The magnetic field generated from an electromagnet is used in the transcranial magnetic stimulation (TMS) of the brain. The following statements suggest some features of TMS:

A. The magnetic field generated in TMS induces an electrical field in the underlying brain area.
B. The electrical field in the brain area alters the membrane potential of the neurons in that locality causing them to depolarize synchronously, which in turn, may change the probability of the firing of neurons.
C. In cognitive neuroscience research, TMS may be used as a tool to induce a ‘virtual lesion’ in a selected region of the cerebral cortex.
D. TMS is safe and non-invasive but the neuronal activity of the stimulated area is disrupted for a long period of time.

Which one of the following options represents the combination of all correct statements?

Correct option is A

Explanation:

 Statement A: Magnetic field induces an electric field in the brain
TMS works on Faraday’s Law of Electromagnetic Induction, where a rapidly changing magnetic field generated by an electromagnet induces an electric field in nearby conductive tissues — in this case, the brain cortex.
This electric field can stimulate neurons and modulate cortical excitability.

 Statement B: Electric field alters membrane potential of neurons
The induced electric current causes a localized depolarization of neurons, affecting their resting membrane potential.
This can lead to action potentials and alteration of neuronal firing probability, either activating or inhibiting neural circuits.

 Statement C: Virtual lesion in cognitive neuroscience
TMS can reversibly disrupt activity in a targeted brain region — a method used to create “virtual lesions”.
This helps researchers understand causal relationships between specific brain areas and cognitive functions (e.g., language, memory, attention).
Unlike permanent lesions, this method is non-invasive and reversible.
​
 Statement D: Long-term disruption
Incorrect. The neuronal effects of TMS are transient, typically lasting milliseconds to several minutes depending on the protocol (e.g., single-pulse, repetitive TMS).
TMS is FDA-approved for clinical use (e.g., depression) and considered safe when used within guidelines.