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Long-Term Plasticity of Visually Evoked Potentials in Humans Is Altered in Major Depression

Long-Term Plasticity of Visually Evoked Potentials in Humans Is Altered in Major Depression. Normann, C., Schmitz, D., Furmaler, A., Doing, C., & Bach, M. Recapped by XXXXXX. Linking LTP with Depression. When plasticity goes awry… Stimulate a neuron, increase post-synaptic response

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Long-Term Plasticity of Visually Evoked Potentials in Humans Is Altered in Major Depression

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  1. Long-Term Plasticity of Visually Evoked Potentials in Humans Is Altered in Major Depression Normann, C., Schmitz, D., Furmaler, A., Doing, C., & Bach, M. Recapped by XXXXXX

  2. Linking LTP with Depression • When plasticity goes awry… • Stimulate a neuron, increase post-synaptic response • Animal models provide insight • 3 weeks of unpredictable stress induce LTD, reverse with antidepressant fluvoxamine • Human data is sparse

  3. Evoking Plasticity • Repeat a visual stimulus to produce “learning” (i.e., perception of the visual stimulus) • Enhancement of visually evoked potentials (VEP) as measured with EEG • Differences between depressed and control? • Frequency- and pattern- specific? • Influence of antidepressants?

  4. Figure 1. The experimental procedure 1200 reversals, 2 rps 40 reversals in 20 seconds 4 VEP response 2 0 VEP Amp -2 -4 100 ms Time (ms)

  5. Figure 2. Response plasticity of VEPs in controls (N = 22) 89.3 +- .6 msec 126.2 +- msec 64.9 +- .5 msec

  6. Figure 3. Frequency and pathway specificity Modulation block replaced with grey screen Modulation block with 19-rps No checkerboard, a flash

  7. Figure 4. Response plasticity of VEPs in depressed patients (N = 10)

  8. Figure 5. SSRI intake (Sertraline) augments VEP plasticity (N=7)

  9. Ratio of the amplitudes of two “paired pulse” VEP’s with an inter-stimulus interval of 80 msec: Depressed vs. Control Ratio of the amplitudes of two “paired pulse” VEP’s with an inter-stimulus interval of 80 msec: Pre- vs. Post SSRI

  10. Plasticity of Evoked Potentials? • For Control • Prolonged exposure to visual stimulus induces LTP • P1 and N1 increased, persists for 20 minutes or more • Frequency and pattern specific (cortical excitability exhibited in this study was purposefully evoked)

  11. Underlying Mechanism in the Current Response Plasticity • Parallel with induction in brain slices • 1st have persistent synaptic activity followed by sustained change in synaptic strength • Freq and pattern specific • Pathway selectivity • VEP plasticity can be modulated • But, non-linear in terms of frequency

  12. Plasticity in Depression? Augmented by anti-depressants? • Significant differences in the C1 and N1 amplitudes compared to controls • Previous studies have shown neuronal activity reduced in many areas • Significant increase of VEP in P1 and N1 after 3 weeks of SSRI (healthy individuals) • Effect of SSRI on healthy individuals is different for depressed: opposite for C1 and P1, increased for N1

  13. Plasticity and Pathophysiology? • Grounds to suggest long-term synaptic plasticity implicated in depression (clinical) • Impaired plasticity > more susceptible to stress affecting “brain circuits” in mood regulation • Counter with antidepressants • Impaired mood regulation > impaired plasticity • Trait markers vs. State markers?

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