On Friday, 22 March 2019 at 2 pm in the Merete Barker Lake Auditorium, Christopher Bailey will defend his PhD thesis, entitled: “Interpretation of BOLD fMRI signals: lessons from the visual stimulation of anaesthetised rats”.

14.03.2019 | Henriette Blæsild Vuust

In his thesis, Christopher has explored properties of neurovascular coupling, i.e., the link between work being performed by networks of neurons in the brain, on the one hand, and the haemodynamics that provide the metabolic substrates for that work, on the other. It is increasingly being recognised that neurovascular coupling depends crucially on the local neuroanatomical architecture, as well as the electro-chemical state of the interacting neuronal populations. This has strong implications on the interpretation of blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals in humans and experimental animals alike.

An in vivo rodent model was chosen as it allowed the use of invasive electrophysiological techniques, as well as ultra-high magnetic field strength (11.7T) for high-sensitivity BOLD imaging. In the first part of the project, a light flash stimulator was implemented and validated, and subsequently applied during acquisition of BOLD and electrical responses to stimuli of different colours and repetition rates. The results show that vascular responsiveness to varying metabolic load is largely conserved across different brain structures, in which BOLD and neuronal responses were tightly associated. However, a dissociation was also observed between BOLD and neuronal responses in the neocortex during sustained high-frequency flash stimulation. The third study was based on the observation that response variability on the time scale of tens of minutes in rat visual cortex was unrelated to stimulus features, but rather to periodic shifts of the cortical network state induced by the choice of anaesthetic (urethane). Similar state alterations are known to occur spontaneously in human subjects undergoing changes in vigilance. The group found evidence that cortical BOLD signal dynamics carry information about the underlying information processing state of the brain. The results emphasise that the ‘baseline’ on top of which responses are induced is at least as influential on the outcome of stimulation as are the properties of the stimuli themselves.

The work presented emphasises the importance of measuring and characterising, rather than assuming, the nature of neuronal work being performed when evaluating its coupling with haemodynamic measures of brain activity. Furthermore, accounting for the ever-changing state of interacting networks is a prerequisite for accurate neurophysiological interpretation of functional brain imaging results. In his dissertation, Christopher introduces the rodent visual system as a highly suitable pre-clinical model for studies of the detailed nature of neurovascular and neurometabolic coupling. Such inquiries are a prerequisite for the application of fMRI to human patient populations in which neuronal processing or vascular/metabolic responses, or both, may be compromised.

The defense is public and will take place in the Merete Barker Auditorium (Building 1253), Aarhus University Lake Auditoriums, Bartholins Allé 3, 8000 Aarhus C.

For more details please contact Christopher Bailey at cjb@cfin.au.dk or +45-26749927.  An electronic version of the thesis is available upon request.

After the defense there will be a small reception outside the auditorium.

ALL ARE WELCOME