Sleep Spindles – As a Biomarker of Brain Function and Plasticity

Alternative & renewable energy sources & technolog

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-dentatothalamo- 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

Transcranial Direct Current Stimulation (tDCS) to Improve Lower Limb Motor Recovery Following Stroke: A Review and Study Proposal

Strokes are the result of restricted blood flow to particular areas of the brain classified by their cause. The neural damage they cause are of growing concern as the number of young adults experiencing strokes has increased by 11% in the last decade. Following stroke, there is an imbalance of inhibitory and excitatory neuronal activity, and disruption of neural networks. These changes lead to neuronal death and loss of synaptic connections that, depending on which part of the brain is affected, result in behavioral deficits such as weakness, limb hemiparesis, and loss of coordination, as well as speech and cognitive impairments. However, this loss of function can be partly recovered due to neuroplastic processes. Non-invasive brain stimulation (NIBS) is an approach that involves implanting electrodes into targeted areas of the brain which are connected to an implantable pulse generator on the skin that delivers chronic electric pulse. There are different forms of stimulation, but one with some established success in improving upper and lower limb mobility, as well as some cognitive symptoms, is transcranial direct current stimulation (tDCS). For the treatment of stroke, tDCS aims to increase excitability of the lesioned areas to improve contralesional mobility. While past research has focused on stimulating well established motor regions, such as the cerebellum, motor cortex, and basal ganglia, sensory systems also play a key role in sending information through the ascending dorsal column medial lemniscal pathway, posterior and anterior spinocerebellar tracts, and spinoreticular tracts. Here is a review of the current research on the integration of sensory and motor information in order to carry out desired movement, a discussion about how these networks are being targeted by tDCS after stroke to help patients regain lower limb movement, and finally, a proposed study in which improvements in balance, gait, and postural stability after anodal tDCS continue up to a year post-treatment in chronic ischemic stroke patients

Early brain activity : Translations between bedside and laboratory

Neural activity is both a driver of brain development and a readout of developmental processes. Changes in neuronal activity are therefore both the cause and consequence of neurodevelopmental compromises. Here, we review the assessment of neuronal activities in both preclinical models and clinical situations. We focus on issues that require urgent translational research, the challenges and bottlenecks preventing translation of biomedical research into new clinical diagnostics or treatments, and possibilities to overcome these barriers. The key questions are (i) what can be measured in clinical settings versus animal experiments, (ii) how do measurements relate to particular stages of development, and (iii) how can we balance practical and ethical realities with methodological compromises in measurements and treatments.Peer reviewe

Brain plasticity and stroke recovery

Brain plasticity and stroke recovery Recovery from stroke is based on the capability of the brain to reorganize its structure and function after lesion. An acute stroke triggers a cascade of time-dependent metabolic and physiological reactions, which enable changes in the organization and function of widespread cortical regions. A wide range of studies, using various functional imaging methods, have thrown light on the reorganizational changes after stroke. However, less is known about the temporal evolution of these changes and their correlation to clinical recovery. In this thesis, different aspects of neurophysiological changes related to sensorimotor recovery were studied in 18 patients with first-ever stroke in the middle cerebral artery territory, affecting upper limb motor function. Follow-up recordings of somatosensory evoked fields (SEF) and spontaneous rhythmic brain activity were performed with whole-head MEG within 1 week (T0), 1 month (T1), and 3 months (T2) after stroke with concomitant evaluation of clinical outcome. MEG suits stroke studies especially well, as it is independent from hemodynamic alterations, and the signals are practically unaffected by morbid tissue. The results indicated that the hand representation in the primary somatosensory cortex (SI) in the affected hemisphere (AH) was transiently enlarged at T1 and returned to normal size concomitantly with clinical improvement of hand function (Study I). Study II showed that the activation in the contralateral secondary somatosensory cortex (cSII) was decreased in the AH at T0 and increased during follow-up. The strength of cSII activation paralleled the recovery of hand function during the 3 months follow-up, suggesting that cSII may be an important region in mediating the somatosensory input to the motor cortex. The results in Study III indicated that afferent-input-modulated motor cortex excitability was increased in the AH in the acute phase after stroke and decreased during follow-up in association with recovery of hand function. Study IV showed that the ~10-Hz oscillations were enhanced in the AH at T1 and T2. Moreover, pathological perilesional low-frequency oscillations were detected in 7/16 patients at T0, and the low-frequency oscillations persisted for at least 3 months in 4 patients. These 4 patients had a worse clinical outcome at T2 than the rest of the patients. The results indicate that even small lesions can cause widespread neurophysiological changes in the cortical network. Certain brain regions, such as SII, seem to be specifically important for the recovery of hand function. The results underline the importance of parallel recovery of the somatosensory and motor systems for fluent hand function. The most evident neurophysiological changes were observed within 1 month after stroke in parallel with steepest improvement of clinical recovery, suggesting that the first 4 weeks are critical for functional recovery.Aivojen muovautuvuus ja aivoinfarktista toipuminen Aivoinfarkti on yksi merkittävimmistä pysyvää invaliditeettia aiheuttavista sairauksista länsimaissa. Vaikka aivoinfarktin akuuttihoito on viime vuosina kehittynyt merkittävästi, aktiivinen kuntoutus on edelleen merkittävin potilaan toipumiseen vaikuttava tekijä. Aivoinfarktista kuntoutuminen perustuu aivojen kykyyn muovautua ja sopeutua ympäristön aiheuttamiin muutoksiin. Aiemmat tutkimukset ovat osoittaneet, että aivovaurion jälkeiset muovautumismuutokset ovat välttämättömiä toipumiselle, mutta edelleen tiedetään varsin vähän siitä, miten muutokset kehittyvät toipumisen myötä ja miten ne korreloivat kuntoutumiseen. Tässä väitöskirjassa tutkittiin magnetoenkefalografian (MEG) avulla, minkälaisia muutoksia akuutti aivoinfarkti aiheuttaa aivojen liike- ja tuntoaivokuorien toiminnassa, ja miten nämä muutokset vaikuttavat potilaan halvausoireista toipumiseen. Erityisesti keskityttiin siihen, miten tuntoaistijärjestelmän vauriot vaikuttavat liikkeen suoritukseen ja mitkä mekanismit vastaavat tunto- ja liikeaivokuorien välisestä tiedonkulusta. Tutkimuksessa seurattiin MEG mittauksin 18 elämänsä ensimmäiseen aivoinfarktiin sairastunutta potilasta, joilla aivoinfarkti aiheutti yläraajan halvausoireen. Potilailta tutkittiin aivojen tuntoherätevasteiden ja rytmisen toiminnan muutoksia viikon sisällä, 1 ja 3 kuukautta sairastumisesta. Kliinistä toipumista seurattiin useilla toimintakykyä mittaavilla testeillä. Tulokset osoittivat, että käden edustusalue sairastuneen aivopuoliskon primaarisella tuntoaivokuorella laajenee ensimmäisen kuukauden aikana. Toipumisen myötä edustusalue palautui normaaliksi 3:n kuukauden seuranta-aikana. Aiemmat eläinkokeet ovat osoittaneet, että edustusalueiden muutokset aivoissa liittyvät ennen kaikkea uuden oppimiseen eikä pelkästään jo osatun taidon toistamiseen. Näin ollen käden edustusalueen laajeneminen saattaa olla yhteydessä motorisen taidon uudelleenoppimiseen ja edustusalueen palautuminen normaaliksi voisi kuvastaa jo opitun taidon ylläpitämistä. Lisäksi tutkimustulokset osoittivat, että aivojen tuntoaivoverkostossa tapahtuu korjaavia muutoksia toipumisen myötä. Tietyt aivoalueet vaikuttivat erityisen tärkeiltä käden motoriselle toipumiselle. Esimerkiksi sekundaarisen tuntoaivokuoren aktivaation voimakkuus kasvoi merkittävästi seurantamittauksissa; ja aktivaation voimakkuus korreloi käden toimintakyvyn paranemiseen. Tulokset osoittivat myös, että tuntoaivokuorelta saapuva palaute vaikuttaa merkittävästi liikeaivokuoren toiminnan palautumiseen vaurion jälkeen. Tulokset alleviivaavat tunto- ja liikeaivoverkoston yhteistoiminnan tärkeyttä käden motorisessa toipumisessa. Suurimmat neurofysiologiset muutokset olivat havaittavissa kuukauden sisällä aivoinfarktiin sairastumisesta, korostaen ensimmäisten 4:n viikon tärkeyttä kuntoutuksessa