Notes

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A collection of fragments of understanding in the pursuit of deeper questions.

Contents

Neuromorphic Pros & Cons

Why Spikes?

  • Background: Signal processing systems that need to process real-world sensory signals and interact with the environment in real-time.
  • Requirements:
    • Low power and low-latency.
    • Local processing, multi-core architectures and distributed computing.
    • Robust communication of signals across long distances through noisy channels.
  • Solution: Use Spikes! The optimal method that minimizes bandwidth and power consumption for achieving this goal, under these constraints, is pulse-frequency modulation.

Why Analog? Advantages

  • Exploit the full potential of emerging memory technologies
    • Control multi-level properties with analog pulse heights.
    • Exploit intrinsic non-linearities.
    • Exploit intrinsic stochasticity.
    • Exploit non-volatility properties.
  • Avoid use of digital clock circuitry.
  • Avoid large DAC/ADC overhead.
  • Minimize power consumption.

PCM-trace Exploit the drift of PCM devices to implement long-lasting eligibility traces. These enable the construction of powerful learning mechanisms for solving complex tasks by bridging the synaptic (ms) and behavioral time-scales (minutes).

Disadvantages Membrane currents measured across 256 neurons, in response to the same inputs differ. How to cope with mismatch? Integrate over space (use populations of neurons) and Integrate over time (use mean rates).

False Myths about Analog Neural Responses

  • Neural Responses are Slow (Population firing rates of neurons can reliably encode weak signal changes approx. 50 times faster than individual neurons, populations of noisy neurons have very fast response times).
  • Neurons need to fire at high firing rates to achieve high precision (E-I Balanced populations can encode signals with high precision and low rates, sparse neural population activity can represent signals with high accuracy).
  • Neurons need to be accurate to propagate precise information across population layers (Neurons need to be noisy to propagate neural activity reliably, to propagate signals using low-firing rates, it is necessary to use inhomogeneous populations of neurons).