Browsing by Subject "magnetoencephalography"

Sort by: Order: Results:

Now showing items 1-16 of 16
  • Paranko, Birgitta (Helsingin yliopisto, 2019)
    Introduction and aims. Multiple different neurobiological alterations have been hypothesized to underlie Major Depression Disorder (MDD), but no unifying theory exists to explain the mechanisms of the disorder. The aberrant brain dynamics in MDD can be seen in the alterations of long-range temporal correlations (LRTCs), which have been proposed to be an indication of criticality in healthy brain. Alterations in LRTCs have been suggested to reflect deficiencies in excitation-inhibition (E/I) balance, neuromodulation or connectivity patterns, which have also been proposed to be the underlying mechanisms of MDD. There has been controversy whether the pathology is related to attenuated or increased LRTCs, and the sources of altered brain dynamics have not yet been localized. The aim of this study was to find in which frequency bands and where in the brain the neuronal LRTCs are altered in MDD on source level. In addition to analyzing the correlations between neuronal LRTCs and depression severity in parcel level, we studied correlations in functional networks to get a better understanding of the system level alterations in MDD. We also studied whether behavioral LRTCs correlate with depression severity or with behavioral performance. Methods. We investigated the long-range temporal correlations in a cohort of 19 depressed subjects by using magnetoencephalography (MEG) for recording brain activity during resting state and response inhibition task and performed DFA analysis on the amplitude envelopes of cortical oscillations. The depression severity was measured with BDI-21 questionnaire. Results and conclusions. We found the LRTCs to be positively correlated with depression severity in the alpha frequency band (8–12Hz) predominantly in the limbic system that underlies emotional control. This result was supported by the parcel level analysis in which correlations between alpha band LRTCs and depression severity were observed in the orbitofrontal cortex and temporal pole, indicating that the hyper-activation of limbic system could explain the negative bias characteristic to depression. Positive correlations were also found in frontoparietal, ventral, and dorsal attentional networks that support cognitive control. Alpha band LRTCs correlated also with behavioral LRTCs during both resting state and task conditions. However, we observed more wide-spread correlations between alpha range LRTCs and depression severity than between neuronal LRTCs and behavioral LRTCs. Behavioral LRTCs correlated with depression severity, but not with behavioral performance. These results indicate that depression is characterized by vast alterations in the brain dynamics and imply that the wide range of different symptoms in MDD could be explained by alterations in the excitation/inhibition balance in the limbic system and cognitive networks.
  • Thiede, A.; Glerean, E.; Kujala, T.; Parkkonen, L. (2020)
    Listening to speech elicits brain activity time-locked to the speech sounds. This so-called neural entrainment to speech was found to be atypical in dyslexia, a reading impairment associated with neural speech processing deficits. We hypothesized that the brain responses of dyslexic vs. normal readers to real-life speech would be different, and thus the strength of inter-subject correlation (ISC) would differ from that of typical readers and be reflected in reading-related measures. We recorded magnetoencephalograms (MEG) of 23 dyslexic and 21 typically-reading adults during listening to ∼10 min of natural Finnish speech consisting of excerpts from radio news, a podcast, a self-recorded audiobook chapter and small talk. The amplitude envelopes of band-pass-filtered MEG source signals were correlated between subjects in a cortically-constrained source space in six frequency bands. The resulting ISCs of dyslexic and typical readers were compared with a permutation-based t-test. Neuropsychological measures of phonological processing, technical reading, and working memory were correlated with the ISCs utilizing the Mantel test. During listening to speech, ISCs were mainly reduced in dyslexic compared to typical readers in delta (0.5–4 Hz) and high gamma (55–90 Hz) frequency bands. In the theta (4−8 Hz), beta (12–25 Hz), and low gamma (25−45 Hz) bands, dyslexics had enhanced ISC to speech compared to controls. Furthermore, we found that ISCs across both groups were associated with phonological processing, technical reading, and working memory. The atypical ISC to natural speech in dyslexics supports the temporal sampling deficit theory of dyslexia. It also suggests over-synchronization to phoneme-rate information in speech, which could indicate more effort-demanding sampling of phonemes from speech in dyslexia. These irregularities in parsing speech are likely some of the complex neural factors contributing to dyslexia. The associations between neural coupling and reading-related skills further support this notion.
  • Ylinen, Sari; Nora, Anni; Service, Elisabet (2020)
    Language learning relies on both short-term and long-term memory. Phonological short-term memory (pSTM) is thought to play an important role in the learning of novel word forms. However, language learners may differ in their ability to maintain word representations in pSTM during interfering auditory input. We used magnetoencephalography (MEG) to investigate how pSTM capacity in better and poorer pSTM groups is linked to language learning and the maintenance of pseudowords in pSTM. In particular, MEG was recorded while participants maintained pseudowords in pSTM by covert speech rehearsal, and while these brain representations were probed by presenting auditory pseudowords with first or third syllables matching or mismatching the rehearsed item. A control condition included identical stimuli but no rehearsal. Differences in response strength between matching and mismatching syllables were interpreted as the phonological mapping negativity (PMN). While PMN for the first syllable was found in both groups, it was observed for the third syllable only in the group with better pSTM. This suggests that individuals with better pSTM maintained representations of trisyllabic pseudowords more accurately during interference than individuals with poorer pSTM. Importantly, the group with better pSTM learned words faster in a paired-associate word learning task, linking the PMN findings to language learning.
  • 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.
  • Sirola, Roosa (Helsingfors universitet, 2013)
    Visual working memory (VWM) maintains information for future usage. Several studies show that the cortical oscillations in the γ-frequency band (from 30 to 120 Hz) are modulated by the VWM performance. However, less is known about the cortical sources underlying the modulation of these oscillations in VWM. To address this question, we recorded human neuronal activity with magneto- and electroencephalography (M/EEG) during a delayed-matching-to-sample VWM task with three different task conditions, within which participants were instructed to focus on different object features in turn. In addition, anatomical data was acquired with magnetic resonance imaging for source modeling purposes. We then estimated the cortical amplitude dynamics across frequencies from three to 90 Hz during the VWM retention period for these three different conditions. We found that the amplitudes of the γ –frequency band oscillations were strengthened in the occipito-temporal cortical areas during the VWM for shapes but not for color or spatial locations. These data suggest that γ –band oscillations are fundamental in VWM, especially for visual stimuli requiring perceptual feature binding. Furthermore, cortical γ –band oscillations were found to be load dependently strengthened in the frontal cortex, where the central executive and attention associated processes are believed to take place. These data support the previous hypotheses stating that γ –band oscillations contribute to the maintenance of object representations in VWM.
  • Leppaaho, Eemeli; Renvall, Hanna; Salmela, Elina; Kere, Juha; Salmelin, Riitta; Kaski, Samuel (2019)
    Brain structure and many brain functions are known to be genetically controlled, but direct links between neuroimaging measures and their underlying cellular-level determinants remain largely undiscovered. Here, we adopt a novel computational method for examining potential similarities in high-dimensional brain imaging data between siblings. We examine oscillatory brain activity measured with magnetoencephalography (MEG) in 201 healthy siblings and apply Bayesian reduced-rank regression to extract a low-dimensional representation of familial features in the participants' spectral power structure. Our results show that the structure of the overall spectral power at 1-90Hz is a highly conspicuous feature that not only relates siblings to each other but also has very high consistency within participants' own data, irrespective of the exact experimental state of the participant. The analysis is extended by seeking genetic associations for low-dimensional descriptions of the oscillatory brain activity. The observed variability in the MEG spectral power structure was associated with SDK1 (sidekick cell adhesion molecule 1) and suggestively with several other genes that function, for example, in brain development. The current results highlight the potential of sophisticated computational methods in combining molecular and neuroimaging levels for exploring brain functions, even for high-dimensional data limited to a few hundred participants.
  • Liljeström, Mia; Kujala, Jan; Stevenson, Claire; Salmelin, Riitta (2015)
  • Salmela, Elina; Renvall, Hanna; Kujala, Jan; Hakosalo, Osmo; Illman, Mia; Vihla, Minna; Leinonen, Eira; Salmelin, Riitta; Kere, Juha (2016)
    Several functional and morphological brain measures are partly under genetic control. The identification of direct links between neuroimaging signals and corresponding genetic factors can reveal cellular-level mechanisms behind the measured macroscopic signals and contribute to the use of imaging signals as probes of genetic function. To uncover possible genetic determinants of the most prominent brain signal oscillation, the parieto-occipital 10-Hz alpha rhythm, we measured spontaneous brain activity with magnetoencephalography in 210 healthy siblings while the subjects were resting, with eyes closed and open. The reactivity of the alpha rhythm was quantified from the difference spectra between the two conditions. We focused on three measures: peak frequency, peak amplitude and the width of the main spectral peak. In accordance with earlier electroencephalography studies, spectral peak amplitude was highly heritable (h(2)>0.75). Variance component-based analysis of 28000 single-nucleotide polymorphism markers revealed linkage for both the width and the amplitude of the spectral peak. The strongest linkage was detected for the width of the spectral peak over the left parieto-occipital cortex on chromosome 10 (LOD=2.814, nominal P
  • 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.
  • Wilenius, Juha; Lauronen, Leena; Kirveskari, Erika; Gaily, Eija; Metsähonkala, Liisa; Paetau, Ritva (2020)
    Objective To evaluate a novel analysis method (SAMepi) in the localization of interictal epileptiform magnetoencephalographic (MEG) activity in parietal lobe epilepsy (PLE) patients in comparison with equivalent current dipole (ECD) analysis. Methods We analyzed the preoperative interictal MEG of 17 operated PLE patients utilizing visual analysis and: (1) ECD with a spherical conductor model; (2) ECD with a boundary element method (BEM) conductor model; and (3) SAMepi - a kurtosis beamformer method. Localization results were compared between the three methods, to the location of the resection and to the clinical outcome. Results Fourteen patients had an epileptiform finding in the visual analysis; SAMepi detected spikes in 11 of them. A unifocal finding in both the ECD and in the SAMepi analysis was associated with a better chance of seizure-freedom (p=0.02). There was no significant difference in the distances from the unifocal MEG localizations to the nearest border of the resection between the different analysis methods. Conclusions Localizations of unifocal interictal spikes detected by SAMepi did not significantly differ from the conventional ECD localizations. Significance SAMepi - a novel semiautomatic analysis method - is useful in localizing interictal epileptiform MEG activity in the presurgical evaluation of parietal lobe epilepsy patients.
  • Kaltiainen, Hanna; Liljeström, Mia; Helle, Liisa; Salo, Anne; Hietanen, Marja; Renvall, Hanna; Forss, Nina (2019)
    Despite the high prevalence of mild traumatic brain injury (mTBI), current diagnostic tools to objectively assess cognitive complaints after mTBI continue to be inadequate. Our aim was to identify neuronal correlates for cognitive difficulties in mTBI patients by evaluating the possible alterations in oscillatory brain activity during a behavioral task known to be sensitive to cognitive impairment after mTBI. We compared oscillatory brain activity during rest and cognitive tasks (Paced Auditory Serial Addition Test [PASAT] and a vigilance test [VT]) with magnetoencephalography between 25 mTBI patients and 20 healthy controls. Whereas VT induced no significant differences compared with resting state in either group, patients exhibited stronger attenuation of 8- to 14-Hz oscillatory activity during PASAT than healthy controls in the left parietotemporal cortex (p
  • Parkkonen, Eeva; Laaksonen, Kristina; Piitulainen, Harri; Parkkonen, Lauri; Forss, Nina (2015)
    Background: Integration of afferent somatosensory input with motor-cortex output is essential for accurate movements. Prior studies have shown that tactile input modulates motor-cortex excitability, which is reflected in the reactivity of the similar to 20-Hz motor-cortex rhythm. similar to 20-Hz rebound is connected to inhibition or deactivation of motor cortex whereas suppression has been associated with increased motor cortex activity. Although tactile sense carries important information for controlling voluntary actions, proprioception likely provides the most essential feedback for motor control. Methods: To clarify how passive movement modulates motor-cortex excitability, we studied with magnetoencephalography (MEG) the amplitudes and peak latencies of suppression and rebound of the similar to 20-Hz rhythm elicited by tactile stimulation and passive movement of right and left index fingers in 22 healthy volunteers. Results: Passive movement elicited a stronger and more robust similar to 20-Hz rebound than tactile stimulation. In contrast, the suppression amplitudes did not differ between the two stimulus types. Conclusion: Our findings suggest that suppression and rebound represent activity of two functionally distinct neuronal populations. The similar to 20-Hz rebound to passive movement could be a suitable tool to study the functional state of the motor cortex both in healthy subjects and in patients with motor disorders.
  • Sami, Saber; Williams, Nitin; Hughes, Laura E.; Cope, Thomas E.; Rittman, Timothy; Coyle-Gilchrist, Ian T. S.; Henson, Richard N.; Rowe, James B. (2018)
    The disruption of brain networks is characteristic of neurodegenerative dementias. However, it is controversial whether changes in connectivity reflect only the functional anatomy of disease, with selective vulnerability of brain networks, or the specific neurophysiological consequences of different neuropathologies within brain networks. We proposed that the oscillatory dynamics of cortical circuits reflect the tuning of local neural interactions, such that different pathologies are selective in their impact on the frequency spectrum of oscillations, whereas clinical syndromes reflect the anatomical distribution of pathology and physiological change. To test this hypothesis, we used magnetoencephalography from five patient groups, representing dissociated pathological subtypes and distributions across frontal, parietal and temporal lobes: amnestic Alzheimer's disease, posterior cortical atrophy, and three syndromes associated with frontotemporal lobar degeneration. We measured effective connectivity with graph theory-based measures of local efficiency, using partial directed coherence between sensors. As expected, each disease caused large-scale changes of neurophysiological brain networks, with reductions in local efficiency compared to controls. Critically however, the frequency range of altered connectivity was consistent across clinical syndromes that shared a likely underlying pathology, whilst the localization of changes differed between clinical syndromes. Multivariate pattern analysis of the frequency-specific topographies of local efficiency separated the disorders from each other and from controls (accuracy 62% to 100%, according to the groups' differences in likely pathology and clinical syndrome). The data indicate that magnetoencephalography has the potential to reveal specific changes in neurophysiology resulting from neurodegenerative disease. Our findings confirm that while clinical syndromes have characteristic anatomical patterns of abnormal connectivity that may be identified with other methods like structural brain imaging, the different mechanisms of neurodegeneration also cause characteristic spectral signatures of physiological coupling that are not accessible with structural imaging nor confounded by the neurovascular signalling of functional MRI. We suggest that these spectral characteristics of altered connectivity are the result of differential disruption of neuronal microstructure and synaptic physiology by Alzheimer's disease versus frontotemporal lobar degeneration.
  • Issakainen, Jani (Helsingin yliopisto, 2021)
    Electroencephalography (EEG) is a non-invasive neurophysiological method for evaluating brain activity by measuring electrical potential at the scalp. The electrical potentials originate mainly from postsynaptic cortical currents created by neuronal activity. It is a valuable tool for both research and clinical practice. EEG can be used e.g. to diagnose epilepsy, focal brain disorders, brain death, and coma. Intermittent photic stimulation (IPS) is an important tool in clinical EEG. Healthcare professionals use it to induce epileptic activity in patients to help diagnose their conditions. In these tests, various IPS frequencies are used with eyes-closed, eyes-open, and eye-closure conditions. IPS test is listed in clinical practice guidelines in EEG globally, and it is mainly used to diagnose photosensitive epilepsy, i.e., to detect epilepsy-related abnormal sensitivity to flickering light. Magnetoencephalography (MEG) is a non-invasive neurophysiological method in which minute magnetic fields — produced by the same postsynaptic currents as in EEG — are measured with special superconductive sensors around the head. MEG is a valuable tool for research and clinical practice with increasing world-wide utilization. The main advantages of MEG over EEG are easier source modelling and higher resolution at cortical areas. IPS has not been introduced to MEG since the IPS stimulators used in EEG are not compatible with MEG. IPS in MEG could improve the analysis of IPS and provide better tools for diagnoses. Currently, data analysis of IPS is typically limited to healthcare professionals examining the visualization of the raw data while looking for induced epileptiform activites and lateralizing them. In this thesis, an MEG-compatible IPS stimulator is introduced and alternative ways of analyzing IPS data for both MEG and EEG are showcased. Although analysis methods were applied with decent signal-to-noise ratios, further research is needed—especially to compare responses between patients with epilepsy and healthy subjects.
  • Rekola, Lauri (Helsingfors universitet, 2017)
    Despite decades of study, no ironclad conclusion has been reached concerning the biological function of sleep in humans. Recent theories have proposed that sleep might play a role in maintaining cortical excitability at safe levels by downregulating excessive intersynaptic connections accumulated during a waking episode. In line with this theory, sleep deprivation has been shown to increase cortical excitability in studies using transcranial magnetic stimulation (TMS) and electroencephalography (EEG). In this pilot study (N=4) we used magnetoencephalography (MEG) to study the effects of 24 hours of sleep deprivation on somatosensory evoked fields (SEFs). Sleep deprivation increased the amplitude of primary somatosensory P35m component by 36%. Our preliminary findings confirm and delineate the previous EEG findings of enhanced somatosensory activation after sleep deprivation, thus indicating increased cortical excitability following sleep loss.