High-Pass Filtering through Short-Term Synaptic Facilitation Amplifies Low-Frequency Modulation of Bursting Input

Area of Science:

• Neuroscience
• Computational Biology
• Systems Neuroscience

Background:

• Short-term synaptic plasticity (STP) typically masks neural signal dynamics under regular activity.
• Multiple-frequency inputs reveal canonical STP effects, but complex oscillatory patterns present unique challenges.
• Understanding how synaptic dynamics filter signals with multiple frequency bands is crucial for neuronal communication.

Purpose of the Study:

• To investigate how dynamic neuromuscular synapses amplify slow modulations in bursting inputs.
• To model the effects of facilitation and depression on the contrast of synaptic responses to modulated bursts.
• To explore the role of synaptic recovery times and postsynaptic mechanisms in signal filtering.

Main Methods:

• Utilized a simple short-term synaptic plasticity (STP) model to analyze synaptic responses.
• Simulated modulated bursting inputs with varying frequencies and spike numbers.
• Employed a biophysical model of a postsynaptic cell to assess voltage-gated conductance contributions.

Main Results:

• Facilitation enhances response contrast to strong/weak bursts, while depression diminishes it.
• High-pass filtering amplifies low-frequency components of modulated bursting, contrary to intuition.
• Synaptic filtering effects depend on release probability, recovery times, and burst period; memory across bursts alters contrast.
• Subthreshold voltage-gated conductances significantly contribute to low-frequency modulation readout.

Conclusions:

• Synaptic dynamics act as filters, with STP significantly influencing signal processing of complex, multi-frequency inputs.
• High-pass filtering of bursting activity can unexpectedly amplify slow modulations, offering new insights into neural signal processing.
• Findings are relevant to sensory processing and the coupling of brain oscillations at different frequencies.