Maya Ellison
Spike-timing dependent plasticity (STDP) is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (or spikes). The phenomenon was first observed by M. M. Taylor in 1973 and later named by Song et al. in 2000. STDP is considered a key mechanism in learning and memory formation and has been observed in multiple brain regions, including the hippocampus. It is a temporally sensitive form of synaptic plasticity, meaning that the efficiency of synaptic transmission is modified by the timing of neural activity. When a presynaptic neuron fires shortly before a postsynaptic neuron, the connection is typically strengthened, whereas if the presynaptic neuron fires after the postsynaptic neuron, the connection is weakened.
| Characteristics | Values |
|---|---|
| Definition | Spike-timing dependent plasticity (STDP) is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (or spikes). |
| Basis | The principle, now known as Hebbian theory, is often summarised as "cells that fire together, wire together". |
| Mechanism | STDP operates over a narrow time window, typically on the order of tens of milliseconds. |
| Synapses | Different synapse types can have quite different forms of STDP function. |
| Learning | STDP is widely utilised in models of circuit-level plasticity, development, and learning. |
| Memory | STDP is thought to be involved in the formation of memory. |
| Neuromodulators | Neuromodulators enable state-dependent plasticity: the brain can promote or prevent STDP under certain conditions. |
| Hippocampus | In hippocampal CA1 pyramidal cells, an STDP protocol that induces long-term depression of GABAergic synapses was found to depend on endocannabinoid release and the activation of presynaptic M2 muscarinic acetylcholine receptors. |
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What You'll Learn
STDP is a form of synaptic plasticity
Spike-timing-dependent plasticity (STDP) is a form of synaptic plasticity. It is a temporally sensitive process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (or spikes). The term STDP refers to the observation that the precise timing of spikes significantly affects the sign and magnitude of synaptic plasticity.
The efficiency of synaptic transmission is modified by the timing of neural activity. When a presynaptic neuron consistently fires just before a postsynaptic neuron, the connection is typically strengthened through a process known as long-term potentiation (LTP). This phenomenon is in line with Hebb theory, summarised as "cells that fire together, wire together". Conversely, if the presynaptic neuron fires after the postsynaptic neuron, the connection is weakened through long-term depression (LTD). This process is dependent on the consistent predictive relationship between the neurons, which is essential for robust learning.
The phenomenon of STDP has been observed in multiple brain regions, including the hippocampus. It is believed to be a key mechanism in learning and memory formation, contributing to the activity-dependent development of neural circuits. STDP operates over a narrow time window, typically on the order of tens of milliseconds.
STDP is considered the first law of synaptic plasticity, and it is widely utilised in models of circuit-level plasticity, development, and learning. However, it is important to note that spike timing is just one of several factors influencing plasticity induction, including firing rate, synaptic cooperativity, and depolarization.
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STDP is a key mechanism in learning and memory formation
Spike-timing dependent plasticity (STDP) is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (or spikes). It is a temporally sensitive form of synaptic plasticity, meaning that the efficiency of synaptic transmission is modified by the timing of neural activity.
The term STDP refers to the observation that the precise timing of spikes significantly affects the sign and magnitude of synaptic plasticity. The process involves the adjustment of synaptic weights, which are plotted as a function of the relative timing between presynaptic spike arrival and postsynaptic firing. This results in an STDP function or learning window, which varies across different synapse types.
In STDP, the order and precise temporal interval between presynaptic and postsynaptic spikes determine the sign and magnitude of long-term potentiation (LTP) or long-term depression (LTD). When a presynaptic neuron fires shortly before a postsynaptic neuron, the connection between them is typically strengthened through LTP. Conversely, if the presynaptic neuron fires after the postsynaptic neuron, the connection is weakened through LTD. This process is often summarized as "cells that fire together, wire together".
STDP is considered a key mechanism in learning and memory formation. It helps explain the activity-dependent development of neural circuits and has been observed in multiple brain regions, including the hippocampus. STDP is widely utilized in models of circuit-level plasticity, development, and learning. It is believed to be involved in the formation of memory and is used to explore orderly signal propagation in neural networks.
Overall, STDP is a fundamental process that enables the brain to adjust synaptic connections, facilitating learning and memory formation through the optimization of neural circuits.
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STDP is dependent on the precise timing of spikes
The precise timing of spikes is a critical factor in the process of spike-timing dependent plasticity (STDP). STDP is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (spikes). The term STDP refers specifically to the observation that the precise timing of spikes significantly affects the sign and magnitude of synaptic plasticity.
The process of STDP is based on the temporal relationship between presynaptic and postsynaptic spikes. When a presynaptic neuron fires shortly before a postsynaptic neuron, the synapse is potentiated, leading to long-term potentiation (LTP). On the other hand, if the presynaptic neuron fires after the postsynaptic neuron, the synapse is depressed, resulting in long-term depression (LTD). This phenomenon is known as Hebbian theory, summarised as "cells that fire together, wire together". Experimental studies have confirmed the critical nature of this precise temporal relationship for synaptic modification.
The timing rules governing STDP can be interpreted as kernels or timing-dependent functions that predict other properties of synaptic plasticity. The change in synaptic weight, or the STDP function, is plotted as a function of the relative timing between presynaptic spike arrival and postsynaptic firing. Different synapse types can exhibit varying forms of STDP functions. STDP is considered a key mechanism in learning and memory formation, contributing to the activity-dependent development of neural circuits.
While the precise timing of spikes is essential, it is important to note that STDP is also influenced by other factors. These factors include the need for multiple spike pairings, the nonlinear summation of plasticity across spike pairs, and the baseline synaptic weight. Additionally, neuromodulators play a significant role in shaping STDP during and after spike pairing. These findings suggest that spike timing is not the sole determinant of plasticity but rather one of several factors within a multi-factor rule.
Overall, the precise timing of spikes is a critical aspect of STDP, a process that adjusts synaptic connections between neurons. By influencing the sign and magnitude of synaptic plasticity, STDP plays a crucial role in learning, memory formation, and the optimisation of neural circuits.
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STDP is influenced by neuromodulators
Spike-timing-dependent plasticity (STDP) is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (spikes). It is a temporally sensitive form of synaptic plasticity, meaning that the efficiency of synaptic transmission is modified by the timing of neural activity. When a presynaptic neuron fires just before a postsynaptic neuron, the connection is typically strengthened through long-term potentiation (LTP). Conversely, if the presynaptic neuron fires after the postsynaptic neuron, the connection is weakened through long-term depression (LTD).
Neuromodulators strongly influence STDP by modifying the timing rules that determine whether a synapse is strengthened or weakened. These changes depend on broader brain states, such as arousal, attention, or reward, allowing synaptic plasticity to be tuned to the behavioural context. Neuromodulators can include acetylcholine, dopamine, noradrenaline, serotonin, and adenosine. For example, in hippocampal experiments, acetylcholine initially caused synaptic weakening, but subsequent dopamine application converted this LTD into LTP. Dopamine can also broaden the STDP time window for potentiation and even rescue LTP if given shortly after spike pairing, acting as a reward timing signal. This sequence of acetylcholine followed by dopamine has been proposed as a mechanism for associating sensory cues or actions with delayed rewards.
In vitro studies have shown that the dopaminergic system, among other neuromodulatory systems, influences timing-dependent plasticity. For instance, in the amygdala, t-LTP was only induced when dopamine was applied or when GABAergic transmission was blocked. Furthermore, dopamine receptor activation is often necessary for timing-dependent plasticity to occur. Neuromodulators can also reverse the sign of plasticity, converting t-LTP into t-LTP or vice versa.
On a larger scale, neuromodulators have been found to influence STDP on three timescales. Firstly, on the scale of tens of milliseconds, they influence the interaction of pre- and postsynaptic spikes to induce plasticity. Secondly, on the scale of seconds, they impact the number of repetitions of pre-post activity required to evoke plasticity. Lastly, on the order of minutes, they influence the time course of plasticity.
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STDP is bidirectional
Spike-timing-dependent plasticity (STDP) is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (or spikes). It is a temporally sensitive form of synaptic plasticity, meaning that the efficiency of synaptic transmission is modified by the timing of neural activity. When a presynaptic neuron fires just before a postsynaptic neuron, the connection is typically strengthened—a process known as long-term potentiation (LTP). If the timing is reversed and the presynaptic neuron fires after the postsynaptic neuron, the connection is weakened through long-term depression (LTD).
The bidirectional nature of STDP was first observed by Henry Markram, who used dual patch-clamp recordings to demonstrate that the order of spike firing between two connected neurons could bidirectionally modify synaptic strength. Markram's findings showed that when the presynaptic neuron fired approximately 10 milliseconds before the postsynaptic neuron, the connection was strengthened, and reversing the order led to weakening. This work provided strong experimental evidence for the bidirectional nature of STDP.
The bidirectional characteristic of STDP is also evident in its ability to transition between potentiation and depression. For example, in the rodent barrel cortex, synapses initially exhibit a unimodal timing rule, where all correlated activity results in potentiation. However, around the onset of the critical period, classical bidirectional Hebbian STDP emerges, allowing for both potentiation and depression depending on the timing of spikes. This developmental switch from "all-to-potentiation" to "timing-sensitive" plasticity is a critical transition in the maturation of neural circuits.
Furthermore, the bidirectional nature of STDP is also observed in the interaction between different neuromodulators. For instance, in hippocampal experiments, acetylcholine was found to induce synaptic weakening, but the subsequent application of dopamine converted this LTD into LTP. The modulatory sequence of acetylcholine followed by dopamine has been proposed as a cellular mechanism for associating sensory cues or actions with delayed rewards, demonstrating the bidirectional nature of STDP in response to neuromodulators.
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Frequently asked questions
Spike-timing dependent plasticity (STDP) is a biological process that adjusts the strength of synaptic connections between neurons based on the relative timing of their action potentials (or spikes).
The concept of STDP was first proposed by M. M. Taylor in 1973. However, the term STDP was coined later in 2000 by Song et al. to describe the phenomenon observed by Markram et al. in 1997.
The key factors that govern STDP include the timing and order of pre- and post-synaptic spikes, the number of spike pairings, baseline synaptic weight, and the influence of neuromodulators.
