Browsing by Subject "oscillations"

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  • Karadeniz, Sami (Helsingin yliopisto, 2019)
    Aims of the present study: Attention-deficit/hyperactivity disorder (ADHD), beginning in childhood and often continuing into adulthood, is a neurodevelopmental condition that impairs an individual’s functioning in everyday life. The disorder is characterized by impairments in attention regulation or impulse control, or both. Many of the symptoms are related to disturbances in attention, the ability to select behaviorally relevant stimuli and to filter out irrelevant information among the overwhelming amount of sensory data. Neural mechanisms of attention have been linked to oscillations in electophysiological brain activity at alpha frequencies (8–13 Hz), but information on alpha oscillations in adult ADHD has remained scarce. The aim of the present study was to examine differences in attention and distractibility related alpha oscillations between adult ADHD patients and neurotypical controls. Methods: Participants were instructed to attend moving spherical objects and to report color changes in the objects. Number of attended objects varied from one (in right or left visual hemifield) to two (one in both hemifields). In addition to the attended objects, participants were at times presented with distractors which they were instructed to ignore. Brain activity during task performance was measured with magnetoencephalography (MEG). Results and discussion: Behavioral performance was similar between the groups. However, alpha oscillations related to distractor processing differed in a statistically significant manner between ADHD patients and controls. Main differences were related to inter-hemispheric interactions, suggesting that attentional deficits in ADHD might be related to abnormalities between inter-hemispheric communication.
  • Juurmaa, Kristiina (Helsingfors universitet, 2017)
    Introduction: Attention-deficit hyperactivity disorder (ADHD) is among the most common childhood psychiatric disorders and is marked by persistent, age-inappropriate levels of inattention, hyperactivity and/or impulsivity. The present study examines cortical oscillations in adults diagnosed with ADHD/ADD during administration of T.O.V.A. (Test of Variables of Attention). T.O.V.A. is a continuous performance test (CPT) that measures the ability to sustain attention for a prolonged period of time. The motivation for the study is to contribute to the diagnostic picture of ADHD through the novel combination of T.O.V.A. with an EEG measurement. Parieto-occipital alpha and frontomedial theta are examined in particular as they have been linked to sustained attention as measured in CPTs. Methods: 53 adults diagnosed with ADHD/ADD and 18 healthy controls were recruited. Concomitant T.O.V.A. and EEG was measured. Oscillatory power in theta and alpha bands was compared between groups and between different behavioural conditions. Results & Conclusions: T.O.V.A. performance of healthy controls was more likely to be within normal limits as compared to ADHD/ADD diagnosed adults, and vice versa. There were moderate significant differences in commission errors, RT variability and d’ (response sensitivity) between groups. The control group tended to manifest higher theta synchronisation during correct inhibition trials. Given differences in behavioural performance, this result might be related to a higher sensitivity to task demands in the control group. However, there were no between-groups differences in frontomedial theta power and parietal or frontal alpha power. Further research should compare groups formed on the basis of not only diagnostic status but also of behavioural performance.
  • Prokic, Emma J.; Stanford, Ian M.; Woodhall, Gavin L.; Williams, Adrian C.; Hall, Stephen D. (2019)
    Spontaneous and "event-related" motor cortex oscillations in the beta (15-30 Hz) frequency range are well-established phenomena. However, the precise functional significance of these features is uncertain. An understanding of the specific function is of importance for the treatment of Parkinson's disease (PD), where attenuation of augmented beta throughout the motor network coincides with functional improvement. Previous research using a discrete movement task identified normalization of elevated spontaneous beta and postmovement beta rebound following GABAergic modulation. Here, we explore the effects of the gamma-aminobutyric acid type A modulator, zolpidem, on beta power during the performance of serial movement in 17 (15M, 2F; mean age, 66 ± 6.3 years) PD patients, using a repeated-measures, double-blinded, randomized, placebo-control design. Motor symptoms were monitored before and after treatment, using time-based Unified Parkinson's Disease Rating Scale measurements and beta oscillations in primary motor cortex (M1) were measured during a serial-movement task, using magnetoencephalography. We demonstrate that a cumulative increase in M1 beta power during a 10-s tapping trial is reduced following zolpidem, but not placebo, which is accompanied by an improvement in movement speed and efficacy. This work provides a clear mechanism for the generation of abnormally elevated beta power in PD and demonstrates that perimovement beta accumulation drives the slowing, and impaired initiation, of movement. These findings further indicate a role for GABAergic modulation in bradykinesia in PD, which merits further exploration as a therapeutic target.
  • Karevaara, Maria (Helsingin yliopisto, 2020)
    Objective: To contribute to the theory-building on hypnosis by studying the possible changes that hypnosis causes in the electroencephalographic (EEG) spectral power in highly hypnotisable individuals. In accordance with previous literature, hypnosis was hypothesised to cause an increase in theta (4–8 Hz) power and a change in gamma (25–45 Hz) power. Methods: Nine highly hypnotisable individuals (8 females) participated. Continuous EEG was recorded at ten electrodes during four conditions: prehypnosis, neutral hypnosis, hypnotic suggestion, and posthypnosis. During all conditions, the participants watched a monotonous video while sinusoidal tones following an oddball paradigm played silently in the background. The participants were instructed not to pay any attention to the tones, and in the suggestion-condition a suggestion to hear all tones as similar in pitch was given. Nine repeated-measures analyses of variance, one for each frequency range, were performed. For research questions 2 and 3, the participants were divided into two groups depending on their responsiveness to a hallucinatory suggestion in the screening phase, and the analyses were then run again. Results: No differences between conditions were found in the theta range, but a decrease was found in the gamma range during hypnosis compared with wakefulness (posthypnosis). Spectral power differences depending on responsiveness to the hallucinatory suggestion were also found. Conclusions: The findings support the hypothesis of changed gamma-frequency power during hypnosis, but not the theory of increased theta frequencies as a marker of hypnosis. A tentative theoretical connection between reduced peripheral awareness and reduced gamma power in hypnosis is presented.
  • Liljeström, Mia; Kujala, Jan; Stevenson, Claire; Salmelin, Riitta (2015)
  • Bäckroos, Sami (Helsingin yliopisto, 2021)
    High pressure inside e.g. blood vessels or other biological cavities is a major risk factor for many preventable diseases. Most of the measuring methods require physical contact or other kinds of projected forces. Both variants can be unpleasant for the patient and additionally physical contact might warrant for either continuous disinfecting or single-use probes, depending on the measurement method and the target body part. We have been experimenting with handheld non-contacting pressure measuring devices based on acoustic waves. These excite mechanical waves, whose velocity varies with pressure, on the surface of a biological cavity. The tried excitation methods are nearly unnoticeable for the patient, allowing for more pleasant and waste free measurements. Using the data from the latest clinical trial, a new analysis algorithm was devised to improve the accuracy of the pressure estimates. Instead of the time-of-flight (TOF) of the main mechanical wave (MMW), the new algorithm estimates the pressure using the MMW and a previously unseen feature, improving the R^2 from 0.60 to 0.72.
  • Palva, J. Matias; Palva, Satu (2018)
    Neuronal oscillations and their inter-areal synchronization may be instrumental in regulating neuronal communication in distributed networks. Several lines of research have, however, shown that cognitive tasks engage neuronal oscillations simultaneously in multiple frequency bands that have distinct functional roles in cognitive processing. Gamma oscillations (30-120Hz) are associated with bottom-up processing, while slower oscillations in delta (1-4Hz), theta (4-7Hz), alpha (8-14Hz) and beta (14-30Hz) frequency bands may have roles in executive or top-down controlling functions, although also other distinctions have been made. Identification of the mechanisms that integrate such spectrally distributed processing and govern neuronal communication among these networks is crucial for understanding how cognitive functions are achieved in neuronal circuits. Cross-frequency interactions among oscillations have been recognized as a likely candidate mechanism for such integration. We advance here the hypothesis that phase-phase synchronization of neuronal oscillations in two different frequency bands, cross-frequency phase synchrony (CFS), could serve to integrate, coordinate and regulate neuronal processing distributed into neuronal assemblies concurrently in multiple frequency bands. A trail of studies over the past decade has revealed the presence of CFS among cortical oscillations and linked CFS with roles in cognitive integration. We propose that CFS could connect fast and slow oscillatory networks and thereby integrate distributed cognitive functions such as representation of sensory information with attentional and executive functions.
  • Jilbert, Tom; Gustafsson, Bo G.; Veldhuijzen, Simon; Reed, Daniel C.; Helmond, Niels A. G. M.; Hermans, Martijn; Slomp, Caroline P. (2021)
    Hypoxia has occurred intermittently in the Baltic Sea since the establishment of brackish-water conditions at similar to 8,000 years B.P., principally as recurrent hypoxic events during the Holocene Thermal Maximum (HTM) and the Medieval Climate Anomaly (MCA). Sedimentary phosphorus release has been implicated as a key driver of these events, but previous paleoenvironmental reconstructions have lacked the sampling resolution to investigate feedbacks in past iron-phosphorus cycling on short timescales. Here we employ Laser Ablation (LA)-ICP-MS scanning of sediment cores to generate ultra-high resolution geochemical records of past hypoxic events. We show that in-phase multidecadal oscillations in hypoxia intensity and iron-phosphorus cycling occurred throughout these events. Using a box model, we demonstrate that such oscillations were likely driven by instabilities in the dynamics of iron-phosphorus cycling under preindustrial phosphorus loads, and modulated by external climate forcing. Oscillatory behavior could complicate the recovery from hypoxia during future trajectories of external loading reductions.