Research Interests

My broader interests revolves around:

• Cortical processing under naturalistic conditions
• How environmental statistics constrain functional architecture
• Evolutionary conservation of sensory processing strategies
• Sensory Cognition
• State-dependent learning models

My current research looks at:

• Multisensory (Audio-Visual) Integration in rodent sensory cortices
• Auditory processing in rat A1 and belt areas
• Role of slow cortical oscillations in auditory processing
• Properties of oscillatory phase resetting in humans

Understanding the neural basis of EEG ‘phase patterns’: bridging human and animal electrophysiology

Introduction

Oscillations dominate encephalographic signals and are assumed to reflect cognitive processes ranging from sensory representation to the routing of sensory information. While most studies focus on the amplitude (power) of oscillations as a marker for cerebral function, recent work has highlighted that the precise temporal structure (phase) of slow oscillations can also carry information about sensory stimulus or task details [1,2,3]. The neural correlates of EEG ‘phase patterns’, however, remain unclear.

Goal

To test whether the stimulus selectivity of low frequency EEG phase patterns indeed reflects the selectivity of neurons in the underlying sensory cortical areas.

Methods

The same set of natural sounds was presented to humans and macaques while EEG (human) and intracortical signals (macaque) were recorded. Stimulus decoding was used to quantify how well individual stimuli can be discriminated using phase and power of the EEG or intracortical field potential (LFP) and using neural firing rates.

Results

We found that stimulus selective patterns of neural firing imprint on the phase structure of slow (mostly theta band) oscillations in EEG and LFP rather than on their amplitudes. We found that sets of stimuli that can be discriminated by the phase pattern of slow oscillations can likely be discriminated also by neural firing rates and vice versa, thereby demonstrating a correlation between EEG phase patterns and firing rates with regard to stimulus decoding.

Conclusion

Our results [4] identify a level of relationship between EEG phase and neural firing that goes beyond known correlations between the strength of neural firing and oscillatory power. They thus enhance the link between sensory cortical neurons and non-invasively measured field potentials and strengthen the interpretation of EEG-based studies and their implications towards the neural dynamics of sensory perception.

Figure 1. Stimulus selectivity correlates across firing rates and EEG phase patterns.

A) Stimulus decoding performance using EEG oscillations reflecting auditory cortex activity (central topography) was better for phase than power and best at theta (4-8Hz) frequencies.

B) Decoding performance of individual neurons correlated more with oscillation (LFP) phase than power.

C) Correlating decoding performance between EEG and intra-cranial data using an across-stimulus-set technique revealed a significant correlation between neural firing rates and EEG phase but not EEG power.

Education

10/2006 - 12/2009 Ph.D. (Neuroscience), summa cum laude

International Graduate School of Neuroscience (IGSN), Ruhr University Bochum, Germany

Thesis: "Properties of the avian visual pallium: Combined voltage-sensitive dye imaging and electrophysiology in pigeon (C.livia)"

Supervisors: Dirk Jancke and Onur Güntürkün

10/2005 - 09/2006 B.Sc.-Ph.D. program qualification training

International Graduate School of Neuroscience (IGSN), Ruhr University Bochum, Germany

2001 - 2005 B.Sc. (Life Science) with honors (concentration in Cellular and Molecular Biology)

National University of Singapore

Research Experience

2010 - current Postdoctoral research scientist, Max Planck Institute for Biological Cybernetics, Tübingen, Germany. Supervisor: Christoph Kayser

2009 - 2010 Postdoctoral researcher, Bernstein Group for Computational Neuroscience, Institute for Neurinformatics, Ruhr University Bochum, Germany. Supervisor: Dirk Jancke

2006 Research Assistant, Dept. of Biopsychology, Ruhr University Bochum. Supervisor: Onur Güntürkün

2005 Research Assistant, Institute for Neuroinformatics, Ruhr University Bochum. Supervisor: Hubert Dinse

2005 Undergraduate Honors Thesis

Molecular Neuroscience Laboratory, Faculty of Medicine, National University of Singapore. Supervisor: Alan Lee Yiu-Wah

2004 UROPS project

Neurophysiology Laboratory, Faculty of Medicine, National University of Singapore. Supervisor: Sanjay Khanna

Publications

Peer-reviewed Journals

1. Ng BS, Grabska-Barwinska A, Güntürkün O, Jancke D. (2010) Dominant vertical orientation processing without clustered maps: Early visual brain dynamics imaged with voltage-sensitive dye in the pigeon visual wulst. J. Neurosci. 30(19):6713-6725.
2. Grabska-Barwinska A, Ng BS, Jancke D. (2011) Orientation selective or not? Measuring significance of tuning to a circular parameter. J. Neurosci. Meth. 203(1):1-9.
3. Rothermel M*, Ng BS*, Grabska-Barwińska A, Hatt H, Jancke D. (2011) Nasal Chemosensory-Stimulation Evoked Activity Patterns in the Rat Trigeminal Ganglion Visualized by In Vivo Voltage-Sensitive Dye Imaging. PLoS ONE 6(10): e26158. doi:10.1371/journal.pone.0026158 [*equal contribution]
4. Ng BS, Logothetis NK, Kayser C (2012) EEG phase patterns reflect the selectivity of neural firing. Cerebral Cortex (accepted)

Poster Presentations and Talks

1. Ng B, Kayser C (2011) Neural correlates of auditory stimulus selectivity encoded by the precise temporal structure of EEG oscillations. Bernstein Conference, Freiburg.
2. Grabska-Barwinska A, Ng B, Jancke D (2009) Reproducibility: a new approach to estimating significance of orientation and direction coding. Bernstein conference, Frankfurt am Main.
3. Ng B, Güntürkün O, Jancke D (2009) Neuronal correlates of luminance change in the pigeon brain, a population code of the visual wulst. T16-5B Meeting of the German Neuroscience Society, Goettingen
4. Ng B, Grabska-Barwinska A, Güntürkün O and Jancke D (2009). Orientation processing without orientation maps in the pigeon analogue to the primary visual cortex. Computational and Systems Neuroscience. Utah, USA
5. Rothermel M^*, Ng B^*, Hatt H, Jancke D (2008). In vivo voltage-sensitive dye imaging of odor representation in the trigeminal ganglion. 369.7/KK19 . SfN 2008, Washington DC [*equal contribution]
6. Ng B, Güntürkün O, Jancke D (2008) Dynamic population coding of luminance change in the avian visual wulst captured by voltage sensitive dye imaging in vivo and electrophysiology. 568.22/KK31. SfN 2008, Washington DC.
7. Ng B, Kirsch J, Güntürkün O, Jancke D (2008). Rapid neuronal dynamics evoked by oriented stimuli in the pigeon visual brain captured by voltage-sensitive dye imaging. CVNS symposium. Tübingen, Germany.
8. Ng B, Kirsch J, Güntürkün O, Jancke D (2007) Lack of orientation maps in an assumed homologue of the primary visual cortex: Functional characterization of visual wulst activity in pigeon using voltage-sensitive dye imaging and electrophysiological recordings. 395.7/KK8 2007. SfN 2007, San Diego
9. Ng B, Güntürkün O, Jancke D “Voltage-sensitive dye imaging in the pigeon`s homologue of the mammalian primary visual cortex” Israel Society for Neuroscience 18th Annual Meeting, Eilat, Israel (2009) [Talk]
10. Ng B "The avian visual wulst: An analogue of the mammalian primary visual cortex?" Oxyopia Symposium Series, School of Optometry, UC Berkeley (2009) [Talk]
11. Ng B "Rock Pigeon (Columba livia): Vision, Brain and Behavior" Biopsychology Research Colloquium, Faculty of Psychology, Ruhr University Bochum (2007) [Talk]