Studying functional magnetic resonance imaging with artificial imaging objects

Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) is an indirect method for measuring information processing in the brain. The method has enabled mapping human brain function in an unprecedented variety of tasks and conditions, and with a spatial resolution of the order of 1 mm. In this dissertation, artificial imaging objects, or phantoms, with adjustable signal intensity were used to simulate and investigate the generation of fMRI signals. The objective was to characterise, and devise means to characterise, fMRI signal components that arise from methodological reasons, impeding the correct physiological interpretation of the signals. The first study involved building an fMRI phantom, where an electric current was applied to introduce magnetic field inhomogeneity within a magnetic resonance signal source. It was shown that the changes of field homogeneity and thus fMRI signal, largely corresponded to the human BOLD changes, even though the physical mechanisms were different. The mechanical properties of phantoms and brain however differ. Thus it was important to look into the attributes of phantoms that would make the fMRI signal from the phantom similar to brain scanning data. The second study examined geometric distortions in the echo-planar imaging method—commonly employed in both fMRI and diffusion tensor imaging—using a purpose-built structural phantom. In the third study, another fMRI activation phantom was built. There the induction wires were located outside the source of the fMRI signal, and thus the partial volume effect limiting the usability of the first fMRI phantom was abated. The phantom was applied to induce artificial activations that could be utilized to deduce periods when simultaneously measured brain activations would yield deviant activation levels due to unphysiological causes. In the last study, an fMRI phantom was used to show that transient fMRI signal components, often witnessed in brain activation data, could occur in the absence of corresponding physiological signal, resulting from the sole signal change

All that glitters is not BOLD: inconsistencies in functional MRI

The blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) signal is a widely-accepted marker of brain activity. The acquisition parameters (APs) of fMRI aim at maximizing the signals related to neuronal activity while minimizing unrelated signal fluctuations. Currently, a diverse set of APs is used to acquire BOLD fMRI data. Here we demonstrate that some fMRI responses are alarmingly inconsistent across APs, ranging from positive to negative, or disappearing entirely, under identical stimulus conditions. These discrepancies, resulting from non-BOLD effects masquerading as BOLD signals, have remained largely unnoticed because studies rarely employ more than one set of APs. We identified and characterized non-BOLD responses in several brain areas, including posterior cingulate cortex and precuneus, as well as AP-dependence of both the signal time courses and of seed-based functional networks, noticing that AP manipulation can inform about the origin of the measured signals.Peer reviewe

Relationship-specific Encoding of Social Touch in Somatosensory and Insular Cortices

Humans use touch to maintain their social relationships, and the emotional qualities of touch depend on who touches whom. However, it is not known how affective and social dimensions of touch are processed in the brain. We measured haemodynamic brain activity with functional magnetic resonance imaging (fMRI) from 19 subjects (10 males), while they were touched on their upper thigh by either their romantic partner, or an unfamiliar female or male confederate or saw the hand of one of these individuals near their upper thigh but were not touched. We used multi-voxel pattern analysis on pre-defined regions of interest to reveal areas that encode social touch in a relationship-specific manner. The accuracy of the machine learning classifier to identify actor for both feeling touch and seeing hand exceeded the chance level in the primary somatosensory cortex, while in the insular cortex accuracy was above chance level only for the touch condition. When classifying the relationship (partner or stranger), while keeping the toucher sex fixed, amygdala (AMYG), orbitofrontal cortex (OFC), and primary and secondary somatosensory cortices were able to discriminate toucher significantly above chance level.These results suggest that information on the social relationship of the toucher is processed consistently across several regions. More complex information about toucher identity is processed in the primary somatosensory and insular cortices, both of which can be considered early sensory areas.</p

Ultra-High Field MRI: Transition to Human 7 T in Finland - Workshop Memorandum

A workshop “Ultra-High Field MRI: Transition to Human 7 T in Finland” was organized at Aalto University on October 8–9, 2015. The organizers included Aalto University School of Science, Finnish Infrastructures for Functional Imaging (FIFI), Aalto NeuroImaging (ANI), Aalto Brain Centre (ABC), and Department of Neuroscience and Biomedical Engineering (NBE). The purpose of the workshop was to demonstrate scientific achievements and possibilities enabled by ultra-high field (UHF) magnetic resonance imaging (MRI). The meeting brought together a group of top-level scientists for two days to give presentations and immerse in discussions. This memorandum not only documents the meeting but also paves the way for making the first human 7 T scanner operational in Finland in the near future

Imaging Real-Time Tactile Interaction With Two-Person Dual-Coil fMRI

Studies of brain mechanisms supporting social interaction are demanding because real interaction only occurs when persons are in contact. Instead, most brain imaging studies scan subjects individually. Here we present a proof-of-concept demonstration of two-person blood oxygenation dependent (BOLD) imaging of brain activity from two individuals interacting inside the bore of a single MRI scanner. We developed a custom 16-channel (8 + 8 channels) two-helmet coil with two separate receiver-coil pairs providing whole-brain coverage, while bringing participants into a shared physical space and realistic face-to-face contact. Ten subject pairs were scanned with the setup. During the experiment, subjects took turns in tapping each other's lip versus observing and feeling the taps timed by auditory instructions. Networks of sensorimotor brain areas were engaged alternatingly in the subjects during executing motor actions as well as observing and feeling them; these responses were clearly distinguishable from the auditory responses occurring similarly in both participants. Even though the signal-to-noise ratio of our coil system was compromised compared with standard 32-channel head coils, our results show that the two-person fMRI scanning is feasible for studying the brain basis of social interaction

Veren hapetustason muutosten fysikaalinen simulointi toiminnallisessa magneettikuvauksessa

Functional magnetic resonance imaging is a popular method in brain research. It can pinpoint secondary metabolic activity following electrical Signalling of neurons. Typically, the extent of an identified activation is several voxels while some of them are activated more than others. The purpose of the current study was to develop a method and device, which would signify whether an activation of certain intensity in a specified voxel of certain size determines the metabolism of the tissue represented by the voxel or does it represent the residual spread intensity of another voxel. In practise, this could clarify the scientific terminology where activations currently described as large could be characterised more precisely in terms of intensity and spread. The work consisted of designing and constructing a phantom system and the accompanying signalling system. The systems were tested and a methodology for the spatial location assurance was developed. The work was done in the Advanced Magnetic Imaging Centre of Helsinki University of Technology.Toiminnallinen magneettikuvaus on paljon käytetty menetelmä aivotutkimuksessa. Sillä voidaan paikallistaa esimerkiksi hermosolujen sähköisen viestimisen seurauksena tapahtuvaa aineenvaihduntaa. Havaitun ilmiön tilavuus on tavallisesti laajuudeltaan useita tilavuuskuvan alkioita ja ilmiön voimakkuus vaihtelee tilavuusalkiosta toiseen. Tämän tutkimuksen tarkoitus oli kehittää menetelmä ja laitteisto, joilla voidaan selvittää, josko on mahdollista, että. tietyssä tilavuuskuvan alkiossa havaittu aktivaatiointensiteetti voi syntyä vain sitä vastaavassa näytetilavuudessa. Vaihtoehtona on ilmiön intensiteetin leviäminen ympäröiviin kuva-alkioihin siten, että signaalilähde, jonka tulkiltaan olevan laaja, voikin olla pienikokoinen ja voimakas. Käytännössä menetelmällä voidaan selventäviä suuriksi luonnehdittujen aktivaatioiden luokittelua laajoihin ja voimakkaisiin. Työ käsitti mittausfantomin ja sen ohjausjärjestelmän suunnittelun ja toteutuksen. Laitteet testattiin ja kehitettiin menetelmä toiminnallisen magneettikuvauksen paikkatarkkuuden varmistamiseen. Työ tehtiin Teknillisen korkeakoulun AMI-keskuksessa

Relationship-specific Encoding of Social Touch in Somatosensory and Insular Cortices

| openaire: EC/H2020/313000/EU//SOCIAL BRAINHumans use touch to maintain their social relationships, and the emotional qualities of touch depend on who touches whom. However, it is not known how affective and social dimensions of touch are processed in the brain. We measured haemodynamic brain activity with functional magnetic resonance imaging (fMRI) from 19 subjects (10 males), while they were touched on their upper thigh by either their romantic partner, or an unfamiliar female or male confederate or saw the hand of one of these individuals near their upper thigh but were not touched. We used multi-voxel pattern analysis on pre-defined regions of interest to reveal areas that encode social touch in a relationship-specific manner. The accuracy of the machine learning classifier to identify actor for both feeling touch and seeing hand exceeded the chance level in the primary somatosensory cortex, while in the insular cortex accuracy was above chance level only for the touch condition. When classifying the relationship (partner or stranger), while keeping the toucher sex fixed, amygdala (AMYG), orbitofrontal cortex (OFC), and primary and secondary somatosensory cortices were able to discriminate toucher significantly above chance level. These results suggest that information on the social relationship of the toucher is processed consistently across several regions. More complex information about toucher identity is processed in the primary somatosensory and insular cortices, both of which can be considered early sensory areas.Peer reviewe

Imaging real-time tactile interaction with two-person dual-coil fMRI

Studies of brain mechanisms supporting social interaction are demanding because real interaction only occurs when persons are in contact. Instead, most brain imaging studies scan subjects individually. Here we present a proof-of-concept demonstration of two-person blood oxygenation dependent (BOLD) imaging of brain activity from two individuals interacting inside the bore of a single MRI scanner. We developed a custom 16-channel (8 + 8 channels) two-helmet coil with two separate receiver-coil pairs providing whole-brain coverage, while bringing participants into a shared physical space and realistic face-to-face contact. Ten subject pairs were scanned with the setup. During the experiment, subjects took turns in tapping each other’s lip versus observing and feeling the taps timed by auditory instructions. Networks of sensorimotor brain areas were engaged alternatingly in the subjects during executing motor actions as well as observing and feeling them; these responses were clearly distinguishable from the auditory responses occurring similarly in both participants. Even though the signal-to-noise ratio of our coil system was compromised compared with standard 32-channel head coils, our results show that the two-person fMRI scanning is feasible for studying the brain basis of social interaction.Peer reviewe

Aerobic fitness, but not physical activity, is associated with grey matter volume in adolescents

Higher levels of aerobic fitness and physical activity are linked to beneficial effects on brain health, especially in older adults. The generalizability of these earlier results to young individuals is not straightforward, because physiological responses (such as cardiovascular responses) to exercise may depend on age. Earlier studies have mostly focused on the effects of either physical activity or aerobic fitness on the brain. Yet, while physical activity indicates the amount of activity, aerobic fitness is an adaptive state or attribute that an individual has or achieves. Here, by measuring both physical activity and aerobic fitness in the same study, we aimed to differentiate the association between these two measures and grey matter volume specifically. Magnetic resonance imaging scans were used to study volumes of 30 regions of interest located in the frontal, motor and subcortical areas of 60 adolescents (12.7–16.2 years old). Moderate-to-vigorous intensity physical activity (MVPA) was measured with hip-worn accelerometers and aerobic fitness was assessed with a 20-m shuttle run. Multiple regression analyses revealed a negative association between aerobic fitness and left superior frontal cortex volume and a positive association between aerobic fitness and the left pallidum volume. No associations were found between MVPA and any brain region of interest. These results demonstrate unequal contribution of physical activity and aerobic fitness on grey matter volumes, with inherent or achieved capacity (aerobic fitness) showing clearer associations than physical activity.peerReviewe