Brain interaction during cooperation: Evaluating local properties of multiple-brain network

Subjects’ interaction is the core of most human activities. This is the reason why a lack of coordination is often the cause of missing goals, more than individual failure. While there are different subjective and objective measures to assess the level of mental effort required by subjects while facing a situation that is getting harder, that is, mental workload, to define an objective measure based on how and if team members are interacting is not so straightforward. In this study, behavioral, subjective and synchronized electroencephalographic data were collected from couples involved in a cooperative task to describe the relationship between task difficulty and team coordination, in the sense of interaction aimed at cooperatively performing the assignment. Multiple-brain connectivity analysis provided information about the whole interacting system. The results showed that averaged local properties of a brain network were affected by task difficulty. In particular, strength changed significantly with task difficulty and clustering coefficients strongly correlated with the workload itself. In particular, a higher workload corresponded to lower clustering values over the central and parietal brain areas. Such results has been interpreted as less efficient organization of the network when the subjects’ activities, due to high workload tendencies, were less coordinated

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Selective attention and speech processing in the cortex

In noisy and complex environments, human listeners must segregate the mixture of sound sources arriving at their ears and selectively attend a single source, thereby solving a computationally difficult problem called the cocktail party problem. However, the neural mechanisms underlying these computations are still largely a mystery. Oscillatory synchronization of neuronal activity between cortical areas is thought to provide a crucial role in facilitating information transmission between spatially separated populations of neurons, enabling the formation of functional networks. In this thesis, we seek to analyze and model the functional neuronal networks underlying attention to speech stimuli and find that the Frontal Eye Fields play a central 'hub' role in the auditory spatial attention network in a cocktail party experiment. We use magnetoencephalography (MEG) to measure neural signals with high temporal precision, while sampling from the whole cortex. However, several methodological issues arise when undertaking functional connectivity analysis with MEG data. Specifically, volume conduction of electrical and magnetic fields in the brain complicates interpretation of results. We compare several approaches through simulations, and analyze the trade-offs among various measures of neural phase-locking in the presence of volume conduction. We use these insights to study functional networks in a cocktail party experiment. We then construct a linear dynamical system model of neural responses to ongoing speech. Using this model, we are able to correctly predict which of two speakers is being attended by a listener. We then apply this model to data from a task where people were attending to stories with synchronous and scrambled videos of the speakers' faces to explore how the presence of visual information modifies the underlying neuronal mechanisms of speech perception. This model allows us to probe neural processes as subjects listen to long stimuli, without the need for a trial-based experimental design. We model the neural activity with latent states, and model the neural noise spectrum and functional connectivity with multivariate autoregressive dynamics, along with impulse responses for external stimulus processing. We also develop a new regularized Expectation-Maximization (EM) algorithm to fit this model to electroencephalography (EEG) data

Augmented maturation of executive functions in musically trained children and adolescents

Musically trained individuals have been found to outperform untrained peers in various tasks specific to music performance. Interestingly, they have also been found to outperform their musically untrained peers in tasks not related to music-making, requiring a wide range of cognitive skills, such as executive functions. In a series of studies with the same participants, this thesis examines the developmental paths of different subcomponents of executive functions in a group of participants in their school years, from childhood until adolescence, while undergoing music training. Their neurocognitive development is compared with that of their musically untrained peers. The aim of the studies was to uncover whether music training is associated with improved executive functions and augmented functioning of the brain mechanisms of executive functions. Performance measures included various neuropsychological test measures and tasks created for neuroimaging experiments. Brain activation measures of executive functions were event-related potentials (ERPs) recorded with electroencephalography, and BOLD activation changes acquired with functional magnetic resonance imaging (fMRI). Differences in these measures between musically trained and untrained participants aged 9-21 were examined, as well as longitudinal change in test performance during six years. The results of the studies showed that music training is associated with the enhancement of various executive functions: working memory maintenance, inhibition, set shifting, and selective attention during childhood and adolescence. However, the improvement in set shifting diminishes with age being virtually nonexistent in early adulthood. Results also showed more efficient functioning of neural mechanisms related to executive functions. Musically trained participants exhibited lower distractibility and enhanced processing of targets during tasks for executive functions. Furthermore, still in late adolescence and early adulthood, musically trained participants had more adult-like responses and more efficient functioning of brain mechanisms for attention and executive control during tasks for executive functions than their untrained peers. Together, the results show that music training is associated with enhancement of brain mechanisms of executive functions and a passing advantage in tasks for executive functions, with the largest differences compared to untrained peers seen in school-age and early adolescence. In late adolescence, the advantage in tasks has disappeared but echoes of enhancement can be still seen in the more mature and more efficient functioning of neural mechanisms of executive functions.Musiikkia harrastaneet suoriutuvat paremmin musiikkiin liittyvissä tehtävissä kuin ne, joilla musiikinharrastustaustaa ei ole. Yllättäen muusikot ja muut musiikin parissa harjaantuneet pärjäävät muuta harrastaneita paremmin myös sellaisissa tehtävissä, jotka eivät liity musiikkiin ja jotka edellyttävät laaja-alaisia kognitiivisia taitoja, kuten toiminnanohjausta. Tämä väitöskirja selvitti toiminnanohjauksen eri osa-alueiden kehityskaarta lapsuudesta varhaisaikuisuuteen sarjalla tutkimuksia, joihin osallistui sama musiikkia harrastavien lasten joukko. Näiden osallistujien neurokognitiivisten toimintojen kehittymistä verrattiin muuta harrastavien osallistujien kehitykseen. Tutkimusten tarkoitus oli selvittää, onko musiikin harrastaminen yhteydessä tehostuneisiin toiminnanohjauksen taitoihin, sekä muutoksiin näitä taitoja tukevien aivomekanismien toiminnassa. Taitoja tutkittiin neuropsykologisilla testimenetelmillä sekä aivokuvantamiskokeita varten erikseen kehitetyillä tehtävillä. Toiminnanohjauksen aivomekanismeja tutkittiin rekisteröimällä aivojen herätevasteita aivosähkökäyrällä, ja aivoalueiden veren happipitoisuudesta riippuvaa vastetta toiminnallisella magneettiresonanssikuvantamisella. Tutkimuksissa vertailtiin musiikkia harrastavien ja muuta harrastavien, 9-21-vuotiaiden osallistujien testisuoriutumisen ja aivojen toiminnan eroja. Lisäksi testisuoriutumisen erojen muutosta seurattiin kuuden vuoden ajan. Tutkimusten tulokset osoittavat, että musiikin harrastaminen on yhteydessä usean toiminnanohjauksen osa-alueen tehostumiseen lapsuudessa. Näihin kuuluivat työmuistin ylläpito ja päivittäminen, inhibitio, vaihtaminen ja valikoiva tarkkaavaisuus. Vaihtamisen tehostuminen vähenee kuitenkin iän myötä siten, että varhaisaikuisuudessa eroja musiikkia ja muuta harrastavien välillä ei testisuoriutumisessa ole. Tulosten mukaan musiikkia harrastavien toiminnanohjauksen aivomekanismit toimivat myös eri tavoin kuin muiden osallistujien. Toiminnanohjausta edellyttävissä tehtävissä musiikkia harrastavilla ilmeni vähäisempää häiriöherkkyyttä ja tehostunutta kohteiden käsittelyä. Lisäksi vielä varhaisaikuisuudessa musiikkia harrastavilla oli kehitysasteeltaan kypsempiä aivovasteita sekä tehokkaampaa toimintaa tarkkaavuuteen ja toiminnanohjaukseen liittyvillä aivoalueilla toiminnanohjauksen tehtävien aikana kuin muilla osallistujilla. Kaiken kaikkiaan tulokset osoittavat, että musiikin harrastaminen on yhteydessä toiminnanohjauksen aivomekanismien tehokkaampaan toimintaan sekä ohimenevästi myös parempaan suoriutumiseen toiminnanohjauksen tehtävissä

Dynamic Oscillatory Interactions Between Neural Attention and Sensorimotor Systems

The adaptive and flexible ability of the human brain to preference the processing of salient environmental features in the visual space is essential to normative cognitive function, and various neurologically afflicted patient groups report negative impacts on visual attention. While the brain-bases of human attentional processing have begun to be unraveled, very little is known regarding the interactions between attention systems and systems supporting sensory and motor processing. This is essential, as these interactions are dynamic; evolving rapidly in time and across a wide range of functionally defined rhythmic frequencies. Using magnetoencephalography (MEG) and a range of novel cognitive paradigms and analytical techniques, this work attempts to fill critical gaps in this knowledge. Specifically, we unravel the role of dynamic oscillatory interactions between attention and three sensorimotor systems. First, we establish the importance of sub-second occipital alpha (8 – 14 Hz) oscillatory responses in visual distractor suppression during selective attention (Chapter 1) and their essential role in fronto-parietal attention networks during visual orienting (Chapter 2). Next, we examine the divergent effects of directed attention on multi-frequency primary somatosensory neural oscillations in the theta (4 – 8 Hz), alpha, and beta (18 – 26 Hz) bands (Chapter 3). Finally, we extend these findings to the motor system (Chapter 4), and find that the frontal and parietal beta-frequency oscillations known to support motor planning and execution are modulated equivalently by differing subtypes of attentional interference, whereas frontal gamma (64 – 84 Hz) oscillations specifically index the superadditive effect of this interference. These findings provide new insight into the dynamic nature of attention-sensorimotor interactions in the human brain, and will be the foundation for groundbreaking new studies of attentional deficits in patients with common neurological disorders (e.g., Alzheimer’s disease, HIV-associated neurocognitive disorders, Parkinson’s disease). With an enhanced knowledge of the temporal and spectral definitions of these impairments, new therapeutic interventions utilizing frequency-targeted neural stimulation can be developed

Sensorimotor Modulations by Cognitive Processes During Accurate Speech Discrimination: An EEG Investigation of Dorsal Stream Processing

Internal models mediate the transmission of information between anterior and posterior regions of the dorsal stream in support of speech perception, though it remains unclear how this mechanism responds to cognitive processes in service of task demands. The purpose of the current study was to identify the influences of attention and working memory on sensorimotor activity across the dorsal stream during speech discrimination, with set size and signal clarity employed to modulate stimulus predictability and the time course of increased task demands, respectively. Independent Component Analysis of 64–channel EEG data identified bilateral sensorimotor mu and auditory alpha components from a cohort of 42 participants, indexing activity from anterior (mu) and posterior (auditory) aspects of the dorsal stream. Time frequency (ERSP) analysis evaluated task-related changes in focal activation patterns with phase coherence measures employed to track patterns of information flow across the dorsal stream. ERSP decomposition of mu clusters revealed event-related desynchronization (ERD) in beta and alpha bands, which were interpreted as evidence of forward (beta) and inverse (alpha) internal modeling across the time course of perception events. Stronger pre-stimulus mu alpha ERD in small set discrimination tasks was interpreted as more efficient attentional allocation due to the reduced sensory search space enabled by predictable stimuli. Mu-alpha and mu-beta ERD in peri- and post-stimulus periods were interpreted within the framework of Analysis by Synthesis as evidence of working memory activity for stimulus processing and maintenance, with weaker activity in degraded conditions suggesting that covert rehearsal mechanisms are sensitive to the quality of the stimulus being retained in working memory. Similar ERSP patterns across conditions despite the differences in stimulus predictability and clarity, suggest that subjects may have adapted to tasks. In light of this, future studies of sensorimotor processing should consider the ecological validity of the tasks employed, as well as the larger cognitive environment in which tasks are performed. The absence of interpretable patterns of mu-auditory coherence modulation across the time course of speech discrimination highlights the need for more sensitive analyses to probe dorsal stream connectivity