Cortical response to levodopa in Parkinson's disease patients with dyskinesias

Tapered cross-linked ZnO nanowire bundle arrays on three-dimensional graphene foam for highly sensitive electrochemical detection of levodopa

It is crucial to accurately and rapidly monitor the levodopa (LD) concentration for accurate classification and treatment of dyskinesia in Parkinson's disease. In this paper, 3D graphene foam (GF) with a highly conductive network is obtained by chemical vapor deposition. 3D GF serves as the substrate for hydrothermal in situ growth of tapered cross-linked ZnO nanowire bundle arrays (ZnO NWBAs), enabling the development of a highly sensitive detection platform for LD. The formation mechanism of a tapered cross-linked ZnO nanowire bundle arrays on 3D GF is put forward. The integration of 3D GF and ZnO NWBAs can accelerate the electron transfer rate and increase the contact area with biomolecules, resulting in high electrochemical properties. The electrode composed of ZnO NWBAs on 3D GF exhibits significant sensitivity (1.66 µA·µM-1·cm-2) for LD detection in the concentration range 0-60 µM. The electrode is able to rapidly and specifically determine LD in mixed AA or UA solution. The selectivity mechanism of the electrode is also explained by the bandgap model. Furthermore, the successful detection of LD in serum demonstrates the practicality of the electrode and its great potential for clinical application.

A comprehensive review of the application of Zr-based metal-organic frameworks for electrochemical sensors and biosensors

A family of inorganic-organic hybrid crystalline materials made up of organic ligands and metal cations or clusters is known as metal-organic frameworks (MOFs). Because of their unique stability, intriguing characteristics, and structural diversity, zirconium-based MOFs (Zr-MOFs) are regarded as one of the most interesting families of MOF materials for real-world applications. Zr-MOFs that have the ligands, metal nodes, and guest molecules enclosed show distinct electrochemical reactions. They can successfully and sensitively identify a wide range of substances, which is important for both environmental preservation and human health. The rational design and synthesis of Zr-MOF electrochemical sensors and biosensors, as well as their applications in the detection of drugs, biomarkers, pesticides, food additives, hydrogen peroxide, and other materials, are the main topics of this comprehensive review. We also touch on the current issues and potential future paths for Zr-MOF electrochemical sensor research.

Clinical diagnostic utility of transcranial magnetic stimulation in neurological disorders. Updated report of an IFCN committee

The review provides a comprehensive update (previous report: Chen R, Cros D, Curra A, Di Lazzaro V, Lefaucheur JP, Magistris MR, et al. The clinical diagnostic utility of transcranial magnetic stimulation: report of an IFCN committee. Clin Neurophysiol 2008;119(3):504-32) on clinical diagnostic utility of transcranial magnetic stimulation (TMS) in neurological diseases. Most TMS measures rely on stimulation of motor cortex and recording of motor evoked potentials. Paired-pulse TMS techniques, incorporating conventional amplitude-based and threshold tracking, have established clinical utility in neurodegenerative, movement, episodic (epilepsy, migraines), chronic pain and functional diseases. Cortical hyperexcitability has emerged as a diagnostic aid in amyotrophic lateral sclerosis. Single-pulse TMS measures are of utility in stroke, and myelopathy even in the absence of radiological changes. Short-latency afferent inhibition, related to central cholinergic transmission, is reduced in Alzheimer's disease. The triple stimulation technique (TST) may enhance diagnostic utility of conventional TMS measures to detect upper motor neuron involvement. The recording of motor evoked potentials can be used to perform functional mapping of the motor cortex or in preoperative assessment of eloquent brain regions before surgical resection of brain tumors. TMS exhibits utility in assessing lumbosacral/cervical nerve root function, especially in demyelinating neuropathies, and may be of utility in localizing the site of facial nerve palsies. TMS measures also have high sensitivity in detecting subclinical corticospinal lesions in multiple sclerosis. Abnormalities in central motor conduction time or TST correlate with motor impairment and disability in MS. Cerebellar stimulation may detect lesions in the cerebellum or cerebello-dentato-thalamo-motor cortical pathways. Combining TMS with electroencephalography, provides a novel method to measure parameters altered in neurological disorders, including cortical excitability, effective connectivity, and response complexity.

The role of neuronavigation in TMS-EEG studies: current applications and future perspectives

Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) allows measuring non-invasively the electrical response of the human cerebral cortex to a direct perturbation. Complementing TMS-EEG with a structural neuronavigation tool (nTMS-EEG) is key for accurately selecting cortical areas, targeting them, and adjusting the stimulation parameters based on some relevant anatomical priors. This step, together with the employment of visualization tools designed to perform a quality check of TMS-evoked potentials (TEPs) in real-time during acquisition, is key for maximizing the impact of the TMS pulse on the cortex and in ensuring highly reproducible measurements within sessions and across subjects. Moreover, storing stimulation parameters in the neuronavigation system can help in reproducing the stimulation parameters within and across experimental sessions and sharing them across research centers. Finally, the systematic employment of neuronavigation in TMS-EEG studies is also key to standardize measurements in clinical populations in search for reliable diagnostic and prognostic TMS-EEG-based biomarkers for neurological and psychiatric disorders.

Adaptive deep brain stimulation: Retuning Parkinson's disease

A brain-machine interface represents a promising therapeutic avenue for the treatment of many neurologic conditions. Deep brain stimulation (DBS) is an invasive, neuro-modulatory tool that can improve different neurologic disorders by delivering electric stimulation to selected brain areas. DBS is particularly successful in advanced Parkinson's disease (PD), where it allows sustained improvement of motor symptoms. However, this approach is still poorly standardized, with variable clinical outcomes. To achieve an optimal therapeutic effect, novel adaptive DBS (aDBS) systems are being developed. These devices operate by adapting stimulation parameters in response to an input signal that can represent symptoms, motor activity, or other behavioral features. Emerging evidence suggests greater efficacy with fewer adverse effects during aDBS compared with conventional DBS. We address this topic by discussing the basics principles of aDBS, reviewing current evidence, and tackling the many challenges posed by aDBS for PD.

Effects of Deep Brain Stimulation and Dopaminergic Medication on Excitatory and Inhibitory Spinal Pathways in Parkinson Disease

PURPOSE

Abnormal activity within the corticospinal system is believed to contribute to the motor dysfunction associated with Parkinson disease. However, the effect of treatment for parkinsonian motor symptoms on dysfunctional descending input to the motor neuron pool remains unclear.

METHODS

We recruited nine patients with PD treated with deep brain stimulation and examined the time course of interaction between a conditioning pulse from transcranial magnetic stimulation and the soleus H-reflex. Patients with Parkinson disease were examined under four treatment conditions and compared with 10 age-matched control subjects.

RESULTS

In healthy controls, transcranial magnetic stimulation conditioning led to early inhibition of the H-reflex (76.2% ± 6.3%) at a condition-test interval of -2 ms. This early inhibition was absent when patients were OFF medication/OFF stimulation (132.5% ± 20.4%; P > 0.05) but was maximally restored toward control levels ON medication/ON stimulation (80.3% ± 7.0%). Of note, early inhibition ON medication/ON stimulation tended to be stronger than when medication (85.4% ± 5.9%) or deep brain stimulation (95.7% ± 9.4%) were applied separately. Late facilitation was observed in controls at condition-test intervals ≥5 ms but was significantly reduced (by 50% to 80% of controls) in Parkinson disease OFF stimulation at condition-test intervals ≥15 ms. The late facilitation was akin to control subjects when patients were ON stimulation.

CONCLUSIONS

The present pilot study demonstrates that the recruitment of early inhibition and late facilitation is disrupted in untreated Parkinson disease and that medication and deep brain stimulation may act together to normalize supraspinal drive to the motor neuron pool.

Impaired reach-to-grasp kinematics in parkinsonian patients relates to dopamine-dependent, subthalamic beta bursts

Excessive beta-band oscillations in the subthalamic nucleus are key neural features of Parkinson’s disease. Yet the distinctive contributions of beta low and high bands, their dependency on striatal dopamine, and their correlates with movement kinematics are unclear. Here, we show that the movement phases of the reach-to-grasp motor task are coded by the subthalamic bursting activity in a maximally-informative beta high range. A strong, three-fold correlation linked beta high range bursts, imbalanced inter-hemispheric striatal dopaminergic tone, and impaired inter-joint movement coordination. These results provide new insight into the neural correlates of motor control in parkinsonian patients, paving the way for more informative use of beta-band features for adaptive deep brain stimulation devices.

On the Use of TMS to Investigate the Pathophysiology of Neurodegenerative Diseases

Neurodegenerative diseases are a collection of disorders that result in the progressive degeneration and death of neurons. They are clinically heterogenous and can present as deficits in movement, cognition, executive function, memory, visuospatial awareness and language. Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation tool that allows for the assessment of cortical function in vivo. We review how TMS has been used for the investigation of three neurodegenerative diseases that differ in their neuroanatomical axes: (1) Motor cortex-corticospinal tract (motor neuron diseases), (2) Non-motor cortical areas (dementias), and (3) Subcortical structures (parkinsonisms). We also make four recommendations that we hope will benefit the use of TMS in neurodegenerative diseases. Firstly, TMS has traditionally been limited by the lack of an objective output and so has been confined to stimulation of the motor cortex; this limitation can be overcome by the use of concurrent neuroimaging methods such as EEG. Given that neurodegenerative diseases progress over time, TMS measures should aim to track longitudinal changes, especially when the aim of the study is to look at disease progression and symptomatology. The lack of gold-standard diagnostic confirmation undermines the validity of findings in clinical populations. Consequently, diagnostic certainty should be maximized through a variety of methods including multiple, independent clinical assessments, imaging and fluids biomarkers, and post-mortem pathological confirmation where possible. There is great interest in understanding the mechanisms by which symptoms arise in neurodegenerative disorders. However, TMS assessments in patients are usually carried out during resting conditions, when the brain network engaged during these symptoms is not expressed. Rather, a context-appropriate form of TMS would be more suitable in probing the physiology driving clinical symptoms. In all, we hope that the recommendations made here will help to further understand the pathophysiology of neurodegenerative diseases.

Gait Initiation in Parkinson's Disease: Impact of Dopamine Depletion and Initial Stance Condition

Postural instability, in particular at gait initiation (GI), and resulting falls are a major determinant of poor quality of life in subjects with Parkinson’s disease (PD). Still, the contribution of the basal ganglia and dopamine on the feedforward postural control associated with this motor task is poorly known. In addition, the influence of anthropometric measures (AM) and initial stance condition on GI has never been consistently assessed. The biomechanical resultants of anticipatory postural adjustments contributing to GI [imbalance (IMB), unloading (UNL), and stepping phase) were studied in 26 unmedicated subjects with idiopathic PD and in 27 healthy subjects. A subset of 13 patients was analyzed under standardized medication conditions and the striatal dopaminergic innervation was studied in 22 patients using FP-CIT and SPECT. People with PD showed a significant reduction in center of pressure (CoP) displacement and velocity during the IMB phase, reduced first step length and velocity, and decreased velocity and acceleration of the center of mass (CoM) at toe off of the stance foot. All these measurements correlated with the dopaminergic innervation of the putamen and substantially improved with levodopa. These results were not influenced by anthropometric parameters or by the initial stance condition. In contrast, most of the measurements of the UNL phase were influenced by the foot placement and did not correlate with putaminal dopaminergic innervation. Our results suggest a significant role of dopamine and the putamen particularly in the elaboration of the IMB phase of anticipatory postural adjustments and in the execution of the first step. The basal ganglia circuitry may contribute to defining the optimal referent body configuration for a proper initiation of gait and possibly gait adaptation to the environment.