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Neuroimaging and brain stimulation in the search for the functional architecture of consciousness

Principal Supervisor: Dr. Davinia Fernández-Espejo, School of Psychology

Co-supervisor: Dr Andrew Bagshaw, School of Psychology

PhD project title: Neuroimaging and brain stimulation in the search for the functional architecture of consciousness

University of Registration: University of Birmingham

Project outline

Defining and assessing consciousness remains one of the most important challenges of contemporary neuroscience, despite decades of work. Consciousness is typically separated into wakefulness (i.e., arousal or level of consciousness) and awareness (i.e., content of consciousness). Wakefulness is relatively easy to define, as a state of eye opening and motor arousal, and to measure by confirming eye opening and/or specific patterns of electrical brain activity. However, awareness relates to the ability to have (and the act of having) an experience of some kind. It is not possible to access somebody else’s subjective experiences and, thus, awareness can only be measured through self-report and / or by making inferences and assumptions on the basis of the behaviour that an individual is able to display.

Wakefulness and awareness interplay to generate sleep-wake cycles in healthy individuals. However, occasionally they dissociate and result in poorly understood neurologic and psychiatric conditions characterised by wakefulness with reduced or absent awareness (e.g., epilepsy, Alzheimer’s disease, schizophrenia, dissociative identity disorder, or the vegetative state). Awareness is arguably a fundamental human function and thus its absence or reduction leads to severe consequences for people’s health, wellbeing, social relationships, and quality of life.

Several studies have identified specific structural and functional impairments in a set of brain regions known as the default mode network (DMN) in states of reduced or absent awareness. The DMN encompasses highly interconnected regions across the medial and lateral fronto-parietal lobes that are known to be active when we are not engaged in any particular task. Its activity is related to self-referential processes, daydreaming, mind-wandering, etc. In parallel, other studies have revealed a second network, encompassing cortical regions in the dorsal fronto-parietal lobes, whose activity appears to anti-correlate with the DMN and mediate external awareness.

This PhD project will use state-of-the-art functional magnetic resonance imaging (fMRI) methods to study how the dynamics within and between these brain networks are associated with different degrees of internal (self-) and external awareness. This will involve application of simultaneous multislice acquisitions which can improve temporal resolution dramatically, as well as dynamic functional connectivity approaches and methods to investigate and summarise network properties from graph theory. The improved spatiotemporal resolution of these methods will allow a detailed examination of the link between network dynamics and behaviour. Moreover, we will use a non-invasive form of brain stimulation, known as transcranial direct current stimulation (tDCS), to modulate the activity in these networks and study the resulting enhancements (or reductions) in awareness. The student will conduct several experiments in which tDCS will be administered outside and inside the MRI scanner to characterise both its behavioural (performance in a number of awareness tasks) and neural (brain dynamics in fMRI) effects in the healthy brain. Importantly, in the MRI studies, tDCS will be administered concurrently with the acquisition of fMRI data, which will allow for the characterisation of the effects of the stimulation both offline (before and after stimulation) and online (during stimulation).

References:

  • Crone JS, Schurz M, Höller Y, Bergmann J, Monti M, Schmid E, Trinka E, Kronbichler M. Impaired consciousness is linked to changes in effective connectivity of the posterior cingulate cortex within the default mode network. Neuroimage. 2015;110:101-9.

  • Fernández-Espejo D, Soddu A, Cruse D, Palacios EM, Junque C, Vanhaudenhuyse A, Rivas E, Newcombe V, Menon D, Pickard J, Laureys S, Owen A. A role for the default mode network in the structural bases of disorders of consciousness. Annals of Neurology, 2012;72(3):335-43.
  • Fernández-Espejo D, Rossit S, Owen AM. A Thalamocortical Mechanism for the Absence of Overt Motor Behavior in Covertly Aware Patients. JAMA Neurol. 2015;72(12):1442-50.
  • Hale JR, White TP, Mayhew SD, Wilson RS, Rollings DT, Khalsa S, Arvanitis TN, Bagshaw AP. Altered thalamocortical and intra-thalamic functional connectivity during light sleep compared with wake. Neuroimage 125 657 – 667 (2016)
  • Khalsa S, Hale JR, Goldstone A, Wilson RS, Mayhew SD, Bagary M, Bagshaw AP. Habitual sleep durations and subjective sleep quality predict white matter differences in the human brain. Neurobiol Sleep Circadian Rhythms 3 17 – 25 (2017)
  • Khalsa S, Mayhew SD, Przezdzik I, Wilson RS, Hale JR, Goldstone A, Bagary M, Bagshaw AP. Variability in cumulative habitual sleep duration predicts waking functional connectivity. Sleep 39(1) 97 – 95 (2016) 

BBSRC Strategic Research Priority: Molecules, Cells and Systems

Techniques that will be undertaken during the project:

  • Designing, planning, and running novel paradigms to quantify awareness.

  • Functional magnetic resonance imaging (fMRI).

  • Non-invasive brain stimulation (i.e., transcranial direct current stimulation)

  • Advanced signal processing and statistical analyses.

  • Computational modelling

Contact: Dr. Davinia Fernández-Espejo, School of Psychology