Do astrocytes respond to light, sound, or electrical stimulation?

Astrocytes are not only the most populous cell type in the human brain, but they also have the most extensive and diverse sets of connections, across synapses, axons, blood vessels, as well as having their own internal network. Unsurprisingly, they are associated with many brain functions; from the synaptic transmission to energy metabolism and fluid homeostasis, and from cerebral blood flow and blood-brain barrier maintenance to neuroprotection, memory, immune defenses and detoxification, sleep, and early development. And yet, notwithstanding these key roles, so many current therapeutic approaches to a range of brain disorders have largely neglected their potential involvement. In this review, we consider the role of astrocytes in three brain therapies; two are emerging treatments (photobiomodulation and ultrasound), while the other is well-established (deep brain stimulation). In essence, we explore the issue of whether external sources, such as light, sound, or electricity, can influence the function of astrocytes, as they do neurons. We find that, when taken all together, each of these external sources can influence many, if not, all of the functions associated with astrocytes. These include influencing neuronal activity, prompting neuroprotection, reducing inflammation (astrogliosis) and potentially increasing cerebral blood flow and stimulating the glymphatic system. We suggest that astrocytes, just like neurons, can respond positively to each of these external applications and that their activation could each impart many beneficial outcomes on brain function; they are likely to be key players underpinning the mechanisms behind many therapeutic strategies.

Remote photobiomodulation targeted at the abdomen or legs provides effective neuroprotection against parkinsonian MPTP insult.

Photobiomodulation (PBM)-the irradiation of tissue with low-intensity light-mitigates neuropathology in rodent models of Parkinson's disease (PD) when targeted at the head ('transcranial PBM'). In humans, however, attenuation of light energy by the scalp and skull necessitates a different approach. We have reported that targeting PBM at the body also protects the brain by a mechanism that spreads from the irradiated tissue ('remote PBM'), although the optimal peripheral tissue target for remote PBM is currently unclear. This study compared the neuroprotective efficacy of remote PBM targeting the abdomen or leg with transcranial PBM, in mouse and non-human primate models of PD. In a pilot study, the neurotoxin MPTP was used to induce PD in non-human primates; PBM (670 nm, 50 mW/cm2 , 6 min/day) of the abdomen (n = 1) was associated with fewer clinical signs and more surviving midbrain dopaminergic cells relative to MPTP-injected non-human primates not treated with PBM. Validation studies in MPTP-injected mice (n = 10 per group) revealed a significant rescue of midbrain dopaminergic cells in mice receiving PBM to the abdomen (~80%, p < .0001) or legs (~80%, p < .0001), with comparable rescue of axonal terminals in the striatum. Strikingly, this degree of neuroprotection was at least as, if not more, pronounced than that achieved with transcranial PBM. These findings confirm that remote PBM provides neuroprotection against MPTP-induced destruction of the key circuitry underlying PD, with both the abdomen and legs serving as viable remote targets. This should provide the impetus for a comprehensive investigation of remote PBM-induced neuroprotection in other models of PD and, ultimately, human patients.

Unsupervised adaptation of an ECoG based brain-computer interface using neural correlates of task performance.

Brain-computer interfaces (BCIs) translate brain signals into commands to external effectors, and mainly target severely disabled users. The usability of BCIs may be improved by reducing their major constraints, such as the necessity for special training sessions to initially calibrate and later keep up to date the neural signal decoders. In this study, we show that it is possible to train and update BCI decoders during free use of motor BCIs. In addition to the neural signal decoder controlling effectors (control decoder), one more classifier is proposed to detect neural correlates of BCI motor task performances (MTP). MTP decoders reveal whether the actions performed by BCI effectors matched the user's intentions. The combined outputs of MTP and control decoders allow forming training datasets to update the control decoder online and in real time during free use of BCIs. The usability of the proposed auto-adaptive BCI (aaBCI) is demonstrated for two principle BCIs paradigms: with discrete outputs (4 classes BCI, virtual 4-limb exoskeleton), and with continuous outputs (cursor 2D control). The proof of concept was performed in an online simulation study using an ECoG dataset collected from a tetraplegic during a BCI clinical trial. The control decoder reached a multiclass area under the ROC curve of 0.7404 using aaBCI, compared to a chance level of 0.5173 and to 0.8187 for supervised training for the multiclass BCI, and a cosine similarity of 0.1211 using aaBCI, compared to a chance level of 0.0036 and to 0.2002 for supervised training for the continuous BCI.

The effect of photobiomodulation on the brain during wakefulness and sleep.

Over the last seventy years or so, many previous studies have shown that photobiomodulation, the use of red to near infrared light on body tissues, can improve central and peripheral neuronal function and survival in both health and in disease. These improvements are thought to arise principally from an impact of photobiomodulation on mitochondrial and non-mitochondrial mechanisms in a range of different cell types, including neurones. This impact has downstream effects on many stimulatory and protective genes. An often-neglected feature of nearly all of these improvements is that they have been induced during the state of wakefulness. Recent studies have shown that when applied during the state of sleep, photobiomodulation can also be of benefit, but in a different way, by improving the flow of cerebrospinal fluid and the clearance of toxic waste-products from the brain. In this review, we consider the potential differential effects of photobiomodulation dependent on the state of arousal. We speculate that the effects of photobiomodulation is on different cells and systems depending on whether it is applied during wakefulness or sleep, that it may follow a circadian rhythm. We speculate further that the arousal-dependent photobiomodulation effects are mediated principally through a biophoton - ultra-weak light emission - network of communication and repair across the brain.

An adaptive closed-loop ECoG decoder for long-term and stable bimanual control of an exoskeleton by a tetraplegic.

Objective.The article aims at addressing 2 challenges to step motor brain-computer interface (BCI) out of laboratories: asynchronous control of complex bimanual effectors with large numbers of degrees of freedom, using chronic and safe recorders, and the decoding performance stability over time without frequent decoder recalibration.Approach.Closed-loop adaptive/incremental decoder training is one strategy to create a model stable over time. Adaptive decoders update their parameters with new incoming data, optimizing the model parameters in real time. It allows cross-session training with multiple recording conditions during closed loop BCI experiments. In the article, an adaptive tensor-based recursive exponentially weighted Markov-switching multi-linear model (REW-MSLM) decoder is proposed. REW-MSLM uses a mixture of expert (ME) architecture, mixing or switching independent decoders (experts) according to the probability estimated by a 'gating' model. A Hidden Markov model approach is employed as gating model to improve the decoding robustness and to provide strong idle state support. The ME architecture fits the multi-limb paradigm associating an expert to a particular limb or action.Main results.Asynchronous control of an exoskeleton by a tetraplegic patient using a chronically implanted epidural electrocorticography (EpiCoG) recorder is reported. The stable over a period of six months (without decoder recalibration) eight-dimensional alternative bimanual control of the exoskeleton and its virtual avatar is demonstrated.Significance.Based on the long-term (>36 months) chronic bilateral EpiCoG recordings in a tetraplegic (ClinicalTrials.gov, NCT02550522), we addressed the poorly explored field of asynchronous bimanual BCI. The new decoder was designed to meet to several challenges: the high-dimensional control of a complex effector in experiments closer to real-world behavior (point-to-point pursuit versus conventional center-out tasks), with the ability of the BCI system to act as a stand-alone device switching between idle and control states, and a stable performance over a long period of time without decoder recalibration.

Exploring the Use of Intracranial and Extracranial (Remote) Photobiomodulation Devices in Parkinson's Disease: A Comparison of Direct and Indirect Systemic Stimulations.

In recent times, photobiomodulation has been shown to be beneficial in animal models of Parkinson's disease, improving locomotive behavior and being neuroprotective. Early observations in people with Parkinson's disease have been positive also, with improvements in the non-motor symptoms of the disease being evident most consistently. Although the precise mechanisms behind these improvements are not clear, two have been proposed: direct stimulation, where light reaches and acts directly on the distressed neurons, and remote stimulation, where light influences cells and/or molecules that provide systemic protection, thereby acting indirectly on distressed neurons. In relation to Parkinson's disease, given that the major zone of pathology lies deep in the brain and that light from an extracranial or external photobiomodulation device would not reach these vulnerable regions, stimulating the distressed neurons directly would require intracranial delivery of light using a device implanted close to the vulnerable regions. For indirect systemic stimulation, photobiomodulation could be applied to either the head and scalp, using a transcranial helmet, or to a more remote body part (e.g., abdomen, leg). In this review, we discuss the evidence for both the direct and indirect neuroprotective effects of photobiomodulation in Parkinson's disease and propose that both types of treatment modality, when working together using both intracranial and extracranial devices, provide the best therapeutic option.

The Riemannian spatial pattern method: mapping and clustering movement imagery using Riemannian geometry.

Objective. Over the last decade, Riemannian geometry has shown promising results for motor imagery classification. However, extracting the underlying spatial features is not as straightforward as for applying common spatial pattern (CSP) filtering prior to classification. In this article, we propose a simple way to extract the spatial patterns obtained from Riemannian classification: the Riemannian spatial pattern (RSP) method, which is based on the backward channel selection procedure.Approach. The RSP method was compared to the CSP approach on ECoG data obtained from a quadriplegic patient while performing imagined movements of arm articulations and fingers.Main results.Similar results were found between the RSP and CSP methods for mapping each motor imagery task with activations following the classical somatotopic organization. Clustering obtained by pairwise comparisons of imagined motor movements however, revealed higher differentiation for the RSP method compared to the CSP approach. Importantly, the RSP approach could provide a precise comparison of the imagined finger flexions which added supplementary information to the mapping results.Significance.Our new RSP method illustrates the interest of the Riemannian framework in the spatial domain and as such offers new avenues for the neuroimaging community. This study is part of an ongoing clinical trial registered with ClinicalTrials.gov, NCT02550522.

Deep brain stimulation of the subthalamic nucleus in obsessive-compulsives disorders: long-term follow-up of an open, prospective, observational cohort.

BACKGROUND: Obsessive-compulsive disorder (OCD) is a major cause of disability in western country and responsible for severe impairment of quality of life. About 10% of patients present with severe OCD symptoms and require innovative treatment such as deep brain stimulation (DBS). Among possible targets, the non-motor subthalamic nucleus (STN) is a key node of the basal ganglia circuitry, strongly connected to limbic cortical areas known to be involved in OCD. METHOD: We analysed, in a prospective, observational, monocentric, open label cohort, the effect of chronic non-motor STN-DBS in 19 patients with treatment-resistant OCD consecutively operated in a single centre. Severity of OCD was evaluated using the Yale and Brown Obsessive-Compulsive Scale (YBOCS). YBOCS scores at 6, 12 and 24 months postoperatively were compared with baseline. Responders were defined by >35% improvement of YBOCS scores. Global Assessment Functioning (GAF) scale was used to evaluate the impact of improvement. RESULTS: At a 24-month follow-up, the mean YBOCS score improved by 53.4% from 33.3±3.5 to 15.8±9.1 (95% CI 11.2-20.4; p<0.0001). Fourteen out of 19 patients were considered as responders, 5 out of 19 being improved over 75% and 10 out of 19 over 50%. GAF scale improved by 92% from 34.1±3.9 to 66.4±18.8 (95% CI 56.7-76.1; p=0.0003). The most frequent adverse events consisted of transient DBS-induced hypomania and anxiety. CONCLUSION: Chronic DBS of the non-motor STN is an effective and relatively safe procedure to treat severe OCD resistant to conventional management.

Dementia and subthalamic deep brain stimulation in Parkinson disease: A long-term overview.

OBJECTIVES: To assess the prevalence and the cumulative incidence of dementia at short-, medium- and long-term follow-up after deep brain stimulation (DBS) of the subthalamic nucleus (STN) (at 1, 5, and 10 years) and to evaluate potential risk factors for postoperative dementia. METHODS: The presence of dementia (according to the DSM-V) was retrospectively evaluated at each postoperative follow-up in patients with Parkinson disease (PD) who underwent bilateral STN-DBS. Preoperative and perioperative risk factors of developing postoperative dementia were also investigated. Demographic data, disease features, medications, comorbidities, nonmotor symptoms, PD motor scales, neuropsychological scales at baseline, and perioperative complications were collected for each patient. RESULTS: A total of 175 patients were included, and 104 were available at 10-year follow-up. Dementia prevalence was 2.3% at 1 year, 8.5% at 5 years, and 29.8% at 10 years. Dementia cumulative incidence at 1, 5, and 10 years was 2.3%, 10.9%, and 25.7%, respectively. The corresponding dementia incidence rate was 35.6 per 1,000 person-years. Male sex, higher age, hallucinations, lower frontal score at baseline, and perioperative cerebral hemorrhage were predictors of dementia. CONCLUSIONS: In patients with PD with longstanding STN-DBS, dementia prevalence and incidence are not higher than those reported in the general PD population. Except for few patients with perioperative cerebral hemorrhage, STN-DBS is cognitively safe, and does not provide dementia risk factors in addition to those reported for PD itself. Identification of dementia predictors in this population may improve patient selection and information concerning the risk of poor cognitive outcome.

Space-Time-Frequency Multi-Sensor Analysis for Motor Cortex Localization Using Magnetoencephalography.

Brain source imaging and time frequency mapping (TFM) are commonly used in magneto/electro encephalography (M/EEG) imaging. However, these methods suffer from important limitations. Source imaging is based on an ill-posed inverse problem leading to instability of source localization solutions, has a limited capacity to localize high frequency oscillations and loses its robustness for induced responses (ill-defined trigger). The drawback of TFM is that it involves independent analysis of signals from a number of frequency bands, and from co-localized sensors. In the present article, a regression-based multi-sensor space-time-frequency analysis (MSA) approach, which integrates co-localized sensors and/or multi-frequency information, is proposed. To estimate task-specific brain activations, MSA uses cross-validated, shifted, multiple Pearson correlation, calculated from the time-frequency transformed brain signal and the binary signal of stimuli. The results are projected from the sensor space onto the cortical surface. To assess MSA performance, the proposed method was compared to the weighted minimum norm estimate (wMNE) source imaging method, in terms of spatial selectivity and robustness against an ill-defined trigger. Magnetoencephalography (MEG) recordings were performed in fourteen subjects during two motor tasks: finger tapping and elbow flexion/extension. In particular, our results show that the MSA approach provides good localization performance when compared to wMNE and statistically significant improvement of robustness against ill-defined trigger.

An exoskeleton controlled by an epidural wireless brain-machine interface in a tetraplegic patient: a proof-of-concept demonstration.

BACKGROUND: Approximately 20% of traumatic cervical spinal cord injuries result in tetraplegia. Neuroprosthetics are being developed to manage this condition and thus improve the lives of patients. We aimed to test the feasibility of a semi-invasive technique that uses brain signals to drive an exoskeleton. METHODS: We recruited two participants at Clinatec research centre, associated with Grenoble University Hospital, Grenoble, France, into our ongoing clinical trial. Inclusion criteria were age 18-45 years, stability of neurological deficits, a need for additional mobility expressed by the patient, ambulatory or hospitalised monitoring, registration in the French social security system, and signed informed consent. The exclusion criteria were previous brain surgery, anticoagulant treatments, neuropsychological sequelae, depression, substance dependence or misuse, and contraindications to magnetoencephalography (MEG), EEG, or MRI. One participant was excluded because of a technical problem with the implants. The remaining participant was a 28-year-old man, who had tetraplegia following a C4-C5 spinal cord injury. Two bilateral wireless epidural recorders, each with 64 electrodes, were implanted over the upper limb sensorimotor areas of the brain. Epidural electrocorticographic (ECoG) signals were processed online by an adaptive decoding algorithm to send commands to effectors (virtual avatar or exoskeleton). Throughout the 24 months of the study, the patient did various mental tasks to progressively increase the number of degrees of freedom. FINDINGS: Between June 12, 2017, and July 21, 2019, the patient cortically controlled a programme that simulated walking and made bimanual, multi-joint, upper-limb movements with eight degrees of freedom during various reach-and-touch tasks and wrist rotations, using a virtual avatar at home (64·0% [SD 5·1] success) or an exoskeleton in the laboratory (70·9% [11·6] success). Compared with microelectrodes, epidural ECoG is semi-invasive and has similar efficiency. The decoding models were reusable for up to approximately 7 weeks without recalibration. INTERPRETATION: These results showed long-term (24-month) activation of a four-limb neuroprosthetic exoskeleton by a complete brain-machine interface system using continuous, online epidural ECoG to decode brain activity in a tetraplegic patient. Up to eight degrees of freedom could be simultaneously controlled using a unique model, which was reusable without recalibration for up to about 7 weeks. FUNDING: French Atomic Energy Commission, French Ministry of Health, Edmond J Safra Philanthropic Foundation, Fondation Motrice, Fondation Nanosciences, Institut Carnot, Fonds de Dotation Clinatec.

Long-Term Sheep Implantation of WIMAGINE®, a Wireless 64-Channel Electrocorticogram Recorder.

This article deals with the long-term preclinical validation of WIMAGINE® (Wireless Implantable Multi-channel Acquisition system for Generic Interface with Neurons), a 64-channel wireless implantable recorder that measures the electrical activity at the cortical surface (electrocorticography, ECoG). The WIMAGINE® implant was designed for chronic wireless neuronal signal acquisition, to be used e.g., as an intracranial Brain-Computer Interface (BCI) for severely motor-impaired patients. Due to the size and shape of WIMAGINE®, sheep appeared to be the best animal model on which to carry out long-term in vivo validation. The devices were implanted in two sheep for a follow-up period of 10 months, including idle state cortical recordings and Somato-Sensory Evoked Potential (SSEP) sessions. ECoG and SSEP demonstrated relatively stable behavior during the 10-month observation period. Information recorded from the SensoriMotor Cortex (SMC) showed an SSEP phase reversal, indicating the cortical site of the sensorimotor activity was retained after 10 months of contact. Based on weekly recordings of raw ECoG signals, the effective bandwidth was in the range of 230 Hz for both animals and remarkably stable over time, meaning preservation of the high frequency bands valuable for decoding of the brain activity using BCIs. The power spectral density (in dB/Hz), on a log scale, was of the order of 2.2, -4.5 and -18 for the frequency bands (10-40), (40-100), and (100-200) Hz, respectively. The outcome of this preclinical work is the first long-term in vivo validation of the WIMAGINE® implant, highlighting its ability to record the brain electrical activity through the dura mater and to send wireless digitized data to the external base station. Apart from local adhesion of the dura to the skull, the neurosurgeon did not face any difficulty in the implantation of the WIMAGINE® device and post-mortem analysis of the brain revealed no side effect related to the implantation. We also report on the reliability of the system; including the implantable device, the antennas module and the external base station.

Suicide and suicide attempts after subthalamic nucleus stimulation in Parkinson disease.

OBJECTIVE: To determine the postoperative attempted and completed suicide rates after subthalamic nucleus deep brain stimulation (STN-DBS) in a single-center cohort and to determine factors associated with attempted and completed suicide. METHODS: We retrospectively included all patients with Parkinson disease (PD) who underwent bilateral STN-DBS surgery at the Grenoble University Hospital between 1993 and 2016. For each patient who committed or attempted suicide, 2 patients with PD with STN-DBS without any suicidal behaviors were matched for age (±1 year), sex, and year of surgery (±2 years). Clinical data were collected from medical records. Detailed preoperative and postoperative neuropsychological evaluations, including frontal and Beck Depression Inventory (BDI) scores, were gathered. RESULTS: A total of 534 patients with PD were included. Completed and attempted suicide percentages were 0.75% (4 of 534) and 4.11% (22 of 534), respectively. The observed suicide rate in the first postoperative year (187.20 of 100,000 per year, 1 of 534) was higher than the expected National Observatory on Suicide Risks rate adjusted for age and sex (standardized mortality ratio 8.1). This rate remained similar over the second and third postoperative years. In a comparison of the 26 patients completing/attempting suicide and the 52 controls, the first group showed more frequent history of suicidal ideation/suicide attempts and psychotic symptoms, higher percentage of family psychiatric history, higher psychiatric medication use, and higher preoperative frontal and BDI scores on neuropsychological evaluations. CONCLUSIONS: Suicide behaviors can occur after STN-DBS, especially during the first 3 years. A careful multidisciplinary assessment and long-term follow-up are recommended to recognize and treat this potentially preventable risk for mortality.

Deep Brain Stimulation of the Pedunculopontine Nucleus Area in Parkinson Disease: MRI-Based Anatomoclinical Correlations and Optimal Target.

BACKGROUND: Experimental studies led to testing of deep brain stimulation (DBS) of the pedunculopontine nucleus (PPN) as a new therapy to treat freezing of gait (FOG) in Parkinson disease (PD). Despite promising initial results fueling a growing interest toward that approach, several clinical studies reported heterogeneity in patient responses. Variation in the position of electrode contacts within the rostral brainstem likely contributes to such heterogeneity. OBJECTIVE: To provide anatomoclinical correlations of the effect of DBS of the caudal mesencephalic reticular formation (cMRF) including the PPN to treat FOG by comparing the normalized positions of the active contacts among a series of 11 patients at 1- and 2-yr follow-up and to provide an optimal target through an open-label study. METHODS: We defined a brainstem normalized coordinate system in relation to the pontomesencephalic junction. Clinical evaluations were based on a composite score using objective motor measurements and questionnaires allowing classification of patients as "bad responders" (2 patients), "mild responders" (1 patient) and "good responders" (6 patients). Two patients, whose long-term evaluation could not be completed, were excluded from the analysis. RESULTS: Most effective DBS electrode contacts to treat FOG in PD patients were located in the posterior part of the cMRF (encompassing the posterior PPN and cuneiform nucleus) at the level of the pontomesencephalic junction. CONCLUSION: In the present exploratory study, we performed an anatomoclinical analysis using a new coordinate system adapted to the brainstem in 9 patients who underwent PPN area DBS. We propose an optimal DBS target that allows a safe and efficient electrode implantation in the cMRF.

Evidence for encephalopsin immunoreactivity in interneurones and striosomes of the monkey striatum.

In this study, we examined the cellular distribution of encephalopsin (opsin 3; OPN3) expression in the striatum of non-human primates. In addition, because of our long standing interest in Parkinson's disease and neuroprotection, we examined whether parkinsonian (MPTP; 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) insult and/or photobiomodulation (670 nm) had any impact on encephalopsin expression in this key area of the basal ganglia. Striatal sections of control naïve monkeys, together with those that were either MPTP- and/or photobiomodulation-treated were processed for immunohistochemistry. Our results revealed two populations of striatal interneurones that expressed encephalopsin, one of which was the giant, choline acetyltransferase-containing, cholinergic interneurones. The other population had smaller somata and was not cholinergic. Neither cell group expressed the calcium-binding protein, parvalbumin. There was also rich encephalopsin expression in a set of terminals forming striosome-like patches across the striatum. Finally, we found that neither parkinsonian (MPTP) insult nor photobiomodulation had any effect on encephalopsin expression in the striatum. In summary, our results revealed an extensive network of encephalopsin containing structures throughout the striatum, indicating that external light is in a position to influence a range of striatal activities at both the interneurone and striosome level.

A Long-Term BCI Study With ECoG Recordings in Freely Moving Rats.

BACKGROUND: Brain Computer Interface (BCI) studies are performed in an increasing number of applications. Questions are raised about electrodes, data processing and effectors. Experiments are needed to solve these issues. OBJECTIVE: To develop a simple BCI set-up to easier studies for improving the mathematical tools to process the ECoG to control an effector. METHOD: We designed a simple BCI using transcranial electrodes (17 screws, three mechanically linked to create a common reference, 14 used as recording electrodes) to record Electro-Cortico-Graphic (ECoG) neuronal activities in rodents. The data processing is based on an online self-paced non-supervised (asynchronous) BCI paradigm. N-way partial least squares algorithm together with Continuous Wavelet Transformation of ECoG recordings detect signatures related to motor activities. Signature detection in freely moving rats may activate external effectors during a behavioral task, which involved pushing a lever to obtain a reward. RESULTS: After routine training, we showed that peak brain activity preceding a lever push (LP) to obtain food reward was located mostly in the cerebellar cortex with a higher correlation coefficient, suggesting a strong postural component and also in the occipital cerebral cortex. Analysis of brain activities provided a stable signature in the high gamma band (∼180Hz) occurring within 1500 msec before the lever push approximately around -400 msec to -500 msec. Detection of the signature from a single cerebellar cortical electrode triggers the effector with high efficiency (68% Offline and 30% Online) and rare false positives per minute in sessions about 30 minutes and up to one hour (∼2 online and offline). CONCLUSIONS: In summary, our results are original as compared to the rest of the literature, which involves rarely rodents, a simple BCI set-up has been developed in rats, the data show for the first time long-term, up to one year, unsupervised online control of an effector.

Erratum to: Greater occipital nerve infiltration under MR guidance: Feasibility study and preliminary results.

The original version of this article, published on 12 July 2017, unfortunately contained mistakes. The following corrections have therefore been made in the original.

Greater occipital nerve infiltration under MR guidance: Feasibility study and preliminary results.

OBJECTIVE: To assess the feasibility of greater occipital nerve (GON) intermediate site infiltration with MRI guidance. METHODS: Eleven consecutive patients suffering from chronic refractory cranio-facial pain who underwent 16 GON infiltrations were included in this prospective study. All of the procedures were performed on an outpatient basis in the research facility of our institution, with a 1.5 T scanner. The fatty space between inferior obliquus and semispinalis muscles at C1-C2 level was defined as the target. Technical success was defined as the ability to accurately inject the products at the target, assessed by post-procedure axial and sagittal proton density-weighted sequences. Clinical success was defined as a 50% pain decrease at 1 month. RESULTS: Technical success was 100%. GON was depicted in 6/11 cases on planning MRI sequences. Mean duration of procedure was 22.5 min (range 16-41). Clinical success was obtained in 7/11 included patients (63.6%) with a mean self-reported improvement of 78%. CONCLUSION: Interventional MR-guidance for GON infiltration is a feasible technique offering similar results to an already established effective procedure. It may appear as a useful tool in specific populations, such as young patients and repeat infiltrations, and should be considered in these settings. KEY POINTS: • MR guidance for GON infiltration is a feasible technique. • Preliminary results are in agreement with other guidance modalities. • MR guidance may be seen as a useful tool in specific populations. • Specific populations include young patients and repeat infiltrations. • Target patients may also include patients with potentionally previously reported complications (torticollis).