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PubMed2005

Correspondence of microelectrode mapping with magnetic resonance imaging for subthalamic nucleus procedures.

BACKGROUND: Magnetic resonance imaging (MRI) and microelectrode recording (MER) are commonly used to guide stereotactic procedures on the subthalamic nucleus (STN). Little is known about the correlation between the position of the STN as seen on MRI and that as determined by MER mapping. We compared these in 10 patients with Parkinson's disease. METHODS: The position of the STN was determined by intraoperative MER findings and stereotactic axial T2 magnetic resonance images with 2-mm slice thickness. Images were reconstructed in a 3-dimensional workstation. The anterior, posterior, medial, lateral, dorsal, and ventral borders of the STN defined with the MRI were measured relative to the midcommissural point. The location of STN activity during MER was reconstructed relative to the midcommissural point for comparison. RESULTS: Twenty-nine tracks recorded with microelectrodes provided clear spans of STN-like activity in 18 STN nuclei. The coordinates of MER were, in general, within the borders of the STN defined with the MRI. However, when analyzed individually, some of the tracks had STN-like activity outside the borders of the MRI-defined nucleus (mostly <1 mm). Three tracks had STN-like activity recorded between 2 and 3 mm more anterior than the anterior border of the nucleus defined with the MRI. CONCLUSIONS: There was a good correlation between MER and the borders of the STN defined in the MRI, except for the anterior-posterior axis, in which MER indicated that the STN extended more anteriorly than as suggested by MRI. This should be taken into account in STN surgery.

Action Potentials↗

PubMed2000

Anticipatory errors after unilateral lesions of the subthalamic nucleus in the rat: evidence for a failure of response inhibition.

The nature of anticipatory responding in rats with unilateral subthalamic nucleus lesions was examined. Rats were trained to respond toward visual targets that were preceded by 1 of 4 different cues. For normal rats, a cue invokes an involuntary attentional orienting that enhances processing of the target at the location of attention. The cue is also a salient stimulus to which a response must be suppressed. Therefore, this task was used to investigate possible attentional impairments, as well as the ability of a lesioned rat to suppress competing motor programs. Responding under target control was not affected by the lesion. There was an increase in anticipatory responses before target onset, which could be accounted for by a failure to inhibit contralateral responses.

Animals↗

PubMed2001

Chronic bilateral electrical stimulation of the subthalamic nucleus for the treatment of advanced Parkinson's disease.

Preliminary reports in patients with Parkinson's disease (PD) showed that subthalamic nucleus (STN) stimulation was able to reverse parkinsonian state. Since 1998 we evaluated the safety and the efficacy of STN stimulation in 7 patients affected by advanced PD. All patients were included using CAPIT protocol. Motor functions and quality of life were evaluated, before and after surgery, with UPDRS and PDQ38, respectively. At the 6-month follow-up, the off medication/on stimulation UPDRS motor score improved by 50.6% and the on medication/on stimulation by 20.3%. Motor fluctuations were reduced by 57.2% and dyskinesias by 73.5%. The total L-dopa equivalent daily dose was reduced by 40.7%. PDQ38 ameliorated by 49.9%. We did not observe any perioperatory complication and only mild and tolerable side effects after stimulation.

Aged↗

PubMed2003

High frequency stimulation of the subthalamic nucleus has beneficial antiparkinsonian effects on motor functions in rats, but less efficiency in a choice reaction time task.

Chronic subthalamic nucleus high frequency stimulation (STN HFS) improves motor function in Parkinson's disease. However, its efficacy on cognitive function and the mechanisms involved are less known. The aim of this study was to assess the effects of STN HFS in hemiparkinsonian awake rats performing different specific motor tests and a cognitive operant task. Unilateral STN HFS applied in unilaterally DA-depleted rats decreased the apomorphine-induced circling behaviour and reduced catalepsy induced by the neuroleptic haloperidol. DA-depleted rats exhibited severe deficits in the operant task, among which the inability to perform the task was not alleviated by STN HFS. However, in a few animals showing less impairment, STN HFS significantly reduced the contralateral neglect induced by the lesion. These results are the first to demonstrate a beneficial effect of STN HFS applied in awake rats on basic motor functions. However, STN HFS appears to be less effective on impaired cognitive functions.

Adrenergic Agents↗

PubMed2002

The subthalamic nucleus has neurofibrillary tangles in argyrophilic grain disease and advanced Alzheimer's disease.

Neurofibrillary tangles (NFT) are present in the subthalamic nucleus (STN) of progressive supranuclear palsy and corticobasal degeneration, two sporadic tauopathies with preferential accumulation of tau with four repeats in the microtubule binding domain (4R tau). Since recent evidence suggests that argyrophilic grain disease (AGD) is also a 4R tauopathy, we hypothesized that the STN may also be affected in AGD. Tau immunostaining was used to evaluate NFT in the STN in 18 cases of AGD compared with 18 non-AGD cases matched for age, sex and Braak stage. AGD cases had significantly more NFT in the STN than non-AGD cases (P=0.008) with no relationship between NFT score and Braak stage. Surprisingly, NFT were also found in the STN of some non-AGD cases, notably in cases with advanced Braak stage (i.e. Alzheimer's disease). When AGD and non-AGD were considered as a whole there was a correlation between neurofibrillary degeneration in the STN and Braak stage. This study demonstrates that neurofibrillary degeneration is frequent in the STN in AGD, but also detected in non-AGD cases with advanced Braak stage.

Aged↗

PubMed2005

Subthalamic nucleus stimulation in tremor dominant parkinsonian patients with previous thalamic surgery.

Before the introduction of high frequency stimulation of the subthalamic nucleus (STN), many disabled tremor dominant parkinsonian patients underwent lesioning or chronic electrical stimulation of the thalamus. We studied the effects of STN stimulation in patients with previous ventral intermediate nucleus (VIM) surgery whose motor state worsened. Fifteen parkinsonian patients were included in this study: nine with unilateral and two with bilateral VIM stimulation, three with unilateral thalamotomy, and one with both unilateral thalamotomy and contralateral VIM stimulation. The clinical evaluation consisted of a formal motor assessment using the Unified Parkinson's Disease Rating Scale (UPDRS) and neuropsychological tests encompassing a 50 point frontal scale, the Mattis Dementia Rating Scale, and the Beck Depression Inventory. The first surgical procedure was performed a mean (SD) of 8 (5) years after the onset of disease. STN implantation was carried out 10 (4) years later, and duration of follow up after beginning STN stimulation was 24 (20) months. The UPDRS motor score, tremor score, difficulties in performance of activities of daily living, and levodopa equivalent daily dose significantly decreased after STN stimulation. Neither axial symptoms nor neuropsychological status significantly worsened after the implantation of the STN electrodes. The parkinsonian motor state is greatly improved by bilateral STN stimulation even in patients with previous thalamic surgery, and STN stimulation is more effective than VIM stimulation in tremor dominant parkinsonian patients.

Adult↗

PubMed2003

High frequency stimulation of the subthalamic nucleus improves treadmill locomotion in unilateral 6-hydroxydopamine lesioned rats.

This study investigated the influence of electrical stimulation of the subthalamic nucleus (STN) on motor impairment induced by unilateral 6-hydroxydopamine (6-OHDA) lesions in the medial forebrain bundle. Rats were trained to walk on a treadmill and then implanted with microelectrode arrays in and near the STN. The neurotoxin 6-OHDA was injected into the medial forebrain bundle (MFB) unilaterally to produce a targeted lesion of the dopaminergic system. Successful lesions produced impaired treadmill walking behavior. High frequency stimulation (HFS) of the STN improved treadmill walking immediately and restored normal walking patterns. The same HFS failed to evoke visible side effects such as stepping, turning, raising of the head or facial muscle contraction in the absence of treadmill movement, or to change rotational behaviors elicited by the dopamine (DA) agonist apomorphine in unilateral lesioned rats. This suggests that the stimulation did not cause movement by an activation of brainstem locomotor regions or an increase attention leading to movement. Apomorphine-induced rotation may represent an imbalance of dopaminergic activation which remains during HFS. This work may provide a rodent model for deep brain stimulation (DBS) in patients with Parkinson's disease, and be suitable for further investigation of the neural mechanisms underlying the therapeutic effects of DBS.

Animals↗

PubMed2004

High-frequency stimulation of both zona incerta and subthalamic nucleus induces a similar normalization of basal ganglia metabolic activity in experimental parkinsonism.

High-frequency stimulation (HFS) of the subthalamic nucleus (STN) alleviates dramatically motor symptoms in Parkinson's disease, and recently it has been suggested that zona incerta (ZI) stimulation might be as beneficial to patients. We used in situ cytochrome oxidase (CoI) mRNA hybridization to investigate and compare the effects of HFS of the STN and the ZI on metabolic activity of the STN, globus pallidus (GP), and substantia nigra reticulata (SNr) in normal rats as well as in rats with 6-hydroxydopamine (6-OHDA) lesion, an animal model of Parkinson's disease. In normal rats, HFS of the STN, as well as of the ZI, induced a significant decrease in CoI mRNA expression within the STN and SNr but an increase within the GP. In 6-OHDA rats, HFS of the STN reversed dopamine denervation-induced changes in the expression of CoI mRNA in the STN, SNr, and GP. Similar results were obtained with HFS of the ZI except for the STN, which showed only a trend toward normalization. These data suggest that the ZI, as well as the STN, are implicated in the functional mechanism of HFS supporting the involvement of GABA transmission for the reduction of neuronal activity in the basal ganglia output structures.

Animals↗

PubMed2004

Unilateral stimulation of the subthalamic nucleus in Parkinson disease: a double-blind 12-month evaluation study.

OBJECT: Bilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been established as an effective treatment for Parkinson disease (PD). Nevertheless, bilateral surgical procedures can be associated with frequent and severe complications. The aim in the present study was to assess the safety and efficacy of unilateral STN stimulation, and the need for a second procedure. METHODS: Twelve patients with PD underwent unilateral DBS of the STN and were followed up for 12 months. Patients were assessed at baseline and at each visit in a double-blind fashion by analyzing the Unified PD Rating Scale (UPDRS), ambulation speed, and home diaries. Levodopa-off/stimulation-on UPDRS motor scores were improved by 26 +/- 8% (p < 0.05, mean +/- standard deviation [SD]) compared with the baseline levodopa-off score; there was a 50% improvement in contralateral features, a 17% improvement ipsilaterally, and a 36% improvement in axial features. The mean ambulation speed increased by 83 +/- 44% (p < 0.01, mean +/- SD). The medication-on time with dyskinesias was significantly reduced (p < 0.01) and the daily levodopa dose was reduced by 19 +/- 6% (p < 0.05, mean +/- SD). There were no clinically significant side effects. CONCLUSIONS: Unilateral DBS of the STN is safe and well tolerated, and may provide sufficient benefit so that additional surgery is not required.

Adult↗

PubMed1987

Organization of efferent projections of the subthalamic nucleus in the squirrel monkey as revealed by retrograde labeling methods.

The cellular origin and degree of collateralization of the subthalamostriatal, subthalamonigral and subthalamopallidal projections in the squirrel monkey (Saimiri sciureus) were studied using lectin-conjugated horseradish peroxidase (WGA-HRP), Nuclear yellow (NY) and Fast blue (FB) as retrograde tracers. In a first experimental group, WGA-HRP was injected in the left putamen and the right caudate nucleus. Following these injections numerous retrogradely labeled neurons occurred in the dorsolateral two-thirds of the subthalamic nucleus on the putamen-injected side, whereas a smaller number of positive cells were found in the ventromedial third of the same nucleus on the caudate-injected side. In a second experimental group NY was injected in the putamen whereas FB was delivered in the substantia nigra on the same side of the brain. After putaminonigral injections subthalamic cells containing the tracer injected in the putamen (about 75-80% of all retrogradely labeled neurons) occurred in the dorsolateral two-thirds of the nucleus, whereas those containing the tracer injected in the substantia nigra (about 20-25% of all positive subthalamic cells) were confined to the ventromedial third of the structure. Approximately 5-10% of all subthalamic positive neurons were double-labeled following putaminonigral injections. In a third experimental group, NY was injected in the caudate nucleus and FB in the substantia nigra on the same side. After such injections cells retrogradely labeled with NY or FB were present in about equal number and appeared closely intermingled in the ventromedial third of the subthalamic nucleus. Less than 10% of all positive subthalamic neurons were double-labeled following caudatonigral injections. In a fourth experimental group, NY was delivered in the globus pallidus and FB in the substantia nigra on the same side. In these animal cells containing the tracer delivered in the pallidum were about 4 times more numerous than those labeled with the tracer injected in the substantia nigra, and approximately 10-20% of all positive subthalamic neurons were double-labeled following pallidonigral injections. Most of these double-labeled cells occurred in the zone where the two populations of single-labeled cells overlapped. Finally, in a last experimental group, NY was injected in the pedunculopontine nucleus on one side and in the substantia nigra on the other. Following these injections cells containing the tracer delivered in the pedunculopontine nucleus were found to be 5-6 times less numerous than those labeled after substantia nigra injections...

Animals↗

PubMed1999

Apomorphine test: a predictor for motor responsiveness to deep brain stimulation of the subthalamic nucleus.

The value of the apomorphine test as a predictor of the clinical outcome of deep brain stimulation of the subthalamic nucleus (STN) was evaluated in patients with advanced idiopathic Parkinson's disease (IPD) or multiple system atrophy (MSA). Thirteen IPD patients with severe diurnal fluctuations and one MSA patient not responding to dopaminergic drugs were assessed with the Unified Parkinson's Disease Rating Scale (UPDRS) and the timed finger tapping test (FTT), measured preoperatively on and off apomorphine and postoperatively on and off STN stimulation. UPDRS motor items 20-25 were assessed intraoperatively on and off STN stimulation when the clinically effective target was approached. The motor response to immediate intraoperative and long-term STN stimulation was correlated with results of the apomorphine test. The response to immediate intraoperative STN stimulation was accurately predicted by apomorphine challenge in all 13 IPD patients. Clinical outcome following long-term STN stimulation was correlated significantly with preoperative changes due to apomorphine measured with the UPDRS motor scores (r = 0.7125, P < 0.01) and FTT (r = 0.9276, P < 0.001). Moreover, comparison of long-term STN stimulation to preoperative drug treatment displayed a significant reduction in the duration of off-phases and a significant increase in the duration of on-phases. However, in the single patient with MSA no beneficial response was obtained either to apomorphine or to STN stimulation intraoperatively and during the postoperative externalized test period. Our results indicate that the apomorphine test can predict the outcome of immediate and long-term STN stimulation and may help in the selection of candidates for surgery.

Aged↗

PubMed2001

Subthalamic nucleus lesions are neuroprotective against terminal 6-OHDA-induced striatal lesions and restore postural balancing reactions.

Inactivation of the subthalamic nucleus (STN) by deep brain stimulation or lesioning can ameliorate symptoms in Parkinson' disease (PD) and may alter the underlying progressive degenerative process. We evaluated the effects of STN lesions in a terminal lesion model of PD in rats. Multiple intrastriatal 6-OHDA injections (4 x 7 microg) resulted in a partial loss of striatal TH-positive innervation (-30 to -40%) and nigral dopaminergic neurons (-60%), which was associated with behavioral deficits as observed in drug-induced rotational asymmetry, side-stepping, and postural balancing reactions. Unilateral ibotenic acid lesions of the STN did produce a 50-60% loss of STN neurons based on stereological analysis, which did not induce a functional impairment in rotational asymmetry or spontaneous sensorimotor behaviors. When STN lesions were performed 1 week prior to the 6-OHDA terminal striatal lesions, a significant rescue effect (+23%) on nigral dopaminergic neurons against terminal 6-OHDA neurotoxicity could be demonstrated, whereas striatal TH-positive fiber loss was not attenuated in these animals. In addition, animals with combined STN and striatal lesions exhibited a significant recovery in postural balancing reactions induced by 6-OHDA terminal lesions and did not show a significant impairment in any of the other behavioral parameters examined. Taken together, STN lesions can exert neuroprotective effects on nigral dopamine neurons in a partial lesion model of PD which result in recovery of spontaneous sensorimotor behavior. These findings may therefore provide new insights into the functional interaction between the glutamatergic and the dopaminergic neurotransmitter systems and foster novel therapeutic concepts for the early and middle phases of Parkinson's disease.

Animals↗

PubMed2006

Pretargeting for the implantation of stimulation electrodes into the subthalamic nucleus: a comparative study of magnetic resonance imaging and ventriculography.

OBJECTIVE: The optimal imaging modality for preoperative targeting of the subthalamic nucleus (STN) for high-frequency stimulation is controversially discussed. Commonly used methods were stereotactic magnetic resonance imaging (MRI), stereotactic ventriculography, and fusion between MRI and stereotactic computer tomography. All of these techniques not only have their own advantages but also specific limitations and drawbacks. The purpose of this study was to evaluate the accuracy of the preoperative MRI targeting as compared with ventriculography in terms of both the STN target as well as the internal landmarks. METHODS: Thirty patients with Parkinson's disease who underwent bilateral surgery for STN-high-frequency stimulation received both stereotactic ventriculography and stereotactic MRI. The theoretical target was determined by each of these two imaging modalities. The final electrode placement was performed after extensive electrophysiological evaluation using microrecording and microstimulation. The real target was assumed to be given by the electrode contact with the best clinical result assessed by the United Parkinson's Disease Rating Scale in the postoperative follow-up. In addition, the coordinates of the two landmarks, anterior commissure and posterior commissure, were determined using both imaging methods. RESULTS: The mean targeting error was 4.1 +/- 1.7 mm (mean +/- standard deviation) for MRI and 2.4 +/- 1.1 mm for ventriculography (P < 0.0001). The mean target mismatch between the two imaging methods was 2.9 +/- 1.2 mm. The length of the anterior commissure-posterior commissure distance differed significantly (P < 0.0001) between MRI (27.6 +/- 1.6 mm) and ventriculography (25.0 +/- 1.3 mm). The mismatch was mainly induced by an anterior diplacement of the anterior commissure by 1.9 +/- 2.2 mm (P < 0.0001) in MRI determination, as compared with ventriculography. CONCLUSION: Our findings show that the indirect targeting of the STN using coordinates based on radiological landmarks is more accurate than the direct targeting using anatomic visualization of the target structure. Regardless of the imaging procedure, electrophysiological mapping is required for optimal electrode placement, although in 20% of cases, the target determined by MRI falls out of the radius explored by electrophysiology.

Brain Mapping↗

PubMed2001

Subthalamic nucleus stimulation for Parkinson disease: benefits observed in levodopa-intolerant patients.

OBJECT: A blinded evaluation of the effects of subthalamic nucleus (STN) stimulation was performed in levodopa-intolerant patients with Parkinson disease (PD). These patients (Group I, seven patients) were moderately or severely disabled (Hoehn and Yahr Stages III-V during the off period), but were receiving only a small dose of medication (levodopa-equivalent dose [LED] 0-400 mg/day) because they suffered unbearable side effects. The results were analyzed in comparison with those obtained in patients with advanced PD (Group II, seven patients) who were severely disabled (Hoehn and Yahr Stages IV and V during the off period), but were treated with a large dose of medication (500-990 mg/day). METHODS: The patients were evaluated twice at 6 to 8 months after surgery. To determine the actual benefits afforded by STN stimulation to their overall daily activities, the patients were maintained on their medication regimen with optimal doses and schedules. Stimulation was turned off overnight for at least 12 hours. It was turned on in the morning (or remained turned off), and each patient's best and worst scores on the Unified Parkinson's Disease Rating Scale during waking daytime activity were recorded as on- and off-period scores, respectively. The order of assessment with respect to whether stimulation was occurring was determined randomly. The STN stimulation markedly improved daily activity and total motor scores in Group I patients. The percentage time of immobility (Hoehn and Yahr Stages IV and V) became 0% in patients who were intermittently immobile while not receiving stimulation. Improvements were demonstrated in tremor, rigidity. akinesia, and gait subscores. The STN stimulation produced less marked but still noticeable improvements in the daily activity and total motor scores in Group II patients. The percentage time of immobility as well as the LED was reduced in patients who displayed intermittent immobility with pronounced motor fluctuations while not receiving stimulation. Improvements were demonstrated in tremor, rigidity, and dyskinesia subscores in these patients. In contrast, STN stimulation did not improve the overall daily activities at all in patients who had become unresponsive to a tolerable dose of levodopa and were continuously immobile, even though these patients' tremor and rigidity subscores were still improved by stimulation. CONCLUSIONS: Consistent with earlier findings, the great benefit of STN stimulation in levodopa-intolerant patients is that STN stimulation can reduce the level of required levodopa medication. This suggests that STN stimulation could be a therapeutic option for patients with less-advanced PD by allowing levodopa medication to be maintained at as low a dose as possible, and to prevent adverse reactions to the continued use of large-dose levodopa.

Adult↗

PubMed1989

The role of the subthalamic nucleus in experimental chorea. Evidence from 2-deoxyglucose metabolic mapping and horseradish peroxidase tracing studies.

In previous studies we have shown that hemichorea can be induced in the conscious monkey by localized injection of gamma-aminobutyric acid (GABA) antagonists into the contralateral lentiform complex. It has been argued that the primary site of drug action in inducing chorea is the lateral segment of the globus pallidus. In the present study, the neural mechanisms which underlie this experimental dyskinesia were investigated by two separate approaches. First, the efferent projections of the lentiform complex were mapped using neuroanatomical tracing techniques. This involved injecting horseradish peroxide into sites which had previously given chorea when injected with the GABA antagonist bicuculline. Secondly, the 2-deoxyglucose (2-DG) metabolic mapping technique was applied to animals during active dyskinesia. This procedure permitted the autoradiographic measurement of local cerebral glucose uptake which was used as an index of regional synaptic activity. In both instances, the strongest labelling was seen in the dorsolateral region of the subthalamic nucleus. On the basis of this finding it is suggested that the pallidosubthalamic pathway plays a crucial role in the mediation of experimentally-induced chorea. Specifically, the pallidosubthalamic pathway arising from the lateral pallidal segment is abnormally overactive, which causes physiological inhibition of the subthalamic nucleus. The pattern of 2-DG uptake in the medial segment of the globus pallidus and thalamus was similar to that seen in animals with experimentally-induced ballism. This similarity is interpreted as suggesting that a common neural mechanism underlies both experimentally-induced chorea and ballism.

Animals↗

PubMed2002

Long-term follow up of subthalamic nucleus stimulation in Parkinson's disease.

Twenty-two patients with PD received bilateral implants for high frequency stimulation of the subthalamic nucleus. The patients were treated for more than 1 year (up to 36 months). At the last visit, the Unified Parkinson Disease Rating Scale (UPDRS) motor score without medication improved by 50.2% (p < 0.001) and the UPDRS activities of daily living score improved by 68.4% (p < 0.001). The most common long-lasting adverse events were hypophonia and dysarthria; transient events were increased sexuality and mania. The surgical procedure induced transient intraoperative psychosis in seven patients.

Activities of Daily Living↗

PubMed2005

Frequency-correlated decreases of motor cortex activity associated with subthalamic nucleus stimulation in Parkinson's disease.

According to the classical model of basal ganglia organization, deep brain stimulation (DBS) in the subthalamic nucleus (STN) for the treatment of Parkinson's disease (PD) blocks overactive excitatory projections to inhibitory basal ganglia output structures. This would release the break on thalamofrontal neurons alleviating the poverty of movement, the hallmark of PD. Such parallels to a functional lesion certainly simplify the mechanism of STN DBS. Here, we applied parametric analyses of H2(15)O positron emission tomography (PET) scans at rest while systematically varying stimulation frequency in 6 patients with STN DBS for akinetic PD. A strong positive correlation of rCBF to increasing stimulation frequency was detected around the STN bilaterally. More importantly, we show that gradual increases in STN stimulation frequency are tightly correlated with decreases in motor cortex activity. This demonstrates an active modulation of resting activity within the subcortical stimulation target and within motor cortex by STN DBS. Rather than a possible downstream effect, we propose to consider the tight correlations between DBS frequency and motor cortex activity in the context of an upstream modulation of direct efferents to the STN from primary motor and premotor cortices.

Aged↗

PubMed2004

Quality index for the quantification of the information recorded along standard microelectrode tracks to the subthalamic nucleus in parkinsonian patients.

OBJECTIVE: To quantify the usefulness of the neuronal activity recorded on a standard microelectrode track to the subthalamic nucleus (STN) for the determination of the transition between the thalamus and the STN. METHODS: The study is based on analysis of 689 extracelullar single units recorded on 70 tracks passing through the thalamus and the STN. Using four neuron parameters that were correlated with electrode depth, a quality index (QI) for each track was computed and compared with the subjective assessment by the electrophysiologist of the track quality. RESULTS: Subjectively, the transition between the thalamus and the STN was detected in 49 tracks (usual track) and not detected on 21 tracks (unusual tracks). Objectively, spike frequency, cell burst index (BI), signal relative root mean square (RMS) and spike relative amplitude were correlated with electrode depth and used to compute track QI. The average QI index of usual and unusual tracks was 0.25 +/- 0.9 and 0.85 +/- 0.15 (mean +/- confidence interval at P < 0.001), respectively. In 20 patients, QI correlates with post-operative measurement of electrode length in the STN. CONCLUSION: These results demonstrate that simple statistical analysis taking into account the variation of single-unit characteristics with electrode depth can discriminate between useful and useless tracks for the determination of the STN localisation.

Electrophysiology↗