Differences In LTP-like Plasticity Between Subthreshold Depression And Healthy Individuals

Synaptic plasticity refers to the ability of the brain to undergo lasting changes in synaptic function,commonly in the form of long-term potentiation(LTP)and long-term depression(LTD).Visual evoked potentials(VEP)is a non-invasive method that has been widely used to explore human LTP-like plasticity.Depression is one of the most common mental disorders.Impaired synaptic plasticity is one of the causes of mental disorders such as depression and bipolar disorder.So far,there have been few studies examining whether synaptic plasticity is impaired in people with depression.Subthreshold depression(St D)is a subtype of depression with a high risk of developing major depression.Since visual evoked potentials cannot directly explore the chemical expression of synaptic plasticity,the result explored in this study is mainly an expression of synaptic plasticity-like.Through two studies,we aimed to explore the differences in subthreshold depressed individuals and healthy individuals in different levels of LTP-like plasticity.We conducted two studies,study 1 exploring this plasticity-like difference from low-level stimuli,and the study 2 exploring the difference in emotional modulation ability between subthreshold depressed individuals and healthy individuals from high-level stimuli.Study 1 used a checkerboard flip task with a flipping frequency of 2 Hz,and a mixed design of 2(group: subthreshold depression group,contral group)× 2(time: pretest,posttest)was adopted.It was found that the checkerboard reversal stimulus produced the expected VEP components: C1,P1,and N1.Previous studies have shown that P1-N1 peak-to-peak amplitude is a robust indicator of VEP plasticity,so this indicator was also analyzed in the current study.However,we were unable to find a significant difference in VEP plasticity between the two groups on these four components.Study 2 used the combination of implicit emotion judgment task and emotion modulation task.We adopted a mixed design of 2(group: subthreshold depression group,contral group)× 2(time:pretest,posttest)× 3(emotion: happy,neutral,sad).The results showed that on N170 and P2 component,subthreshold depressed individuals had significantly greater modulation ability than healthy individuals in sad.Our results further demonstrate the negative bias in depressed individuals,subthreshold depressed individuals have a stronger ability to modulate negative emotions of sadness.