Plastizität im motorischen System: Funktionelle Konnektivität und dynamische Interaktionen beim Erlernen motorischer Sequenzen

Die vorliegende Dissertation untersucht drei Aspekte motorischen Sequenzlernens: Die initiale Lernphase anhand einer expliziten Finger-Tapping Aufgabe, die frühe Konsolidierungsphase bei Wachheit unter Einfluss verschiedener Interferenzaufgaben und der Einfluss der frühen schlafgebundenen Konsolidierung auf die Transformation impliziten in explizites Wissen. Ausgangspunkt für die Fragestellungen ist das Rahmenmodell des motorischen Sequenzlernens auf behavioraler Ebene (beispielsweise Walker, Brakefield, Morgan, Hobson, & Stickgold, 2002) und Befunde zur funktionellen Konnektivität innerhalb des beteiligten neuronalen Netzwerkes (Doyon & Benali, 2005; Nakamura, Sakai, & Nakahara, 2002). Auf neuronaler Ebene konnte die effektive Konnektivität innerhalb des motorischen Netzwerkes bei Schreibkrampfpatienten während einer expliziten Finger-Tapping Aufgabe im Vergleich zu gesunden Kontrollprobanden charakterisiert werden (Rothkirch et al., 2018a). Es ergaben sich spezifische Änderungen in der kortiko-cerebellären und kortiko-striatalen Schleife, die mit früheren Befunden der funktionellen Konnektivität im Einklang stehen. In einer zweiten bildgebenden Untersuchung (Rothkirch et al., 2018b) an gesunden Probanden ergaben sich Hinweise auf einen frühen neuronalen Konsolidierungseffekt einer implizit erlernten motorischen Sequenz durch eine Interaktion mit einer deklarativen Gedächtnisaufgabe. In einer Meta-Analyse beleuchteten wir die Transformation implizit erworbener Fertigkeiten in explizites Faktenwissen durch schlafgebundene Konsolidierung. Dabei wurde die implizit-explizit Transformation nicht ausschließlich, aber unter besonderer Berücksichtigung motorischen Sequenzlernens untersucht. Es ergaben sich Hinweise für schlafgebundene Konsolidierungsprozesse im Sinne eines kontinuierlichen qualitativen Wandels von implizit gelernten Informationen zu explizitem Wissen, die auch bei motorischem Sequenzlernen eine Rolle spielen könnten (Rothkirch et al., unveröffentlicht)

Does Post-task Declarative Learning Have an Influence on Early Motor Memory Consolidation Over Day? An fMRI Study

Previous studies demonstrated the influence of the post-learning period on procedural motor memory consolidation. In an early period after the acquisition, motor skills are vulnerable to modifications during wakefulness. Indeed, specific interventions such as world-list learning within this early phase of motor memory consolidation seem to enhance motor performance as an indicator for successful consolidation. This finding highlights the idea that manipulations of procedural and declarative memory systems during the early phase of memory consolidation over wakefulness may influence off-line consolidation. Using functional magnetic resonance imaging (fMRI) during initial motor sequence learning and motor sequence recall, we indirectly assess the influence of a secondary task taken place in the early phase of memory consolidation. All participants were scanned using fMRI during the learning phase of a serial reaction time task (SRTT) at 8 a.m. Afterwards, they were randomly assigned to one of five conditions. One group performed a declarative verbal, one a declarative nonverbal learning task. Two groups worked on attention tasks. A control group passed a resting condition. Participants stayed awake the whole day and performed the SRTT in the MRI scanner 12 h later at 8 p.m. At the behavioral level, the analysis of the reaction times failed to show a significant group difference. The primary analysis assessing fMRI data based on the contrast (sequence – random) between learning and retrieval also did not show any significant group differences. Therefore, our main analysis do not support the hypothesis that a secondary task influences the retrieval of the SRTT. In a more liberal fMRI analysis, we compared only the sequence blocks of the SRTT from learning to recall. BOLD signal decreased in the ipsilateral cerebellum and the supplementary motor area solely in the verbal learning group. Although our primary analysis failed to show significant changes between our groups, results of the secondary analysis could be an indication for a beneficial effect of the verbal declarative task in the early post-learning phase. A nonverbal learning task did not affect the activation within the motor network. Further studies are needed to replicate this finding and to assess the usefulness of this manipulation

Dynamic causal modeling revealed dysfunctional effective connectivity in both, the cortico-basal-ganglia and the cerebello-cortical motor network in writers' cramp

Writer's cramp (WC) is a focal task-specific dystonia characterized by sustained or intermittent muscle contractions while writing, particularly with the dominant hand. Since structural lesions rarely cause WC, it has been assumed that the disease might be caused by a functional maladaptation within the sensory-motor system. Therefore, our objective was to examine the differences between patients suffering from WC and a healthy control (HC) group with regard to the effective connectivity that describes causal influences one brain region exerts over another within the motor network. The effective connectivity within a network including contralateral motor cortex (M1), supplementary motor area (SMA), globus pallidus (GP), putamen (PU) and ipsilateral cerebellum (CB) was investigated using dynamic causal modeling (DCM) for fMRI. Eight connectivity models of functional motor systems were compared. Fifteen WC patients and 18 age-matched HC performed a sequential, five-element finger-tapping task with the non-dominant and non-affected left hand within a 3 T MRI-scanner as quickly and accurately as possible. The task was conducted in a fixed block design repeated 15 times and included 30 s of tapping followed by 30 s of rest. DCM identified the same model in WC and HC as superior for reflecting basal ganglia and cerebellar motor circuits of healthy subjects. The M1-PU, as well as M1-CB connectivity, was more strongly influenced by tapping in WC, but the intracortical M1-SMA connection was more facilitating in controls. Inhibiting influences originating from GP to M1 were stronger in controls compared to WC patients whereby facilitating influences the PU exerts over CB and CB exerts over M1 were not as strong. Although the same model structure explains the given data best, DCM confirms previous research demonstrating a malfunction in effective connectivity intracortically (M1-SMA) and in the cortico-basal ganglia circuitry in WC. In addition, DCM analysis demonstrates abnormal reciprocal excitatory connectivity in the cortico-cerebellar circuitry. These results highlight the dysfunctional cerebello-cortical as well as basalganglio-cortical interaction in WC. Keywords: Dynamic causal modeling, Focal hand dystonia, Writer's cramp, Network disorder, Cerebellu