tDCS is complementary to, and can be used in parallel with, methods such as TMS.

Different tDCS protocols can enhance or disrupt attention, learning, and memory.

Neural oscillations can be modified by tDCS, affecting perception and cognition.

In recent years there has been an exponential rise in the number of studies employing transcranial direct current stimulation (tDCS) as a means of gaining a systems-level understanding of the cortical substrates underlying behaviour. These advances have allowed inferences to be made regarding the neural operations that shape perception, cognition, and action. Here we summarise how tDCS works, and show how research using this technique is expanding our understanding of the neural basis of cognitive and motor training. We also explain how oscillatory tDCS can elucidate the role of fluctuations in neural activity, in both frequency and phase, in perception, learning, and memory. Finally, we highlight some key methodological issues for tDCS and suggest how these can be addressed.

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Glossary

an electrode with a positive charge.

stimulation applied via the anode, typically associated with increased cortical excitability and decreased levels of the neurotransmitter GABA.

stimulation applied via the cathode, typically associated with decreased cortical excitability and decreased levels of the neurotransmitter glutamate.

an electrode with a negative charge.

measurement of electrical activity on the scalp, typically via multiple electrodes. Neural activity is reflected by small changes in electrical potential.

type of magnetic resonance imaging that allows the non-invasive measurement of metabolites (including neurotransmitters). MRS provides the concentrations of detectable metabolites in the measured area of the brain.

activity in a muscle induced, in this context, by a TMS pulse applied to the primary motor cortex. MEPs are measured via electrodes placed on the skin over the targeted muscle, and are used as a measure of cortico-spinal excitability.

stimulation applied at rest, before or after a task is undertaken.

stimulation applied while a participant undertakes a task.

a form of tDCS in which the current oscillates at a given frequency.

changes in structural or functional pathways in the brain in response to experience.

for a single target region in the brain, the second electrode is referred to as the reference. This electrode can be placed over a non-brain region (e.g., the cheek or mastoid) or a brain area thought not to be involved in the relevant process(es). The reference electrode is sometimes referred to as the ‘return’ electrode.

an area of the cortex targeted with tDCS.

measurement of the blood oxygen level-dependent (BOLD) signal while a participant is at rest. rsfMRI allows analysis of brain activity and networks in the absence of any specific task.

a form of stimulation in which the current duration or intensity are substantially smaller than in active stimulation. Sham stimulation can be thought of as a placebo condition.

non-invasive electrical stimulation of the brain via electrodes place on the scalp. Typically, a current is ramped up, held constant for a period of time (most commonly 8–15 min), and then ramped down.

non-invasive brain stimulation using a magnetic field to induce an electric current in underlying brain tissue.

a change in electric potentials measured with EEG in response to a TMS pulse.

a change in electric potentials measured with EEG in response to a visual stimulus or a TMS pulse over visual cortex.