* Question

Briefly describe Hebb theory and STDP learning mechanism

* Answer

Hebbian Learning (Hebb Theory):

Hebb’s theory, often summarized as “cells that fire together, wire together,” is a principle in neurobiology that describes how neural connections strengthen based on the correlation of neuronal activity. Specifically:

• When two neurons are repeatedly activated at the same time, the synapse between them becomes stronger.
• The theory is based on the idea that if neuron A consistently contributes to the firing of neuron B, the connection between them is strengthened, making it easier for A to trigger B in the future.

Hebb’s learning rule is fundamental in understanding synaptic plasticity and is often expressed mathematically as:

• Δw = η * x * y, where:

• Δw is the change in synaptic weight,
• η is the learning rate,
• x and y are the activity levels of the pre- and postsynaptic neurons.

Spike-Timing-Dependent Plasticity (STDP):

STDP is a more specific and biologically plausible form of Hebbian learning. It involves the timing of spikes between pre- and postsynaptic neurons:

• If the presynaptic neuron fires before the postsynaptic neuron(in a short time window), the synapse is strengthened (long-term potentiation, LTP).
• If the postsynaptic neuron fires before the presynaptic neuron, the synapse is weakened(long-term depression, LTD).

The key idea of STDP is that the exact timing of spikes matters. A precise correlation between the neurons’ firing times can enhance or diminish the connection strength, making it a more sophisticated form of Hebbian learning.

In summary:

• Hebbian learningis the general principle of strengthening synaptic connections based on correlated activity.
• STDPrefines this by incorporating the relative timing of neuronal spikes to determine whether the connection is strengthened or weakened.