Neurons don't quite touch — they shout across a tiny gap called a synapse, and the more two neurons fire together, the louder that shout becomes. That strengthening is plasticity: literally how a memory gets wired into you.
The gap that makes the brain flexible
Most neurons do not touch. At a chemical synapse, an arriving spike triggers the release of neurotransmitter molecules across a tiny gap; they bind receptors on the next cell and nudge its voltage. Excitatory transmitters (like glutamate) push toward firing; inhibitory ones (like GABA) push away. Every thought is a running tally of these pushes.
Long-term potentiation (LTP) is the lasting strengthening of a synapse that has been repeatedly and strongly active. It is the leading cellular model of learning and memory — experience literally reshapes the connections.
Plasticity cuts both ways: synapses strengthen with use (LTP) and weaken with disuse (long-term depression). This constant retuning lets the same fixed set of neurons store new memories throughout life.
- Picture a neuron receiving 5 excitatory inputs (+1 each) and 3 inhibitory inputs (−1 each) in a short window.
- Sum the inputs. If threshold requires a net of +3, does the neuron fire?
- Now silence 2 excitatory inputs and add 1 inhibitory. Recompute the sum — does it still fire?
- Explain how inhibition can veto a decision even when excitation is present.
What you should see: You modeled synaptic integration as a weighted sum and saw why inhibition is as important as excitation in shaping output.