Biology subjects

Kienitz, R.

Publications and source records attributed to Kienitz, R..

5 recordsLinked to original sources

bioRxiv2025

Hippocampal network activity changes during early epileptogenesis predict subsequent epilepsy

The circuit mechanisms underlying focal epileptogenesis are, despite of decades of epilepsy research, still incompletely understood. In this study, we aimed to characterize the changes in hippocampal network activity induced by a potentially epileptogenic insult. In rats, long-lasting electrical perforant pathway stimulation leads in a high percentage of animals to the development of temporal lobe epilepsy. However, a subset of animals remains resilient against the stimulation. We monitored alterations of neuronal activity by chronically recording the local field potential (LFP) from the hippocampal dentate gyrus before, during and after the potentially epileptogenic insult. Intriguingly, epilepsy animals identified by subsequent spontaneous epileptic seizures were characterized by a transient increase in the aperiodic exponent suggesting a shift towards a reduced local excitation-to-inhibition (E/I) ratio during the first days after the perforant path stimulation. Furthermore, these animals developed a strong impairment of theta oscillation prevalence and regularity during early epileptogenesis. In contrast, resilient non-epilepsy animals without spontaneous seizures neither showed this modulation in E/I ratio nor a corruption of hippocampal theta activity. In fact, the increase in the aperiodic exponent on the first day after completion of the electrical stimulation paradigm could predict epileptogenesis with very high fidelity (AUC 0.92) and correlated significantly with later seizure rate. This finding opens the opportunity to dissect mechanisms of epileptogenesis and to test the effectiveness of anti-epileptogenesis treatment in very early disease stages by allowing identification of individuals at high risk. Furthermore, it might offer a potential explanation for the frequently observed failure of anti-epileptogenesis drugs boosting GABAergic inhibition.

neuroscience↗

bioRxiv2025

Hexagonal modulation of theta rhythmic attentional sampling of visual space

Spatial attention improves visual perception by selecting behaviorally relevant sensory signals. Traditionally, attention has been conceptualized as a static spotlight, while recent evidence posited that attention operates as a moving spotlight that samples visual space sequentially in discrete snapshots that are clocked by theta rhythms ([~]3-8 Hz). While theta rhythmic attentional sampling has mainly been observed in fronto-parietal and occipital areas, theta oscillations also hallmark entorhinal-hippocampal grid-cell networks, which encode physical space in hexagonal patterns that guide overt exploration and navigation. We hypothesized that visual attention might rely on the same underlying principles and sample visual space in a hexagonal, grid-like configuration. To test this hypothesis, twenty participants performed a cue-guided attention task that probed behavioral performance as a function of space and time. Reaction times were assessed as a function of spatial location and varying cue-target intervals, which revealed prominent, spatially-structured theta rhythms. Specifically, higher theta power was evident at spatial locations that were aligned to multiples of 60{degrees}, consistent with an underlying hexagonal organization. Participants that exhibited stronger hexagonal sampling relied less on the spatial cue to guide their attentional allocation. In sum, these findings suggest that covert visual attention relies on an underlying hexagonal grid-like structure known from the entorhinal-hippocampal system and highlight that theta rhythms reflect a common organizing principle for spatial cognition. Significance StatementAttention prioritizes sensory inputs to optimize behavior. But how does attention sample the environment in space and time? Here, we demonstrate that attentional sampling of visual space is not uniform, but preferentially explores locations that are oriented along a hexagonal pattern, reminiscent of the spatial configuration of entorhinal-hippocampal grid cells. Moreover, covert attentional sampling was clocked by theta oscillations (3-8 Hz). In sum, these findings provide evidence for a shared neural basis of underlying spatial attention and navigation and reveal that theta rhythms orchestrate sampling behaviors in space and time as a unifying principle underlying spatial cognition.

neuroscience↗

bioRxiv2024

Temporal Lobe Epilepsy is dominated by Region Specific Interictal Cortical Inhibition

Epilepsy is typically characterized by excessive neuronal excitability, manifesting as seizures and interictal epileptiform discharges (IEDs) in the EEG. However, the dynamics of excitation and inhibition (E/I balance) remain poorly understood. Here, we leverage the aperiodic exponent of the EEG power spectrum--a marker indicative of synaptic inhibition--to investigate shifts in E/I balance during antiseizure medication (ASM) tapering in patients with mesial temporal lobe epilepsy (TLE). We analyzed EEG data from 28 TLE patients and 25 controls with non-epileptic episodes (NEE) undergoing presurgical video EEG monitoring. Unexpectedly, TLE patients showed a localized increase in the aperiodic exponent in the ipsilesional temporal lobe during ASM tapering, absent in controls. This inhibition increase correlated with seizure latency and predicted seizure occurrence. Intracranial recordings from 10 TLE patients revealed higher aperiodic exponents in the lateral temporal cortex compared to the hippocampus, suggesting stronger inhibition in the lateral cortex. Notably, hippocampal IEDs triggered transient inhibitory responses in the lateral cortex, accompanied by increased high-frequency activity and disrupted hippocampus-to-lateral connectivity. These findings suggest that TLE likely involves complex inhibitory mechanisms beyond the epileptic focus in the interictal period, with neocortical inhibition potentially containing epileptic activity, and offers a new tool to map epileptic brain regions.

neuroscience↗

bioRxiv2021

Stimulus dependence of theta rhythmic activity in primate V1 and its potential relevance for visual perception

Theta-band (3-8 Hz) neural oscillations are integral to sensory processing and active exploration. Traditionally associated with higher-order areas such as hippocampus and prefrontal cortex, recent studies identified theta rhythmic modulations in the primary visual cortex (V1) of mice during locomotion, suggesting sensory processing functions. Here, we demonstrate that careful optimization of visual stimulus size and contrast can induce robust theta oscillations in macaque V1. During visual detection, monkeys reaction times fluctuated rhythmically at the theta frequency of V1 neural activity, with detection performance correlated to the theta phase. These findings suggest that induced theta oscillations may reflect an intrinsic temporal filtering mechanism of V1 neurons, highlighting the importance of early sensory cortical dynamics in shaping perceptual timing.

neuroscience↗

bioRxiv2018

Rhythmic neural spiking and attentional samplingarising from cortical receptive field interactions

Growing evidence suggests that distributed spatial attention may invoke theta (3-9 Hz) rhythmic sampling processes. The neuronal basis of such attentional sampling is however not fully understood. Here we show using array recordings in visual cortical area V4 of two awake macaques that presenting separate visual stimuli to the excitatory center and suppressive surround of neuronal receptive fields elicits rhythmic multi-unit activity (MUA) at 3-6 Hz. This neuronal rhythm did not depend on small fixational eye movements. In the context of a distributed spatial attention task, during which the monkeys detected a spatially and temporally uncertain target, reaction times (RT) exhibited similar rhythmic fluctuations. RTs were fast or slow depending on the target occurrence during high or low MUA, resulting in rhythmic MUA-RT cross-correlations at at theta frequencies. These findings suggest that theta-rhythmic neuronal activity arises from competitive receptive field interactions and that this rhythm may subserve attentional sampling.\n\nHighlightsO_LICenter-surround interactions induce theta-rhythmic MUA of visual cortex neurons\nC_LIO_LIThe MUA rhythm does not depend on small fixational eye movements\nC_LIO_LIReaction time fluctuations lock to the neuronal rhythm under distributed attention\nC_LI

neuroscience↗