Formation and consolidation of memory Flashcards
The Role of Neurons in Memory Formation - neurons, neurotransmitters, synaptic vesicles
§ Neuron: nerve cells that receive, process and transmit information; responsible for communication within the body.
§ Neurotransmitter: chemicals that help the communication across nerve synapses.
§ Synaptic vesicles: small sacs that contain neurotransmitters and are located within the terminal buttons.
When a neuron fires, these sacs release their neurotransmitters into the synaptic cleft for the receptor sites of the dendrites of other neurons.
Structure of neurons
§ Dendrites: its main purpose is to receive information from other neurons (looks tree-like).
§ Soma: the cell body that controls the metabolism and maintenance of the cell; largest part of neuron.
§ Axon: a nerve fibre that carries information away from the soma towards cells which communicate with the neuron (the part of a neuron along which the electrochemical nerve impulse is transmitted).
Communication between neurons
m§ Synapse: junction between two neurons where the terminal buttons of the presynaptic neuron comes into close proximity with the receptor sites on the dendrites of a postsynaptic neuron.
§ Synaptic transmission: the process of the communication between neurons whereby neurotransmitters are sent from the presynaptic neuron to the synapse shared with the postsynaptic neuron (the activity of this neuron is affected indicating that neurons communicate via a chemical process).
§ Dendrites receive neurotransmitters from the synapse → Information is passed in the form of electrical impulses through the soma along the axon → Neurotransmitters are sent from the terminal buttons to the receptor sites on the dendrites of another neuron via the synapse shared between the two neurons.
The Work of Kandel (Neurons and Memory)
§ Eric Richard Kandel researched the Aplysia (sea hare) in studies of memory and learning.
§ Aplysia are ideal to study as they have approx. 20 000 large neurons (millimetre wide and visible to the human eye) whilst humans have billions.
§ Kandel studied the sensory and motor neurons by stimulating the siphon (inserting microelectrodes into the neurons, touching the tail with a glass rod, etc.) which trained them for simple reflex tasks (e.g. withdrawal of its gill).
§ After repeated stimulation of the siphon with any subsequent danger to the gill, the Aplysia began to withdraw its gill less and less (this process is called habituation [reduction of response when exposed to repeated stimulation] suggesting that the Aplysia had developed a memory that could last for days or even weeks).
Work of Kendel - functional and structural changes
o Increased levels of neurotransmitter produced and released by the neurons.
o The number of branches of dendrites increases resulting in the strengthening of the synapse between the neurons.
o New synaptic connections were formed making it easier for neurotransmitters to be transmitted from the pre-synaptic neuron and post-synaptic neuron.
o STM: only involves increased levels of neurotransmitter.
Long-term Potentiation: the long-lasting strengthening of synaptic connections of neurons resulting in the enhanced functioning of neurons. It refers to when neurons in a circuit are activated through use, allowing the flow of information in the circuit to become easier
Role of hippocampus in memory formation
n- Located in the medial temporal lobe near the amygdala, and is connected directly to the frontal lobe, amygdala and thalamus; it is a finger-sized curved structure and is similar to a seahorse
- The hippocampus is critical for the act of consolidation (permanent storage of a memory); it is not the memory itself, it is the mechanism that allows us to make those memories solid.
- Functioning of the hippocampus can be disrupted by psychological factors (stress, anxiety, and depression), brain trauma (head injury), health-related conditions (Alzheimer’s disease) and various other conditions, ultimately causing dementia. .
- Hippocampus shows a pattern of rapid and then gradual decline of neural pathways as we age.
- Helps with formation of explicit (long-term declarative) memories and difficult tasks which draw upon declarative memory (e.g. learning to spell unfamiliar words).
- Helps consolidate explicit memories (long-term declarative memories); transfer STM to LTM.
o Acts as a memory formation area.
- Helps transfer new memory for storage.
o Hippocampus transfers explicit (declarative) memory to relevant parts of the brain for permanent storage.
o Occurs during less busy times (e.g. during slow-wave sleep).
- Due to its close relationship with the amygdala, the hippocampus plays a vital role in linking emotions to memories and establishing the background/context for each new memory (e.g. location situation etc.)
Role of amygdala in memory formation
- An almond-shaped structure located in the medial temporal lobe, almost directly behind the temple and beneath the cortex of the temporal lobe.
- Helps with formation of emotional content in memories.
o Has special role in the memory for emotions shown on faces.
- Helps with formation of implicit memories including classical conditioning.
o Particularly central in emotional and aggression implicit learning.
- Helps regulate emotions (e.g. fear, aggression).
o These regulated emotions enhance the memorability of an event which is stated as declarative memory.
o For declarative memory to have emotional content, the amygdala has a role in activating the hippocampus and thus enhancing the consolidation of the declarative memory.
Consolidation of memory
Consolidation: a process in which new memories are transferred into LTM.
§ Consolidation theory: describes the way in which memory is processed and stored through neuropsychological processes.
§ It is an ongoing process; when new information is associated with information already stored in LTM, this already stored information is retrieved, ultimately strengthening the neural connections.
§ Retrieved memory must be reconsolidated (memory is vulnerable to disruption during this time), as this allows existing memories to be refined, corrected or modified.
- for memory to be permamnently stored we need 3 conditions: physical change, no disruption and time
Consolidation theory condition - physical change
- LTM happens through growth of dendrites
- LTM are stored in the same areas that were originally involved in processing of sensory input
Consolidation of memory condition - no disruption
- there is a period where memories are susceptible to alteration by new relevant info
- process can be disrupted by injury, amount of attention paid to info and arousal (anxitet. alterness)
- information can be altered or completely lost
- every time we retrieve a memory it is again subject to alteration
Consolidation theory condition - time
- neural connections that have had more time to strengthen are less likely to be disrupted
- evidence to suggest that it can take several years before memories are no longer vulnerable to disruption or change
