Comparing MEG and EEG in detecting the ∼20-Hz rhythm modulation to tactile and proprioceptive stimulation

Modulation of the ∼20-Hz brain rhythm has been used to evaluate the functional state of the sensorimotor cortex both in healthy subjects and patients, such as stroke patients. The ∼20-Hz brain rhythm can be detected by both magnetoencephalography (MEG) and electroencephalography (EEG), but the comparability of these methods has not been evaluated. Here, we compare these two methods in the evaluating of ∼20-Hz activity modulation to somatosensory stimuli. Rhythmic ∼20-Hz activity during separate tactile and proprioceptive stimulation of the right and left index finger was recorded simultaneously with MEG and EEG in twenty-four healthy participants. Both tactile and proprioceptive stimulus produced a clear suppression at 300–350 ms followed by a subsequent rebound at 700–900 ms after stimulus onset, detected at similar latencies both with MEG and EEG. The relative amplitudes of suppression and rebound correlated strongly between MEG and EEG recordings. However, the relative strength of suppression and rebound in the contralateral hemisphere (with respect to the stimulated hand) was significantly stronger in MEG than in EEG recordings. Our results indicate that MEG recordings produced signals with higher signal-to-noise ratio than EEG, favoring MEG as an optimal tool for studies evaluating sensorimotor cortical functions. However, the strong correlation between MEG and EEG results encourages the use of EEG when translating studies to clinical practice. The clear advantage of EEG is the availability of the method in hospitals and bed-side measurements at the acute phase.Peer reviewe

Reproducibility of corticokinematic coherence

Corticokinematic coherence (CKC) between limb kinematics and magnetoencephalographic (MEG) signals reflects cortical processing of proprioceptive afference. However, it is unclear whether strength of CKC is reproducible across measurement sessions. We thus examined reproducibility of CKC in a follow-up study. Thirteen healthy right-handed volunteers (7 females, 21.7 +/- 4.3 yrs) were measured using MEG in two separate sessions 12.6 +/- 1.3 months apart. The participant was seated and relaxed while his/her dominant or non-dominant index finger was continuously moved at 3 Hz (4 min for each hand) using a pneumatic movement actuator. Finger kinematics were recorded with a 3-axis accelerometer. Coherence was computed between finger acceleration and MEG signals. CKC strength was defined as the peak coherence value at 3 Hz form a single sensor among 40 pre-selected Rolandic gradiometers contralateral to the movement. Pneumatic movement actuator provided stable proprioceptive stimuli and significant CKC responses peaking at the contralateral Rolandic sensors. In the group level, CKC strength did not differ between the sessions in dominant (Day-1 0.40 +/- 0.19 vs. Day-2 0.41 +/- 0.17) or non-dominant (0.35 +/- 0.16 vs. 0.36 +/- 0.17) hand, nor between the hands. Intraclass-correlation coefficient (ICC) values indicated excellent inter-session reproducibility for CKC strength for both dominant (0.86) and non-dominant (0.97) hand. However, some participants showed pronounced inter-session variability in CKC strength, but only for the dominant hand. CKC is a promising tool to study proprioception in long-term longitudinal studies in the group level to follow, e.g., integrity of cortical proprioceptive processing with motor functions after stroke.Peer reviewe

Reproducibility of corticokinematic coherence

Corticokinematic coherence (CKC) between limb kinematics and magnetoencephalographic (MEG) signals reflects cortical processing of proprioceptive afference. However, it is unclear whether strength of CKC is reproducible across measurement sessions. We thus examined reproducibility of CKC in a follow-up study. Thirteen healthy right-handed volunteers (7 females, 21.7 +/- 4.3 yrs) were measured using MEG in two separate sessions 12.6 +/- 1.3 months apart. The participant was seated and relaxed while his/her dominant or non-dominant index finger was continuously moved at 3 Hz (4 min for each hand) using a pneumatic movement actuator. Finger kinematics were recorded with a 3-axis accelerometer. Coherence was computed between finger acceleration and MEG signals. CKC strength was defined as the peak coherence value at 3 Hz form a single sensor among 40 pre-selected Rolandic gradiometers contralateral to the movement. Pneumatic movement actuator provided stable proprioceptive stimuli and significant CKC responses peaking at the contralateral Rolandic sensors. In the group level, CKC strength did not differ between the sessions in dominant (Day-1 0.40 +/- 0.19 vs. Day-2 0.41 +/- 0.17) or non-dominant (0.35 +/- 0.16 vs. 0.36 +/- 0.17) hand, nor between the hands. Intraclass-correlation coefficient (ICC) values indicated excellent inter-session reproducibility for CKC strength for both dominant (0.86) and non-dominant (0.97) hand. However, some participants showed pronounced inter-session variability in CKC strength, but only for the dominant hand. CKC is a promising tool to study proprioception in long-term longitudinal studies in the group level to follow, e.g., integrity of cortical proprioceptive processing with motor functions after stroke.Peer reviewe

Evidence for genetic regulation of the human parieto-occipital 10-Hz rhythmic activity

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 PPeer reviewe

Beta Rhythm Modulation in the Evaluation of Cortical Sensorimotor Function

Primäärisellä tunto- ja liikeaivokuorella (SM1) syntyvän ~20 Hz taajuisen beta-rytmin voimakkuus reagoi aktiivisiin ja passiivisiin liike- ja tuntoärsykkeisiin sekä liikkeiden kuvittelemiseen. Beta-rytmi vaimenee (ns. beta-vaimeneminen) pian liikkeen tai tuntoärsykkeen jälkeen ja sitä seuraa beta-rytmin voimistuminen (ns. beta-vahvistuminen). Beta-vaimenemisen ajatellaan heijastavan SM1-aivokuoren eksitaatiota ja beta-vahvistumisen inhibitiota. Beta-rytmin moduloitumista onkin täten ehdotettu SM1-aivokuoren toiminnallista tilaa kuvaavaksi neurofysiologiseksi mittariksi. SM1-aivokuoren eksitaatio-inhibition säätely on välttämätöntä hermoston uudelleenmuovautumiskyvylle ja vaurioiden korjautumiselle, ja siten beta-rytmin modulaatio voisi toimia hyödyllisenä biomarkkerina esimerkiksi tutkittaessa uusien lääkehoitojen ja kuntoutusmenetelmien toimivuutta aivoinfarktista toipumisen yhteydessä. Beta-rytmin modulaation toistettavuus sekä sitä mahdolliset häiritsevät tekijät, kuten alentuneen vireystason vaikutus, tunnetaan kuitenkin huonosti. Tämä voi heikentää sen käytettävyyttä biomarkkerina erityisesti kliinisissä seurantatutkimuksissa. Näiden tekijöiden lisäksi väitöskirjan tavoitteena oli selvittää beta-rytmin modulaation vertailtavuus MEG- ja EEG-rekisteröintien välillä. EEG:n käyttö helpottaisi merkittävästi beta-rytmin modulaation käyttöä biomarkkerina kliinisessä ympäristössä EEG:n huomattavasti paremman saatavuuden vuoksi. Viimeisessä osatyössä tutkittiin SM1-aivokuoren eksitaatio-inhibition tasapainoa nuorilla, joilla on hemipleginen tai dipleginen CP-vamma. Kaikissa väitöskirjan tutkimuksissa beta-rytmin moduloimiseen käytettiin etusormen tunto- ja/tai liikeaistiärsykkeitä. Beta-rytmin voimakkuuden muutosten analysoinnissa käytettiin TSE-menetelmällä (engl. temporal spectral evolution). Tulokset osoittavat MEG:n ja EEG:n havaitsevan hyvin beta-rytmin modulaatiota, vaikka se näkyi voimakkaampana MEG:llä mitattuna. Pitkittäistutkimus osoitti beta-rytmin modulaation olevan hyvin toistettava vuoden aikavälillä ja lisäksi alentuneen vireystilan ei todettu vaikuttavan merkitsevästi beta-rytmin modulaation ryhmätasolla. Diplegisessä CP-vammassa SM1-aivokuoren eksitaation ja inhibition havaittiin muuttuneen molemmissa aivopuoliskoissa, mutta vastaavia muutoksia ei nähty hemiplegisessä CP-vammassa. Väitöskirjan tulokset osoittavat beta-rytmin modulaation olevan luotettava ja helposti toteutettava menetelmä SM1-aivokuoren toiminnan tutkimiseen. Menetelmää voidaan tulevaisuudessa mahdollisesti käyttää biomarkkerina esim. potilaan toipumispotentiaalin arvioinnissa.The cortical ~20-Hz beta rhythm that arises mainly from the primary sensorimotor (SM1) cortex reacts to voluntary movements or motor imagery as well as to somatosensory stimuli. The decrease in beta power shortly after somatosensory stimulus or movement is called beta suppression, and the subsequent increase in beta power is called beta rebound. Beta suppression has been proposed to reflect excitation and the rebound inhibition of the SM1 cortex. As excitatory–inhibitory regulation of the SM1 cortex is essential for brain plasticity and recovery, beta modulation may be a useful biomarker to objectively assess the effect of various interventions, such as medical therapies and rehabilitation methods, on the recovery of stroke patients. However, the reproducibility of beta modulation and how it is affected by confounding factors such as reduced alertness during MEG or EEG recordings are still poorly known, which may weaken its reliability as a biomarker, especially in clinical follow-up studies. The objective of this dissertation was to investigate these issues in healthy subjects. In addition, the beta modulation strength was compared between MEG and EEG recordings to evaluate EEG as an alternative method to MEG, since EEG would facilitate the availability of studies in clinical applications. In addition, the SM1 cortex beta modulation dynamics were explored in adolescents with hemiplegic and diplegic cerebral palsy (CP). In the series of studies, the beta rhythm was modulated with tactile and/or proprioceptive finger stimulation. The stimulus-related beta rhythm changes were analyzed using temporal spectral evolution. The results showed that both MEG and EEG successfully detected beta modulation well, although the suppression and rebound strengths were more pronounced in MEG. The long-term reproducibility of beta modulation was found to be good, and the reduced alertness did not significantly change the strength of beta modulation at the group level. In adolescents with diplegic CP, the SM1 cortex excitation and inhibition were bilaterally altered, but no similar changes were detected in hemiplegic CP. Overall, the results showed that beta modulation offers a feasible, reliable, and easy-to-implement method to detect the cortical function of the SM1, which may in the future be used as a biomarker, for example, in the evaluation of the recovery potential of patients

Liikeaivokuoren rytmisen toiminnan voimakkuuden ja taajuuden periytyvyys: MEG-tutkimus

Tämä opinnäytetyö on osa suurempaa Aalto-yliopiston O.V. Lounasmaa -laboratorion aivotutkimusyksikössä tehtävää tutkimuskokonaisuutta, jonka tarkoituksena on etsiä perinnöllisiä piirteitä aivotoiminnasta sisarusten välillä ja paikantaa kyseisten piirteiden kanssa korreloivia geenialueita. Ihmisen normaalissa aivotoiminnassa esiintyy eri taajuisia perusrytmejä. Aivorytmit ovat valveilla vaimeampia ja nopeampia kuin unessa, ja ne tyypillisesti vaimenevat myös aivoalueiden aktivoituessa liikkeen tai erilaisten ärsykkeiden seurauksena. Aivorytmeissä on aikaisemmissa EEG:llä tehdyissä tutkimuksissa havaittu perinnöllisiä piirteitä, mutta aivorytmien syntyyn vaikuttavista geeneistä on olemassa toistaiseksi vain vähän tietoa. Tässä osatyössä tarkasteltiin lähemmin liikeaivokuorella syntyvän 20 Hz:n taajuisen myy-rytmin perinnöllisiä piirteitä sisarusten välillä. Työssä mitattiin spontaania aivotoimintaa yli sadalta sisarusparilta magnetoenkefalografilla (MEG) levossa silmät auki sekä käsien puristusliikkeen aikana. Kahden tilanteen aikaisia taajuusspektrejä, jotka kuvastavat aivotoiminnan eri taajuuksia ja niiden voimakkuuksia, vertailtiin sisarusten välillä. Myy-rytmin 20 Hz:n huipputaajuuksissa ja -voimakkuuksissa oli yksilöllistä vaihtelua, mutta tulokset osoittavat myös tilastollisesti merkitsevästi samankaltaisia piirteitä sisarusten välillä niin huipputaajuuksissa kuin niiden voimakkuuksissa. Silmät auki lepotilanteessa nähtiin tilastollisesti merkitsevä samankaltaisuus sisarusten välillä sekä huipputaajuuksissa että -voimakkuuksissa, kun taas käsien puristusliikkeen aikana samankaltaisuutta oli lähinnä huipputaajuuksissa. Työssä löydettyjä sisarusten välillä samankaltaisia aivovasteita tullaan myöhemmässä vaiheessa hyödyntämään geenien kytkentäanalyyseissä. Yhdistämällä kahden täysin erilaisen tutkimusmenetelmän avulla saatuja tietoja pyritään löytämään täysin uudenlaista tietoa aivotoiminnan muodostumiseen vaikuttavista geeneistä.The current study is a part of a larger research project that aims at, finding inherited features in brain activity between siblings and locating the corresponding gene areas. The human brain produces a number of basic rhythms at different frequencies. The brain rhythms are typically weaker and of higher frequency at awake than during sleep. Rhythms reduce in amplitude during the movements and by different external stimuli. Previous EEG studies in twins have pointed out heritable features in brain rhythms, but there is only very limited information on how and which genes would influence the rhythms. In the current study we focused on the 20-Hz mu rhythm generated at the motor cortex, and on its heritability between siblings. We measured spontaneous brain activity over a hundred sibling pairs with magnetoencephalography (MEG). During the measurements, the subjects were sitting and keeping their eyes open, first in resting stage and then doing hand squeezing movements. The measurement data was analyzed by calculating frequency spectras that reflect the different frequencies and intensities of brain activity in both situations. The peak frequency and intensity of the 20-Hz rhythm was measured and compared between siblings. Lot of individual variation in the peak frequencies and intensities of the 20-Hz rhythm was observed, but the results also pointed out statistically significant similarities between siblings in the peak frequencies and intensities of the 20-Hz rhythmic activity. A significant correlation between the siblings, both in frequencies and intensities, was observed in resting condition. Significant correlation in the hand squeezing condition was observed mainly for the peak frequencies. The results of the current study will be next utilized in genetic analysis. By combining these different research methods, we aim at finding completely new kind of information on how our genetic layout affects the formation of brain responses

fMRI-tutkimuskokemuksen laatu koehenkilöiden näkökulmasta

Aalto-yliopiston AMI–keskuksessa osallistuu vuosittain satoja vapaaehtoisia koehenkilöitä toiminnallisella magneettikuvausmittauksella (functional magnetic resonance imaging, fMRI) tehtäviin tieteellisiin tutkimusprojekteihin. Vapaaehtoisten koehenkilöiden tutkimuksiin liittyvistä kokemuksista ja näkemyksistä on olemassa vain vähän tutkittua tietoa, mutta tiedosta olisi hyötyä niin koehenkilöiden tutkimuskokemuksen kehittämisen, tutkimuksen laadun parantamisen ja koehenkilöiden osallistumishalukkuuden lisäämisen kannalta. Koehenkilöiden fMRI-tutkimukseen liittyviä kokemuksia tutkitiin kyselytutkimuksella, johon saatiin vastaus 62:lta koehenkilöltä. Aineisto kerätiin tammi – syyskuussa 2016. Kyselytutkimuksen aiheet käsittelivät koehenkilöiden kokemuksia fMRI-tutkimukseen liittyvästä ohjauksesta, huomioimisesta, tutkimushenkilökunnan toiminnasta, tutkimusympäristöstä, tukimukseen liittyvistä tunteista ja siihen liittyvistä mahdollisista sivuvaikutuksia. Koehenkilöt olivat pääasiassa tyytyväisiä saamaansa ohjaukseen ja he kokivat tuleensa hyvin huomioiduiksi tutkimuksen aikan. Tutkimukseen osallistumista pidetiin turvallisena ja mielenkiintoisena ja tutkimushenkilökunnan toiminta sai lähinnä positiivista palautetta. Tutkimusympäristöä pidettiin siistinä ja luotettavana, mutta tutkimuspaikalle löytämisessä oli selkeästi hankaluuksia. Ensimmäistä kertaa fMRI–tutkimukseen osallistuneet koehenkilöt jännittivät tutkimusta muita enemmän ja suurin osa koehenkilöistä ilmoitti olleensa väsyneitä niin ennen tutkimusta kuin sen aikana. Kyselytutkimuksesta saatujen tulosten avulla AMI–keskuksen toimintaa voidaan kehittää entistä paremmin koehenkilöiden tarpeet huomioivaksi. Ensimmäistä kertaa fMRI-tutkimuksen osallistuviin koehenkilöihin tulisi kiinnittää erityistä huomioita ja pyrkiä vähentämään heidän tutkimukseen liittyvää jännitystä. Jännityksellä ja stressillä voi olla vaikutusta fMRI-tutkimuksesta saatuihin tuloksiin ja niiden luotettavuuteen. Myös koehenkilöiden väsymys ja vireystilan lasku vaikuttavat tutkimustuloksiin ja tutkimuksen onnistumiseen. Opastusta tutkimuspaikalle tulisi parantaa entisestään.Each year hundreds of volunteers participate in functional magnetic resonance imaging (fMRI) research at the AMI center in Aalto University. However, only limited information is available regarding the experience from the participants’ point of view. This information would be beneficial for both researcher and participants as it might improve the experience, the data quality and the participation rate. The fMRI experience was therefore studied using a survey on 62 fMRI participants. The data were collected in January – Sebtember 2016. The topics of the questionnaire dealt with fMRI subjects' experiences and attitudes related to guidance and consideration, staff’s action, research environment and emotions related to fMRI as well as possible side-effects. The findings were generally positive and subjects were satisfied with the guidance and attention. fMRI was considered a safe and interesting experience and the staff was mostly given positive feedback. The research environment was seen clean and reliable, but the subjects had difficulties to find the fMRI study site. It was also revealed that the subjects, especially first-timers, were nervous before and during the fMRI. The majority of the subjects also reported that they were tired before and during the study. The results show that especially first-time participants would benefit if their nervousness could be reduced. Reducing the stress levels would make the experience of fMRI more pleasant for the subjects and may improve the quality of the fMRI results, as both fatigue and alertness are affected by nerves and influence task-compliance and reliability of the study. Improving the guidance on the study site, could thus be further improved

The effect of alertness and attention on the modulation of the beta rhythm to tactile stimulation

Beta rhythm modulation has been used as a biomarker to reflect the functional state of the sensorimotor cortex in both healthy subjects and patients. Here, the effect of reduced alertness and active attention to the stimulus on beta rhythm modulation was investigated. Beta rhythm modulation to tactile stimulation of the index finger was recorded simultaneously with MEG and EEG in 23 healthy subjects (mean 23, range 19-35 years). The temporal spectral evolution method was used to obtain the peak amplitudes of beta suppression and rebound in three different conditions (neutral, snooze, and attention). Neither snooze nor attention to the stimulus affected significantly the strength of beta suppression nor rebound, although a decrease in suppression and rebound strength was observed in some subjects with a more pronounced decrease of alertness. The reduction of alertness correlated with the decrease of suppression strength both in MEG (left hemisphere r = 0.49; right hemisphere r = 0.49, *p < 0.05) and EEG (left hemisphere r = 0.43; right hemisphere r = 0.72, **p < 0.01). The results indicate that primary sensorimotor cortex beta suppression and rebound are not sensitive to slightly reduced alertness nor active attention to the stimulus at a group level. Hence, tactile stimulus-induced beta modulation is a suitable tool for assessing the sensorimotor cortex function at a group level. However, subjects' alertness should be maintained high during recordings to minimize individual variability.Peer reviewe

Feasibility and reproducibility of electroencephalography-based corticokinematic coherence

Corticokinematic coherence (CKC) is the phase coupling between limb kinematics and cortical neurophysiological signals reflecting cortical processing of proprioceptive afference, and is reproducible when estimated with magnetoencephalography (MEG). However, feasibility and reproducibility of CKC based on electroencephalography (EEG) is still unclear and is the primary object of the present report. Thirteen healthy right-handed volunteers (7 females, 21.7 ± 4.3 years) participated two separate EEG sessions 12.6±1.3 months apart. Participants' dominant and non-dominant index finger was continuously moved at 3 Hz for 4 min separately using a pneumatic-movement actuator. Coherence was computed between finger acceleration and three derivations of EEG signals: (1) average reference, (2) bipolar derivations, and (3) surface Laplacian. CKC strength was defined as the peak coherence value at the movement frequency. Intraclass-correlation coefficient values (0.74-0.93) indicated excellent inter-session reproducibility for CKC strength for all derivations and moved fingers. CKC strength obtained with EEG was ~2 times lower compared to MEG but the values were positively correlated across the participants. CKC strength was significantly (p<0.01) higher for bipolar (session-1 0.19±0.09; session-2 0.20±0.10) and surface Laplacian (session-1 0.22±0.09; session-2 0.21±0.09) derivations than for the average reference (session 1 0.10±0.04; session 2, 0.11±0.05). We demonstrated that CKC is feasible and reproducible tool to monitor proprioception using EEG recordings, although the strength of CKC was twice lower for EEG compared to MEG. Laplacian and bipolar (CP3-C1/CP3-C3 and CP4-C2/C4-FC2) EEG derivation(s) are recommended for future research and clinical use of CKC method.peerReviewe

Reproducibility of Rolandic beta rhythm modulation in MEG and EEG

The Rolandic beta rhythm, at ~20 Hz, is generated in the somatosensory and motor cortices and is modulated by motor activity and sensory stimuli, causing a short lasting suppression that is followed by a rebound of the beta rhythm. The rebound reflects inhibitory changes in the primary sensorimotor (SMI) cortex, and thus it has been used as a biomarker to follow the recovery of acute stroke patients. The longitudinal stability of beta rhythm modulation is a prerequisite for its use in long-term follow-ups. We quantified the reproducibility of beta rhythm modulation in healthy subjects in a 1-year-longitudinal study both for MEG and EEG at T0,one month (T1-month, n = 8) and one year (T1-year, n = 19). The beta rhythm (13-25 Hz) was modulated by fixed tactile and proprioceptive stimulations of the index fingers. The relative peak strengths of beta suppression and rebound did not differ significantly between the sessions, and inter-session reproducibility was good or excellent according to intraclass correlation-coefficient values (0.70-0.96) both in MEG and EEG. Our results indicate that the beta rhythm modulation to tactile and proprioceptive stimulation is well reproducible within one year. These results support the use of beta modulation as a biomarker in long-term follow-up studies, e.g., to quantify the functional state of the SMI cortex during rehabilitation and drug interventions in various neurological impairments.peerReviewe