Angus Chadwick PhD

Angus Chadwick

Research Interests

I am interested in the neural substrates of perception and cognition, and in particular the role of brain oscillations in cognitive processes. My PhD focuses on theta and gamma oscillations in the rodent hippocampus. These rhythms are thought to play an important role in spatial cognition and working memory. Currently, I am developing theoretical models of phase codes in hippocampal place cells in order to investigate the resulting population dynamics and their role in spatial cognition. The importance of phase coupling for information transfer between the hippocampus and entorhinal cortex is also a central part of my PhD project.

  Independent Theta Phase Coding Accounts for CA1 Population Sequences and Enables Flexible Remapping
Chadwick, A, Van Rossum, M & Nolan, M 2015, 'Independent Theta Phase Coding Accounts for CA1 Population Sequences and Enables Flexible Remapping' eLIFE. DOI: 10.7554/eLife.03542.001
General Information
Organisations: Edinburgh Neuroscience.
Authors: Chadwick, Angus, Van Rossum, Mark & Nolan, Matthew.
Publication Date: 2 Feb 2015
Publication Information
Category: Article
Journal: eLIFE
ISSN: 2050-084X
Original Language: English
DOIs: 10.7554/eLife.03542.001
  A model of hippocampal cell assembly dynamics based on single-cell theta phase precession
Chadwick, A, Nolan, M & van Rossum, MCW 2013, 'A model of hippocampal cell assembly dynamics based on single-cell theta phase precession' 22nd Annual Computational Neuroscience Meeting: CNS 2013, Paris, France, 13/07/13 - 18/07/13, .
Neural oscillations are associated with a wide variety of cognitive and perceptual processes, both in health and disease. In the hippocampus of rodents during exploratory behaviours, prominent theta and gamma oscillations are observed in the local field potential (LFP). These rhythms are linked to spatial cognition and working memory, but the underlying mechanisms are unclear. At the single-cell and cell assembly levels, two salient features emerge during the theta rhythm - phase precession and spatiotemporal spike sequences. The relationship between these two phenomena is yet to be fully characterised. For example, it is unclear whether the sequential structure of hippocampal cell assemblies is fully explained through independent phase coding at the single-cell level, or whether further coordination is required to account for the observed multi-cell behaviour. We developed a descriptive model of phase coding in individual place cells and used this model to investigate the cell assembly dynamics on a linear track. Under the assumption of independent phase coding, key experimental quantities were derived analytically and their relationship to behavioural variables was analysed and compared to experimental data (e.g., [1]). We showed that experimentally established relationships between behavioural variables such as running speed and cell assembly metrics such as the compression factor and lookahead can be reproduced and understood analytically in terms of the collective behaviour of independent phase coding units.
General Information
Organisations: Institute for Adaptive and Neural Computation .
Authors: Chadwick, Angus, Nolan, Matthew & van Rossum, Mark C. W..
Publication Date: 2013
Publication Information
Category: Poster
Original Language: English
  Spontaneous pre-stimulus oscillations predict direction of ambiguous figure-ground assignment
Brooks, J, Chadwick, A, Romei, V & Rees, G 2013, 'Spontaneous pre-stimulus oscillations predict direction of ambiguous figure-ground assignment' Journal of Vision, vol 13, no. 9, pp. 1029. DOI: 10.1167/13.9.1029
Multi-stable perception is a phenomenon characterized by spontaneous changes in the appearance of a stimulus despite unchanging visual input. A well-known example of multi-stable perception is Rubin’s ambiguous faces/vase stimulus which fluctuates between being seen as two profile faces or as a central vase shape. Previous work has shown that pre-stimulus BOLD activity in face-selective cortex is predictive of which interpretation will be perceived in the subsequent stimulus. Here, we aimed to further characterize the nature of this pre-stimulus neural activity using the high temporal resolution of EEG. On each trial the participants saw exactly the same ambiguous Rubin stimulus with inter-stimulus intervals ranging from 3-15 seconds (Poisson distributed). Trials were separated into those reportedly perceived as faces and those reported as vases. Fixation was monitored with an eyetracker to ensure no fixation differences (and thus no stimulus input differences) between these two sets of trials. As corroboration for participants’ subjective reports, we looked at the amplitude of the post-stimulus N170 ERP component. We found that the N170 was significantly larger for trials reported as faces than those reported as vases suggesting the participants’ subjective perceptions were, in fact, in line with their reports. To assess pre-stimulus activity, we computed the spectral power across 4-30 Hz in the second leading up to each stimulus. We found that theta and beta oscillations preceding the stimulus were predictive of the reported direction of figure-ground assignment. Lower power was observed for face percepts than vase percepts. These findings specify the nature of spontaneous pre-stimulus activity leading up to figure-ground organization. Furthermore, the results provide parameters (e.g. frequency and precise timing) which can be used to prime or stimulate the brain in future experiments to establish a causal link between pre-stimulus activity and perception.
General Information
Organisations: Neuroinformatics DTC.
Authors: Brooks, Joseph, Chadwick, Angus, Romei, Vincenzo & Rees, Geraint.
Number of pages: 1
Pages: 1029
Publication Date: 2013
Publication Information
Category: Article
Journal: Journal of Vision
Volume: 13
Issue number: 9
ISSN: 1534-7362
Original Language: English
DOIs: 10.1167/13.9.1029

Transmission and Decoding of Spike Sequences in the Hippocampus (PhD)