Biology subjects

Baumann, O.

Publications and source records attributed to Baumann, O..

8 recordsLinked to original sources

bioRxiv2024

Lower Aperiodic Activity is Associated with Reduced Verbal Fluency Performance Across Adulthood

Age-related cognitive decline associations with human electroencephalography (EEG) have previously focused on periodic activity. However, EEG primarily consists of non-oscillatory aperiodic activity, characterised with an exponent and offset value. In a secondary analysis of a cohort of 111 healthy participants aged 17 - 71 years, we examined the associations of the aperiodic exponent and offset in resting EEG with a battery of cognitive tests consisting of the Colour-Word Interference Test, Wechsler Adult Intelligence Scale IV Digit Span Test, Rey Auditory Learning Test, Delis-Kaplan Executive Function System Trail Making Test, and the Verbal Fluency Test. Using Principal Component Analysis and K-Means Clustering, we identified clusters of electrodes that exhibited similar aperiodic exponent and offset activity during resting-state eyes-closed EEG. Robust linear models were then used to model how aperiodic activity interacted with age and their associations with performance during each cognitive test. Offset by age interactions were identified for the Verbal Fluency Test, where smaller offsets were associated with poorer performance in adults as early as 33 years of age. Greater aperiodic activity is increasingly related to better verbal fluency performance with age in adulthood.

neuroscience↗

bioRxiv2024

Competition and interdependence define multifaceted interactions of symbiotic Nostoc sp. and Agrobacterium sp. under inorganic carbon limitation

Cyanobacteria of the Nostoc genus are capable of forming symbiotic relationships with plants, thus transitioning to a heterotrophic lifestyle in return for providing bioavailable nitrogen to the host. The diazotrophic photoautotrophs also serve as a hub for specialized heterotrophic bacterial communities whose physiological contributions are poorly understood. By comparing the axenic strain Nostoc punctiforme PCC 73102 and the related strains Nostoc sp. KVJ2 and KVJ3, which still maintain their heterotrophic microbiome, we were able to demonstrate an almost obligate dependence of the cyanobacteria on the heterotrophic partners under carbon-limiting conditions. Detailed analysis of the intimate bilateral relationship between N. punctiforme and the isolate Agrobacterium tumefaciens Het4 using shotgun proteomics and microscopy uncovered a complex partnership characterized, among other traits, by competition for iron and facilitation for carbon. Although competitive interactions with A. tumefaciens Het4 compromise nitrogen fixation and stimulate the degradation of cyanophycin, mutualistic dependency prevails under inorganic carbon limitation. Both the absence of the high affinity bicarbonate uptake transporter SbtA and the prevalent extracarboxysomal localization of the carbon-fixing enzyme RubisCO, as detected by immunofluorescence microscopy, suggest that a weak carbon concentrating mechanism in N. punctiforme enforces a dependence on heterotrophic bacteria. Further, immunofluorescence, electron microscopic and proteomic analyses reveal a pronounced extracellular recycling of proteins under N- and C-limiting conditions. Our study shows that the pivotal influence of heterotrophic bacteria on symbiotic Nostoc strains should be considered when analyzing these cyanobacteria, especially in the free-living state. This work also sheds new light on how Nostoc benefits from the organic carbon provided by plant hosts.

microbiology↗

bioRxiv2023

Gene and allele specific expression underlying the electric signal divergence in African weakly electric fish

In the African weakly electric fish genus Campylomormyrus, electric organ discharge (EOD) signals are strikingly different in shape and duration among closely related species, contribute to pre-zygotic isolation and may have triggered an adaptive radiation. We performed mRNA sequencing on electric organs (EOs) and skeletal muscles (SMs; from which the EOs derive) from three species with short (0.4 ms), medium (5 ms), and long (40 ms) EODs and two different cross-species hybrids. We identified 1,444 up-regulated genes in EO shared by all five species/hybrids cohorts, rendering them candidate genes for EO-specific properties in Campylomormyrus. We further identified several candidate genes, including KCNJ2 and KLF5, their up-regulation may contribute to increased EOD duration. Hybrids between a short (C. compressirostris) and a long (C. rhynchophorus) discharging species exhibit EODs of intermediate duration and showed imbalanced expression of KCNJ2 alleles, pointing towards a cis-regulatory difference at this locus, relative to EOD duration. KLF5 is a transcription factor potentially balancing potassium channel gene expression, a crucial process for the formation of an EOD. Unraveling the genetic basis of the species-specific modulation of the EOD in Campylomormyrus is crucial for understanding the adaptive radiation of this emerging model taxon of ecological (perhaps even sympatric) speciation.

evolutionary biology↗

bioRxiv2023

Test-retest reliability of spectral parameterization by 1/f characterization using SpecParam

SpecParam (formally known as FOOOF) allows for the refined measurements of electroencephalography periodic and aperiodic activity, and potentially provides a non-invasive measurement of excitation:inhibition balance. However, little is known about the psychometric properties of this technique. This is integral for understanding the usefulness of SpecParam as a tool to determine differences in measurements of cognitive function, and electroencephalography activity. We used intraclass correlation coefficients (ICC) to examine the test-retest reliability of parameterized activity across three sessions (90 minutes apart and 30 days later) in 49 healthy young adults at rest with eyes open (EO), eyes closed (EC), and during three EC cognitive tasks including subtraction (Math), music recall (Music), and episodic memory (Memory). ICCs were good for the aperiodic exponent and offset (ICCs > .70) and parameterized periodic activity (ICCs > .66 for alpha and beta power, central frequency, and bandwidth) across conditions. Across all three sessions, SpecParam performed poorly in EO (40% of participants had poor fits over non-central sites) and had poor test-retest reliability for parameterized periodic activity. SpecParam mostly provides reliable metrics of individual differences in parameterized neural activity. More work is needed to understand the suitability of EO resting data for parameterization using SpecParam.

neuroscience↗

bioRxiv2023

Medication-Invariant Resting Aperiodic and Periodic Neural Activity in Parkinson's Disease

Parkinsons Disease (PD) has been associated with greater total power in canonical frequency bands (i.e., alpha, beta) of the resting electroencephalogram (EEG). However, PD has also been associated with a reduction in the proportion of total power across all frequency bands. This discrepancy may be explained by aperiodic activity (exponent and offset) present across all frequency bands. Here, we examined differences in the eyes-open and eyes-closed resting EEG of PD participants (N = 26) on and off medication, and age-matched controls (CTL; N = 26). We extracted power from canonical frequency bands using traditional methods (total alpha and beta power) and extracted separate parameters for periodic (parameterized alpha and beta power) and aperiodic activity (exponent and offset). Cluster-based permutation tests over spatial and frequency dimensions indicated that total alpha and beta power, and aperiodic exponent and offset were greater in PD participants, independent of medication status. After removing the exponent and offset, greater alpha power in PD (vs. CTL) was only present in eyes-open recordings and no reliable differences in beta power were observed. Differences between PD and CTLs in the resting EEG are likely driven by aperiodic activity, suggestive of greater relative inhibitory neural activity and greater neuronal spiking. Our findings suggest that resting EEG activity in PD is characterized by medication-invariant differences in aperiodic activity which is independent of the increase in alpha power with EO. This highlights the importance of considering aperiodic activity contributions to the neural correlates of brain disorders.

neuroscience↗

bioRxiv2019

Non-canonical localization of RubisCO under high light conditions in the toxic cyanobacterium Microcystis aeruginosa PCC7806

The frequent production of the hepatotoxin microcystin and its impact on the life-style of bloom-forming cyanobacteria are poorly understood. Here we report that microcystin interferes with the assembly and the subcellular localization of RubisCO, in Microcystis aeruginosa PCC7806. Immunofluorescence, electron microscopic and cellular fractionation studies revealed a pronounced heterogeneity in the subcellular localization of RubisCO. At high cell density, RubisCO particles are largely separate from carboxysomes in M. aeruginosa and relocate to the cytoplasmic membrane under high-light conditions. We hypothesize that the binding of microcystin to RubisCO promotes its membrane association and enables an extreme versatility of the enzyme. Steady-state levels of the RubisCO CO2 fixation product 3-phosphoglycerate are significantly higher in the microcystin-producing wild type. We also detected noticeable amounts of the RubisCO oxygenase reaction product secreted into the medium that may support the mutual interaction of M. aeruginosa with its heterotrophic microbial community.

microbiology↗

bioRxiv2018

Flexible information coding in frontoparietal cortex across the functional stages of cognitive processing.

Neural activity in frontoparietal cortex shows overlap across cognitive domains and has been proposed to reflect flexible information processing according to current task demands (Dosenbach et al., 2007; Duncan, 2001). However, a strong assertion of flexibility requires investigating activity across stages of cognitive processing. The current study assessed neural activity in Multiple Demand (MD) regions across the stages of processing that form the core of long-standing cognitive models (Welford, 1952). Specifically, many complex tasks share a comparable structure of subsequent operations: target selection, stimulus-response (SR) mapping, and response execution. We independently manipulated the difficulty of target selection and SR mapping in identical stimulus displays and assessed changes in frontoparietal activity with increased demands in either stage. The results confirmed flexibility in MD regions, with enhanced information representation during difficult target selection as well as SR mapping. Additionally, anterior insula (AI) and anterior cingulate cortex (ACC) showed preferential representation of SR stage information, whereas the medial frontal gyrus (MFG) and inferior parietal sulcus (IPS) showed preferential representation of target selection-stage information. Together these results suggest that MD regions dynamically alter the information they represent with changing task demands. This is the first study to demonstrate that MD regions support flexible goal-directed cognition across multiple processing stages. At the same time we show a preference for the representation of information from a specific processing stage in a subset of MD regions.\n\nSignificance StatementGoal-directed cognition in complex tasks is critical to key life outcomes including longevity and academic performance. Nevertheless, the mechanisms underlying cognition in complex tasks are not well understood. Distinct neural networks are critical to the navigation of specific cognitive domains (e.g. attention), but frontoparietal activity shows cross-domain and -task overlap and supports flexible representation of goal-critical information. This study links flexible frontoparietal processing to longstanding models of meta-cognition that propose a unifying structure of operations underlying most tasks: target selection, SR mapping, and response execution. Our results demonstrate that flexible information representation in frontoparietal cortex is not limited to the SR mapping stage, but applies across the functional stages of cognitive processing, thus maximizing neural efficiency and supporting flexible cognition.

neuroscience↗

bioRxiv2017

Evidence against the detectability of a hippocampal place code using functional magnetic resonance imaging

Individual hippocampal neurons selectively increase their firing rates in specific spatial locations. As a population these neurons provide a decodable representation of space that is robust against changes to sensory- and path-related cues. This neural code is sparse and distributed, theoretically rendering it undetectable with population recording methods such as functional magnetic resonance imaging (fMRI). Existing studies nonetheless report decoding spatial codes in the human hippocampus using such techniques. Here we present results from a virtual navigation experiment in humans in which we eliminated visual- and path-related confounds and statistical shortcomings present in existing studies, ensuring that any positive decoding results would be only spatial in nature and would represent a true voxel-place code. Consistent with theoretical arguments derived from electrophysiological data and contrary to existing fMRI studies, our results show that although participants were fully oriented during the navigation task, there was no statistical evidence for a place code.

neuroscience↗