Chaoter 2d Flashcards
What happens when u form memories and learn new info
physical changes occur in your brain. Specifically, neural synapses are modified and synaptic connections are changed, enabling new information to be encoded and stored in your brain
Synaptic plasticity
Synaptic plasticity is the ability of synaptic connections to change over time in response to activity or experience. These changes include the formation, strengthening, or weakening of synaptic connections. In other words, the experiences that you have throughout your lifespan modify the neural synapses in your brain, causing them to physically change.
Neural plasticity and types
As you have learnt, synaptic plasticity is the ability of neural synapses to change in response to activity and experience throughout one’s lifespan. More broadly, neuroplasticity is the ability of the brain to change in response activity and experience. In this way, synaptic plasticity is a form of neuroplasticity that specifically relates to neural synapses.
Other than synaptic plasticity, other examples of neuroplasticity include:
• the formation of new neurons
• increase in brain size or brain mass
• changes to where particular functions are performed in the brain.
Synaptic plasticity mechanism
There are mechanisms of synaptic plasticity that involve changes being made to a synaptic connection between two neurons. These mechanisms are how neural synapses physically change in response to activity and experience. There are three mechanisms of synaptic plasticity that are explained in table 1, which are:
• sprouting • rerouting • pruning.
Sprouting
Sprouting is the ability of dendrites or axons to develop new extensions or branches. This increases the reach of the neuron and enables the formation of new synaptic connections.
Rerouting
Rerouting is the ability of a neuron that is connected to a damaged neuron to create an alternative synaptic connection with an undamaged neuron.
The neuron abandons its synaptic connection with the damaged neuron and forms a new synaptic connection with an undamaged neuron. The synaptic connection is reestablished via an alternative route, restoring brain functioning.
Pruning
Pruning is the elimination
of synaptic connections that
are not adequately activated. When neural synapses are
not used, they are removed or ‘pruned’. This is necessary to accommodate stronger and more essential synaptic connections, consequently enhancing the efficiency of brain functioning.
Things that may change synaptic connections
There are two types of experiences that may cause synaptic connections to change:
1. Synaptic connections may change in response to ageing and maturation, which is known as developmental plasticity.
2. Synaptic connections may change in response to brain trauma or injury, which is known as adaptive plasticity.
Pruning is a mechanism related to developmental plasticity. For example, despite occurring throughout one’s lifespan, pruning occurs most intensely during infancy and adolescence, as synaptic connections that are no longer adequately activated are eliminated. This enables the brain to form stronger and more essential synaptic connections, promoting brain development. In some areas of the brain, the density of synaptic connections of a two-year-old is more than double that of an adult (Huttenlocher, 1990).
In comparison, sprouting and rerouting are mechanisms related to adaptive plasticity. For example,
if a person sustains a brain injury that damages neurons, sprouting enables new synaptic connections to form. Furthermore, rerouting replaces ineffective synaptic connections with effective synaptic connections, enabling the formation of alternative synaptic pathways for effective neural transmission. This enables brain functioning to gradually recover following the injury.
You learnt about sprouting, rerouting, and pruning in the context of developmental plasticity and adaptive plasticity in Units 1&2 Psychology. However, this lesson focuses on these mechanisms of synaptic plasticity in the context of learning and memory.
Memory and learning
M: the process of encoding, storing, and retrieving information that has been previously encountered
L: the process of acquiring knowledge, skills, or behaviours through experience
Synaptic plasticity connection to learning and memory
Learning and memory are extremely important processes that constantly occur throughout your life. You learn new information and form new memories every day as you experience, engage, and interact with your environment. This knowledge that you acquire and possess helps determine who you are as a person. Given their fundamental nature, many scientists and psychologists have sought to understand the neural mechanisms that underlie the processes of learning and memory.
Synaptic plasticity is the fundamental mechanism of memory formation that leads to learning. When you form new memories, neural synapses in your brain physically change in response to these experiences. These changes to synaptic connections establish neural pathways that incorporate these memories and represent what has been learnt. These neural pathways that form during learning are referred to as memory traces, with each memory trace representing a different memory. Figure 4 presents an example of a memory trace being formed due to synaptic plasticity as a person learns how to ride a bike.
Forms of synaptic plasticity that underline learning and memory
There are two forms of synaptic plasticity that underlie learning and memory. These are:
• long-term potentiation
• long-term depression.
Long-term potentiation and long-term depression involve the long-lasting strengthening or weakening of synaptic connections in neural pathways in response to increased or decreased coactivation. These forms of synaptic plasticity work together to maintain an optimal number of synaptic connections, and therefore neural pathways, in the brain. This ensures that the brain can effectively encode learnt information and establish new memory traces, promoting learning and memory. You will learn about long-term potentiation and long-term depression in the following sections of the lesson.
Long term potentiation
Long-term potentiation is the long-lasting and experience-dependent strengthening of synaptic connections that are regularly coactivated. It is an experience-dependent form of synaptic plasticity because neural synapses are strengthened in response to frequent and repeated use during learning and memory.
During learning and memory, neurotransmitters are repeatedly released into the synaptic gap by the axon terminals of the presynaptic neuron and received by receptor sites on the dendrites of the postsynaptic neuron. This repeated coactivation of the presynaptic neuron and postsynaptic neuron, or this repeated high-intensity stimulation of the postsynaptic neuron, strengthens the synaptic connection between these neurons.
The increased strength of synaptic connections involves structural changes occurring to the neural synapse. These structural changes are the result of the increased release of neurotransmitters, specifically glutamate, into the neural synapse due to long-term potentiation. Structural changes include:
• increased number of receptor sites on the dendrites of the postsynaptic neuron.
• bushier dendrites on the postsynaptic neuron due to sprouting.
• increased number of synaptic connections between neurons due to sprouting.
Figure 5 presents the changes that occur to a neural synapse due to long-term potentiation, and the subsequent strengthening of a synaptic connection.
The increased strength of synaptic connections in a neural pathway makes postsynaptic neurons more receptive to neural signals from presynaptic neurons and consequently more readily activated. This increases the efficiency of synaptic transmission along the neural pathway. In this way, when this specific neural pathway is activated once again, neural signals are transmitted more rapidly and efficiently.
Lesson link
In lesson 2C Neurotransmitters and neuromodulators, you learnt that glutamate has an important role in synaptic plasticity, and therefore learning and memory. Specifically, you learnt that the excitatory effects of glutamate strengthen synaptic connections between neurons that are repeatedly coactivated. Expanding upon this, the release of glutamate into the neural synapse enables this neural synapse to undergo structural changes, such as an increased number of receptor sites. These structural changes strengthen the synaptic connection between the presynaptic neuron and the postsynaptic neuron, increasing the excitability of the postsynaptic neuron. In this way, glutamate has an important role in long-term potentiation.
Long term depression
Long-term depression is the long-lasting and experience-dependent weakening of synaptic connections between neurons that are not regularly coactivated. It is an experience-dependent form of synaptic plasticity because neural synapses are weakened in response to infrequent use.
If a neural pathway that has been previously established during learning and memory is no longer regularly activated, long-term depression weakens the synaptic connections in this neural pathway that is no longer necessary. The weakening of a neural synapse involves the infrequent release of neurotransmitters into the synaptic gap by the axon terminals of the presynaptic neuron. This low-intensity stimulation of the postsynaptic neuron weakens the synaptic connection between the presynaptic neuron and the postsynaptic neuron.
The decreased strength of synaptic connections involves structural changes occurring to the neural synapse. These structural changes are a result of the decreased release of neurotransmitters into the neural synapse due to long-term depression. Structural changes include:
• decreased number of receptor sites on the dendrites of the postsynaptic neuron. • decreased number of dendrites on the postsynaptic neuron due to pruning.
• decreased number of synaptic connections between neurons due to pruning.
The decreased strength of synaptic connections in a neural pathway makes postsynaptic neurons less receptive to neural signals from presynaptic neurons and consequently less readily activated. This decreases the efficiency of synaptic transmission along the neural pathway.
By weakening memory traces that are not regularly activated, long-term depression enables the brain to accommodate more necessary memory traces that represent more relevant information, and are consequently activated more frequently. In this way, long-term depression regulates the number of synaptic connections in the brain, ensuring an optimal number is present for learning and memory. Furthermore, it is important to understand that these weakened memory traces can be restrengthened through long-term potentiation if they are later reactivated.
Long term potentiation example
Playing the guitar becomes easier for Florence
4. Memory trace that represents the process of playing the guitar is formed and strengthened.
3. Synaptic connections are strengthened.
2. Synaptic connections involved in playing the guitar are repeatedly coactivated.
1. Florence repeatedly practises the guitar
