Maarten Bot

Tremor-specific neuronal oscillation pattern in dorsal subthalamic nucleus of parkinsonian patients.

BACKGROUND Subthalamic nucleus (STN) deep brain stimulation effectively improves parkinsonian symptoms. It is hypothesized that distinct functional territories with different neurophysiologic activity within the STN relate to different symptoms. OBJECTIVE The aim of the study was to identify distinctive characteristics of STN neuronal activity related to tremor by directly comparing tremor sides with no-tremor sides. In addition, we studied the spatial pattern of frequency distributions within the STN in more detail. METHODS We analyzed intraoperative STN single/multiunit recordings from 33 tremor sides and 23 no-tremor sides. STN tracks were normalized to a length of 1 and subdivided into eight successive layers. The power spectral density was split into six frequency bands: theta (3-8 Hz), alpha (9-12 Hz), lower beta (13-20 Hz), upper beta (21-30 Hz), lower gamma (31-59 Hz), and upper gamma (60-100 Hz). RESULTS Tremor sides presented predominant theta frequency oscillations in the most dorsal layers of the STN, whereas in no-tremor sides beta frequencies predominated. Oscillatory activity was stronger in the dorsal STN than in the ventral, and this pattern was specific for frequencies in the theta, alpha, and beta bands, but not in the gamma bands. CONCLUSIONS Our study supports the hypothesis that the presence of tremor is associated with a distinctive neuronal oscillations pattern. In particular, we demonstrate the specificity of the association of theta frequencies in the dorsal STN with tremor. Identification of symptom-specific characteristics of intraoperative microrecordings in the STN may lead to refinement of targeting for each patient, tailored to the specific clinical presentation.

Accuracy of Intraoperative Computed Tomography during Deep Brain Stimulation Procedures: Comparison with Postoperative Magnetic Resonance Imaging

Objective: To determine the accuracy of intraoperative computed tomography (iCT) in localizing deep brain stimulation (DBS) electrodes by comparing this modality with postoperative magnetic resonance imaging (MRI). Background: Optimal lead placement is a critical factor for the outcome of DBS procedures and preferably confirmed during surgery. iCT offers 3-dimensional verification of both microelectrode and lead location during DBS surgery. However, accurate electrode representation on iCT has not been extensively studied. Methods: DBS surgery was performed using the Leksell stereotactic G frame. Stereotactic coordinates of 52 DBS leads were determined on both iCT and postoperative MRI and compared with intended final target coordinates. The resulting absolute differences in X (medial-lateral), Y (anterior-posterior), and Z (dorsal-ventral) coordinates (ΔX, ΔY, and ΔZ) for both modalities were then used to calculate the euclidean distance. Results: Euclidean distances were 2.7 ± 1.1 and 2.5 ± 1.2 mm for MRI and iCT, respectively (p = 0.2). Conclusion: Postoperative MRI and iCT show equivalent DBS lead representation. Intraoperative localization of both microelectrode and DBS lead in stereotactic space enables direct adjustments. Verification of lead placement with postoperative MRI, considered to be the gold standard, is unnecessary.

Intraoperative x-ray to measure distance between DBS leads: A reliability study†‡

Many factors can jeopardize the accuracy of deep brain stimulation (DBS) lead placement. Confirmation of lead placement while the patient is still in the operating room would be advantageous. Intraoperative MRI or CT can identify placement errors, but these modalities can be cost‐ or time prohibitive. Intraoperative fluoroscopy may give information on the accuracy of the Y coordinate, but the accuracy of the X coordinate usually cannot be confirmed. When an object of known dimensions is present in the brain, such as a unilateral DBS lead, its dimensions can be used to calculate unknown distances. The objective of this study was to determine if intraoperative AP skull x‐ray accurately predicts the distance between DBS electrodes using postoperative MRI as the gold standard.

Pallidotomy suppresses beta power in the subthalamic nucleus of Parkinson’s disease patients

Parkinsonian patients, who have had a unilateral pallidotomy, may require bilateral deep brain stimulation of the subthalamic nucleus (STN), due to disease progression. The current model of the basal ganglia circuitry does not predict a direct effect of pallidotomy on the neuronal activity of the ipsilateral STN. To date, only three studies have investigated the effect of pallidotomy on overall activity of the STN or neuronal firing rate, but not on the spectral content of the neuronal oscillatory activity. Moreover, none of these studies attempted to differentiate the effects on the dorsal (sensory‐motor) and ventral (associative‐limbic) parts of the STN. We studied the effect of pallidotomy on spectral power in six frequency bands in the STN ipsilateral and contralateral to pallidotomy from seven patients and in 60 control nuclei of patients without prior functional neurosurgery, and investigated whether this effect is different on the dorsal and ventral STN. The data show that pallidotomy suppresses beta power (13–30 Hz) in the ipsilateral STN. This effect tends predominantly to be present in the dorsal part of the STN. In addition, spectral power in the frequency range 3–30 Hz is significantly higher in the dorsal part than in the ventral part. The effect of pallidotomy on STN neural activity is difficult to explain with the current model of basal ganglia circuitry and should be envisaged in the context of complex modulatory interactions in the basal ganglia.

Electrode Penetration of the Caudate Nucleus in Deep Brain Stimulation Surgery for Parkinson’s Disease

Objective: To evaluate the possible influence of electrode trajectories penetrating the caudate nucleus (CN) on cognitive outcomes in deep brain stimulation (DBS) surgery for Parkinson’s disease (PD). Background: It is currently unclear how mandatory CN avoidance during trajectory planning is. Design/Methods: Electrode trajectories were determined to be inside, outside, or in border region of the CN. Pre- and postoperative neuropsychological tests of each trajectory group were compared in order to evaluate possible differences in cognitive outcomes 12 months after bilateral STN DBS. Results: One hundred six electrode tracks in 53 patients were evaluated. Bilateral penetration of the CN occurred in 15 (28%) patients, while unilateral penetration occurred in 28 (53%). In 19 (36%) patients tracks were located in the border region of the CN. There was no electrode penetration of the CN in 10 (19%) patients. No difference in cognitive outcomes was found between the different groups. Conclusion: Cognitive outcome was not influenced by DBS electrode tracks penetrating the CN. It is both feasible and sensible to avoid electrode tracks through the CN when possible, considering its function and anatomical position. However, penetration of the CN can be considered without major concerns regarding cognitive decline when this facilitates optimal trajectory planning due to specific individual anatomical variations.

Accuracy of Microelectrode Trajectory Adjustments during DBS Assessed by Intraoperative CT

Background/Aims: Microelectrode recording (MER)-guided deep brain stimulation (DBS) aims to place the DBS lead in the optimal electrophysiological target. When single-track MER or test stimulation yields suboptimal results, trajectory adjustments are made. The accuracy of these trajectory adjustments is unknown. Intraoperative computed tomography can visualize the microelectrode (ME) and verify ME adjustments. We aimed to determine the accuracy of ME movements in patients undergoing MER-guided DBS. Methods: Coordinates following three methods of adjustment were compared: (1) those within the default “+” configuration of the ME holder; (2) those involving rotation of the default “+” to the “x” configuration; and (3) those involving head stage adjustments. Radial error and absolute differences between coordinates were determined. Results: 87 ME movements in 59 patients were analyzed. Median (IQR) radial error was 0.59 (0.64) mm. Median (IQR) absolute x and y coordinate errors were 0.29 (0.52) and 0.38 (0.44) mm, respectively. Errors were largest after rotating the multielectrode holder to its “x”-shaped setup. Conclusion: ME trajectory adjustments can be made accurately. In a considerable number of cases, errors exceeding 1 mm were found. Adjustments from the “+” setup to the “x” setup are most prone to inaccuracies.

Deep Brain Stimulation for Essential Tremor: Aligning Thalamic and Posterior Subthalamic Targets in 1 Surgical Trajectory

BACKGROUND Ventral intermediate nucleus (VIM) deep brain stimulation (DBS) and posterior subthalamic area (PSA) DBS suppress tremor in essential tremor (ET) patients, but it is not clear which target is optimal. Aligning both targets in 1 surgical trajectory would facilitate exploring stimulation of either target in a single patient. OBJECTIVE To evaluate aligning VIM and PSA in 1 surgical trajectory for DBS in ET. METHODS Technical aspects of trajectories, intraoperative stimulation findings, final electrode placement, target used for chronic stimulation, and adverse and beneficial effects were evaluated. RESULTS In 17 patients representing 33 trajectories, we successfully aligned VIM and PSA targets in 26 trajectories. Trajectory distance between targets averaged 7.2 (range 6-10) mm. In all but 4 aligned trajectories, optimal intraoperative tremor suppression was obtained in the PSA. During follow-up, active electrode contacts were located in PSA in the majority of cases. Overall, successful tremor control was achieved in 69% of patients. Stimulation-induced dysarthria or gait ataxia occurred in, respectively, 56% and 44% of patients. Neither difference in tremor suppression or side effects was noted between aligned and nonaligned leads nor between the different locations of chronic stimulation. CONCLUSION Alignment of VIM and PSA for DBS in ET is feasible and enables intraoperative exploration of both targets in 1 trajectory. This facilitates positioning of electrode contacts in both areas, where multiple effective points of stimulation can be found. In the majority of aligned leads, optimal intraoperative and chronic stimulation were located in the PSA.