Methods such as transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) non-invasively modulate the activity of circumscribed brain areas, so that the consequences of this manipulation on behaviour can be studied. These studies provide important information about the causal involvement of a brain region in a specific cognitive function and help bridging the gap between studies in healthy volunteers and patients suffering from brain damage. Neuromodulation can also be achieved by pharmacological agents which affect the activity of the brain neurotransmitter systems.