Most scientific work performed for investigating neuronal correlates of cognitive functions describes the neuronal activity, which is observed while subjects perform a task. These observations deliver correlative evidence in favor of or against the research hypothesis. However, correlative evidence is not a proof of principle, since the underlying correlation could be the result of other dependencies within the brain that are simply not part of the observed site. An excellent example of a significant correlation without any causal relation is, for example, the number of ice cream and sunglasses sold. They do strongly correlate, but neither of them is causal for the increase of the other (www.towardsdatascience.com).
As an experimental lab, we use a technique to overcome this so-called causality problem. To observe causal relationships between neurons, we interfere with the system of observation and analyze how the interference at one neuron affects neurons at other sites. For this, we apply very small electric pulses into the brain tissue, which results in the immediate spiking of a few neurons. We then investigate how these electrically evoked spikes, which would typically not be present, effect other neurons at higher or lower stages of the processing hierarchy. We also analyze how these pulses affect behavior, and when the transmission of these pulses is most effective. Utilizing the electrical stimulation, we investigate, for example, how relevant information is preferentially routed and processed within the visual cortex.