Papers by Wolfgang Klimesch
Scientific Reports, 2021
Brain–heart synchronization is fundamental for emotional-well-being and brain–heart desynchroniza... more Brain–heart synchronization is fundamental for emotional-well-being and brain–heart desynchronization is characteristic for anxiety disorders including specific phobias. Recording BOLD signals with functional magnetic resonance imaging (fMRI) is an important noninvasive diagnostic tool; however, 1–2% of fMRI examinations have to be aborted due to claustrophobia. In the present study, we investigated the information flow between regions of interest (ROI’s) in the cortex and brain stem by using a frequency band close to 0.1 Hz. Causal coupling between signals important in brain–heart interaction (cardiac intervals, respiration, and BOLD signals) was studied by means of Directed Transfer Function based on the Granger causality principle. Compared were initial resting states with elevated anxiety and final resting states with low or no anxiety in a group of fMRI-naïve young subjects. During initial high anxiety the results showed an increased information flow from the middle frontal gyr...
Frontiers in Physiology, 2019
Recently, we reported on the unusual "switch-off" of respiratory sinus arrhythmia (RSA) by analyz... more Recently, we reported on the unusual "switch-off" of respiratory sinus arrhythmia (RSA) by analyzing heart rate (HR) beat-to-beat interval (RRI) signals and respiration in five subjects during a potentially anxiety-provoking first-time functional magnetic resonance imaging (fMRI) scanning with slow spontaneous breathing waves (Rassler et al., 2018). This deviation from a fundamental physiological phenomenon is of interest and merits further research. Therefore, in this study, the interplay between blood-oxygen leveldependent (BOLD) activity in the cerebellum/brain stem, RRI, and respiration was probed. Both the cardiovascular and the respiratory centers are located in the medulla oblongata and pons, indicating that dominant slow rhythmic activity is present in the brain stem. The recording of BOLD signals provides a way to investigate associated neural activity fluctuation in the brain stem. We found slow spontaneous breathing waves associated with two types of slow BOLD oscillations with dominant frequencies at 0.10 and 0.15 Hz in the brain stem. Both BOLD oscillations were recorded simultaneously. One is hypothesized as vessel motion-based phenomenon (BOLDv) associated with the start of expiration; the other one as pattern associated with neural activity (BOLDn) acting as a driving force for spontaneous inspiration and RRI increase (unusual cessation of RSA) about 2-3 s after BOLDv. This time delay of 2-3 s corresponds to the neurovascular coupling time.
Social Cognitive and Affective Neuroscience, 2016
Today's stressors largely arise from social interactions rather than from physical threat. Howeve... more Today's stressors largely arise from social interactions rather than from physical threat. However, the dominant laboratory model of emotional learning relies on physical stimuli (e.g. electric shock) whereas adequate models of social conditioning are missing, possibly due to more subtle and multilayered biobehavioral responses to such stimuli. To fill this gap, we acquired a broad set of measures during conditioning to negative social unconditioned stimuli, also taking into account long-term maintenance of conditioning and inter-individual differences. Fifty-nine healthy participants underwent a classical conditioning task with videos of actors expressing disapproving (US-neg) or neutral (US-neu) statements. Static images of the corresponding actors with a neutral facial expression served as CSþ and CSÀ, predicting US-neg and US-neu, respectively. Autonomic and facial-muscular measures confirmed differential unconditioned responding whereas experiential CS ratings, event-related potentials, and evoked theta oscillations confirmed differential conditioned responding. Conditioning was maintained at 1 month and 1 year follow-ups on experiential ratings, especially in individuals with elevated anxiety and depressive symptoms, documenting the efficiency of social conditioning and its clinical relevance. This novel, ecologically improved conditioning paradigm uncovered a remarkably efficient multi-layered social learning mechanism that may represent a risk factor for anxiety and depression.
Sleep, 2004
Twenty-four healthy subjects (12 men) aged between 20 and 30 years. Interventions: Declarative me... more Twenty-four healthy subjects (12 men) aged between 20 and 30 years. Interventions: Declarative memory task or nonlearning control task before sleep. Measurement and Results: This study measured spindle activity during stage 2 sleep following a (declarative) word-pair association task as compared to a control task. Participants performed a cued recall in the evening after learning (160 word pairs) as well as in the subsequent morning after 8 hours of undisturbed sleep with full polysomnography. Overnight change in the number of recalled words, but not absolute memory performance, correlated significantly with increased spindle activity during the experimental night (r 24 = .63, P < .01). Time spent in each sleep stage could not account for this relationship. Conclusion: A growing body of evidence supports the active role of sleep for information reprocessing. Whereas past research focused mainly on the distinct rapid eye movement and slow-wave sleep, these results indicate that increased sleep stage 2 spindle activity is related to an increase in recall performance and, thus, may reflect memory consolidation.
Somnologie - Schlafforschung und Schlafmedizin, 2015
Involvement of sleep spindles in overnight declarative memory stabilization. Effects of time of i... more Involvement of sleep spindles in overnight declarative memory stabilization. Effects of time of incidence and spindle type Abstract Objective. Numerous studies point to the involvement of sleep spindles and slow waves in memory processes, particularly in hippocampus-dependent declarative memory. We have shown previously that the overnight change in recall performance in a declarative word pair association task correlates significantly with increased spindle activity during the night after learning compared to a control night. The current study re-evaluates this relationship in detail and explores whether the observed positive correlation of two spindle parameters measured during stage 2 (S2) sleep with overnight stabilization depend on the time of night (early vs. late) and spindle type (fast vs. slow). Methods. The study included 24 healthy volunteers aged 20-30 years. Two counterbalanced nights served as either control con
Brain Topography, 1998
The question is examined whether the extent of changes in relative band power as measured by even... more The question is examined whether the extent of changes in relative band power as measured by event-related desynchronization (ERD) depends on absolute band power. The results for target stimuli of a simple oddball task indicate that the prestimulus (reference) level of absolute band power has indeed a strong influence on ERD. Whereas for the alpha band large band power in the reference interval is related to a strong degree of alpha suppression as measured by ERD, the opposite holds true for the theta band. Here, a low level of band power during the reference interval is related to a pronounced increase in band power during the processing of the target stimulus. In contrast to alpha and theta, ERD in the delta band is not influenced by the magnitude of band power in the reference interval.
Neuro endocrinology letters, 2006
In the present study, we tested the hypothesis that gender - dependent differences in novelty see... more In the present study, we tested the hypothesis that gender - dependent differences in novelty seeking, leadership, and sympathy might correlate with testosterone titre. Since several studies report that the impact of testosterone on personality traits is more visible under emotional challenging situations, we harvested saliva testosterone upon an anticipated stressor (academic examination) and under basal conditions. 19 female and 23 male adolescents (17 to 19 years of age) completed standardized questionnaires on sensation seeking, anxiety, and social interaction. Two weeks later, they had to write an anticipated, rigorous examination in mathematics in their school. Before and after the examination, saliva had been harvested from each subject and testosterone titre has been estimated. Saliva testosterone was quantified using a luminescence immunoassay (LIA). Each subject completed questionnaires on sensations seeking according to Zuckerman (SSS - V), anxiety (STAI), and social inte...
Functional neurology
Patients with altered states of consciousness continue to constitute a major challenge in terms o... more Patients with altered states of consciousness continue to constitute a major challenge in terms of clinical assessment, treatment and daily management. Furthermore, the exploration of brain function in severely brain-damaged patients represents a unique lesional approach to the scientific study of consciousness. Electroencephalography is one means of identifying covert behaviour in the absence of motor activity in these critically ill patients. Here we focus on a language processing task which assesses whether vegetative (n=10) and minimally conscious state patients (n=4) (vs control subjects, n=14) understand semantic information on a sentence level ("The opposite of black is... white/yellow/nice"). Results indicate that only MCS but not VS patients show differential processing of unrelated ("nice") and antonym ("white") words in the form of parietal alpha (10-12Hz) event-related synchronization and desynchronization (ERS/ERD), respectively. Controls s...
Frontiers in Human Neuroscience, 2013
Brain Research, 2014
Ongoing intrinsic brain activity in resting, but awake humans is dominated by alpha oscillations.... more Ongoing intrinsic brain activity in resting, but awake humans is dominated by alpha oscillations. In human, individual alpha frequency (IAF) is associated with cognitive performance. Noticeable, performance in cognitive and emotional tasks in women is associated with menstrual cycle phase and sex hormone levels, respectively. In the present study, we correlated frequency of alpha oscillation in resting women with menstrual cycle phase, sex hormone level, or use of oral contraceptives. Electroencephalogram (EEG) was recorded from 57 women (aged 24.0773.67 years) having a natural menstrual cycle as well as from 57 women (aged 22.3772.20 years) using oral contraceptives while they sat in an armchair with eyes closed. Alpha frequency was related to the menstrual cycle phase. Luteal women showed highest and late follicular women showed lowest IAF or center frequency. Furthermore, IAF as well as center frequency correlated negatively with endogenous estradiol level, but did not reveal an association with endogenous progesterone. Women using oral contraceptives showed an alpha frequency similar to women in the early follicular phase. We suggest that endogenous estradiol modulate resting alpha frequency.
Trends in Cognitive Sciences, 2012
Alpha-band oscillations are the dominant oscillations in the human brain and recent evidence sugg... more Alpha-band oscillations are the dominant oscillations in the human brain and recent evidence suggests that they have an inhibitory function. Nonetheless, there is little doubt that alpha-band oscillations also play an active role in information processing. In this article, I suggest that alpha-band oscillations have two roles (inhibition and timing) that are closely linked to two fundamental functions of attention (suppression and selection), which enable controlled knowledge access and semantic orientation (the ability to be consciously oriented in time, space, and context). As such, alpha-band oscillations reflect one of the most basic cognitive processes and can also be shown to play a key role in the coalescence of brain activity in different frequencies.
PLoS ONE, 2013
There is growing evidence of the active involvement of sleep in memory consolidation. Besides hip... more There is growing evidence of the active involvement of sleep in memory consolidation. Besides hippocampal sharp wave-ripple complexes and sleep spindles, slow oscillations appear to play a key role in the process of sleepassociated memory consolidation. Furthermore, slow oscillation amplitude and spectral power increase during the night after learning declarative and procedural memory tasks. However, it is unresolved whether learning-induced changes specifically alter characteristics of individual slow oscillations, such as the slow oscillation up-state length and amplitude, which are believed to be important for neuronal replay. 24 subjects (12 men) aged between 20 and 30 years participated in a randomized, within-subject, multicenter study. Subjects slept on three occasions for a whole night in the sleep laboratory with full polysomnography. Whereas the first night only served for adaptation purposes, the two remaining nights were preceded by a declarative word-pair task or by a non-learning control task. Slow oscillations were detected in non-rapid eye movement sleep over electrode Fz. Results indicate positive correlations between the length of the up-state as well as the amplitude of both slow oscillation phases and changes in memory performance from pre to post sleep. We speculate that the prolonged slow oscillation up-state length might extend the timeframe for the transfer of initial hippocampal to long-term cortical memory representations, whereas the increase in slow oscillation amplitudes possibly reflects changes in the net synaptic strength of cortical networks.
Binding processes: Neurodynamics and functional role in memory and action
Neuroscience & Biobehavioral Reviews, 2010
Memory & Cognition, 1992
Verbal Processes in Visual Short- and Long-Term Memory: Evidence Against the Hypothesis of Independent Visual and Verbal Codes?
International Journal of Psychology, 1982
The assumption of independent visual and verbal codes was tested by the use of a special kind of ... more The assumption of independent visual and verbal codes was tested by the use of a special kind of visual recognition task. Subjects had to distinguish between targets and similar distractors which differed only in terms of perspective cues. It is argued that in this case the recognition performance depends entirely on the accuracy of visual codes, and that verbalizing the tachistoscopically exposed targets cannot lead to an improvement if the assumption of independent visual and verbal codes is correct. The results however show that visual characteristics are better retained if targets have been verbalized. It is concluded, therefore, that verbalizing a visual short-term memory code not only leads to a better semantic description but also to a better identification of “purely” visual information.
European Journal of Neuroscience, 2006
Stage 2 sleep spindles have been previously viewed as useful markers for the development and inte... more Stage 2 sleep spindles have been previously viewed as useful markers for the development and integrity of the CNS and were more currently linked to ‘offline re‐processing’ of implicit as well as explicit memory traces. Additionally, it had been discussed if spindles might be related to a more general learning or cognitive ability. In the present multicentre study we examined the relationship of automatically detected slow (< 13 Hz) and fast (> 13 Hz) stage 2 sleep spindles with: (i) the Raven's Advanced Progressive Matrices (testing ‘general cognitive ability’); as well as (ii) the Wechsler Memory scale‐revised (evaluating memory in various subdomains). Forty‐eight healthy subjects slept three times (separated by 1 week) for a whole night in a sleep laboratory with complete polysomnographic montage. Whereas the first night only served adaptation and screening purposes, the two remaining nights were preceded either by an implicit mirror‐tracing or an explicit word‐pair asso...
Brain Research, 2011
In this article, a theory is presented which assumes that the visual P1 reflects the same cogniti... more In this article, a theory is presented which assumes that the visual P1 reflects the same cognitive and physiological functionality as alpha (with a frequency of about 10 Hz). Whereas alpha is an ongoing process, the P1 is the manifestation of an event-related process. It is suggested that alpha and the P1 reflect inhibition that is effective during early access to a complex knowledge system (KS). Most importantly, inhibition operates in two different ways. In potentially competing and task irrelevant networks, inhibition is used to block information processing. In task relevant neural networks, however, inhibition is used to increase the signal to noise ratio (SNR) by enabling precisely timed activity in neurons with a high level of excitation but silencing neurons with a comparatively low level of excitation. Inhibition is increased to modulate the SNR when processing complexity and network excitation increases and when certain types of attentional demandssuch as topdown control, expectancy or reflexive attentionincrease. A variety of findings are reviewed to demonstrate that they can well be interpreted on the basis of the suggested theory. One interesting aspect thereby is that attentional benefits (reflected e.g., by a larger P1 for attended as compared to unattended items at contralateral sites) and costs (reflected e.g., by a larger P1 at ipsilateral sites) can both be interpreted in terms of inhibition. In the former case an increased P1 is associated with a more effective processing of the presented item (due to an inhibition modulated increase in SNR), in the latter case, however, with a suppression of item processing (due to inhibition that blocks information processing).
Biological Psychology, 2012
Even though it is known that sleep benefits declarative memory consolidation, the role of sleep i... more Even though it is known that sleep benefits declarative memory consolidation, the role of sleep in the storage of temporal sequences has rarely been examined. Thus we explored the influence of sleep on temporal order in an episodic memory task followed by sleep or sleep deprivation. Thirty-four healthy subjects (17 men) aged between 19 and 28 years participated in the randomized, counterbalanced, between-subject design. Parameters of interests were NREM/REM cycles, spindle activity and spindle-related EEG power spectra. Participants of both groups (sleep group/sleep deprivation group) performed retrieval in the evening, morning and three days after the learning night. Results revealed that performance in temporal order memory significantly deteriorated over three days only in sleep deprived participants. Furthermore our data showed a positive relationship between the ratios of the (i) first NREM/REM cycle with more REM being associated with delayed temporal order recall. Most interestingly, data additionally indicated that (ii) memory enhancers in the sleep group show more fast spindle related alpha power at frontal electrode sites possibly indicating access to a yet to be consolidated memory trace. We suggest that distinct sleep mechanisms subserve different aspects of episodic memory and are jointly involved in sleep-dependent memory consolidation.
Applied Psychophysiology and Biofeedback, 2006
The functional significance of sleep spindles for overnight memory consolidation and general lear... more The functional significance of sleep spindles for overnight memory consolidation and general learning aptitude as well as the effect of four 10-minute sessions of spindle frequency (11.6-16 Hz, sigma) neurofeedback-training on subsequent sleep spindle activity and overnight performance change was investigated. Before sleep, subjects were trained on a paired-associate word list task after having received either neurofeedback training (NFT) or pseudofeedback training (PFT). Although NFT had no significant impact on subsequent spindle activity and behavioral outcomes, there was a trend for enhanced sigma band-power during NREM (stage 2 to 4) sleep after NFT as compared to PFT. Furthermore, a significant positive correlation between spindle activity during slow wave sleep (in the first night half) and overall memory performance was revealed. The results support the view that the considerable inter-individual variance in sleep spindle activity can at least be partly explained by differences in the ability to acquire new declarative information. We conclude that the short NFT before sleep was not sufficient to efficiently enhance phasic spindle activity and/or to influence memory processing. NFT was, however, successful in increasing sigma power, presumably because sigma NFT effects become more easily evident in actually trained frequency bands than in associated phasic spindle activity.
Brain Research Reviews, 1999
Evidence is presented that EEG oscillations in the alpha and theta band reflect cognitive and mem... more Evidence is presented that EEG oscillations in the alpha and theta band reflect cognitive and memory performance in particular. Good Ž. Ž. performance is related to two types of EEG phenomena i a tonic increase in alpha but a decrease in theta power, and ii a large phasic Ž. event-related decrease in alpha but increase in theta, depending on the type of memory demands. Because alpha frequency shows large interindividual differences which are related to age and memory performance, this double dissociation between alpha vs. theta and tonic vs. phasic changes can be observed only if fixed frequency bands are abandoned. It is suggested to adjust the frequency windows of alpha and theta for each subject by using individual alpha frequency as an anchor point. Based on this procedure, a consistent interpretation of a Ž variety of findings is made possible. As an example, in a similar way as brain volume does, upper alpha power increases but theta power. decreases from early childhood to adulthood, whereas the opposite holds true for the late part of the lifespan. Alpha power is lowered and theta power enhanced in subjects with a variety of different neurological disorders. Furthermore, after sustained wakefulness and during the transition from waking to sleeping when the ability to respond to external stimuli ceases, upper alpha power decreases, whereas Ž. theta increases. Event-related changes indicate that the extent of upper alpha desynchronization is positively correlated with semantic long-term memory performance, whereas theta synchronization is positively correlated with the ability to encode new information. The reviewed findings are interpreted on the basis of brain oscillations. It is suggested that the encoding of new information is reflected by Ž. theta oscillations in hippocampo-cortical feedback loops, whereas search and retrieval processes in semantic long-term memory are reflected by upper alpha oscillations in thalamo-cortical feedback loops.
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Papers by Wolfgang Klimesch