Biology subjects

Köster, M.

Publications and source records attributed to Köster, M..

4 recordsLinked to original sources

bioRxiv2025

Infant Brains Tick at 4Hz - Resonance Properties of the Developing Visual System

Neural rhythms of the infant brain are not well understood. Testing the rhythmic properties of the adult visual system with periodic or broadband visual stimulation elicited neural resonance phenomena at [~]10Hz alpha rhythm. To investigate the rhythmic properties of the infant brain upon visual stimulation, eight-month-olds (N = 42) were presented with visual stimuli flickering at discrete frequencies (2, 4, 6, 8, 10, 15, 20, and 30Hz) and broadband (i.e., aperiodic) stimulation, while recording a high-density electroencephalogram (EEG). Infants visual system entrained to the harmonics of the periodic stimulation frequencies (first to third). Crucially, a 4Hz rhythm emerged independent of stimulation frequency and the impulse response function (IRF) of the broadband sequence revealed a perceptual echo, reverberating visual information at 4Hz. This echo lasted for about 1 second, extended into frontal sensors, and selectively resonated the 4Hz component of the input signal. In a complementary adult sample, we confirm an alpha response upon periodic and broadband stimulation. To conclude, perturbing the infant visual system elicited a neural response and resonant activity at the 4Hz theta rhythm, which contrasts with the 10Hz alpha rhythm found in the adult visual system. Neural processing dynamics are thus essential to understand early brain development in full. Significance StatementThis study tested resonance properties of the infant visual system upon perturbation. For the visual stimulation at discrete frequencies between 2 and 30Hz, the infant brain responded at 4Hz independent of the stimulation frequency. Following broadband stimulation, a perceptual echo at 4Hz emerged - resonating the 4Hz component of visual information over several cycles. These findings reveal that the 4Hz theta rhythm is an inherent processing dynamic of the infant visual system, contrasting with the 10Hz rhythm found in adults. The processing dynamics of the human visual system undergo fundamental changes from infancy into adulthood.

neuroscience↗

bioRxiv2022

Synchronicity of viral shedding in molossid bat maternity colonies

Infection dynamics in vertebrates are driven by biological and ecological processes. For bats, population structure and reproductive cycles have major effects on RNA virus transmission. On Reunion Island, previous studies have shown that parturition of pregnant females and aggregation of juvenile Reunion free-tailed bats (Mormopterus francoismoutoui) are associated to major increase in the prevalence of bats shedding viruses. The synchronicity of such shedding pulses, however, is yet to be assessed, between viruses but also maternity colonies. Based on 3422 fresh faeces collected every two to five weeks during four consecutive birthing seasons, we report the prevalence of bats shedding astroviruses (AstVs), coronaviruses (CoVs), and paramyxoviruses (PMVs) in two maternity colonies on Reunion Island. We found that the proportion of bats shedding viruses is highly influenced by sampling collection dates, and therefore by the seasonality of parturition. We highlight that virus shedding patterns are reproducible among years and colonies for CoVs and at a lesser extent for PMVs, but not for AstVs. We also report 1% of bats harbouring double infections, mostly CoVs and PMVs, but none shedding simultaneously AstVs, CoVs and PMVs.

ecology↗

bioRxiv2020

Young Infants Process Prediction Errors at the Theta Rhythm

Examining how young infants respond to unexpected events is key to our understanding of their emerging concepts about the world around them. From a predictive processing perspective, it is intriguing to investigate how the infant brain responds to unexpected events (i.e., prediction errors), because they require infants to refine their predictions about the environment. Here, to better understand prediction error processes in the infant brain, we presented 9-month-olds (N = 36) a variety of physical and social events with unexpected versus expected outcomes, while recording their electroencephalogram (EEG). We found a pronounced response in the ongoing 4 - 5 Hz theta rhythm for the processing of unexpected (in contrast to expected) events, for a prolonged time window (2 s) and across all scalp-recorded electrodes. The condition difference in the theta rhythm was not related to the condition difference in infants event-related activity to unexpected (versus expected) events in the negative central (Nc) component (.4 - .6 s), a component, which is commonly analyzed in infant violation of expectation studies using EEG. These findings constitute critical evidence that the theta rhythm is involved in the processing of prediction errors from very early in human brain development. We discuss how the theta rhythm may support infants refinement of basic concepts about the physical and social environment.

neuroscience↗

bioRxiv2017

Memory entrainment by visually evoked theta-gamma coupling in the human brain

It is an integral function of the human brain to sample novel information from the environment and to update the internal representation of the external world. The formation of new memories is assumed to be orchestrated by neuronal oscillations, the rhythmic synchronization of neuronal activity within and across cell assemblies. Specifically, successful encoding of novel information is associated with increased theta oscillations (3-8Hz) and theta coupled gamma activity (40-120Hz), and a decrease in alpha oscillations (8-12Hz). However, given the correlative nature of neurophysiological recordings, the causal role of neuronal rhythms in human memory encoding is still unclear. Here, we experimentally enhance the formation of novel memories by a visual brain stimulation at an individually adjusted theta frequency, in contrast to the stimulation at an individual alpha frequency. Critically, the memory entrainment effect by the theta stimulation was not explained by theta power per se, but was driven by visually evoked theta-gamma coupling in wide spread cortical networks. These findings provide first evidence for a functional role of the theta rhythm and the theta-gamma neuronal code in human episodic memory. Yet more strikingly, the entrainment of mnemonic network mechanisms by a simplistic visual stimulation technique provides a proof of concept that internal rhythms align with visual pacemakers, which can entrain complex cognitive functions in the wake human brain.

neuroscience↗