Table 1. Examples of synaptic plasticity deficits associated with human depression.

Described are studies that compared measures of plasticity responses in individuals with major depressive disorder (MDD) compared to healthy controls (HC). After visual stimuli exposure, visually evoked responses are postsynaptic potentials recorded from the occipital region via electroencephalogram (EEG). Paired associative stimulation protocols involve ulnar nerve stimulation coupled with single-pulse transcranial magnetic stimulation (TMS) to the motor cortex to elicit a motor-evoked response assessed by peripheral motor-evoked potentials (MEPs). Theta burst stimulation (TBS) involves a shorter duration of TMS administration compared to non-TBS TMS due to the delivery of recurrent pulses in the theta range (4-7 Hz) at a high frequency to produce an alternating electromagnetic field that activates cortical neurons resulting in peripheral MEP responses. This table represents a subset of relevant studies and is not a complete listing of all available studies. DLPFC, dorsolateral prefrontal cortex; HC, healthy controls; LTD, long-term depression; LTP, long-term potentiation; TBS, theta burst stimulation.

Study	Group studied	Method	Outcome
Normann [213]	40 MDD; 74 HC	Visually-evoked EEG responses	Impaired cortical synaptic transmission and LTP-like responses
Kuhn [214]	27 MDD; 27 HC	Paired associative stimulation evoked MEPs	Impaired cortical LTP-like responses
Noda [215]	29 MDD; 28 HC	Paired associative stimulation evoked MEPs	Impaired DLPFC LTP-like responses
Player [216]	23 MDD; 23 HC	Paired associative stimulation evoked MEPs	Impaired cortical LTP-like responses
Yu [217]	31 MDD; 29 HC (all females)	Continuous TBS-evoked MEPs	Impaired cortical LTD-like activity