The functional role of the subthalamic nucleus in cognitive and limbic circuits

Neural correlates of STN DBS-induced cognitive variability in Parkinson disease

BACKGROUND

Although deep brain stimulation of the subthalamic nucleus (STN DBS) in Parkinson disease (PD) improves motor function, it has variable effects on working memory (WM) and response inhibition (RI) performance. The purpose of this study was to determine the neural correlates of STN DBS-induced variability in cognitive performance.

METHODS

We measured bilateral STN DBS-induced blood flow changes (PET and [(15)O]-water on one day) in the supplementary motor area (SMA), dorsolateral prefrontal cortex (DLPFC), anterior cingulate cortex (ACC), and right inferior frontal cortex (rIFC) as well as in exploratory ROIs defined by published meta-analyses. STN DBS-induced WM and RI changes (Spatial Delayed Response and Go-No-Go on the next day) were measured in 24 PD participants. On both days, participants withheld PD medications overnight and conditions (OFF vs. ON) were administered in a counterbalanced, double-blind manner.

RESULTS

As predicted, STN DBS-induced DLPFC blood flow change correlated with change in WM, but not RI performance. Furthermore, ACC blood flow change correlated with change in RI but not WM performance. For both relationships, increased blood flow related to decreased cognitive performance in response to STN DBS. Of the exploratory regions, only blood flow changes in DLPFC and ACC were correlated with performance.

CONCLUSIONS

These results demonstrate that variability in the effects of STN DBS on cognitive performance relates to STN DBS-induced cortical blood flow changes in DLPFC and ACC. This relationship highlights the need to further understand the factors that mediate the variability in neural and cognitive response to STN DBS.

Single electrode and multiple electrode guided electrical stimulation of the subthalamic nucleus in advanced Parkinson's disease

OBJECTIVE

It is still debated to what extent intraoperative electrophysiological techniques contribute to the outcome of subthalamic nucleus (STN) deep brain stimulation (DBS). Intraoperative electrophysiological recordings for identification of the STN can be made with one electrode or with multiple, simultaneously implanted electrodes. The latter provide more detailed information about the electrophysiological boundaries of the STN; however, implantation of several electrodes at one time might increase the risk of bleeding. Here we report the results of a study of patients with advanced Parkinson's disease, in which one group of patients underwent bilateral STN DBS with electrophysiological recordings from a single electrode, and the other group received STN DBS with multiple (five or fewer) simultaneously implanted electrodes.

PATIENTS AND METHODS

Fifty-five patients suffering from advanced Parkinson's disease who underwent bilateral STN stimulation were included in this study. Thirty-two patients underwent STN DBS guided by a single semi-microelectrode, and 23 patients underwent STN DBS guided with simultaneously implanted multiple microelectrodes. All patients were examined preoperatively and 3 and 12 months postoperatively with regard to activities of daily living, motor functions, and neuropsychological functions.

RESULTS

We found that the simultaneous implantation of multiple electrodes does not increase the risk of bleeding or any other major intracranial complication. The use of multiple electrodes resulted in better motor results when compared with patients who underwent STN DBS guided with a single recording electrode. There were significantly more improvements in patients' tremor and rigidity, and as a consequence, a better total Unified Parkinson Disease Rating Scale, Part III score was identified during the medication-off phase. Despite better motor effects, patients treated with multiple electrodes showed subtle deterioration in neuropsychological functions, particularly in memory function.

CONCLUSION

STN DBS performed with multiple electrophysiological recording electrodes resulted in better motor outcome but induced specific mild declines in neuropsychological functions.

Unilateral vs. bilateral STN DBS effects on working memory and motor function in Parkinson disease

Bilateral subthalamic nucleus deep brain stimulation (STN DBS) can reduce working memory while improving motor function in Parkinson disease (PD), but findings are variable. One possible explanation for this variability is that the effects of bilateral STN DBS on working memory function depend in part on functional or disease asymmetry. The goal of this study was to determine the relative contributions of unilateral DBS to the effects seen with bilateral DBS. Motor (Unified Parkinson Disease Rating Scale Part III, UPDRS) and working memory function (Spatial Delayed Response, SDR) were measured in 49 PD patients with bilateral STN DBS while stimulators were Both-off, Left-on, Right-on and Both-on in a randomized, double-blind manner. Patients were off PD medications overnight. Effects of unilateral DBS were compared to effects of bilateral STN DBS. Mean UPDRS and SDR responses to Left-on vs. Right-on conditions did not differ (p>.20). However, improvement in contralateral UPDRS was greater and SDR performance was more impaired by unilateral DBS in the more affected side of the brain than in the less affected side of the brain (p=.008). The effect of unilateral DBS on the more affected side on contralateral UPDRS and SDR responses was equivalent to that of bilateral DBS. These results suggest that motor and working memory function respond to unilateral STN DBS differentially depending on the asymmetry of motor symptoms.

Mood improvement after deep brain stimulation of the internal globus pallidus for tardive dyskinesia in a patient suffering from major depression

Deep brain stimulation (DBS) has the unique characteristic to very precisely target brain structures being part of functional brain circuits in order to reversibly modulate their function. It is an established adjunctive treatment of advanced Parkinson's disease and has virtually replaced ablative techniques in this indication. Several cases have been published relating effectiveness in neuroleptics-induced tardive dyskinesia. It is also investigated as a potential treatment of mood disorders. We report on the case of a 62 years old female suffering from a treatment refractory major depressive episode with comorbid neuroleptic-induced tardive dyskinesia. She was implanted a deep brain stimulation treatment system bilaterally in the globus pallidus internus and stimulated for 18 months. As well the dyskinesia as also the symptoms of depression improved substantially as measured by the Hamilton Rating Scale of Depression (HRSD) score and the Burke-Fahn-Marsden-Dystonia-Rating-Scale (BFMDRS) score. Scores dropped for HRSD from 26 at baseline preoperatively to 13 after 18 months; and for BFMDRS from 27 to 17.5. This case illustrates the potential of deep brain stimulation as a technique to be investigated in the treatment of severe and disabling psychiatric and movement disorders. DBS at different intracerebral targets being actually investigated for major depression might have similar antidepressant properties because they interact with the same cortico-basal ganglia-thalamocortical network found to be dysfunctional in major depression.

Inhibition of 5-HT neuron activity and induction of depressive-like behavior by high-frequency stimulation of the subthalamic nucleus

Bilateral, high-frequency stimulation (HFS) of the subthalamic nucleus (STN) is the surgical therapy of choice for movement disability in advanced Parkinson's disease (PD), but this procedure evokes debilitating psychiatric effects, including depressed mood, of unknown neural origin. Here, we report the unexpected finding that HFS of the STN inhibits midbrain 5-hydroxytryptamine (5-HT) neurons to evoke depression-related behavioral changes. We found that bilateral HFS of the STN consistently inhibited (40-50%) the firing rate of 5-HT neurons in the dorsal raphe nucleus of the rat, but not neighboring non-5-HT neurons. This effect was apparent at clinically relevant stimulation parameters (> or =100 Hz, > or =30 microA), was not elicited by HFS of either neighboring or remote structures to the STN, and was still present in rat models of PD. We also found that bilateral HFS of the STN evoked clear-cut, depressive-like behavior in a widely used experimental paradigm of depression (forced swim test), and this effect was also observed in a PD model. Importantly, the depressive-like behavior elicited by HFS of the STN was reversed by a selective 5-HT-enhancing antidepressant, thereby linking the behavioral change to decreased 5-HT neuronal activity. Overall, these findings link reduced 5-HT function to the psychiatric effects of HFS of the STN observed in PD patients and provide a rational basis for their clinical management. More generally, the powerful interaction between the STN and 5-HT system uncovered here offers insights into the high level of comorbidity of basal ganglia disease and mood disorder.

Motor and Nonmotor Symptom Follow-Up in Parkinsonian Patients after Deep Brain Stimulation of the Subthalamic Nucleus

OBJECTIVE

To evaluate motor and nonmotor symptoms in patients with Parkinson's disease undergoing bilateral deep brain stimulation of the subthalamic nucleus (STN DBS).

METHODS

Thirty-six consecutive patients receiving bilateral STN stimulation implants were evaluated preoperatively as well as 12 and 24 months after surgery. Motor symptoms were assessed through the Unified Parkinson's Disease Rating Scale (UPDRS). Data concerning nonmotor symptoms were collected from items of the UPDRS and 2 additional questions from clinical charts regarding constipation and urological dysfunction.

RESULTS

STN DBS was effective in controlling motor symptoms; concerning nonmotor symptoms, sleep quality and constipation improved after surgery as compared to baseline. Salivation, swallowing and sensory complaints were ameliorated to a comparable degree by the medication on state, whether preoperatively or postoperatively. With a lower dose of dopaminergic medication, however, the medication on state appeared to be a much larger percentage of the day postoperatively. No significant variations were detected in intellectual impairment, depression, thought disorders, motivation, falling unrelated to freezing, nausea, orthostatic hypotension and urological dysfunction.

CONCLUSIONS

STN DBS effectively controls motor symptoms, while nonmotor features of advanced Parkinson's disease patients are mostly unchanged after surgery, even though some specific aspects, notably sleep complaints and constipation, are ameliorated.

High frequency stimulation of the subthalamic nucleus improves speed of locomotion but impairs forelimb movement in Parkinsonian rats

The subthalamic nucleus (STN) plays an important role in motor and non-motor behavior in Parkinson's disease, but its involvement in gait functions is largely unknown. In this study, we investigated the role of the STN on gait in a rat model of PD using the CatWalk method. Parkinsonian rats received bilateral high frequency stimulation (HFS) with different stimulation amplitudes of the STN. Rats were rendered parkinsonian by bilateral injections of 6-hydroxydopamine (6-OHDA) into the striatum. One group of 6-OHDA animals was implanted bilaterally with stimulation electrodes at the level of the STN. Stimulations were performed at 130 Hz (frequency), 60 micros (pulse width) and varying amplitudes of 0, 3, 30 and 150 microA. Rats were evaluated in an automated quantitative gait analysis method (CatWalk method). After behavioral evaluations, rats were killed and the brains processed for histological stainings to determine the impact of the dopaminergic lesion (tyrosine hydroxylase immunohistochemistry) and the localization of the electrode tip (hematoxylin-eosin histochemistry). Results show that bilateral 6-OHDA infusion significantly decreased (70%) the number of dopaminergic cells in the substantia nigra pars compacta (SNc). Due to 6-OHDA treatment, the gait parameters changed considerably. There was a general slowness. The most pronounced effects were seen at the level of the hind paws. Due to implantation of STN electrodes the step pattern changed. STN electrical stimulation improved the general slowness but induced slowing of the forelimb movement. Furthermore, we found that HFS with a medium amplitude significantly changed speed, the so-called dynamic aspect of gait. The static features of gait were only significantly influenced with low amplitude. Remarkably, STN stimulation affected predominantly the forepaws/limbs.

Effects of STN DBS on memory guided force control in Parkinson's disease (June 2007)

This study examined the control of elbow force in nine patients with Parkinson's disease when visual feedback was available and when visual feedback was removed to determine how medication (Meds) and unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) affect memory guided force control. Patients were examined in each of four treatment conditions: 1) off treatment; 2) Meds; 3) STN DBS; and 4) Meds plus STN DBS. With visual feedback available, there was no difference in force output across treatment conditions. When visual feedback was removed force output drifted under the target in both the off-treatment and the Meds conditions. However, when on STN DBS or Meds plus STN DBS force output drifted above the target. As such, only STN DBS had a significant effect on force output in the vision removed condition. Increased force output when on STN DBS may have occurred due to disruptions in the basal ganglia-thalamo-cortical circuitry. We suggest that modulation of output of the internal segment of the globus pallidus by STN DBS may drive the effect of STN DBS on memory guided force control.

Translational principles of deep brain stimulation

Deep brain stimulation (DBS) has shown remarkable therapeutic benefits for patients with otherwise treatment-resistant movement and affective disorders. This technique is not only clinically useful, but it can also provide new insights into fundamental brain functions through direct manipulation of both local and distributed brain networks in many different species. In particular, DBS can be used in conjunction with non-invasive neuroimaging methods such as magnetoencephalography to map the fundamental mechanisms of normal and abnormal oscillatory synchronization that underlie human brain function. The precise mechanisms of action for DBS remain uncertain, but here we give an up-to-date overview of the principles of DBS, its neural mechanisms and its potential future applications.

Stimulation of subterritories of the subthalamic nucleus reveals its role in the integration of the emotional and motor aspects of behavior

Two parkinsonian patients who experienced transient hypomanic states when the subthalamic nucleus (STN) was stimulated during postoperative adjustment of the electrical parameters for antiparkinsonian therapy agreed to have the mood disorder reproduced, in conjunction with motor, cognitive, and behavioral evaluations and concomitant functional neuroimaging. During the experiment, STN stimulation again induced a hypomanic state concomitant with activation of cortical and thalamic regions known to process limbic and associative information. This observation suggests that the STN plays a role in the control of a complex behavior that includes emotional as well as cognitive and motor components. The localization of the four contacts of the quadripolar electrode was determined precisely with an interactive brain atlas. The results showed that (i) the hypomanic state was caused only by stimulation through one contact localized in the anteromedial STN; (ii) both this contact and the contact immediately dorsal to it improved the parkinsonian motor state; (iii) the most dorsal and ventral contacts, located at the boundaries of the STN, neither induced the behavioral disorder nor improved motor performance. Detailed analysis of these data led us to consider a model in which the three functional modalities, emotional, cognitive, and motor, are not processed in a segregated manner but can be subtly combined in the small volume of the STN. This nucleus would thus serve as a nexus that integrates the motor, cognitive, and emotional components of behavior and might consequently be an effective target for the treatment of behavioral disorders that combine emotional, cognitive, and motor impairment.

High-frequency stimulation of the subthalamic nucleus modulates the activity of pedunculopontine neurons through direct activation of excitatory fibres as well as through indirect activation of inhibitory pallidal fibres in the rat

Recent data suggest a potential role of pedunculopontine nucleus (PPN) electrical stimulation in improving gait and posture in Parkinson's disease. Because the PPN receives fibres from the subthalamic nucleus (STN), we investigated the effects of STN-high-frequency stimulation (HFS) on PPN neuronal activity in intact rats and in rats bearing either an ibotenate lesion of the entopeduncular nucleus (EP) or a lesion of the substantia nigra (SN). The main response of PPN neurons to STN single-shock stimulations in the three experimental groups was a short latency (4.5 +/- 2.1 ms) and brief (15.3 +/- 6.5 ms) excitation. This response was maintained during 1-5 s of STN-HFS (130 Hz, 60 micros, 100-1000 microA). In EP-lesioned rats the percentage (75.0%) of PPN neurons showing a modulation of activity following STN-HFS was significantly higher compared with that observed in intact (39.7%) and in SN-lesioned rats (35.4%). Furthermore, in EP-lesioned rats the most frequent response of PPN neurons following STN-HFS was a 5-20 s excitation, which was present in 76.6% of responsive neurons in comparison to 15.4% and 9.1% of neurons responsive in intact and in 6-hydroxydopamine-lesioned rats, respectively. Neurons responsive to STN-HFS in the three experimental groups showed either a sharp positively skewed distribution of interspike intervals or multisecond oscillations in autocorrelograms. The results support that STN-HFS modulates the PPN through a balance of excitatory and inhibitory influences, which may be independent from the dopaminergic nigral neurons. In the absence of inhibitory EP fibres, the direct excitatory influence exerted by the STN on the PPN appears to predominate.

Brain networks underlining verbal fluency decline during STN-DBS in Parkinson's disease: an ECD-SPECT study

We prospectively evaluated 20 patients with Parkinson's disease (PD) preoperatively and 12 months after subthalamic nucleus-deep brain stimulation (STN-DBS). All patients had clinical (UPDRS III) and neuropsychological evaluations as well as brain perfusion SPECT-ECD. Clinical and cognitive data were compared with 12 matched PD patients who had not undergone surgery. STN-DBS patients improved in motor symptoms and reduced medications but selectively declined in category fluency (p<0.01). No clinical and cognitive changes were found in the control group at follow-up. Worsening fluency was associated with perfusion decrements in left dorsolateral prefrontal cortex, anterior cingulate cortex and ventral caudate nucleus (p<.001).

A physiologically plausible model of action selection and oscillatory activity in the basal ganglia

The basal ganglia (BG) have long been implicated in both motor function and dysfunction. It has been proposed that the BG form a centralized action selection circuit, resolving conflict between multiple neural systems competing for access to the final common motor pathway. We present a new spiking neuron model of the BG circuitry to test this proposal, incorporating all major features and many physiologically plausible details. We include the following: effects of dopamine in the subthalamic nucleus (STN) and globus pallidus (GP), transmission delays between neurons, and specific distributions of synaptic inputs over dendrites. All main parameters were derived from experimental studies. We find that the BG circuitry supports motor program selection and switching, which deteriorates under dopamine-depleted and dopamine-excessive conditions in a manner consistent with some pathologies associated with those dopamine states. We also validated the model against data describing oscillatory properties of BG. We find that the same model displayed detailed features of both gamma-band (30-80 Hz) and slow (approximately 1 Hz) oscillatory phenomena reported by Brown et al. (2002) and Magill et al. (2001), respectively. Only the parameters required to mimic experimental conditions (e.g., anesthetic) or manipulations (e.g., lesions) were changed. From the results, we derive the following novel predictions about the STN-GP feedback loop: (1) the loop is functionally decoupled by tonic dopamine under normal conditions and recoupled by dopamine depletion; (2) the loop does not show pacemaking activity under normal conditions in vivo (but does after combined dopamine depletion and cortical lesion); (3) the loop has a resonant frequency in the gamma-band.

Different cerebral cortical areas influence the effect of subthalamic nucleus stimulation on parkinsonian motor deficits and freezing of gait

Inconsistent response in freezing of gait (FOG) with levodopa treatment or STN DBS makes the pathogenesis difficult to understand. We studied brain areas associated with the expression of STN DBS effect on parkinsonian motor deficits and FOG. Ten Parkinson's disease patients with typical FOG were included. One month before STN DBS, we performed [(18)F]-deoxyglucose PET scans and measured the UPDRS motor and modified FOG (mFOG) scores during levodopa off and on periods. At two months after STN DBS, same rating scores were measured. The percentage improvement of mFOG and UPDRS motor scores by STN DBS during levodopa off period was calculated. We searched for brain areas in which glucose metabolism correlated with the improvement of mFOG and UPDRS motor scores by DBS. During levodopa off period, STN DBS improved the UPDRS motor scores by 32.3% and the mFOG scores by 56.6%. There was no correlation between the improvements of both scores. The improvement of UPDRS motor score by DBS correlated with the metabolic activities of rostral supplementary motor area (Brodmann's area 8; BA8), anterior cingulate cortex (BA32), and prefrontal cortex (BA9). On the other hand, there was a positive correlation between the improvement of mFOG score by DBS and the metabolic activity of the parietal, occipital, and temporal sensory association cortices. In conclusion, dysfunction of different cerebral cortical areas limits the beneficial effects of DBS on parkinsonian motor deficits and FOG.

Neuropsychological performance following staged bilateral pallidal or subthalamic nucleus deep brain stimulation for Parkinson's disease

Deep brain stimulation (DBS) has the potential to significantly reduce motor symptoms in advanced Parkinson's disease (PD). Controversy remains about non-motor effects of DBS and the relative advantages of treatment at two brain targets, the globus pallidus internus (GPi) and the subthalamic nucleus (STN). We investigated effects of DBS on neuropsychological functioning in 42 patients with advanced PD randomly assigned to receive staged bilateral DBS surgery of either the GPi or STN. Patients underwent neuropsychological assessment prior to and 6 months after unilateral surgery. Twenty-nine subsequently underwent surgery to the contralateral side and completed a second follow-up neuropsychological evaluation 15 months later. Unilateral treatment resulted in small but statistically significant reductions in performance on several measures, including verbal fluency and working memory. A similar pattern was observed after bilateral treatment. Reductions in verbal associative fluency were significant only after left-sided treatment. There were few significant differences related to treatment at the two surgical targets. Supplementary analyses suggested that decrements in select neuropsychological domains following DBS are unrelated to age or post-surgical reduction in dopaminergic medication dose. Findings are discussed with reference to possible causes of neuropsychological decline and the need for further controlled studies of specific neuropsychological effects of DBS.

Protection of nigral cell death by bilateral subthalamic nucleus stimulation

In Parkinson disease (PD), the subthalamic nucleus (STN) becomes hyperactive (disinhibited), which is reported to cause excitotoxic damage to midbrain dopaminergic neurons. Here, we examined whether silencing of the hyperactive STN by chronic bilateral deep brain stimulation (DBS) increased the survival of midbrain dopaminergic neurons in a rat model of PD. High-precision design-based stereologic examination of the total number of neurons and tyrosine tydroxylase (TH) immunoreactive neurons in the substantia nigra pars compacta revealed that STN DBS resulted in a significant survival of these neurons. These data provide the first evidence in vivo that bilateral STN DBS is useful for protecting midbrain dopaminergic neurons from cell death in PD.

Motor and cognitive improvement by deep brain stimulation in a transgenic rat model of Huntington's disease

Altered activity of the globus pallidus externus (GPe) is responsible for at least part of the cognitive and motor symptoms of Huntington's disease (HD). In this study, we tested the hypothesis that bilateral globus pallidus (GP; equivalent of GPe in primates) deep brain stimulation (DBS) improves cognitive and motor symptoms in the first transgenic rat model of HD (tgHD rats). GP DBS with clinically relevant stimulation parameters resulted in a significant improvement of cognitive dysfunction and reduced the number of choreiform movements. This data indicate that GPe DBS can be used to treat cognitive and motor dysfunction in HD.

Targets for deep brain stimulation in Parkinson's disease

The use of stimulation electrodes implanted in the brain to control severely disabling neurological and psychiatric conditions is an exciting and fast emerging area of neuroscience. An excellent example is Parkinson's disease (PD), in which tens of thousands of patients have now been implanted with stimulation electrodes. Patients with PD underwent deep brain stimulation (DBS) at the level of the thalamus, globus pallidus internus, subthalamic nucleus, pedunculopontine nucleus and prelemniscal radiation. The results of these interventions revealed that each target has its own specific stimulation-related positive and negative effects. Clinicians can choose their DBS target based on the situation of their individual PD patients. In the authors' opinion, patient-specific targeting should be preferred over disease-specific targeting. In this review, the authors give an overview of the targets that have been used for DBS in PD and discuss patient-specific targeting.

The subthalamic nucleus: From response selection to execution

The involvement of the subthalamic nucleus in physiological and pathological motor behaviour has now largely been established. Clinical observations in patients suffering from Parkinson disease treated with Deep Brain Stimulation of the STN show that these patients can suffer from postoperative changes in non-motor behaviour mainly involving alterations in cognitive functions. The involvement of the STN in cognition has initially been demonstrated by non-human studies investigating the effects of STN lesions and stimulations on cognitive parameters. In the present review, we discuss the findings of these preclinical studies on cognitive parameters and outline the anatomical and functional place of the STN in the basal ganglia cognitive circuit.