Depression-biased reverse plasticity rule is required for stable learning at top-down connections

Area of Science:

• Neuroscience
• Computational Neuroscience
• Synaptic Plasticity

Background:

• Top-down synapses are vital for neocortical cognition but their development and specificity remain poorly understood.
• Sensory processing involves lower cortical areas activating before higher ones, creating unique pre- and post-synaptic activity timing at top-down synapses.
• This reversed timing suggests conventional spike-timing dependent plasticity (STDP) rules may be insufficient for top-down connections.

Purpose of the Study:

• To investigate the developmental rules governing top-down synaptic plasticity in the neocortex.
• To determine which spike-timing dependent plasticity (STDP) rules can establish stable, diverse, and non-looping top-down synaptic weight distributions.
• To introduce and evaluate a temporally reversed STDP (rSTDP) rule for top-down synapses.

Main Methods:

• Utilized a two-layer neural network model to simulate synaptic development.
• Employed analytical methods and integrate-and-fire simulations to test different STDP rules.
• Introduced and analyzed a novel depression-biased reversed STDP (rSTDP) rule.

Main Results:

• Only depression-biased rSTDP, not classical STDP, yielded stable and diverse top-down synaptic weights.
• The findings remained consistent with the addition of homeostatic mechanisms, multiplicative STDP, and external input.
• Model predictions align with recent neurophysiological evidence of reversed STDP at distal synapses.

Conclusions:

• A temporally reversed STDP (rSTDP) rule is necessary for the stable and diverse development of top-down neocortical synapses.
• This finding has significant implications for understanding the neural basis of cognition and synaptic specificity.
• The study provides a computational framework supported by experimental evidence for understanding synaptic development in hierarchical neural circuits.