Non-invasive brain stimulation and vision rehabilitation: a clinical perspective

Figures & data

Table 1. Table summarising the key features and proposed mechanisms for TMS and tES.

	Key Features	Proposed mechanisms
TMS	Non-invasive method that stimulates cortical neurons via electromagnetic induction.^Citation2 The induced electric field drives ionic currents, causing localised hyperpolarisation or depolarisation of neuronal membranes. Once the membrane depolarisation reaches a certain threshold, it triggers the firing of action potentials.^Citation3	Modulation of synaptic efficacy and long-term potentiation through NMDA modulation.^Citation4–6 Modulation of GABA-mediated intracortical inhibition.^Citation7–9 Enhanced sensitivity to weak external inputs through stochastic resonance (tRNS).^Citation10 Frequency specific modulation of brain oscillations with (tACS).^Citation11,Citation12
tES	Non-invasive technique that delivers electrical currents to the scalp to modulate neural activity in underlying brain regions.^Citation1 The electrical current applied alters neuronal excitability by altering the membrane permeability of voltage-gated ion channels.^Citation13 Unlike TMS, tES does not directly induce action potentials.

Figure 1. (A) A TMS coil placed over a targeted brain region, and (B) A tES system.

Figure 2. Schematic showing facilitatory and inhibitory TMS and tES protocols. There is no inhibitory tRNS protocol. MSO = maximum stimulator intensity.

Figure 3. Simplified schematic showing the insertion of a receptor (e.g., NMDA receptor) to the synaptic membrane in response to an increase in intracellular Ca⁺², demonstrating long term potentiation (LTP; top right). Removal of a receptor from the membrane is shown for long term depression (LTD; top left), resulting in a decreased postsynaptic response. Long term potentiation and depression mediate the strengthening and weakening of synaptic connections, respectively, resulting in increased and decreased postsynaptic responses (bottom right and left panels).

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