The role of neural oscillations in the visual system and their relation to conscious perception Miaomiao Yu Doctor of Philosophy University of York Psychology June 2020 Thesis Abstract Neural oscillations are intrinsically linked with attention, vigilance and featural sensitivity and therefore often associated with visual perception. However, the neural oscillation literature remains conflicted on several issues. Here, I describe four experiments investigating these conflicts using a variety of experimental and analysis techniques. We first explored the relationship between the inhibitory neurotransmitter GABA and gamma frequency oscillations in the rodent visual cortex. We found no evidence that synaptic and extrasynaptic GABA concentration altered gamma oscillations, suggesting that GABAergic inhibition cannot be linked directly to GABA concentration and instead depend on postsynaptic receptor kinetics. The second chapter examined how spontaneous alpha activity related to performance in an orientation discrimination task. Alpha amplitude was a significant predictor of reaction time but not task accuracy. The results suggested that alpha can modulate visual perception through top-down mechanisms. Interestingly, we also found that the relationship between alpha activity and task accuracy was determined by the subject’s task expertise. The third chapter examined how exogenous rhythms (generated by chromatic gratings) within visual cortex may interact with ongoing endogenous oscillations. Univariate analysis of single EEG channels revealed significantly higher endogenous power during chromatic than achromatic stimulation. An additional multivariate classifier showed distinct patterns of activity at very high frequencies, suggesting phase coupling between exogenous and endogenous signals. This finding was extended in the final chapter, which examined the neural correlates of rapid chromatic stimulation. Robust BOLD responses were found even when stimuli flickered above the consciously perceptible frequency, indicating that the temporal filtering stage limiting perception is later than V4. Additionally, chromatic preference in ‘colour area’ V4 was strongly dependent on stimulus frequency. 2 List of Contents Thesis Abstract ......................................................................................................... 2 List of Contents ......................................................................................................... 3 List of Tables ............................................................................................................. 7 List of Figures ............................................................................................................ 9 Acknowledgements ................................................................................................. 11 Author’s Declarations ............................................................................................. 13 1 Chapter 1: Introduction to endogenous oscillations and their role in visual perception ................................................................................................................ 14 1.1 Introduction to neural oscillations .......................................................... 14 1.1.1 Production of neural oscillations .................................................................... 15 1.2 Conflicts in the literature: endogenous rhythms and visual perception 16 1.2.1 The role of GABA in gamma oscillations ........................................................ 17 1.2.2 The role of endogenous oscillations in visual perception ............................... 26 1.3 Rationale for the current thesis ............................................................... 44 2 Chapter 2: The effects of GABA and tiagabine on kainate-induced gamma oscillations in rodent visual cortex slices ............................................................ 47 2.1 Abstract ..................................................................................................... 47 2.2 Introduction ............................................................................................... 49 2.3 Methods ..................................................................................................... 52 2.3.1 Rodent model ................................................................................................. 52 2.3.2 Drugs .............................................................................................................. 52 2.3.3 Extracellular recording ................................................................................... 53 2.3.4 Experimental procedure ................................................................................. 54 2.3.5 Data analysis .................................................................................................. 55 2.4 Results ....................................................................................................... 56 2.4.1 Overview of data ............................................................................................ 56 3 2.4.2 The effect of increasing GABA dosages on gamma oscillations .................... 57 2.4.3 The effect of tiagabine on gamma oscillations ............................................... 58 2.5 Discussion ................................................................................................. 63 2.5.1 The movement of GABA molecules after exogenous application of GABA ... 64 2.5.2 Effects of increasing synaptic GABA concentration ....................................... 65 2.5.3 Correlation between gamma amplitude and frequency .................................. 66 2.5.4 Future directions ............................................................................................ 67 2.5.5 Conclusion ..................................................................................................... 68 3 Chapter 3: Can prestimulus alpha power predict performance accuracy and reaction time in an orientation discrimination task? .................................... 70 3.1 Abstract ..................................................................................................... 70 3.2 Introduction ............................................................................................... 71 3.3 Methods ..................................................................................................... 74 3.3.1 Participants .................................................................................................... 74 3.3.2 EEG recording and apparatus ........................................................................ 74 3.3.3 Stimulus design .............................................................................................. 75 3.3.4 EEG data processing and artifact removal ..................................................... 76 3.3.5 Psychophysics data processing ..................................................................... 77 3.3.6 Data analysis .................................................................................................. 77 3.4 Results ....................................................................................................... 78 3.4.1 Univariate analyses: linear regression and mixed effect model ..................... 80 3.4.2 Relationship between alpha power and orientation threshold ........................ 87 3.4.3 Laterality of alpha power modulation ............................................................. 89 3.4.4 Multivariate analysis: SVM ............................................................................. 90 3.5 Discussion ................................................................................................. 91 3.5.1 Relationship between expertise and alpha .................................................... 93 3.5.2 Future Directions ............................................................................................ 95 3.5.3 Conclusion ..................................................................................................... 98 4 Chapter 4: Frequency domain classification of chromatic SSVEP signals ... 100 4.1 Abstract ................................................................................................... 100 4.2 Introduction ............................................................................................. 101 4 4.3 Methods ................................................................................................... 104 4.3.1 Participant .................................................................................................... 104 4.3.2 EEG recording and apparatus ...................................................................... 105 4.3.3 Stimulus design ............................................................................................ 105 4.3.4 Experimental Procedure ............................................................................... 106 4.3.5 EEG data processing ................................................................................... 106 4.3.6 Data analysis ................................................................................................ 109 4.4 Results ..................................................................................................... 111 4.4.1 Univariate analyses ...................................................................................... 111 4.4.2 Multivariate analysis ....................................................................................