6 research outputs found
Electrical Brain Stimulation Improves Cognitive Performance by Modulating Functional Connectivity and Task-Specific Activation
Excitatory anodal transcranial direct current stimulation (atDCS) can improve human cognitive functions, but neural underpinnings of its mode of action remain elusive. In a cross-over placebo ("sham") controlled study we used functional magnetic resonance imaging (fMRI) to investigate neurofunctional correlates of improved language functions induced by atDCS over a core language area, the left inferior frontal gyrus (IFG). Intrascanner transcranial direct current stimulation-induced changes in overt semantic word generation assessed behavioral modulation; task-related and task-independent (resting-state) fMRI characterized language network changes. Improved word-retrieval during atDCS was paralleled by selectively reduced task-related activation in the left ventral IFG, an area specifically implicated in semantic retrieval processes. Under atDCS, resting-state fMRI revealed increased connectivity of the left IFG and additional major hubs overlapping with the language network. In conclusion, atDCS modulates endogenous low-frequency oscillations in a distributed set of functionally connected brain areas, possibly inducing more efficient processing in critical task-relevant areas and improved behavioral performance
Transcranial direct current stimulation over multiple days improves learning and maintenance of a novel vocabulary
Introduction: Recently, growing interest emerged in the enhancement of human potential by means of non-invasive brain stimulation. In particular, anodal transcranial direct current stimulation (atDCS) has been shown to exert beneficial effects on motor and higher cognitive functions. However, the majority of transcranial direct current stimulation (tDCS) studies have assessed effects of single stimulation sessions that are mediated by transient neural modulation. Studies assessing the impact of multiple stimulation sessions on learning that may induce long-lasting behavioural and neural changes are scarce and have not yet been accomplished in the language domain in healthy individuals
VerÀnderungen in PlastizitÀt und Kognition durch neurovaskulÀre Erkrankungen und non-invasive Hirnstimulation
Plasticity is a milestone in neuroscientific investigations into the
biological mechanisms of learning. Plasticity is critically reduced in older
adults and in individuals with neurovascular disorders that encompass changes
in cerebral blood supply. Mechanisms underlying this altered plasticity are
important to understand in order to develop future preventive and therapeutic
strategies. Pathological and interventional changes in plasticity are thus the
focus of the current thesis. In three interrelated studies, this thesis
explores the underpinning of cognitive deterioration and the neural changes
accompanying cognitive enhancement. The first study tested the associations
between cerebral autoregulation (vasomotor reactivity, VMR), magnetic
resonance imaging (MRI) measurements of structural and functional
connectivity, and cognitive performance in patients with unilateral occlusive
processes of the internal cerebral artery (ICA, n=14) and matched controls
(n=11). Patients revealed lower VMR in the affected hemisphere (AH), decrease
in whole-brain microstructure and in inter- and intra-hemispheric functional
connections. Moreover, reduced VMR in the AH correlated with reduced
microstructure in frontal areas and connectivity in the default-mode network
(DMN). This suggests that disconnections within critical brain networks might
mediate the effects of impaired VMR on cognition. The second study tested the
short-term changes induced by transcranial direct current stimulation (tDCS)
on language performance and the underlying neuronal mechanisms of these
behavioral gains. Blood-oxygen level dependent (BOLD) activity and functional
networks under real and sham tDCS were measured in 24 young healthy subjects.
Here, tDCS over a core language area improved semantic fluency, decreased
activity in the stimulated region and facilitated connections within the
language network. The results point to a critical link between enhanced
network connectivity and increased neural efficiency which might be necessary
for improved task performance. The third study investigated long-lasting
behavioral gains induced by training in combination with tDCS during language
learning. In this study, 40 young healthy subjects acquired a novel vocabulary
during 5 consecutive days under real or sham tDCS and were tested in two
memory tasks on a daily basis. The results indicate that tDCS facilitated
language acquisition and retention of the learned vocabulary. Findings from
the three interconnected studies thus lead to the suggestion that tDCS could
assist patients with occlusion / stenosis of the ICA, in which loss of
cognition might be mediated by structural and functional changes in
connectivity. A potential preventive therapy with tDCS could target these
regions in frontal and parietal cortices, with the aim to improve cognition in
these patients.PlastizitÀt stellt einen Meilenstein in der neurowissenschaftlichen
Erforschung der biologischen Lernmechanismen dar. PlastizitÀt ist bei Àlteren
Menschen, sowie bei neurovaskulÀren Erkrankungen, welche mit VerÀnderungen im
zerebralen Blutfluss einhergehen, deutlich reduziert. Ein besseres VerstÀndnis
der PlastizitĂ€tsmechanismen, könnte zukĂŒnftig dazu beitragen, neue prĂ€ventive
und therapeutische MaĂnahmen zu entwickeln. Der Fokus dieser Arbeit liegt
daher auf pathologischen und interventionsbedingten VerÀnderungen der
PlastizitÀt. Innerhalb dieser Dissertationsschrift wurden in drei
zusammenhÀngenden Studien die Ursachen kognitiven Abbaus, sowie die mit
kognitiven Verbesserungen assoziierten neuronalen VerÀnderungen untersucht.
Die erste Studie analysierte ZusammenhÀnge zwischen zerebraler Autoregulation
(Vasomotor-ReaktivitÀt, VMR), kognitiver LeistungsfÀhigkeit, sowie Parametern
struktureller und funktioneller KonnektivitÀt, die mittels
Magnetresonanztomographie (MRT) erhoben wurden, bei Patienten (n=14) mit
unilateralen Verschlussprozessen der Arteria carotis interna (ICA) im
Vergleich zu einer Kontrollgruppe (n=11). Die Patienten zeigten verminderte
VMR in der betroffenen HemisphÀre (bH), verringerte Mikrostruktur im gesamten
Gehirn sowie in der inter- und intrahemisphÀrischen funktionellen
KonnektivitÀt. Des Weiteren ging verminderte VMR innerhalb der bH mit
verringerter Mikrostruktur in frontalen Arealen sowie verringerter
KonnektivitÀt innerhalb des Default-mode-Netzwerks (DMN) einher. Dies lÀsst
vermuten, dass Störungen innerhalb aufgabenrelevanter Gehirnnetzwerke die
Effekte einer beeintrÀchtigten VMR auf die GedÀchtnisleistung vermitteln. Die
zweite Studie untersuchte mittels transkranieller Gleichstromstimulation
(tDCS) induzierte KurzzeitverÀnderungen auf die Sprachleistung, sowie deren
zugrunde liegenden neuronalen Mechanismen. Die vom Blutsauerstoffgehalt
abhÀngige AktivitÀt und funktionale Netzwerke wurden mittels tDCS- und
Scheinstimulation bei 24 jungen gesunden Probanden gemessen. Eine Platzierung
der tDCS-Elektroden oberhalb der Kernareale des Sprachzentrums fĂŒhrte zu
verminderter AktivitÀt innerhalb der stimulierten Region, zu einer
verbesserten semantischen Sprachkompetenz, sowie zu begĂŒnstigten Verbindungen
innerhalb des Sprachennetzwerks. Die Ergebnisse weisen auf eine entscheidende
Verbindung zwischen verstÀrkter NetzwerkkonnektivitÀt und erhöhter neuronaler
Effizienz hin, welche möglicherweise notwendig fĂŒr verbesserte
GedÀchtnisleistungen sind. Die dritte Studie untersuchte langfristige
GedÀchtnissteigerungen, die durch Kombination aus kognitivem Training und tDCS
wÀhrend einer Sprachlernaufgabe induziert wurden. In dieser Studie erlernten
40 junge gesunde Probanden innerhalb eines Zeitraums von fĂŒnf
aufeinanderfolgenden Tagen einen neuen Wortschatz. WĂ€hrend zweimaligen
tÀglichen GedÀchtnisaufgaben wurde bei den Probanden entweder tDCS- oder
Scheinstimulation angewendet. Die Ergebnisse legen nahe, dass tDCS eine
begĂŒnstigende Wirkung auf Spracherwerb und Beibehaltung des erlernten
Wortschatzes hat. Zusammenfassend weisen die Ergebnisse der drei vorliegenden
Studien darauf hin, dass tDCS eine unterstĂŒtzende Wirkung bei Patienten mit
GefĂ€ĂverschlĂŒssen/Stenosen der ICA haben könnte, deren GedĂ€chtnisverlust ĂŒber
strukturelle und funktionelle KonnektivitÀtsverÀnderungen vermittelt sein
könnte. Eine potentielle prÀventive tDCS-Therapie könnte speziell auf Regionen
abzielen, die in Zusammenhang mit dem DMN im frontalen und parietalen Kortex
stehen, um die kognitive LeistungsfÀhigkeit betroffener Patienten zu
verbessern
Improving emotional prosody detection in the attending ear by cathodal tDCS suppression of the competing channel
Currently it is assumed that cathodal stimulation (in transcranial direct current stimulation, tDCS) degrades the neural firing rate, and thus it is believed to degrade cognitive performance. Here we challenge this assumption by predicting that under high competition the cathodal stimulation might act as a noise filter, leading to an improved performance. We presented auditory targets with different emotional valence using a dichotic listening paradigm. We found that cathodal, but not anodal stimulation of the right IFG generated better prosody comprehension. Cathodal stimulation in competitive situations, such as the dichotic listening paradigm, can act like a noise filter, and may in fact enhance cognitive performance. This study contributes to understanding the way the IFG is engaged with prosody functions, and explains the cathodal effects of tDCS. This might lead to the development of more efficient brain stimulation protocols
Additional file 1 of Bridging language barriers in developing valid health policy research tools: insights from the translation and validation process of the SHEMESH questionnaire
Additional file 1. The final Hebrew version of the SHEMESH questionnaire