Abstract
Experience-dependent modulation of the visual evoked potential (VEP) is a promising proxy measure of synaptic plasticity in the cerebral cortex. However, existing studies are limited by small to moderate sample sizes as well as by considerable variability in how VEP modulation is quantified. In the present study, we used a large sample (n = 415) of healthy volunteers to compare different quantifications of VEP modulation with regards to effect sizes and retention of the modulation effect over time. We observed significant modulation for VEP components C1 (Cohen's d = 0.53), P1 (d = 0.66), N1 (d=-0.27), N1b (d=-0.66), but not P2 (d = 0.08), and in three clusters of total power modulation, 2–4 min after 2 Hz prolonged visual stimulation. For components N1 (d=-0.21) and N1b (d=-0.38), as well for the total power clusters, this effect was retained after 54–56 min, by which time also the P2 component had gained modulation (d = 0.54). Moderate to high correlations (0.39≤ρ≤0.69) between modulation at different postintervention blocks revealed a relatively high temporal stability in the modulation effect for each VEP component. However, different VEP components also showed markedly different temporal retention patterns. Finally, participant age correlated negatively with C1 (χ2=30.4), and positively with P1 modulation (χ2=13.4), whereas P2 modulation was larger for female participants (χ2=15.4). There were no effects of either age or sex on N1 and N1b potentiation. These results provide strong support for VEP modulation, and especially N1b modulation, as a robust measure of synaptic plasticity, but underscore the need to differentiate between components, and to control for demographic confounders.
Highlights
Due to the essential role of synaptic plasticity in learning and memory (Takeuchi et al, 2013), as well as its likely role in the etiology of a range of psychiatric disorders (Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014; Stephan et al, 2006), several non-invasive methodologies for studying long term potentiation (LTP)-like synaptic plasticity in humans have been developed
Initial group level analyses demonstrated that, across visual evoked potential (VEP) components, the highest amplitudes and the largest modulation effects were exhibited at the occipital Oz electrode (Fig. 3A-B), which was selected for individual level analyses
Experience-dependent VEP modulation was apparent as amplitude changes from baseline to the first postintervention assessment for both the C1 (d = 0.53, rr = 0.70), P1 (d = 0.66, rr = 0.76), N1 (d = −0.27, rr = 0.62), N1b (d = −0.66, rr = 0.77), but not P2 (d = 0.08, p = 0.10, rr = 0.53) components, with highly similar effects for both the C1 (d = 0.44, rr = 0.67), P1 (d = 0.55, rr = 0.72), N1 (d = −0.26, rr = 0.61), N1b (d = −0.71, rr = 0.77) and the P2 (d = 0.08, p = 0.10, rr = 0.54) components at the immediately following second postintervention assessment
Summary
Due to the essential role of synaptic plasticity in learning and memory (Takeuchi et al, 2013), as well as its likely role in the etiology of a range of psychiatric disorders (Schizophrenia Working Group of the Psychiatric Genomics Consortium, 2014; Stephan et al, 2006), several non-invasive methodologies for studying long term potentiation (LTP)-like synaptic plasticity in humans have been developed. Among these approaches, the application of high frequency or prolonged visual stimulation to manipulate visual evoked potentials (VEPs) measured using electroencephalography (EEG) has proven especially promising (Cooke and Bear, 2012).
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