Biology subjects

Backhaus, W.

Publications and source records attributed to Backhaus, W..

3 recordsLinked to original sources

bioRxiv2023

Early functional connectivity alterations in contralesional motor networks influence outcome after severe stroke

Connectivity studies have significantly extended the knowledge on motor network alterations after stroke. Compared to interhemispheric or ipsilesional networks, changes in the contralesional hemisphere are poorly understood. Data obtained in the acute stage after stroke and in severely impaired patients are remarkably limited. This study aimed to investigate early functional connectivity changes of the contralesional parieto-frontal motor network and their relevance for the functional outcome after severe motor stroke. Resting-state functional imaging data were acquired in 19 patients within the first two weeks after severe stroke. Nineteen healthy participants served as a control group. Functional connectivity was calculated from five key motor areas of the parieto-frontal network on the contralesional hemisphere as seed regions and compared between the groups. Connections exhibiting stroke-related alterations were correlated with clinical follow-up data obtained after 3 to 6 months. The main finding was an increase in coupling strength between the contralesional supplementary motor area and the sensorimotor cortex. This increase was linked to persistent clinical deficits at follow-up. Thus, an upregulation in contralesional motor network connectivity might be an early pattern in severely impaired stroke patients. It might carry relevant information regarding the outcome which adds to the current concepts of brain network alterations and recovery processes after severe stroke.

neuroscience↗

bioRxiv2019

Effects of transcranial alternating-current stimulation to secondary motor areas on cortical oscillations in stroke patients

BackgroundThere is growing evidence that secondary motor areas are relevant for recovery after motor stroke. Communication among brain areas occurs via synchronization of oscillatory activity which can potentially be modulated via transcranial alternating-current stimulation (tACS).\n\nHypothesisWe hypothesized that tACS to secondary motor areas of the stroke-lesioned hemisphere leads to modulation of task-related connectivity among primary and secondary motor areas, reflected in metrics of EEG coupling in the frequency domain.\n\nMethodsWe applied focal tACS at 1mA peak-to-peak intensity to ipsilesional ventral premotor cortex (PMv) and supplementary motor area (SMA) in chronic stroke patients while they moved their impaired hand. To probe effects of stimulation on cortical oscillations, several task-related EEG-based connectivity metrics (coherence, imaginary coherence, phase-locking value, mutual information) were assessed before and after each stimulation.\n\nResultsOverall, we found significant but weak modulations of the motor network by tACS. Stimulation of PMv reduced task-related coupling between (i) both primary motor cortices (M1) (coherence, -0.0514{+/-}0.0665 (mean{+/-}SD, active stimulation) vs. 0.0085{+/-}0.0888 (sham), p=0.0029) and (ii) between ipsilesional M1 and contralesional PMv (coherence, - 0.0386{+/-}0.0703 vs. 0.0226{+/-}0.0694, p=0.0283; phase-locking value, -0.0363{+/-}0.0581 vs. 0.0036{+/-}0.0497, p=0.0097) compared with sham stimulation.\n\nConclusionsIn this exploratory analysis, tACS to the ipsilesional PMv induced a weak decrease of task-related connectivity between ipsilesional M1 and contralesional M1 and PMv. As an excess of interhemispheric coupling is under discussion as maladaptive phenomenon of motor reorganization after stroke (e.g., bimodal balance-recovery model), tACS-induced reduction of coupling might be an interesting approach to assist re-normalization of the post-stroke motor network.

neuroscience↗

bioRxiv2019

Sensory and auditory evoked responses mimic synchronization of cortical oscillations induced by Transcranial Magnetic Stimulation

BackgroundEntrainment of cortical oscillations by repetitive Transcranial Magnetic Stimulation (rTMS) is an attractive approach to modulate brain function non-invasively in humans. Here, we applied rTMS in order to modulate oscillatory activity in ventral premotor cortex (PMv), primary motor cortex (M1), and anterior intraparietal sulcus (aIPS). These areas are thought to contribute to recovery after motor stroke and our overarching goal is to enhance their impact by rTMS. To this end, we established a setup with bifocal, neuronavigated rTMS combined with EEG and tested its technical feasibility. MethodsBifocal zero-phase lag synchronized rTMS at 11Hz was applied in seven young healthy volunteers to the target pairs (i) PMv and M1 and (ii) aIPS and M1. Adapting to the close vicinity between target areas, we used two small, commercially available coils and applied subthreshold stimuli in order to avoid motor evoked potentials (MEPs). Besides a parieto-occipital sham stimulation, we also included auditory and sensory stimulation in a further control experiment. ResultsFirst, subthreshold TMS led to a phase synchronization and evoked time-averaged potentials in the EEG. However, the same findings could be elicited by peripheral, somatosensory stimulation combined with auditory stimulation. Second, despite the small coils neuronavigation analysis showed that in most participants aIPS and M1 or PMv and M1 could not precisely be targeted due to their vicinity and restriction in coil positioning. Third, bifocal subthreshold rTMS tended to sum up where the induced fields showed the greatest overlap resulting in overt MEPs and thus raising potential safety issues. ConclusionsThe presented data show refinements for bifocal rTMS studies regarding (i) spurious entrainment or resetting effects on brain oscillations, (ii) precise anatomical targeting of areas in close vicinity, and (iii) summing up of overlapping induced electrical fields.

neuroscience↗