Biology subjects

Volkmann, J.

Publications and source records attributed to Volkmann, J..

5 recordsLinked to original sources

bioRxiv2026

Deep brain stimulation of the mesencephalic locomotor centre induces stimulation-dependent behavioural states beyond locomotion

Deep brain stimulation (DBS) of the mesencephalic locomotor region (MLR) has been explored to treat gait disturbances. However, clinical outcomes of MLR-DBS have been disappointing overall, with only modest benefits in some individuals and unwanted effects, including anxiety, reported in others. Preclinical studies in several species, by contrast, show that MLR-DBS can improve locomotor and gait deficits, although defensive behaviours in response to stimulation have also been reported in some species. To investigate this discrepancy, we examined frequency- and amplitude-dependent effects of MLR-DBS in healthy rats, combining semi-supervised and unsupervised behavioural analyses. High-frequency, high-amplitude DBS (80-130 Hz), but not low-frequency stimulation (20-60 Hz), elicited hyperlocomotion intermixed with acute defensive-like behaviours. Low-frequency stimulation instead promoted phases of immobility. Consistently, only high-frequency DBS induced region-specific c-Fos expression in the MLR. Complex behaviours, including hyperlocomotion, rearing, tail rattling, and periods of immobility, were most pronounced in animals with the DBS electrode tip localized to the cuneiform nucleus (CnF) of the MLR. Using AAV tracer constructs for bright labelling of CaMKII-positive neurons and their axons, we identified prominent ascending projections from the CnF to the thalamus, substantia nigra pars compacta, zona incerta, hypothalamus, subthalamic nucleus, and central amygdala (CeA). Retrograde tracing confirmed the CnF-to-CeA projection independently. These findings show that the MLR is anatomically connected to higher-order centres linking motor and defensive networks, with DBS frequency and amplitude critically shaping behavioural outcomes that extend beyond locomotion.

neuroscience↗

bioRxiv2026

Probabilistic mouse-human brain correspondence by multimodal optimal transport

The mouse is the principal model for brain mechanism and disease, allowing experiments that cannot be performed in humans. However, findings often translate poorly because homologous regions differ in relative size and some human territories have no clear mouse counterpart. Here we present OTTER, which learns mouse-human brain correspondence as a probabilistic, parcel-resolution coupling using multimodal fused Gromov-Wasserstein optimal transport, integrating functional and structural connectivity with spatial position and curated homologies. OTTER recovers established homologues on a transcriptomic benchmark and preserves broad cross-species organisation along the cortical areal hierarchy. Applying the coupling to human functional connectivity reveals a graded decline in mouse-based reconstruction across evolutionarily expanded association cortex, with the lowest values in lateral prefrontal territory. Finally, the bidirectional map generates testable human predictions from mouse experiments and ranks mouse circuits corresponding to human clinical targets.

neuroscience↗

bioRxiv2026

A precise atlas of the human subcortex

Clinical interventions and neuroimaging in the subcortex require anatomical definitions that exceed the resolution and anatomical detail of currently available deformable brain atlases. Here, we introduce a high-resolution human brain atlas comprising 95 manually segmented grey and white matter structures as well as 82 white matter tracts compiled from a multitude of resources including ex-vivo MRI, histology, fibre dissections, and neuroanatomy textbooks. The atlas is defined at an isotropic resolution of 100 m and can be precisely deformed to individual subject brain anatomy. By providing precise definitions of both grey and white matter structures within and around the basal ganglia, thalamus, subthalamus, midbrain and cerebellum, the atlas provides a foundational resource for stereotactic surgery and subcortical brain imaging research, as well as for development of next-generation neuromodulation strategies.

neuroscience↗

bioRxiv2019

Cellular and synaptic adaptations of neural circuits processing skylight polarization in the fly

Specialized ommatidia harboring polarization-sensitive photoreceptors exist in the dorsal rim area (DRA) of virtually all insects. Although downstream elements have been described both anatomically and physiologically throughout the optic lobes and the central brain of different species, little is known about their cellular and synaptic adaptations and how these shape their functional role in polarization vision. We have previously shown that in the DRA of Drosophila melanogaster, two distinct types of modality-specific distal medulla cell types (Dm-DRA1 and Dm-DRA2) are post-synaptic to long visual fiber photoreceptors R7 and R8, respectively. Here we describe additional neuronal elements in the medulla neuropil that manifest modality-specific differences in the DRA region, including DRA-specific neuronal morphology, as well as differences in the structure of pre- or post-synaptic membranes. Furthermore, we show that certain cell types (medulla tangential cells and octopaminergic neuromodulatory cells) specifically avoid contacts with polarization-sensitive photoreceptors. Finally, while certain transmedullary cells are specifically absent from DRA medulla columns, other subtypes show specific wiring differences while still connecting the DRA to the lobula complex, as previously been described in larger insects. This hints towards a complex circuit architecture with more than one pathway connecting polarization-sensitive DRA photoreceptors with the central brain.

neuroscience↗

bioRxiv2018

Cortical network fingerprints predict deep brain stimulation outcome in dystonia

BackgroundDeep brain stimulation (DBS) is an effective evidence-based therapy for dystonia. However, no unequivocal predictors of therapy responses exist. We investigate whether patients optimally responding to DBS present distinct brain network organization and structural patterns.\n\nMethodsBased on a German multicentre cohort of eighty-two dystonia patients with segmental and generalized dystonia, who received DBS implantation in the globus pallidus internus patients were classified based on the clinical response 36 months after DBS, as superior-outcome group or moderate-outcome group, as above or below 70% motor improvement, respectively. Fifty-one patients met MRI-quality and treatment response requirements (mean age 51.3 {+/-} 13.2 years; 25 female) and were included into further analysis. From preoperative MRI we assessed cortical thickness and structural covariance, which were then fed into network analysis using graph theory. We designed a support vector machine to classify subjects for the clinical response based on group network properties and individual grey matter fingerprints.\n\nResultsThe moderate-outcome group showed cortical atrophy mainly in the sensorimotor and visuomotor areas and disturbed network topology in these regions. From all the structural integrity of the cortical mantle explained about 45% of the stimulation amplitude. Classification analyses achieved 88% of accuracy using individual grey matter atrophy patterns to predict DBS outcome.\n\nConclusionsThe analysis of cortical integrity and network properties could be developed into independent predictors to identify dystonia patients who benefit from DBS.

neuroscience↗