarily receiving the afferent tactile input. Strengthened intrinsic connectivity within the sensorimotor network after rSS was found not only in the postcentral gyrus contralateral to the stimulated hand, but also in associative brain regions, where iFC correlated positively with tactile performance or learning. We also observed that rSS led to attenuation of the network at higher cortical levels, which possibly promotes facilitation of tactile discrimination. We found that resting-state BOLD fluctuations are linked to behavioral performance and sensory learning, indicating that network fluctuations at rest are predictive of behavioral changes and neuroplasticity.

Altered Behavioral and Autonomic Pain Responses in Alzheimer's Disease Are Associated with Dysfunctional Affective, Self-Reflective and Salience Network Resting-State Connectivity

While pain behaviors are increased in Alzheimer's disease (AD) patients compared to healthy seniors (HS) across multiple disease stages, autonomic responses are reduced with advancing AD. To better understand the neural mechanisms underlying these phenomena, we undertook a controlled cross-sectional study examining behavioral (Pain Assessment in Advanced Dementia, PAINAD scores) and autonomic (heart rate, HR) pain responses in 24 HS and 20 AD subjects using acute pressure stimuli. Resting-state fMRI was utilized to investigate how group connectivity differences were related to altered pain responses. Pain behaviors (slope of PAINAD score change and mean PAINAD score) were increased in patients vs.

CONTROLS

Autonomic measures (HR change intercept and mean HR change) were reduced in severe vs. mildly affected AD patients. Group functional connectivity differences associated with greater pain behavior reactivity in patients included: connectivity within a temporal limbic network (TLN) and between the TLN and ventromedial prefrontal cortex (vmPFC); between default mode network (DMN) subcomponents; between the DMN and ventral salience network (vSN). Reduced HR responses within the AD group were associated with connectivity changes within the DMN and vSN-specifically the precuneus and vmPFC. Discriminant classification indicated HR-related connectivity within the vSN to the vmPFC best distinguished AD severity. Thus, altered behavioral and autonomic pain responses in AD reflects dysfunction of networks and structures subserving affective, self-reflective, salience and autonomic regulation.

Alterations of resting-state fMRI measurements in individuals with cervical dystonia

Cervical dystonia (CD) is a neurological disorder with typical symptoms of involuntary and abnormal movements and postures of the head. CD-associated alterations of functional brain networks have not been well characterized. Previous studies of CD using resting-state functional MRI (rfMRI) are limited in two aspects: (i) the analyses were not directly focused on the functional brain network related to head movement and (ii) rfMRI measurements other than functional connectivity (FC) were not investigated. The present study examined alterations of FC in CD by capitalizing on newly identified brain regions supporting isometric head rotation (Prudente et al.: J Neurosci 35 (2015) 9163-9172). In addition to FC, which only reflects inter-regional signal synchronization, local, or intraregional alterations were also examined using rfMRI measurements of the fractional amplitude of low-frequency fluctuations and regional homogeneity (ReHo). Finally, with alterations of different rfMRI measures identified, a support vector machine (SVM) learning algorithm was implemented for group classification. The results revealed both inter- (FC) and intra-regional (ReHo) alterations extensively distributed in both cortical and subcortical structures; and common alterations of these measures were identified bilaterally in the postcentral gyrus as well as in the basal ganglia and thalamus. Of the rfMRI features examined, seven of them (four FC and three ReHo measures) survived the SVM procedure of recursive feature elimination and together provided the highest group classification accuracy of 90.6%. The present findings extend previous studies of rfMRI in CD and offer insight into the underlying pathophysiology of the disorder in relation to network dysfunction and somatosensory disturbances. Hum Brain Mapp 38:4098-4108, 2017. © 2017 Wiley Periodicals, Inc.

Pain reduction due to novel sensory-motor training in Complex Regional Pain Syndrome I – A pilot study

Background and aims

Patients suffering from Complex Regional Pain Syndrome (CRPS) of the upper limb show a changed cortical representation of the affected hand. The lip area invades the former hand area contralateral to the affected hand. This change in cortical representation is correlated to the intensity of ongoing pain in patients with CRPS. Further studies revealed that restoration of the original representation coincides with a decrease of pain. Sensory-motor training protocols can increase and/or relocate cortical somatosensory and motor representation areas of the fingers, as shown, for example, in Braille reading individuals and professional violin players. Further, there is evidence that sensory-motor discrimination training has a beneficial effect on both the intensity of pain and the mislocalization of sensory-motor cortical areas in CRPS patients. Based on these propositions, we developed a novel sensory-motor self-training paradigm for CRPS patients to use in a home-based manner.

Methods

Ten CRPS patients performed the sensory-motor training for 2 weeks. The training consists of a braille-like haptic task with different training modes (bi-manual, speed and memory training). During the training, as well as 1 week before and after, patients were asked to fill out pain diaries. Furthermore, measures of impairment were acquired at baseline and post training.

Results

Patients showed significant pain reduction after the 2 week training period. The overall disability as well as the depression scores showed a trend to improve after the 2 week training. The reduction in pain was correlated with the total amount of training performed.

Conclusions

This is a first proof of principle study of a novel sensory-motor self-training protocol to reduce pain in CRPS patients. The more consistent the patients trained the larger the pain reduction. Sensory-motor training, which can be performed on a regular basis at home might provide a novel interventional strategy to improve symptoms of CRPS.

Implications

Although a larger study needs to be conducted to confirm our findings, including long-term follow-up, the results show, that a sensory-motor home-based training is a strategy worth exploring further for the reduction of pain as well as high frequency training for patients with CRPS.

Priming Hand Motor Training with Repetitive Stimulation of the Fingertips; Performance Gain and Functional Imaging of Training Effects

BACKGROUND

Application of repetitive electrical stimulation (rES) of the fingers has been shown to improve tactile perception and sensorimotor performance in healthy individuals.

OBJECTIVE

To increase motor performance by priming the effects of active motor training (arm ability training; AAT) using rES.

METHODS

We compared the performance gain for the training increase of the averaged AAT tasks of both hands in two groups of strongly right-handed healthy volunteers. Functional Magnetic Resonance Imaging (fMRI) before and after AAT was assessed using three tasks for each hand separately: finger sequence tapping, visually guided grip force modulation, and writing. Performance during fMRI was controlled for preciseness and frequency. A total of 30 participants underwent a two-week unilateral left hand AAT, 15 participants with 20 minutes of rES priming of all fingertips of the trained hand, and 15 participants without rES priming.

RESULTS

rES-primed AAT improved the trained left-hand performance across all training tasks on average by 32.9%, non-primed AAT improved by 29.5%. This gain in AAT performance with rES priming was predominantly driven by an increased finger tapping velocity. Functional imaging showed comparable changes for both training groups over time. Across all participants, improved AAT performance was associated with a higher contralateral primary somatosensory cortex (S1) fMRI activation magnitude during the grip force modulation task.

CONCLUSIONS

This study highlights the importance of S1 for hand motor training gain. In addition, it suggests the usage of rES of the fingertips for priming active hand motor training.

The application of a mathematical model linking structural and functional connectomes in severe brain injury

Following severe injuries that result in disorders of consciousness, recovery can occur over many months or years post-injury. While post-injury synaptogenesis, axonal sprouting and functional reorganization are known to occur, the network-level processes underlying recovery are poorly understood. Here, we test a network-level functional rerouting hypothesis in recovery of patients with disorders of consciousness following severe brain injury. This hypothesis states that the brain recovers from injury by restoring normal functional connections via alternate structural pathways that circumvent impaired white matter connections. The so-called network diffusion model, which relates an individual's structural and functional connectomes by assuming that functional activation diffuses along structural pathways, is used here to capture this functional rerouting. We jointly examined functional and structural connectomes extracted from MRIs of 12 healthy and 16 brain-injured subjects. Connectome properties were quantified via graph theoretic measures and network diffusion model parameters. While a few graph metrics showed groupwise differences, they did not correlate with patients' level of consciousness as measured by the Coma Recovery Scale — Revised. There was, however, a strong and significant partial Pearson's correlation (accounting for age and years post-injury) between level of consciousness and network diffusion model propagation time (r = 0.76, p < 0.05, corrected), i.e. the time functional activation spends traversing the structural network. We concluded that functional rerouting via alternate (and less efficient) pathways leads to increases in network diffusion model propagation time. Simulations of injury and recovery in healthy connectomes confirmed these results. This work establishes the feasibility for using the network diffusion model to capture network-level mechanisms in recovery of consciousness after severe brain injury.

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A “functional rerouting” hypothesis in recovery from brain injury is tested.

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The connectome-based network diffusion model measures functional rerouting.

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Recovery in severe brain injury correlates with a network diffusion model parameter.

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Simulation in healthy connectomes independently validates the results in patients.

Altered interhemispheric resting state functional connectivity during passive hyperthermia

PURPOSE

This study examines the effect of passive hyperthermia on interhemispheric resting state functional connectivity and the correlation between interhemispheric resting state functional connectivity and efficiency of a succedent working memory task.

MATERIALS AND METHODS

We performed voxel-mirrored homotopic connectivity (VMHC) analyses on resting state MRI data and a one-back task from 14 healthy subjects in both HT (hyperthermia, 50 °C) conditions and normal control (NC, 25 °C) conditions. The group analyses of the differences for VMHC between the two conditions and the correlation analysis between the VMHC and the reaction time (RT) of the one-back task were performed with the statistical parametric mapping software package and the software REST.

RESULTS

Compared with NC conditions, HT conditions increased VMHC in the cuneus, the postcentral gyrus, and the fusiform gyrus. No region showed decreased VMHC in the HT group in comparison with the NC group. For NC conditions, negative correlations were demonstrated between RT of the one-back task and VMHC in bilateral superior temporal gyrus, and bilateral middle frontal gyrus; for HT conditions, negative correlations were demonstrated between RT and VMHC in bilateral inferior frontal gyrus, bilateral middle frontal gyrus, as well as cerebellum posterior lobe.

CONCLUSION

Passive heat stress can impact the interhemispheric information interactions at resting state and the VMHC deficits may play an important role in cognitive dysfunction.

Interrelation of resting state functional connectivity, striatal GABA levels, and cognitive control processes

Important issues for cognitive control are response selection processes, known to depend on fronto-striatal networks with recent evidence suggesting that striatal gamma-amino butyric acid (GABA) levels play an important role. Regional GABA concentrations have also been shown to modulate intrinsic connectivity, e.g. of the default mode network. However, the interrelation between striatal GABA levels, basal ganglia network (BGN) connectivity, and performance in cognitive control is elusive. In the current study, we measure striatal GABA levels using magnetic resonance spectroscopy (MRS) and resting state parameters using functional magnetic resonance imaging (fMRI). Resting state parameters include activity within the BGN, as determined by the low frequency power (LFP) within the network, and the functional connectivity between the BGN and somatomotor network (SMN). Specifically, we examine the interrelation between GABA, resting state parameters, and performance (i.e., accuracy) in conflict monitoring using a Simon task. Response control was affected by striatal GABA+ levels and activity within the BGN, especially when response selection was complicated by altered stimulus-response mappings. The data suggest that there are two mechanisms supporting response selection accuracy. One is related to resting state activity within the BGN and modulated by striatal GABA+ levels. The other is related to decreased cortico-striatal network connectivity, unrelated to the GABAergic system. The inclusion of all three factors (i.e., striatal GABA+ levels, activity within the BGN, and BGN-SMN network connectivity) explained a considerable amount of variance in task accuracy. Striatal neurobiochemical (GABA+) and parameters of the resting state BGN represent important modulators of response control.

Enhanced tactile acuity through mental states

Bodily training typically evokes behavioral and perceptual gains, enforcing neuroplastic processes and affecting neural representations. We investigated the effect on somatosensory perception of a three-day Zen meditation exercise, a purely mental intervention. Tactile spatial discrimination of the right index finger was persistently improved by only 6 hours of mental–sensory focusing on this finger, suggesting that intrinsic brain activity created by mental states can alter perception and behavior similarly to external stimulation.