The mechanism of transcranial magnetic stimulation in cognition

Abstract

Despite the widespread usage of transcranial magnetic stimulation (TMS) in clinical and basic research, the exact mechanisms of action and interactions with ongoing neural activity remain unclear. However, thanks to recent biophysical studies on electromagnetic induction of neural tissue (Wagner et al., 2009) we now know more about some basic properties of TMS effects. This basic knowledge is important in planning and interpreting TMS studies and in cognitive neuroscience experiments a theoretical framework is also necessary. TMS data have traditionally been interpreted in the ''virtual brain lesion'' framework (Walsh and Cowey, 1998). The terminology was proposed by analogy with neuropsychological and animal lesion studies and TMS is described as inducing a temporary, reversible lesion in the stimulated area, avoiding problems related to cortical plasticity and functional reorganisation (Walsh and Pascual-Leone, 2003). Based on this interpretation, TMS has been utilised to define the putative role of areas during the execution of cognitive tasks, and this approach has been very productive. Semantically, the term ''virtual lesion'' identifies the effect induced by TMS as blocking the function of a population of neurons that are temporarily ''lesioned'' by the TMS pulse. Nevertheless, the TMS pulse induces a depolarisation of a group of neurons that in turn might activate other neurons, and the final behavioural outcome depends on the role of the stimulated area in relation to the network engaged in such a task (Sack and Linden, 2003). The ''virtual lesion'' hypothesis has, however, confused people on the issue of how TMS can possibly lead to enhanced performance (e.g., Harris et al., 2008b; Walsh et al.,

Dorsolateral prefrontal cortex, working memory and episodic memory processes: insight through transcranial magnetic stimulation techniques

“…Finally, we report and discuss the potential clinical application of TMS of the DLPFC for the treatment of neuronal and psychiatric disorders, such as anxiety and depression. This has made TMS such a useful tool for investigating the causal relationships between cortical areas and behavior in normal and pathological cases [14] .…”

Seeing touch in the somatosensory cortex: A TMS study of the visual perception of touch

“…In this study, we sought to address this issue by means of Transcranial Magnetic Stimulation (TMS). TMS allows researchers to investigate causality in the brain-behaviour relationship, by temporarily interacting with the activity of neurons in brain areas that are underneath the magnetic field, which is administered by a coil positioned over the scalp [Miniussi et al, 2009;Pascual-Leone et al, 2000]. One advantage of TMS over other neuroimaging methods is that TMS can be used to demonstrate that a brain region is causally essential for performing a given task.…”

rTMS stimulation on left DLPFC increases the correct recognition of memories for emotional target and distractor words

“…We used a repetitive stimulation (rTMS) paradigm, which creates a "perturbation" and offers a unique opportunity to directly interfere with the functioning of a cortical area during the execution of a memory task. Thus, this paradigm can manipulate the causal relationships between neural activity and a subject's performance (Miniussi, Ruzzoli, & Walsh, 2010). High-frequency electrical stimulation is known to induce long-term potentiation, whereas low-frequency stimulation induces long-term depression (Miniussi et al, 2008).…”