Deep Brain Areas Research Articles

O17 Controlled stimulation of deep brain areas using navigated TMS with a standard coil

Introduction TMS has mainly been used- and is often believed to only be suitable for stimulation of superficial cortical areas. However, standard coils have also been used to target deeper volumes, alternatively specially designed coils have been developed for this purpose. We aimed to validate the use of standard coils for the stimulation of deep volumes. We used a system for navigated TMS where the stimulus induced electrical field strength in any location of the brain can be estimated. In the process, we also studied if the use of a midline parieto-occipital location as site for sham-stimulation could be justified. Methods Healthy adults were stimulated using a standard figure-of-eight coil in the Eximia system (Nexstim Ltd). The RMT for activation of the APB and AH muscles on the dominant side were defined. Four scalp locations were stimulated, each with three different intensities in relation to the RMTs: Three scalp locations with shortest Euclidian distance to dACC, insular and hippocampal cortices respectively, one location at the proposed site for sham-stimulation. Results All locations could be stimulated in all subjects. The intensity at the superficial cortical area under the coil, needed to produce sufficient (as compared to the RMTs) electrical field strengths at the deep locations dACC and insula were within a reasonable range (1.5–2 RMT), whereas hippocampal structures were not possible to stimulate using this set up. The sham stimulation location seems to be adequate in terms of not producing significant field strengths over motor cortices. Discussion If navigated stimulation and estimation of electrical field strengths are utilised, a standard TMS setup can be used to stimulate deep structures such as the dACC and insular cortex in a biologically reasonable fashion. A midline parieto-occipital location may be used as a locus for sham-stimulation in studies investigating motor cortex stimulation.

Fast varifocal two-photon microendoscope for imaging neuronal activity in the deep brain.

Fluorescence microendoscopy is becoming a promising approach for deep brain imaging, but the current technology for visualizing neurons on a single focal plane limits the experimental efficiency and the pursuit of three-dimensional functional neural circuit architectures. Here we present a novel fast varifocal two-photon microendoscope system equipped with a gradient refractive index (GRIN) lens and an electrically tunable lens (ETL). This microendoscope enables quasi-simultaneous imaging of the neuronal network activity of deep brain areas at multiple focal planes separated by 85-120 µm at a fast scan rate of 7.5-15 frames per second per plane, as demonstrated in calcium imaging of the mouse dorsal CA1 hippocampus and amygdala in vivo.

Quantify neuromagnetic network changes from pre-ictal to ictal activities in absence seizures

ObjectiveThe cortico–thalamo–cortical network plays a key role in childhood absence epilepsy (CAE). However, the exact interaction between the cortex and the thalamus remains incompletely understood. This study aimed to investigate the dynamic changes of frequency-dependent neural networks during the initialization of absence seizures. MethodsMagnetoencephalography data from 14 patients with CAE were recorded during and between seizures at a sampling rate of 6000Hz and analyzed in seven frequency bands. Neuromagnetic sources were volumetrically scanned with accumulated source imaging. Effective connectivity networks of the entire brain, including the cortico–thalamo–cortical network, were evaluated at the source level through Granger causality analysis. ResultsThe low-frequency (1–80Hz) activities showed significant frontal cortical and parieto–occipito–temporal junction source localization around seizures. The high-frequency (80–250Hz) oscillations showed predominant activities consistently localized in deep brain areas and medial frontal cortex. The increased cortico–thalamic effective connectivity was observed around seizures in both low- and high-frequency ranges. The direction was predominantly from the cortex to the thalamus at the early time, although the cortex that drove connectivity varied among subjects. ConclusionsThe cerebral cortex plays a key role in driving the cortico–thalamic connections at the early portion of the initialization of absence seizures. The oscillatory activities in the thalamus could be triggered by networks from various regions in the cortex. SignificanceThe dynamic changes of neural network provide evidences that absence seizures are probably resulted from cortical initialized cortico–thalamic network.

Immune-Induced Fever Is Dependent on Local But Not Generalized Prostaglandin E2 Synthesis in the Brain.

Fever occurs upon binding of prostaglandin E2 (PGE2) to EP3 receptors in the median preoptic nucleus of the hypothalamus, but the origin of the pyrogenic PGE2 has not been clearly determined. Here, using mice of both sexes, we examined the role of local versus generalized PGE2 production in the brain for the febrile response. In wild-type mice and in mice with genetic deletion of the prostaglandin synthesizing enzyme cyclooxygenase-2 in the brain endothelium, generated with an inducible CreERT2 under the Slco1c1 promoter, PGE2 levels in the CSF were only weakly related to the magnitude of the febrile response, whereas the PGE2 synthesizing capacity in the hypothalamus, as reflected in the levels of cyclooxygenase-2 mRNA, showed strong correlation with the immune-induced fever. Histological analysis showed that the deletion of cyclooxygenase-2 in brain endothelial cells occurred preferentially in small- and medium-sized vessels deep in the brain parenchyma, such as in the hypothalamus, whereas larger vessels, and particularly those close to the neocortical surface and in the meninges, were left unaffected, hence leaving PGE2 synthesis largely intact in major parts of the brain while significantly reducing it in the region critical for the febrile response. Furthermore, injection of a virus vector expressing microsomal prostaglandin E synthase-1 (mPGES-1) into the median preoptic nucleus of fever-refractive mPGES-1 knock-out mice, resulted in a temperature elevation in response to LPS. We conclude that the febrile response is dependent on local release of PGE2 onto its target neurons and not on the overall PGE2 production in the brain.SIGNIFICANCE STATEMENT By using mice with selective deletion of prostaglandin synthesis in brain endothelial cells, we demonstrate that local prostaglandin E2 (PGE2) production in deep brain areas, such as the hypothalamus, which is the site of thermoregulatory neurons, is critical for the febrile response to peripheral inflammation. In contrast, PGE2 production in other brain areas and the overall PGE2 level in the brain do not influence the febrile response. Furthermore, partly restoring the PGE2 synthesizing capacity in the anterior hypothalamus of mice lacking such capacity with a lentiviral vector resulted in a temperature elevation in response to LPS. These data imply that the febrile response is dependent on the local release of PGE2 onto its target neurons, possibly by a paracrine mechanism.

An imaging features of primary central nervous system lymphoma

Objective To explore the brain imaging features of primary central nervous system lymphoma (PCNSL). Methods A total of 32 patients with histologically confirmed PCNSL in Department of Neurosurgery, Fuzhou General Hospital of Nanjing Military Command form August 2010 to August 2016 were retrospectively analyzed for their CT and MR features. Results Fifty lesions were identified in this series of 32 patients including 18 cases (56%) with a single lesion and 14 cases (44%) with multiple lesions.PCNSLs were mostly located in the deep brain areas (76%, 38/50)such as the basal ganglia and corpus callosum, and less commonly shallow brain regions (24%, 12/50). Mild to moderate perilesional edema was seen in 38 out of 50 (76%) cases.On CT images, 44 (88%) lesions were isointense or mildly hyperintense, 6 (12%) lesions presented as mild hypointense, and 11 cases demonstrated significant enhancement with contrast. Most lesions(92%, 46/50)varied from hypointense to isointense on T1-weighted MRI and from isointense to hyperintense on T2-weighted images. Forty-five lesions (90%) presented as hyperintense on DWI.Contrast-enhanced MRI images showed obvious homogenous enhancement with various shapes such as lump-like, crack-like, butterfly-like, satellite-like, fist-like and indentation sign. Pathological studies confirmed 30 cases of diffuse large B-cell lymphoma and 2 cases of T-cell lymphoma. Conclusion Certain imagingand pathological features are associated with PCNSL, which would facilitate its diagnosis and differential diagnosis. Key words: Lymphoma; Central nervous system; Magnetic resonance imaging; Tomography, X-ray computed; Disease attributes

Controlled stimulation of deep brain areas using navigated TMS with a standard coil

Introduction: TMS has mainly been used- and is often believed to only be suitable for stimulation of superficial cortical areas. However, standard coils have also been used to target deeper volumes, alternatively specially designed coils have been developed for this purpose. We aimed to validate the use of standard coils for the stimulation of deep volumes. We used a system for navigated TMS where the stimulus induced electrical field strength in any location of the brain can be estimated. In the process, we also studied if the use of a midline parieto-occipital location as site for sham-stimulation could be justified.

Stereotaxic Adeno-associated Virus Injection and Cannula Implantation in the Dorsal Raphe Nucleus of Mice.

Optogenetic methods are now widespread in neuroscience research. Here we present a detailed surgical procedure to inject adeno-associated viruses and implant optic fiber cannulas in the dorsal raphe nucleus (DRN) of living mice. Combined with transgenic mouse lines, this protocol allows specific targeting of serotonin-producing neurons in the brain. It includes fixing a mouse in a stereotaxic frame, performing a craniotomy, virus injection and fiber implantation. Animals can be later used in behavioral experiments, combined with optogenetic manipulations (Dugué et al., 2014; Correia et al., 2017) or monitoring of neuronal activity (Matias et al., 2017). The described procedure is a fundamental step in both optogenetic and fiber photometry experiments of deep brain areas. It is optimized for serotonin neurons in the DRN, but it can be applied to any other cell type and brain region. When using transgenic mouse lines that express functionally relevant levels of optogenetic tools or reporter lines, the virus injection step can be skipped and the protocol is reduced to the cannula implantation procedure.

Quantitative neuromagnetic signatures of aberrant cortical excitability in pediatric chronic migraine.

BackgroundReports have suggested that abnormal cortical excitability may be associated with acute migraines. The present study quantitatively assesses the degree of cortical excitability in chronic migraine as compared to acute migraine and healthy controls within the pediatric population.MethodsWe investigated 27 children suffering from chronic migraine, 27 children suffering from acute migraine, and 27 healthy controls using a magnetoencephalography (MEG) system, recording at a sampling rate of 6000 Hz. All groups were age-matched and gender-matched. Neuromagnetic brain activation was elicited by a finger-tapping motor task. The spatiotemporal and spectral signatures of MEG data within a 5–2884 Hz range were analyzed using Morlet wavelet transform and beamformer analyses.ResultsCompared with controls, the chronic migraine group showed (1) significantly prolonged latencies of movement-elicited magnetic fields (MEFs) between 5 and 100 Hz; (2) increased spectral power between 100 and 200 Hz, and between 2200 and 2800 Hz; and (3) a higher likelihood of neuromagnetic activation in the ipsilateral sensorimotor cortices, supplementary motor area, and occipital regions. Compared with acute migraine group, chronic migraine patients showed (1) significantly higher odds of having strong MEFs after 150 ms; and (2) significantly higher odds of having neuromagnetic activation from the deep brain areas.ConclusionsResults demonstrated that chronic migraine subjects were not only different from the healthy controls, but also different from acute migraine subjects. The chronification of migraines may be associated with elevated cortical excitability, delayed and spread neural response, as well as aberrant activation from deep brain areas.

A silicon-based microelectrode array with a microdrive for monitoring brainstem regions of freely moving rats

Objective. Exploring neural activity behind synchronization and time locking in brain circuits is one of the most important tasks in neuroscience. Our goal was to design and characterize a microelectrode array (MEA) system specifically for obtaining in vivo extracellular recordings from three deep-brain areas of freely moving rats, simultaneously. The target areas, the deep mesencephalic reticular-, pedunculopontine tegmental-and pontine reticular nuclei are related to the regulation of sleep-wake cycles. Approach. The three targeted nuclei are collinear, therefore a single-shank MEA was designed in order to contact them. The silicon-based device was equipped with 3 × 4 recording sites, located according to the geometry of the brain regions. Furthermore, a microdrive was developed to allow fine actuation and post-implantation relocation of the probe. The probe was attached to a rigid printed circuit board, which was fastened to the microdrive. A flexible cable was designed in order to provide not only electronic connection between the probe and the amplifier system, but sufficient freedom for the movements of the probe as well. Main results. The microdrive was stable enough to allow precise electrode targeting into the tissue via a single track. The microelectrodes on the probe were suitable for recording neural activity from the three targeted brainstem areas. Significance. The system offers a robust solution to provide long-term interface between an array of precisely defined microelectrodes and deep-brain areas of a behaving rodent. The microdrive allowed us to fine-tune the probe location and easily scan through the regions of interest.

Mapping human preictal and ictal haemodynamic networks using simultaneous intracranial EEG-fMRI

Accurately characterising the brain networks involved in seizure activity may have important implications for our understanding of epilepsy. Intracranial EEG-fMRI can be used to capture focal epileptic events in humans with exquisite electrophysiological sensitivity and allows for identification of brain structures involved in this phenomenon over the entire brain. We investigated ictal BOLD networks using the simultaneous intracranial EEG-fMRI (icEEG-fMRI) in a 30 year-old male undergoing invasive presurgical evaluation with bilateral depth electrode implantations in amygdalae and hippocampi for refractory temporal lobe epilepsy. One spontaneous focal electrographic seizure was recorded. The aims of the data analysis were firstly to map BOLD changes related to the ictal activity identified on icEEG and secondly to compare different fMRI modelling approaches.Visual inspection of the icEEG showed an onset dominated by beta activity involving the right amygdala and hippocampus lasting 6.4 s (ictal onset phase), followed by gamma activity bilaterally lasting 14.8 s (late ictal phase). The fMRI data was analysed using SPM8 using two modelling approaches: firstly, purely based on the visually identified phases of the seizure and secondly, based on EEG spectral dynamics quantification. For the visual approach the two ictal phases were modelled as ‘ON’ blocks convolved with the haemodynamic response function; in addition the BOLD changes during the 30 s preceding the onset were modelled using a flexible basis set. For the quantitative fMRI modelling approach two models were evaluated: one consisting of the variations in beta and gamma bands power, thereby adding a quantitative element to the visually-derived models, and another based on principal components analysis of the entire spectrogram in attempt to reduce the bias associated with the visual appreciation of the icEEG.BOLD changes related to the visually defined ictal onset phase were revealed in the medial and lateral right temporal lobe. For the late ictal phase, the BOLD changes were remote from the SOZ and in deep brain areas (precuneus, posterior cingulate and others). The two quantitative models revealed BOLD changes involving the right hippocampus, amygdala and fusiform gyrus and in remote deep brain structures and the default mode network-related areas.In conclusion, icEEG-fMRI allowed us to reveal BOLD changes within and beyond the SOZ linked to very localised ictal fluctuations in beta and gamma activity measured in the amygdala and hippocampus. Furthermore, the BOLD changes within the SOZ structures were better captured by the quantitative models, highlighting the interest in considering seizure-related EEG fluctuations across the entire spectrum.

New approaches for the neuroimaging of gene expression.

New approaches for the neuroimaging of gene expression.

Efficacy and safety of deep transcranial magnetic stimulation for major depression: a prospective multicenter randomized controlled trial.

Major depressive disorder (MDD) is a prevalent and disabling condition, and many patients do not respond to available treatments. Deep transcranial magnetic stimulation (dTMS) is a new technology allowing non-surgical stimulation of relatively deep brain areas. This is the first double-blind randomized controlled multicenter study evaluating the efficacy and safety of dTMS in MDD. We recruited 212 MDD outpatients, aged 22-68 years, who had either failed one to four antidepressant trials or not tolerated at least two antidepressant treatments during the current episode. They were randomly assigned to monotherapy with active or sham dTMS. Twenty sessions of dTMS (18 Hz over the prefrontal cortex) were applied during 4 weeks acutely, and then biweekly for 12 weeks. Primary and secondary efficacy endpoints were the change in the Hamilton Depression Rating Scale (HDRS-21) score and response/remission rates at week 5, respectively. dTMS induced a 6.39 point improvement in HDRS-21 scores, while a 3.28 point improvement was observed in the sham group (p=0.008), resulting in a 0.76 effect size. Response and remission rates were higher in the dTMS than in the sham group (response: 38.4 vs. 21.4%, p=0.013; remission: 32.6 vs. 14.6%, p=0.005). These differences between active and sham treatment were stable during the 12-week maintenance phase. dTMS was associated with few and minor side effects apart from one seizure in a patient where a protocol violation occurred. These results suggest that dTMS constitutes a novel intervention in MDD, which is efficacious and safe in patients not responding to antidepressant medications, and whose effect remains stable over 3 months of maintenance treatment.

Endothelin-1-induced mini-stroke in the dorsal hippocampus or lateral amygdala results in deficits in learning and memory.

Functional and structural alterations in brain connectivity associated with brain ischemia have been extensively studied. However, the mechanism whereby local ischemia in deep brain region affect brain functions is still unknown. Here, we first established a mini-stroke model by infusion of endothelin-1 (ET-1) into the dorsal hippocampus or the lateral amygdala, and then investigated how these mini-infarcts affected brain functions associated with these regions. We found that rats with ET-1 infusion showed deficit in recall of contextual fear memory, but not in learning process and recall of tone fear memory. In novel object task, ET-1 in the hippocampus also eliminated object identity memory. ET-1 in the lateral amygdale affected acquisition of fear conditioning and disrupted retention of tone-conditioned fear, but did not impair retention of contextual fear. These findings suggest that ET-1-induced mini-infarct in deep brain area leads to functional deficits in learning and memory associated with these regions.

Steady-state BOLD response modulates low frequency neural oscillations.

Neural oscillations are the intrinsic characteristics of brain activities. Traditional electrophysiological techniques (e.g., the steady-state evoked potential, SSEP) have provided important insights into the mechanisms of neural oscillations in the high frequency ranges (>1 Hz). However, the neural oscillations within the low frequency ranges (<1 Hz) and deep brain areas are rarely examined. Based on the advantages of the low frequency blood oxygen level dependent (BOLD) fluctuations, we expected that the steady-state BOLD responses (SSBRs) would be elicited and modulate low frequency neural oscillations. Twenty six participants completed a simple reaction time task with the constant stimuli frequencies of 0.0625 Hz and 0.125 Hz. Power analysis and hemodynamic response function deconvolution method were used to extract SSBRs and recover neural level signals. The SSEP-like waveforms were observed at the whole brain level and at several task-related brain regions. Specifically, the harmonic phenomenon of SSBR was task-related and independent of the neurovascular coupling. These findings suggested that the SSBRs represent non-linear neural oscillations but not brain activations. In comparison with the conventional general linear model, the SSBRs provide us novel insights into the non-linear brain activities, low frequency neural oscillations, and neuroplasticity of brain training and cognitive activities.

A latent force model for describing electric propagation in deep brain stimulation: a simulation study.

Deep brain stimulation (DBS) is a neurosurgical method used to treat symptoms of movement disorders by implanting electrodes in deep brain areas. Often, the DBS modeling approaches found in the literature assume a quasi-static approximation, and discard any dynamic behavior. Nevertheless, in a real DBS system the stimulus corresponds to a wave that changes as a function of time. It is clear that DBS demands an approach that takes into account the time-varying behavior of the input stimulus. In this work, we present a novel latent force model for describing the dynamic electric propagation occurred during DBS. The performance of the proposed model was studied by simulations under different conditions. The results show that our approach is able to take into account the time variations of the source and the produced field. Moreover, by restricting our model it is possible to obtain solutions for electrostatic formulations, here experimental results were compared with the finite element method. Additionally, our approach allows a solution to the inverse problem, which is a valuable clinical application allowing the appropriate tuning of the DBS device by the expert physician.

Development of tube tetrodes and a multi-tetrode drive for deep structure electrophysiological recordings in the macaque brain

Understanding the principles that underlie information processing by neuronal networks requires simultaneous recordings from large populations of well isolated single units. Twisted wire tetrodes (TWTs), typically made by winding together four ultrathin wires (diameter: 12–25μm), are ideally suited for such population recordings. They are advantageous over single electrodes; both with respect to quality of isolation as well as the number of single units isolated and have therefore been used extensively for superficial cortical recordings. However, their limited tensile strength poses a difficulty to their use for recordings in deep brain areas. We therefore developed a method to overcome this limitation and utilize tetrodes for electrophysiological recordings in the inferotemporal cortex of rhesus macaque. We fabricated a novel, stiff tetrode called the tube tetrode (TuTe) and developed a multi-tetrode driving system for advancing up to 5 TuTes through a ball and socket chamber to precise locations in the temporal lobe of a rhesus macaque. The signal quality acquired with TuTes was comparable to conventional TWTs and allowed excellent isolation of multiple single units. We describe here a simple method for constructing TuTes, which requires only standard laboratory equipment. Further, our TuTes can be easily adapted to work with other microdrives commonly used for electrophysiological investigation in the macaque brain and produce minimal damage to the cortex along its path because of their ultrathin diameter. The tetrode development described here could allow studying neuronal populations in deep lying brain structures previously difficult to reach with the current technology.

Predictors of massive intracerebral hemorrhages in arterial hypertension

In 125 autopsies cases of massive intracerebral hemorrhages (ICH), caused by arterial hypertension (AH), retrospective clinical analysis and macro- and microscopic investigation of brain and its vascular system were conducted. There were 54 females and 71 males aged from 21 to 75 (average age is 53±11). 78% of patients suffered from essential AH, 22% – from nephrogenic AH. In 50% of cases duration of AH was over 10 years. In 62% of cases the disease was severe, with uneffective treatment, and often hypertensive cerebral crises. Over 30% of these patients suffered from strokes. In all cases brain analysis showed large ICHs (over 40 cm3), which in 84% of cases were located in cerebral hemispheres (lateral ICHs – 49%, mixed – 38%, medial – 13%), in brainstem – 9%, and in cerebellum – 7%. In 79% of cases massive penetration of blood into ventricular system was noted. Macroscopic analysis revealed local brain changes in 63% of all cases: 35% in the form of large post-haemorrhagic cysts, 44% in the form of a single or multiple lacunar infarcts (LIs). In 38% of cases with multiple LIs lacunar condition of brain was diagnosed. In 16% of these cases both cysts and multiple LIs were revealed. Local changed were found in the same deep brain areas as ICHs: more often in basal ganglions and cerebral white matter, and less often – in thalamus, pons and cerebellum. In microscopic examination morphological changes characteristic of hypertensive angioencephalopathy were detected: LIs, incomplete necrosis foci, white matter spongiosis, perivascular encephalolysis foci, criblurs, microhemorrhages. Examination of hemorrhage foci revealed structural elements of LIs located on the edge and around hemorrhage. According to our data, we suppose, that previous local and diffuse brain tissue changes, which are typical for hypertensive angioencephalopathy and lacunar condition, are predictors of massive ICHs.

A simple implantation method for flexible, multisite microelectrodes into rat brains

A long term functional and reliable coupling between neural tissue and implanted microelectrodes is the key issue in acquiring neural electrophysiological signals or therapeutically excite neural tissue. The currently often used rigid micro-electrodes are thought to cause a severe foreign body reaction resulting in a thick glial scar and consequently a poor tissue-electrode coupling in the chronic phase. We hypothesize, that this adverse effect might be remedied by probes compliant to the soft brain tissue, i.e., replacing rigid electrodes by flexible ones. Unfortunately, this flexibility comes at the price of a low stiffness, which makes targeted low trauma implantation very challenging. In this study, we demonstrate an adaptable and simple method to implant extremely flexible microprobes even to deep areas of rat's brain. Implantation of flexible probes is achieved by rod supported stereotactic insertion fostered by a hydrogel (2% agarose in PBS) cushion on the exposed skull. We were thus able to implant very flexible micro-probes in 70 rats as deep as the rodent's subthalamic nucleus. This work describes in detail the procedures and steps needed for minimal invasive, but reliable implantation of flexible probes.

An information theoretic model of information processing in the Drosophila olfactory system: the role of inhibitory neurons for system efficiency

Fruit flies (Drosophila melanogaster) rely on their olfactory system to process environmental information. This information has to be transmitted without system-relevant loss by the olfactory system to deeper brain areas for learning. Here we study the role of several parameters of the fly's olfactory system and the environment and how they influence olfactory information transmission. We have designed an abstract model of the antennal lobe, the mushroom body and the inhibitory circuitry. Mutual information between the olfactory environment, simulated in terms of different odor concentrations, and a sub-population of intrinsic mushroom body neurons (Kenyon cells) was calculated to quantify the efficiency of information transmission. With this method we study, on the one hand, the effect of different connectivity rates between olfactory projection neurons and firing thresholds of Kenyon cells. On the other hand, we analyze the influence of inhibition on mutual information between environment and mushroom body. Our simulations show an expected linear relation between the connectivity rate between the antennal lobe and the mushroom body and firing threshold of the Kenyon cells to obtain maximum mutual information for both low and high odor concentrations. However, contradicting all-day experiences, high odor concentrations cause a drastic, and unrealistic, decrease in mutual information for all connectivity rates compared to low concentration. But when inhibition on the mushroom body is included, mutual information remains at high levels independent of other system parameters. This finding points to a pivotal role of inhibition in fly information processing without which the system efficiency will be substantially reduced.

Preliminary application of intraoperative magnetic resonance imaging combined with neuronavigation in glioma surgery

Objective To review preliminary experiences in glioma resection in an integrated operating room equipped with 1.5T intraoperative magnetic resonance imaging (iMRI) and neuronavigation. Methods Clinical data of 49 cases of gliomas located in deep brain or eloquent areas were retrospectively analyzed, focusing on the influence of iMRI and neuronavigation on the surgical strategy, the extent of resection and preservation outcomes of patients' neural function. Results iMRI scan were performed in each case for 1 to 3 times, averaging (1.57 ± 0.68) times. First iMRI of 49 cases revealed that 17 cases of gliomas were completely removed, and 32 cases had different residual tumors, indicating that iMRI frequently affected or modified the surgical strategy of glioma (32/49, 65.31%). Tumors in 9 cases were not completely removed because diffusion tensor imaging (DTI) navigation and intraoperative neurophysiological monitoring found that the lesions were close to the eloquent areas or deep anatomical structures. Twenty three patients with residual tumors underwent further resection guided by iMRI (23/49, 46.94% ). As a result, the complete resection rate of tumors increased from 34.69% (17/49) to 81.63% (40/49). Compared to preoperative situation, follow⁃up study 6 months after the operation found that neural function of 19 cases were improved, and another 30 cases were equal or close to preoperative level without any tumor progression. Conclusion The integration of 1.5T iMRI and neuronavigation helps to maximize the safe removal of the tumors and minimize dysfunction, increasing the accuracy and safety of glioma surgery. DOI：10.3969/j.issn.1672⁃6731.2012.06.008