Research Summary

Gamma rhythm as a tool to investigate neural processing

Neural mechanisms underlying complex behaviour involve coordination of millions of neurons, which can be studied by recording brain signals using different types of electrodes, from microelectrodes inserted in monkeys that provide information about local circuits, to electroencephalogram (EEG) in humans that reflects global properties of the network. The long-term goal of this research is to bridge these scales, so that complex behaviour such as attention can be studied at both circuit and network levels. To this end, we have built a setup to record simultaneously from four scales in the monkey: spikes, local field potential (LFP), electrocorticogram (ECoG) and EEG, as well as EEG from humans. In addition to studying attentional mechanisms, we aim to use this setup for brain-computer interfacing and in diagnosis of mental disorders.

Neural processes underlying cognition are often associated with oscillations at different frequencies that can be recorded using micro- as well as macro-electrodes. One such rhythm is called “gamma” (30-80 Hz), which is modulated by attention, memory and perception, and can also be induced in visual cortex by appropriate stimuli. Further, magnitude and centre frequency of gamma can be manipulated by changing stimulus properties such as size, contrast, orientation and speed, often over a time-scale of a few hundred milliseconds and over fairly localized regions of the cortex. Finally, properties of gamma also depend on processes such as excitation- inhibition interactions, gain control and normalization. Together, this makes gamma rhythm an attractive marker to study neural circuits. We study the dependence of gamma on the properties of visual/auditory stimuli as well as behaviour across multiple scales in both monkeys and humans, and build models that explain this dependence, to better understand the neural circuitry.