The clinical use of deep brain stimulation (DBS) is among the most important advances in the clinical neurosciences in the past two decades. As a surgical tool, DBS can directly measure pathological brain activity and can deliver adjustable stimulation for therapeutic effect in neurological and psychiatric disorders correlated with dysfunctional circuitry. The development of DBS has opened new opportunities to access and interrogate malfunctioning brain circuits and to test the therapeutic potential of regulating the output of these circuits in a broad range of disorders. Despite the success and rapid adoption of DBS, crucial questions remain, including which brain areas should be targeted and in which patients. This Review considers how DBS has facilitated advances in our understanding of how circuit malfunction can lead to brain disorders and outlines the key unmet challenges and future directions in the DBS field. Determining the next steps in DBS science will help to define the future role of this technology in the development of novel therapeutics for the most challenging disorders affecting the human brain.

Competing interestsJ. K. K. is a consultant for Medtronic and Boston Scientific. P. B. is a consultant for Medtronic. W. M. G. is the Director, Chief Scientific Officer and share owner of Deep Brain Innovations, LLC. He also receives royalty payments for licensed patents on temporal patterns of deep brain stimulation. M. I. H. has received travel expenses and honoraria from Boston Scientific for speaking at meetings. A. H. was supported by the German Research Council (DFG grant 410169619) and reports lecture fees from Medtronic and Boston Scientific unrelated to the present work. P. A. T. works as a consultant for Boston Scientific Neuromodulation. J. V. works as a consultant to Boston Scientific, Medtronic, and Newronika and has received honoraria for lectures from Boston Scientific and Medtronic as well as research grants from Boston Scientific and Medtronic. A. M. L. has served as a consultant for Boston Scientific, Medtronic, Aleva, and Abbott and is a co-founder of Functional Neuromodulation. All other authors declare no competing interests. Peer review informationNature Reviews Neurology thanks V. Visser-Vandewalle and Y. Temel for their contribution to the peer review of this work. Publisher's noteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Objectives: To provide a revised version of earlier guidelines published in 2006. Background: Primary dystonias are chronic and often disabling conditions with a widespread spectrum mainly in young people. Diagnosis: Primary dystonias are classified as pure dystonia, dystonia plus or paroxysmal dystonia syndromes. Assessment should be performed using a validated rating scale for dystonia. Genetic testing may be performed after establishing the clinical diagnosis. DYT1 testing is recommended for patients with primary dystonia with limb onset before age 30, and in those with an affected relative with early-onset dystonia. DYT6 testing is recommended in early-onset or familial cases with craniocervical dystonia or after exclusion of DYT1. Individuals with early-onset myoclonus should be tested for mutations in the DYT11 gene. If direct sequencing of the DYT11 gene is negative, additional gene dosage is required to improve the proportion of mutations detected. A levodopa trial is warranted in every patient with early-onset primary dystonia without an alternative diagnosis. In patients with idiopathic dystonia, neurophysiological tests can help with describing the pathophysiological mechanisms underlying the disorder. Treatment: Botulinum toxin (BoNT) type A is the first-line treatment for primary cranial (excluding oromandibular) or cervical dystonia; it is also effective on writing dystonia. BoNT/B is not inferior to BoNT/A in cervical dystonia. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for primary generalized or cervical dystonia, after medication or BoNT have failed. DBS is less effective in secondary dystonia. This treatment requires a specialized expertise and a multidisciplinary team.

Here we test the hypothesis that there are distinct temporal patterns of synchronized neuronal activity in the pallidum that characterize untreated and treated parkinsonism and dystonia. To this end we recorded local field potentials (LFPs) from the caudal and rostral contact pairs of macroelectrodes implanted into the pallidum of patients for the treatment of Parkinson's disease (12 cases recorded on and off medication, 17 macroelectrodes) and dystonia (10 cases, 19 macroelectrodes). Percentage LFP power in the 11-30 Hz band was decreased and that in the 4-10 Hz band increased across both contact pairs in treated Parkinson's disease compared with untreated Parkinson's disease. Dystonic patients had even less 11-30 Hz power and greater 4-10 Hz power compared with untreated or treated Parkinson's disease patients. The change in the 4-10 Hz band in patients with dystonia was particularly manifest in the more rostral contact pair, presumed to be within or bridging the globus pallidus externus. We conclude that untreated and treated Parkinson's disease and dystonia are characterized by different spatiotemporal patterns of activity in the human pallidum.

Navigate PD was an educational program established to supplement existing guidelines and provide recommendations on the management of Parkinson's disease (PD) refractory to oral/transdermal therapies. It involved 103 experts from 13 countries overseen by an International Steering Committee (ISC) of 13 movement disorder specialists. The ISC identified 71 clinical questions important for device-aided management of PD. Fifty-six experts responded to a web-based survey, rating 15 questions as 'critically important;' these were refined to 10 questions by the ISC to be addressed through available evidence and expert opinion. Draft guidance was presented at international/national meetings and revised based on feedback. Key take-home points are: • Patients requiring levodopa >5 times daily who have severe, troublesome 'off' periods (>1-2 h/day) despite optimal oral/transdermal levodopa or non-levodopa-based therapies should be referred for specialist assessment even if disease duration is <4 years. • Cognitive decline related to non-motor fluctuations is an indication for device-aided therapies. If cognitive impairment is mild, use deep brain stimulation (DBS) with caution. For patients who have cognitive impairment or dementia, intrajejunal levodopa infusion is considered as both therapeutic and palliative in some countries. Falls are linked to cognitive decline and are likely to become more frequent with device-aided therapies. • Insufficient control of motor complications (or drug-resistant tremor in the case of DBS) are indications for device-aided therapies. Levodopa-carbidopa intestinal gel infusions or subcutaneous apomorphine pump may be considered for patients aged >70 years who have mild or moderate cognitive impairment, severe depression or other contraindications to DBS.