A. Pesenti

Movement-related modulation of neural activity in human basal ganglia and its L-DOPA dependency: recordings from deep brain stimulation electrodes in patients with Parkinson's disease.

Abstract. Through electrodes implanted for deep brain stimulation in three patients (5 sides) with Parkinsons disease, we recorded the electrical activity from the human basal ganglia before, during and after voluntary contralateral finger movements, before and after L-DOPA. We analysed the movement-related spectral changes in the electroencephalographic signal from the subthalamic nucleus (STN) and from the internal globus pallidus (GPi). Before, during and after voluntary movements, signals arising from the human basal ganglia contained two main frequencies: a high β (around 26 Hz), and a low β (around 18 Hz). The high β (around 26 Hz) power decreased in the STN and GPi, whereas the low β (around 18 Hz) power decrease was consistently found only in the GPi. Both frequencies changed their power with a specific temporal modulation related to the different movement phases. L-DOPA specifically and selectively influenced the spectral power changes in these two signal bands.

Limb immobilization for the treatment of focal occupational dystonia

Background: Occupational focal upper-limb dystonia is characterized by involuntary muscle contractions that selectively interfere with the execution of specific motor tasks such as writing or playing a musical instrument. Occupational dystonias have a severe social impact, especially in certain professions. The available medical treatments offer little benefit. Methods: In eight patients with idiopathic occupational focal dystonia of the upper limb, the dystonic forearm and hand were immobilized with a plastic splint for mean (±SD) 4.5 ± 0.75 weeks. Before splinting (base line) and at various intervals afterwards (4, 12, and 24 weeks), the authors assessed the severity of dystonia and the patients’ motor performance objectively (Arm Dystonia Disability Scale and Tubiana and Chamagne Score) and subjectively (Self-Rating Score). Results: Assessment 4 weeks after splint removal, when patients had regained normal voluntary movements, showed that the severity of dystonia and the patients’ performance of the impaired motor task had improved; the benefit persisted unchanged at later follow-up visits (Arm Dystonia Disability Scale: base line 20.6 ± 30.2%; after 4 weeks 83.9 ± 23.8%, p = 0.007; after 12 weeks 83.9 ± 23.8%, p = 0.007; after 24 weeks 79.7 ± 29.5%, p = 0.015. Tubiana and Chamagne Score: base line 28.6 ± 22.7%; after 4 weeks 80.0 ± 23.1%, p = 0.015; after 12 weeks 80.0 ± 23.1%, p = 0.015; after 24 weeks 74.3 ± 32.1%, p = 0.031. Self-Rating Score: base line 20.6 ± 19.3%; after 4 weeks 63.7 ± 25.2%, p = 0.015; after 12 weeks 66.9 ± 28.1%, p = 0.015; after 24 weeks 70.6 ± 31.8%, p = 0.015). At the 24-week visit the improvement disappeared in one patient, was moderate in three, and marked in four. Conclusions: Limb immobilization can be a simple, effective, safe, and inexpensive treatment for focal occupational upper-limb dystonia.

Anatomo-clinical correlation of intraoperative stimulation-induced side-effects during HF-DBS of the subthalamic nucleus

Abstract. The efficacy of deep brain stimulation of the subthalamic nucleus (STN) is dependent on the accuracy of targeting. In order to reduce the number of passes and, consequently, the duration of surgery and risk of bleeding, we have set up a new method based on direct magnetic resonance imaging (MRI) localisation of the STN. This procedure allows a short duration of the neurophysiological session (one or two initial tracks). Whenever a supplementary track is needed, the stimulation-induced side effects are analysed to choose from one of the remaining holes in Bens gun. A good knowledge of anatomical structures surrounding the STN is mandatory to relate side effects to the actual position of the track. In our series of 11 patients (22 sides, 37 tracks), the most common and reproducible side effects were those characterised by motor, sensorial, oculomotor and vegetative signs and symptoms. Moreover, the therapeutic window (distance between the current intensity needed to obtain the best clinical effect and the intensity capable to induce side effects) predicted clinical efficacy in the long-term, and contributed to the choice of which among the examined tracks had to be implanted with the chronic macroelectrode.

Visualisation of the subthalamic nucleus: a multiple sequential image fusion (MuSIF) technique for direct stereotaxic localisation and postoperative control

Abstract. A novel multiple, sequential image fusion (MuSIF) procedure merging stereotaxic CT with frameless magnetic resonance imaging (MRI) is used since June 2000 to visualise and directly localise the subthalamic nucleus (STN) on T2 images. In 13 consecutive Parkinsons cases, intraoperative recording and stimulation verified bilateral electrode implantation guided by fused T2 images. In 85% of sides, final implantation opted for visualised target track. Implanted electrode position on postoperative T2 images matched planned target. Clinical follow-up reproduces literatures best results. This MuSIF technique, effective for direct STN targeting, has practical advantages: MRI can be performed regardless of surgery time; regular MR scanning to correct real image distortion is unneeded; and the need for multiple localising tracks is reduced by enabling us to account for each patients STN anatomy.

γ-Hydroxybutyric acid for alcohol-sensitive myoclonus with dystonia

Alcohol-sensitive myoclonus can be associated with dystonic spasms.1 Conventional treatments and anticonvulsants occasionally produce some benefit, but not comparable with the improvement induced by alcohol.1 We report a patient with alcohol-sensitive myoclonus and dystonia who had a consistent and substantial benefit from oral γ-hydroxybutyric acid (GHB). Oral GHB is a drug that is effective both in the treatment of alcohol withdrawal2,3 and in maintaining abstinence from alcohol.4 A 37-year-old man was evaluated for severe disabling myoclonic jerks of the upper limbs, axial muscles, neck and cranial muscles, which were associated with dystonic spasms of the upper limbs and of the neck muscles. According to the Chadwick–Marsden Evaluation Scale for myoclonus,5,6 the patient’s score was 26 points. The hyperkinesias were not stimulus sensitive. They worsened under emotional stress and during the day, but the patient could control involuntary movements …

The subthalamic nucleus in Parkinson's disease: Power spectral density analysis of neural intraoperative signals

Abstract.To test a new tool for the neurophysiological identification of the human subthalamic nucleus (STN) during stereotactic surgery for the implantation of deep-brain-stimulation (DBS) electrodes, we analysed off-line the intraoperative signals recorded from patients with Parkinson’s disease. We estimated the power spectral density (PSD) along each penetration track (8 patients, 13 sides) and determined the spatial correlation of the PSD with the target location estimated from neuroimaging procedures (“anatomical target”), and with the final target location derived from standard intraoperative neurophysiological procedures for STN localization (“clinical target”). At each step we recorded the ‘on-line’ signal for 120 seconds; because the PSD was estimated by calculating the periodogram for 6-second epochs of neural signal, we had 20 epochs at each step. When the electrode track crossed the STN, the PSD in the 0.25-2.5 kHz band increased, peaking on average <0.5 mm cranial to the clinical target and 1.00±1.51 mm caudal to the anatomical target. When the track was outside the nucleus, the PSD remained unchanged. Even on recordings with low signal-tonoise ratio, off-line PSD analysis of neural signals showed a good correspondence with the target indicated by the surgical team. On-line intraoperative estimation of the PSD may be a simple, reliable, rapid and complementary approach to electrophysiological monitoring during STN surgery for Parkinson’s disease.

Subthalamic somatosensory evoked potentials in Parkinson's disease.

Deep brain stimulation (DBS) of subthalamic nucleus (STN) is an effective treatment for advanced Parkinsons disease. It also provides an opportunity to record neural activity from the human basal ganglia. In this study, to investigate the involvement of the human STN in sensory functions, we recorded somatosensory evoked potentials (SEPs) elicited by contralateral median‐nerve stimulation, from STN electrodes implanted for DBS in patients with Parkinsons disease. We suggest that the STN N18 component of SEPs in Parkinsons disease is a mainly local field potential elicited by muscle afferent input to the nucleus.

Transient improvement induced by motor fatigue in focal occupational dystonia: the handgrip test.

Muscle fatigue induced by a previous sustained contraction temporarily decreases the motor output, transiently worsening motor performance. Whether muscle fatigue alters motor performance also in dystonia—a disorder whose main pathophysiological abnormality is motor overflow—remains unknown. To assess the effects of muscle fatigue in patients with focal occupational upper limb dystonia, we studied the effect of a previous maximum fatiguing voluntary contraction on motor performance in 10 musicians with focal occupational dystonia, in 3 musicians with hand motor impairment due to non‐dystonic disorders, and in 5 normal musicians. The fatiguing task consisted of grasping a spring handgrip as long as possible until the task failed. In dystonic musicians, a fatiguing contraction significantly improved motor performance. The improvement lasted less than 5 minutes and appeared only after fatigue of the affected upper limb. In contrast, in musicians with non‐dystonic motor impairment, motor performance remained unchanged or worsened, and normal musician performance consistently worsened.

Postcontraction depression of reciprocal inhibition in human forearm muscles

We tested whether a preceding muscle contraction changes reciprocal inhibition (RI) between forearm antagonists. RI was studied in 14 healthy subjects by assessing changes in the H reflex (evoked by median‐nerve stimulation) in forearm flexor muscles after conditioning radial‐nerve stimulation at 0‐ and 20‐ms intervals. The maximum sizes of the M wave (Mmax) and H reflex (Hmax) were also measured. After a long‐lasting maximum voluntary handgrip contraction (mean ± SEM: 3.9 ± 0.6 min) of ipsilateral forearm muscles, Mmax and Hmax were unchanged but RI was diminished. After contraction of the contralateral homologous muscles and after contraction elicited by ipsilateral muscle stimulation, RI remained unchanged. These results show that a preceding maximum voluntary contraction (lasting 30 s or more) reduces the activity of the spinal inhibitory interneurons mediating RI. This finding may imply the need to reinterpret results from RI studies in normal subjects and in patients with movement disorders.