Online Lecture by Supratim Ray

Gamma oscillations and SSVEPs as tools to investigate brain function in health and disease

Abstract: Brain signals often show intrinsic oscillations at “gamma” frequency range (30-80 Hz), which can be induced by presenting visual stimuli such as bars and gratings. Stimulus-induced gamma oscillations are modulated by high-level cognitive processes such as attention and memory and are abnormal in patients suffering from mental disorders such as Autism and Schizophrenia. An oscillatory signal can also be generated in the visual brain areas by presenting a flickering visual stimulus, which generates the well-known steady state visually evoked potential (SSVEP). Both gamma oscillations and SSVEPs provide ways to investigate neural processes underlying high-level cognition. In the first part, I will show that when two visual stimuli are presented at different flickering rates (a very common design in attention studies), the resulting SSVEPs interact in highly non-trivial ways. Using microelectrode recordings from awake monkeys, we try to understand the neural mechanisms underlying these interactions. In the second part, I will discuss how stimulus induced gamma oscillations and SSVEPs vary with healthy ageing in a large cohort of elderly subjects (>50 years) and in Alzheimer’s Disease.