Synaptic plasticity, LTP and LTD: VCE Psychology Unit 3
“Synaptic plasticity, resulting from long-term potentiation and long-term depression, which together act to modify connections between neurons (sprouting, rerouting and pruning), as the fundamental mechanism of memory formation that leads to learning”
Synaptic plasticity is the brain's ability to strengthen or weaken connections between neurons with experience, and it is the fundamental mechanism of memory and learning. Long-term potentiation (LTP) is the lasting strengthening of a synapse after repeated high-frequency stimulation, driven by glutamate, and underlies memory formation. Long-term depression (LTD) is the lasting weakening of a synapse after low-frequency or absent stimulation, which refines the network. These changes appear physically as sprouting (growing new connections), rerouting (forming new connections to undamaged neurons) and pruning (removing unused connections). Repetition and rehearsal improve memory because each repetition further potentiates the relevant synapse.
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What this dot point is asking
VCAA wants you to explain synaptic plasticity as the brain's ability to change its neural connections with experience, name and contrast long-term potentiation (LTP) and long-term depression (LTD), describe the structural changes of sprouting, rerouting and pruning, and state clearly that these changes are the biological mechanism that allows memory to form and learning to occur.
The answer
Synaptic plasticity is the ability of the synapse (the connection between two neurons) to strengthen or weaken over time in response to changes in activity. It is the fundamental physical basis of both learning (a relatively permanent change in behaviour due to experience) and memory (the storage and later retrieval of that experience).
Long-term potentiation
Long-term potentiation (LTP) is the long-lasting strengthening of synaptic connections that results from the repeated, high-frequency stimulation of a synapse. When a presynaptic neuron repeatedly and persistently activates a postsynaptic neuron, the connection between them becomes more efficient, so that future signals pass across the synapse more easily.
The neurotransmitter glutamate is central here. Repeated activation increases the number and sensitivity of receptors on the postsynaptic neuron, so the same signal produces a larger response. The familiar phrase is that neurons that fire together, wire together. LTP is widely regarded as the cellular basis of forming a new memory.
Long-term depression
Long-term depression (LTD) is the long-lasting weakening of synaptic connections that results from low-frequency stimulation or from connections that are no longer used. LTD reduces the efficiency of a synapse, making it harder for a signal to pass across.
LTD is not simply forgetting that has gone wrong. It is an active and useful process: by weakening connections that are rarely used, the brain clears space and sharpens the connections that matter, improving the precision of what is stored. LTP and LTD work together, one strengthening and one weakening, to fine-tune the network.
The structural changes
Plasticity produces three observable changes in the physical structure of neurons.
- Sprouting. The growth of new dendritic branches or axon terminals, creating new connection points so a neuron can form additional synapses.
- Rerouting. Establishing a new connection to an undamaged neuron, often used to bypass a damaged or blocked pathway so information can still travel.
- Pruning. The elimination of synaptic connections that are weak or no longer used, which streamlines the network and is closely linked to LTD.
Together, sprouting and rerouting build and redirect connections, while pruning removes the unnecessary ones. The result is a network shaped by experience.
Putting it together
When you practise a skill or rehearse information, the relevant synapses are repeatedly activated. LTP strengthens those synapses, sprouting and rerouting add and redirect connections, and pruning removes the pathways you no longer use. Over time the network is physically reorganised so that the learned response is fast and reliable. This is why repetition and rehearsal improve memory: each repetition further potentiates the synapse.
This biological account explains a behavioural fact you already know from the learning models. Pavlov's repeated pairing of bell and food, or a student's repeated revision, work because each repetition strengthens the underlying synaptic connection through LTP.
Synaptic plasticity is the ability of synapses to strengthen or weaken with use. Long-term potentiation is the lasting strengthening of a synapse after repeated high-frequency activation. Long-term depression is the lasting weakening of a synapse after low-frequency or absent activation.
LTP strengthens synapses and underlies the formation of memory; LTD weakens synapses and refines the network. Sprouting and rerouting add or redirect connections; pruning removes them. Strengthening and weakening operate together, not in opposition.
- Treating LTD as failure or damage
- LTD is a normal, useful process that refines memory by weakening unused connections; it is not the brain breaking down.
- Confusing potentiation with the neurotransmitter
- Glutamate is the neurotransmitter involved; LTP is the lasting change in the synapse that its repeated release produces. Name both, do not merge them.
- Mixing up the structural terms
- Sprouting grows new connections, rerouting redirects to a new neuron, pruning removes connections. Define each precisely rather than using them interchangeably.
- Saying plasticity only happens in childhood
- Synaptic plasticity occurs across the whole lifespan; it is the reason adults can still learn.
Exam-style questions
Questions in the style of VCAA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
2025 VCAA-style5 marksChildren learn how to hold a pencil at an early age. As they develop writing skills, this grip is improved to allow them to form letters. Explain how long-term potentiation and long-term depression work together to modify the connections between neurons as a child learns to hold a pencil.Show worked answer →
Five marks: define LTP and LTD, then explain how they act together to refine the neural connections for the skill.
Long-term potentiation (LTP). Repeated, co-ordinated activation of a synapse strengthens it, making the postsynaptic neuron more likely to fire. As the child repeatedly practises a useful grip, the neural pathways for that movement are repeatedly activated, so LTP strengthens these connections (supported by sprouting of new connections and increased glutamate transmission).
Long-term depression (LTD). Synapses that are used little or in an uncoordinated way are weakened, making the postsynaptic neuron less likely to fire. The connections for the early, inefficient grip are used less as the child improves, so LTD weakens them (associated with pruning of redundant pathways).
Working together. LTP and LTD operate at the same time: LTP reinforces the pathways for the correct, efficient grip while LTD weakens and prunes the pathways for the clumsy early grip. This combined strengthening and weakening reshapes the neural circuits so the efficient movement becomes more automatic, which is learning.
Markers reward correct definitions of LTP and LTD, the link to sprouting and pruning, and an explanation that the two processes jointly refine the connections as the skill improves.
Source: VCAA 2025 VCE Psychology examination (question wording lightly abridged). The marking notes are our own, not the official assessment guide.
2023 VCAA-style1 markWhich of the following is correct for long-term potentiation and long-term depression? A. LTP involves sprouting and rerouting and increased glutamate transmission; LTD involves pruning and rerouting. B. LTP reduces the efficacy of neuronal synapses through pruning; LTD strengthens the efficacy of neuronal synapses through sprouting. C. LTP strengthens the efficacy of neuronal synapses through increased secretion of glutamate; LTD reduces the efficacy of neuronal synapses through pruning of redundant pathways. D. LTP is characterised by a decrease in post-synaptic strength caused by pruning of synapses; LTD is characterised by an increase in post-synaptic glutamate transmission.Show worked answer →
Answer: C. This is a 1 mark multiple-choice item.
Long-term potentiation (LTP) is the long-lasting strengthening of synaptic connections, associated with increased glutamate transmission and sprouting. Long-term depression (LTD) is the long-lasting weakening of connections, associated with the pruning of redundant pathways. C correctly states both.
B and D reverse the two processes (making LTP weaken and LTD strengthen synapses), which is incorrect. A wrongly attributes increased glutamate and sprouting features in a way that does not correctly distinguish strengthening (LTP) from weakening (LTD).
Source: VCAA 2023 VCE Psychology examination (question wording lightly abridged). The marking notes are our own, not the official assessment guide.