Biology subjects

Ruhnau, P.

Publications and source records attributed to Ruhnau, P..

6 recordsLinked to original sources

bioRxiv2026

Digital-twin optimized transcranial temporal interference electrical stimulation alters rat brain activity patterns and metabolism including deep structures

Non-invasive deep-brain stimulation (DBS) using transcranial alternating current stimulation (tACS) with temporal interference (TI) has emerged as a promising approach for therapeutic applications in motor and neuropsychiatric disorders. Here, we present a preclinical TI tACS protocol for adult rats that follows a systems approach: an anatomically realistic finite-element digital twin of the rat head is used to optimize electrode placement and injected currents for a deep target, and the model predictions are then tested in vivo. We combine, minimal invasive TI tACS with functional MRI (fMRI) to characterize stimulation-related brain-wide neural responses, alterations in functional connectivity, and changes in neurotransmitter levels. The optimized montage targeted in particular the ventral (motor-related) thalamus. Stimulation-evoked fMRI revealed robust bilateral activation across both subcortical and cortical regions, such as the thalamus, hippocampus, amygdala, retrosplenial and anterior cingulate cortex, which, in turn, reflects direct and indirect activations of brain circuitries by TI tACS. Changes in the connectivity patterns during resting-state fMRI were limited (e.g., fimbria of the hippocampus), but partially overlapped with regional stimulation-evoked fMRI. Therefore, we assume only a short-term influence of TI on neural networks following a single stimulation. MR spectroscopy indicated a trend towards an increased glutamate/GABA ratio in the thalamus. Overall, we demonstrate that TI is a feasible and effective approach for non-invasive DBS in rodents, and that digital twin-based optimization combined with in vivo validation provides a workflow towards individualized stimulation and a foundation for future mechanistic and translational studies in disease models.

neuroscience↗

bioRxiv2025

Balancing Efficiency and Compensation: Age-related Theta and Alpha Dynamics in High-load Working Memory

Working memory (WM) declines with age, yet older adults often preserve performance through compensatory mechanisms. Oscillatory dynamics in the theta and alpha bands are central to these adaptations, but their distinct roles across maintenance, manipulation, and recall remain unclear. We examined behavioural and neural differences in WM using electroencephalography (EEG) during verbal (Letter Span) and visuospatial (Corsi Block) tasks under retention and manipulation conditions. Behaviourally, older adults preserved performance in the Letter Span but showed deficits in the Corsi Test, suggesting domain-specific declines, while higher task demands reduced accuracy across both groups. At the neural level, younger adults exhibited stronger mid-frontal and temporal theta activity, supporting more efficient recruitment of WM processes and stronger performance associations. Older adults showed attenuated theta power, indicative of neural saturation, and appeared to compensate through alpha-mediated mechanisms during the delay period (maintenance / manipulation): reduced alpha suppression in the Letter Span facilitated rehearsal and updating, whereas increased upper alpha in the Corsi Test protected stored visuospatial information. These findings suggest theta oscillations underpin core WM functions, whereas alpha oscillations flexibly support compensatory strategies in ageing.

neuroscience↗

bioRxiv2025

Boosting Brainpower in Ageing: Task-Specific and Transfer Effects of tDCS-Enhanced Working Memory Training

Ageing is associated with neural alterations that impair cognitive abilities, particularly working memory (WM)--the capacity to temporarily store and manipulate information essential for daily functioning. Transcranial Direct Current Stimulation (tDCS) has shown promise in enhancing WM in older adults by modulating cortical excitability and promoting neuroplasticity. However, findings on the combined effects of tDCS and WM training remain inconsistent, particularly regarding transfer effects to non-trained WM tasks (near transfer) or other cognitive domains (far transfer). This study examined the behavioural and neural effects of tDCS on distinct WM phases (encoding, retention/manipulation, recall) in older adults. Over three weeks, participants underwent six sessions of adaptive WM training paired with tDCS targeting the left dorsolateral prefrontal cortex (DLPFC). Neural activity was assessed via EEG, focusing on theta and alpha bands. Participants were divided into tDCS and placebo groups and completed two WM tests, the Letter Span and Corsi Test, with retention and manipulation conditions. Results showed no additional behavioural or neural benefits of tDCS. However, both groups exhibited near-transfer effects that persisted one-month post-training. Neural changes varied by task: the Letter Span showed increased alpha power during manipulation, indicating enhanced maintenance of information during that phase, while the Corsi Test showed reduced left-hemisphere theta power during recall, reflecting reduced hemispheric asymmetry. Inter-individual variability likely contributed to inconsistencies and a lack of correlations between outcomes. These findings highlight the importance of personalised tDCS protocols and suggest adaptive WM training can yield enduring cognitive and neural benefits in older adults.

neuroscience↗

bioRxiv2020

Increases in parieto-occipital alpha-band power reflect involuntary spatial attention due to a task-distracting deviant sound

Imagine you are focusing on the traffic on a busy street to ride your bike safely when suddenly you hear the siren of an ambulance. This unexpected sound involuntarily captures your attention and interferes with ongoing performance. We tested whether this type of distraction involves a spatial shift of attention. We measured behavioral data and magnetoencephalographic alpha power during a crossmodal paradigm that combined an exogenous cueing task and a distraction task. In each trial, a task-irrelevant sound preceded a visual target (left or right). The sound was usually the same animal sound (i.e., standard sound). Rarely, it was replaced by an unexpected environmental sound (i.e., deviant sound). Fifty percent of the deviants occurred on the same side as the target, and 50% occurred on the opposite side. Participants responded to the location of the target. As expected, responses were slower to targets that followed a deviant compared to a standard. Crucially, this distraction effect was mitigated by the spatial relationship between the targets and the deviants: responses were faster when targets followed deviants on the same versus different side, indexing a spatial shift of attention. This was further corroborated by a posterior alpha power modulation that was higher in the hemisphere ipsilateral (vs. contralateral) to the location of the attention-capturing deviant. We suggest that this alpha power lateralization reflects a spatial attention bias. Overall, our data support the contention that spatial shifts of attention contribute to deviant distraction.

neuroscience↗

bioRxiv2017

Local network-level integration mediates effects of transcranial Alternating Current Stimulation

Transcranial alternating current stimulation (tACS) has been proposed as a tool to draw causal inferences on the role of oscillatory activity in cognitive functioning and has the potential to induce long-term changes in cerebral networks. However, the mechanisms of action of tACS are not yet clear, though previous modeling works have suggested that variability may be mediated by local and network-level brain states. We used magnetoencephalography (MEG) to record brain activity from 17 healthy participants as they kept their eyes open (EO) or closed (EC) while being stimulated either with sham, weak, or strong alpha-tACS using a montage commonly assumed to target occipital areas. We reconstructed the activity of sources in all stimulation conditions by means of beamforming. The analysis of resting-state data revealed an interaction of the external stimulation with the endogenous alpha power difference between EO and EC in the posterior cingulate. This region is remote from occipital cortex, which showed strongest EC vs. EO alpha modulation, thus suggesting state-dependency long-range effects of tACS. In a follow-up analysis of this online-tACS effect, we find evidence that this dependency effect could be mediated by functional network changes: connection strength from the precuneus, a region adjusting for a measure of network integration in the two states (EC vs. EO during no-tACS), was significantly correlated with the state-dependency effect in the posterior cingulate (during tACS). No analogous correlation could be found for alpha power modulations in occipital cortex. Altogether, this is the first strong evidence to illustrate how functional network architectures can shape tACS effects.

neuroscience↗

bioRxiv2017

Rubin-vase percept is predicted by prestimulus coupling of category-sensitive occipital regions with frontal cortex

Fluctuations in what an observer perceives can be demonstrated in images that give rise to competing percepts, examples include binocular rivalry, figure-ground illusions, and other phenomena. These stimuli are an important and well-studied stimulus set in studying human conscious perception.\n\nOne such stimulus is the Rubins vase illusion, a bistable stimulus that gives rise to the perception of a vase, or the profile of two faces (hereafter referred to as the facevase stimulus). Research using this stimulus has predominately focused on the neural response whilst viewing it (Andrews et al., 2002; Hasson et al., 2001; Kleinschmidt et al., 1998). An explanation for the phenomenological switch could exist in distinct features of the on-going brain activity, Hesselmann, Kell, Eger, & Kleinschmidt (2008) showed that fluctuating BOLD levels in Fusiform Face Area (FFA) prior to presentation of the face-va ...

neuroscience↗