Browsing by Subject "fMRI"

Tavoitteet: Tämän kandidaatintutkielman tavoitteena on tarkastella, millaista tietoa monimuuttujamenetelmiä hyödyntävät tutkimukset tarjoavat abstraktien käsitteiden aivoperustasta. Kyky käsitteelliseen ajatteluun on keskeinen osa ihmisyyttä ja sitä tarvitaan paitsi kommunikointiin ja ajatteluun myös käytännön toiminnanohjaamiseen. Aivojen semanttisen muistijärjestelmän toiminnasta on esitetty useita erilaisia malleja, joista eniten keskustelua ovat herättäneet erilaiset versiot kehollistuneen kognition mallista sekä hub-and-spoke-mallista. Suuri osa tutkimuksesta on keskittynyt tarkastelemaan konkreettisiin käsitteisiin liittyviä aivovasteita perinteisillä yksimuuttujamenetelmillä. Abstraktien käsitteiden aivovasteita ymmärretään huomattavasti heikommin. Noin viimeisen kymmenen vuoden aikana käsitteellisen ajattelun aivoperustaan liittyvässä tutkimuksessa ovat yleistyneet monimuuttujamenetelmät, jotka tarkastelevat perinteisten aktivaatiovasteiden keskiarvojen sijaan aktivaation hajontaan perustuvaa informaatiota, mikä mahdollistaa uudenlaisen tavan tarkastella semanttiseen prosessointiin liittyviä aivoverkostoja. Menetelmät: Tutkielmaa varten etsittiin vertaisarvioituja tutkimuksia, joissa on tarkasteltu abstraktien käsitteiden aivoperustaa käyttämällä kielellisiä ärsykkeitä ja aivokuvantamismenetelmänä funktionaalista magneettikuvausta (fMRI). Tutkimuksilta edellytettiin, että käsitteisiin liittyvien fMRI-vasteiden analyyseissä on hyödynnetty ensisijaisesti jotakin monimuuttujamenetelmää. Artikkeleita haettiin PubMed, Web of Science ja Google Scholar -tietokannoista käyttämällä monipuolisesti seuraavien hakusanojen yhdistelmiä: Abstract concepts, Abstract words, Concrete concepts, Concrete words, Word imageability, Word concreteness, fMRI, Multivariate, Multivoxel, Cognitive neuroscience, Semantic, Semantic processing Tulokset ja johtopäätökset: Tutkimusnäyttö viittaa siihen, että abstraktien käsitteiden aivovasteet ovat hyvin eroteltavissa paitsi konkreettisista käsitteistä myös eri abstraktien käsitteiden välillä. Lisäksi abstrakteihin käsitteisiin liittyvät aivovasteet vaikuttaisivat olevan huomattavan yhdenmukaisia eri koehenkilöiden välillä, sekä alustavasti myös eri kielten välillä. Vahvan kehollistuneen kognition malli ei saanut tukea tuloksista, mutta sen sijaan hub-and-spoke-mallille keskeiset aivoalueet nousivat korostuneesti esiin abstraktien käsitteiden prosessoinnissa. Myös perinteiset vasemman aivolohkon kielialueet etuotsalohkossa ja temporaalilohkossa nousivat korostuneesti esiin useassa tutkimuksessa.

The aim of this study is to examine the development of selective and divided attention in adolescence using functional magnetic resonance imaging (fMRI) and behavioral measures. Although the prefrontal cortex, a key area for attention and cognitive control, is thought to mature well into adulthood, few studies have examined the development of attention in adolescents and young adults. No fMRI studies have been conducted on the development of divided attention. In this study, development was examined both cross-sectionally and longitudinally to also assess the possible differences in the results they produced, as nearly all previous studies have been cross-sectional. Brain activity was measured from 103 participants aged 13–22 who were divided into three age cohorts. The youngest two cohorts were measured again after 1.5 years for the longitudinal study. While in the scanner, participants performed a sentence congruence task where they were instructed either to attend to only the speech or text stimulus or divide their attention between both modalities simultaneously. The cross-sectional results showed improvement in task performance between the youngest cohort (13– 14y.) and the older cohorts in both selective and divided attention tasks. No difference was found between the older two cohorts (16–17y. and 20–22y.) However, the longitudinal results did not indicate clear performance improvement with age in either task type. According to the longitudinal fMRI results from age 13–14 to 15–16, in the selective attention task brain activity decreased mainly in the medial prefrontal area and activity increased slightly in parietal regions. In the divided attention task, the decreased prefrontal activity was more lateral. From age 16–17 to 18– 19, increased activity in motor regions and precuneus was found in both tasks. In general, the effects were very subtle, possibly due to a short measurement interval and relatively small cohort sizes. The cross-sectional results indicated quite a different pattern of change in brain activity, concentrated on temporal areas. This difference in results emphasizes the importance of conducting longitudinal developmental studies in the future. Although the effects were not large, the longitudinal fMRI results were in line with some previous findings that prefrontal areas are recruited less with age, so that activity in more posterior task-related areas increases. The current results suggest that some fine-tuning of the attention and cognitive control-related network still occurs from adolescence to early adulthood, as the prefrontal cortex and its connections mature.

Attention deficit hyperactivity disorder (ADHD) is a neuropsychiatric disorder characterized by inattention, hyperactivity and impulsivity. The symptoms appear in childhood and, if left untreated, can continue into adulthood affecting the quality of life. Currently, diagnosing a child's ADHD relies on subjective questionnaires filled out by a parent and an interview. The detection of changes in brain activity especially during everyday activities could bring important information that could help inform the diagnostics of ADHD. The changes in brain activity in persons diagnosed with ADHD during familiar, everyday events have been studied very little. However, ADHD brain imaging studies done during resting state and simple tasks have found changes in large-scale brain networks. These networks can be studied using functional connectivity approach, where the degree of synchronous activity in different brain regions is used to determine the connection strength between these regions. In this thesis, using functional magnetic resonance imaging, the differences in the functional connectivity of the whole brain between children diagnosed with ADHD (n=17) and controls (n=19) were investigated during a virtual reality task that simulates everyday life (EPELI), watching natural-like videos, and resting state. Connectivity matrices were generated with the NiLearn Toolbox program using Seitzman and colleagues' (2018) 300-area parcellation. The connectivity of the whole brain was examined using Network-Based Statistics. During movie watching the ADHD group showed increased connectivity compared to the control group in a network that included several areas of the motor cortex. This may indicate a role for these regions in the hyperactivity symptoms of ADHD. The same network also included the right superior temporal gyrus, which has previously been linked to impulsivity symptoms in individuals diagnosed with ADHD. During the virtual reality task and resting state, no differences in connectivity were observed between the groups. However, differences between the experimental situations were revealed in several networks when the connectivity was compared within the groups. Many of these networks were very extensive and included several subcortical and cerebellar structures in addition to cortical areas. Both the control and ADHD groups showed increased connectivity in the resting state compared to EPELI. This could possibly be due to the differences in the participants' actions during the task performance. To the best of the author's knowledge, this study is the first to examine the functional connectivity of brains diagnosed with ADHD during naturalistic stimuli. The clear differences between the controls and the ADHD group during movie watching are promising for future naturalistic brain studies. Based on the results, network models are effective in studying the functional connectivity of ADHD under different conditions. However, consideration for similarity of activities during the virtual task could have led to the detection of larger differences.

Visual working memory refers to the cognitive system responsible for the short-term storage and manipulation of visual information. Prevailing view suggests that there is a trade-off between memory capacity and precision: we can hold more items in memory with lower precision or fewer items with higher precision. Recent functional magnetic resonance imaging (fMRI) studies suggest distributed visual working memory representations in multiple brains areas from sensory visual to the parietal and frontal cortex. This thesis consists of a visual working memory fMRI study, using human faces as stimuli. The purpose of this thesis was to examine the visual working memory precision for angry, neutral and happy faces and the memory representations in the face network, and to directly compare the neural activity while participants discriminated and memorized faces. The participants discriminated and remembered faces precisely and were highly aware of occasional memory lapses, as shown by the confidence ratings of responses. In the primary visual cortex (V1) and fusiform face area (FFA), happy faces elicited higher brain activation than angry or neutral faces. The multivariate analysis of fMRI activation patterns showed correlations between the perception and memory tasks in these areas. Overall, the activations and correlations were higher in the right hemisphere, as expected. The correlations between perception and memory conditions were surprisingly low given the identical stimuli in these conditions. Even small positive correlations in the right V1 and FFA, however, support their role in maintaining facial information in visual working memory.

Aims: Reading ability is a fundamental skill in the modern society, yet some individuals have difficulties in learn-ing to read and write. There is a lot of variability in reading skills, and one reason that can cause reading difficulty is a neurodevelopmental disorder called dyslexia. It is the most common learning disability, and the core deficit in dyslexia lies in word decoding, which is the process of connecting letter combinations into their corresponding auditory representations. Dyslexia is familial and is recognized to have strong genetic background. A dozen dyslexia susceptibility genes have been suggested, but DYX1C1, DCDC2 and KIAA0319 have been associated with dyslexia most commonly. The function of these genes is however not yet fully understood. In previous studies variation in these genes have been linked to struc-tural brain alterations in left hemispheric regions where language is mostly processed. The aim of this study was to examine the connection between dyslexia susceptibility genes DCDC2, DYX1C1 and KI-AA0319 and variation in brain activity during reading tasks in the left middle temporal gyrus (MTG), infe-rior Frontal Gyrus (IFG) and intraparietal sulcus (IPS), by combining functional magnetic resonance imag-ing data and genetic data in a neurotypical population. Previous studies have reported that weaker reading skills are associated with decreased brain activity in these regions, and reading incongruent sentences has been associated with increased brain activity in the left IFG and MTG. Methods: During fMRI, participants were presented with sentences with illogical and logical endings, and judged them as either congruent or incongruent, in distracted and undistracted conditions. Auditory speech stimuli were used as distractor. Regions of Interest analyses were conducted to examine brain activation in the aforementioned brain regions during distracted and non-distracted reading separately for different allelic groups in single nucleotide polymorphisms of the three genes. Results and Conclusions: DYX1C1 showed significant interaction with brain activation in the IPS. A significant interaction of DCDC2 with logic was found in the IFG and IPS showing that individuals carrying susceptibility alleles have reduced brain activation when reading incongruent sentences. Additionally, DCDC2 showed inter-action with distraction in the IFG, as individuals carrying susceptibility alleles had reduced brain activa-tion when a speech distractor was presented. In the MTG, there was a significant interaction of DCDC2 with logic and distractor showing that in different allelic groups, speech distractor modulated the activa-tion elicited by incongruent sentences in different ways. These results provide a link between variation in dyslexia susceptibility genes and brain activation during reading. Previous studies have mostly linked dyslexia susceptibility genes to structural brain alterations, and dyslexia and lower reading skills have been linked to variation in brain activity. The current study therefore expands the current understanding of genetic basis on reading and linguistic processing.

Tiivistelmä Johdanto: Luovuuden yleismääritelmän mukaan luovuuden kriteerit ovat toimivuus ja uudenlaisuus. Luovuuden mittaamiseen on neurotieteessä käytetty etenkin eriytyvää ajattelua eli divergoivaa ajattelua mittaavaa vaihtoehtoisten käyttötapojen testiä (AUT). Aivoissa on laajoja hermoverkkoja, jotka kattavat esimerkiksi otsalohkon, päälakilohkon, takaraivolohkon ja ohimolohkon alueita. Oletusverkko (DN) liittyy itsetuotettuun ajatteluun mielen sisällä. Frontoparietaalinen ohjausverkko (FPN) vaikuttaa toiminnanohjaukseen. Olennaisen tunnistava verkko (SN) puolestaan vaikuttaa sekä DN ja FPCN-verkkoihin ja tunnistaa esimerkiksi tunteellisesti merkittäviä asioita. DN ja FPCN -verkkojen korrelaatiota ja antikorrelaatiota on tutkittu. Tässä katsauksessa: Narratiivisen kirjallisuuskatsauksen menetelmällä tutkittiin, millaista hermoverkkotoimintaa tapahtuu luovuuden, erityisesti ideoiden tuottamisen, aikana, sekä mitä aivojen alueita hermoverkkoihin liittyy. Luovuuden prosessit vaikuttavat olevan tavoitteen ohjaamaa, sillä frontoparietaalinen ohjausverkko (FPCN) osallistuu yhteistyössä oletusverkon ja olennaisen tunnistavan verkon kanssa luovuuden prosessien tuottamiseen. Frontoparietaalinen ohjausverkko toiminnallisesti kytkeytynyt oletusverkkoon siten, että FPCN-verkon kummatkin osaverkot FPCNa ja FPCNb toimivat eri tavoin suhteessa oletusverkkoon. Ideoiden tuottamiseen tarvitaan oletusverkkoa ja puolestaan ideoiden yhdistäminen toimivalla tavalla edellyttää frontoparietaalista ohjausverkkoa. Pohdinta: Luovuuden aikana useampi laaja hermoverkko ja niiden osaverkot toimivat yhteistyössä. Tutkielmassa pohditaan myös luovuuden kognitiivisia prosesseja perustuen tutkimukseen aivojen laajoista hermoverkoista

The goal of this thesis was to examine how the representation of faces and identities has been researched with multivariate brain-imaging analysis methods. The coding of the visual identity of faces is a complex process, which arises from abstract high-level representations that are viewpoint independent. This process has been localized to certain visual brain areas, namely FFA and ATL-FA in humans and AM in macaque monkeys. The coding processes of identities have been researched with functional magnetic resonance imaging (fMRI) and multivariate pattern analysis (MVPA) methods, where the measured brain activity distribution is compared with the distributions predicted by the processing models of identity. Most models are based on face spaces, which are defined by the identities, features or abstract properties of a face. The neural basis for coding of the identity of faces has not yet been resolved. However, the low-level and feature models were best at predicting the data, although low-level models explain mainly the properties of the stimuli and the function of V1. The prototype model was not as successful in predicting the activity distributions as the other models. In general, the models explained the orientation of the faces better than their identity. This might be due to the differences between the brain activities associated with different identities being so subtle that the multivariate pattern analysis cannot differentiate between them. It is also possible that the coding of identity does not happen within the face processing areas, but perhaps in the connections between frontal and face areas. To conclude, the usefulness of fMRI-MVPA in studying identity has been questioned and the methods still need improvement. However, MVPA is a more versatile and sensitive method of investigating the coding of identity than traditional univariate analysis methods.

Models of moral judgment and decision-making are traditionally divided into rationalist and intuitionist models depending on whether moral judgments are thought to be the result of a rational reasoning process or moral intuitions. The social intuitionist model represents intuitionist models of moral judgment and suggests that moral judgments are the result of affectively based moral intuitions and that moral reasoning mainly occurs as a post-hoc rationalization. The objective of this thesis is to review recent neuroimaging studies on moral decision-making and to evaluate the validity of the social intuitionist model in that moral judgments are caused by moral intuitions and not by moral reasoning. Functional magnetic resonance imaging (fMRI) studies examining the neural correlates of moral decision-making indicate that affective processing and abstract reasoning can both result in moral judgments. Brain areas associated with emotion become more activated in moral personal dilemmas than in impersonal dilemmas, whereas impersonal dilemmas engage brain regions associated with working memory. In addition, utilitarian judgments made in difficult personal dilemmas depend more on brain areas associated with cognitive conflict monitoring and cognitive control compared with deontological judgments. Electroencephalographic (EEG) studies support the idea that moral intuitions arise early in the decision-making process. However, affective processing may begin even in the later stages of moral decision-making after moral intuitions have been initiated, thus questioning the role of emotion in moral intuitions. The social intuitionist model has both gained support and been criticized. In the light of neuroimaging studies, it appears that moral reasoning has a more significant role in moral judgments than assumed in the model. In addition, moral intuitions may not be affectively based as assumed in the social intuitionist model. It might be necessary to update the model regarding the role of reasoning in moral judgments and the relationship between emotion and moral intuition. In the future, more comparable experimental designs should be employed to make the comparison of the variety of neuroimaging studies more sensible.

Social cognitive neuroscience is a novel and fast-growing field. This field studies the neural basis of social behaviour with the tools of cognitive neuroscience. Most of the research topics in social cognitive neuroscience concern social cognition. Social cognition is defined to be cognitive information processing about conspecifics such as other people. This thesis presents a new tool to localize brain regions related to social cognition in a brain imaging experiment using functional magnetic resonance imaging (fMRI). Named as Social Localizer, this tool is intended to be a pre-experiment protocol to define so-called regions-of-interest (ROIs) based on a rich set of stimuli presented to the subject during the fMRI scanning. The stimuli were videos, pictures and texts related to social cognition, including biological movement, social interaction, faces, theory-of-mind, body parts and action observation. We ran the Social Localizer with eighteen subjects in order to validate the functionality of the localizer in an fMRI experiment. We also used eye-tracking and keypad response with a one-back-task with the stimuli to make sure that subjects were attending to the stimuli. Overall, the results were promising – we succeeded in localizing many areas central to social cognition. However, the amount of data was not enough for the localizer to specify all ROIs in the individual level. Therefore we decided to combine activations from pairs of stimulus-classes to achieve more consistent results across the group of subjects. In addition, we analyzed the empirical group-level results. These group-level results revealed interesting research questions regarding social cognition that deserve further studying in order to be clarified. In conclusion the Social Localizer provides a promissing tool to define multiple regions-of-interest on social-cognitive criteria. In future studies of social cognition, this tool could be combined with other experimental manipulations to address novel questions in well-defined regions-of-interest.

The present study uses functional magnetic resonance imaging (fMRI) to study the neural basis of naturalistic audiovisual speech processing. The study focuses on how performing different speech-related tasks affects the neural activation observed in the brain. The neural basis of speech processing has been studied for long, but previous experiments have mainly employed paradigms with simple stimuli, such as single phonemes, syllables, and words, and unnatural tasks, such as discrimination and memory tasks. Moreover, current models of speech processing are mainly based on studies using auditory-only stimuli. In natural situations, however, the aim of speech processing is to understand the meaning of what is being said, speech is most often audiovisual, it is often selectively attended to, and the signal-to-noise ratio of the speech signal varies (due to, for example, background noise). The present study aims to study speech processing in a more naturalistic setting that takes into account the above-mentioned factors. Moreover, it compares a situation where speech is processed naturalistically to a situation where speech is processed sub-lexically, as is often done in studies of speech processing. The participants of the present study were 19 healthy adults. They were presented with audiovisual dialogues where two people discuss everyday matters. In the background of the videos, the voice of a third speaker was always present so that the participants had to selectively attend to the dialogues. The auditory and visual qualities of the dialogues were modulated on two different levels. The participants performed three different tasks: 1) A semantic task, during which the participants focused on the semantic content of the dialogues. 2) A phonological task, during which the participants focused on the phonological structure of the speech. 3) A visual task, during which the participants ignored the dialogues and focused on a fixation cross. Task-dependent effects in the neural activation were found in multiple regions of the brain. Selective attention to speech was found to activate regions in the temporal lobes and the left inferior frontal gyrus (LIFG), a result consistent with earlier research. The semantic task was found to activate areas associated with semantic and socio-cognitive processing more than either of the other tasks, while the phonological task activated the posterior portion of the LIFG as well as the ventral portion of the left premotor cortex. Interactions between the effects of task and audiovisual quality were also found in many brain areas. These results show that task-dependent effects in speech processing can be seen in widespread regions of the brain, and that audiovisual quality can modulate activation differentially during different tasks. These findings highlight the importance of using naturalistic stimuli and tasks in studies of speech processing.