Weak DCS causes a relatively strong cumulative boost of synaptic plasticity with spaced learning

Area of Science:

• Neuroscience
• Synaptic Plasticity
• Brain Stimulation

Background:

• Direct current stimulation (DCS) modulates synaptic plasticity in vitro, explaining behavioral effects of transcranial direct current stimulation (tDCS) in humans.
• Previous in vitro studies showed small effects with high electric fields, necessitating research at realistic tDCS intensities.
• Learning effects accumulate over time through spaced learning, a phenomenon leveraged to enhance DCS efficacy.

Purpose of the Study:

• To investigate if DCS effects on synaptic long-term potentiation (LTP) accumulate in a spaced learning paradigm.
• To determine if DCS can reveal significant synaptic plasticity effects at realistic field intensities.
• To compare in vitro DCS efficacy with human tDCS experiments.

Main Methods:

• Utilized a spaced learning model with repeated theta burst stimulation (TBS) in rat hippocampal slices.
• Applied DCS concurrently with TBS during LTP induction in the CA1 region.
• Examined cumulative DCS effects at various electric field intensities.

Main Results:

• DCS during repeated TBS significantly increased LTP.
• Spaced learning effects saturated with strong TBS protocols and high electric fields.
• Weak TBS and low electric fields (2.5 V/m) demonstrated the highest relative efficacy (12% LTP boost per 1 V/m).

Conclusions:

• Weak DCS exhibits a strong cumulative effect on synaptic plasticity via spaced learning.
• Saturation effects may have masked larger effect sizes in prior in vitro studies.
• Relative effect sizes of DCS in vitro now better align with human tDCS findings.