Our Research
Techniques to non-invasively manipulate human brain activity have gained great popularity in cognitive Neuroscience and Psychology. We are interested in how these fascinating techniques can be used to manipulate rhythmic activity in the brain, so-called brain oscillations. These oscillations occur as repetitive, wave-like fluctuations in the electrical activity of the brain and are a prominent feature of its activity that can be found across brain regions and even species. They have been associated to virtually all domains of cogitation, perception and behavior. Some examples include attention, memory, motor functions, vision and audition. In patients suffering from neurological or psychiatric disorders, where these functions are impaired, we commonly observe alterations in the associated oscillatory activity. However, the exact functional role of oscillations in the brain remains poorly understood.
In our research we aim to understand how oscillations shape cognition, perception and behavior and how we can modulate them with non-invasively with rhythmic transcranial stimulation. To this end, we combine transcranial electrical stimulation with computer based behavioral experiments and electroencephalography to measure effects of neurostimulation on brain oscillations and the associated behavioral changes.
We focus on the follwing research areas:
Effects and Mechanisms of Transcranial Alternating Current Stimulation (tACS)
Transcranial alternating current stimulation (tACS) uses weak electric currents applied non-invasively via electrodes attached to the scalp with a conductive paste or saline soaked sponges. While a large proportion of the electric current is shunted through the skin, some of the electricity reaches the underlying brain tissue where it can shift the membrane polarization of neurons. By applying a periodic waveform (usually a sine-wave), tACS leverages the principles of entrainment to target specific oscillations in the brain. Entrainment is a concept from physics describing how oscillators with similar frequencies and a way to exchange energy, adapt to each other. Besides the principles of entrainment, it is likely that prolonged stimulation with tACS induces neuroplastic effects that can outlast stimulation for several minutes or even hours. However, the exact mechanisms in humans are not fully understood. In particular how entrainment during stimulation gives rise to neuroplastic effects after stimulation remains largely elusive.
Variability of brain stimulation effects
Effects of non-invasive brain stimulation techniques, especially those using low-intensity electrical stimulation such as tACS or tDCS show substantial variability across participants often hampering the effective use of these techniques in basic research and clinical applications. A variety of factors influencing outcomes of neurostimulation such as anatomical differences affecting the electric field, the current state of the brain during neurostimulation, or differences in sleep, nicotine consumption, medication are being discussed. With our research we aim to better understand the role of these factors for brain stimulation effects as well as their interrelation in shaping stimulation outcomes. To this end, we make use of multimodal experiments combining electrophysiological recordings of brain stimulation effects with simulations of individual electric fields and behavioral measurements.
The causal role of brain oscillations for cognition, perception and behavior
Brain oscillations are ubiquitous across the brain and have been linked to a variety of functions. However, traditional investigations usually only record oscillatory activity, e.g. via EEG, whilst manipulating experimental parameters. Although this approach has brought extremely rich knowledge about the relation between oscillations and cognition, perception and behavior, it comes with the drawback that it can only show correlations. It is therefore often unclear if oscillatory activity is just a byproduct of the underlying information processing in the brain or plays an active role in it. In order to resolve this question, it is necessary to not just observe, but experimentally manipulate oscillatory activity. Only if such manipulation leads to changes in behavioral performance, we can conclude that an oscillation plays an active role for the process at question. In our research, we use transcranial alternating current stimulation to manipulate brain oscillation in a frequency specific manner to demonstrate such causal relationships between brain oscillations and visual or auditory perception, attention and action control.