Mechanism of memory formation

Glutamate (Glu)

The main excretory neurotransmitter for information transmission throughout the brain. This means that glutamate enhances information transmission by making postsynaptic neurons more likely to fire. In memory formation, glutamate plays a crucial roles in the structural changes that occur, particularly in the growth and strengthening of the synaptic connections between neurons within a memory circuit.

Neurotransmitter

A chemical substance produces by a neuron that carries a message to other neurons or cells in muscles and organs. Generally, a specific type of neurotransmitters have an excitatory effect and consequently stimulate or activate postsynaptic neurons. Other neurotransmitters have an inhibitory effect and block or prevent postsynaptic neurons from firing.

Neurodegenerative disease

A disorder characterised by the progressively decline in the structure, activity and function of brain tissue. Essentially, neurons within the brain tissue ('neuro') gradually become damaged or deteriorate ('degenerate') and lose their function.

Hippocampus

A medial temporal lobe structure that is crucial for long-term structure that is crucial for long - term memory formation. The hippocampus has a crucial role in forming or encoding new declarative explicit memories (semantic and episodic) but not directly in forming or retrieving memories. Damage to the hippocampus does not seem to seriously affect atorage or retrieval of procedural memories, but formation and retrieval of declarative memories are affected. STM (working memory) is different from LTM and that the hippocampus is not involved in short - term storage The hippocampus is widely described as our 'memory formation area', the place where our brain temporarily holds and processes components of the information to be rememebered.

Neuron

A nerve cell that is specialised to receive, process and/or transmit information to other cells within the body. Neurons communicate with each other, and muscles and glands.

Korsakoff's syndrome

A neurodegenerative disease involving severe memory disorders associated with damage to brain structures and areas involved with memory; occurs mainly in individuals who are long - term alcoholics.

Dopamine (DA)

A neurotransmitter believes to be involved in learning (including reward-based learning), memory, schizophrenia, pleasure, motivation, emotional arousal and the control of voluntary movements.

Acetylcholine (ACh)

A neurotransmitter involved in learning, memory, attention, sleeping, dreaming and motor control, is found to be at an abnormally low level in the brains of people suffering from Alzheimer's disease, a type of dementia that is characterised by the gradual deterioration of memory, resulting in very serious memory deficites.

Axon

A single, tube-like extension that carries neural information away from the soma towards other neurons. Information always travels in one direction through a neuron. It is received by dendrites, passes through the soma and exits from the axon.

Amygdala

A small structure (about 1.5 centimetres long) located near to and interconnected with the hippocampus in the medial temporal lobe. We have an amygdala in each hemisphere. The amygdala plays crucial roles in processing and regulating emotional reactions, particularly strong emotions such as fear and anger. For example, your amygdala enables you to detect possible danger when approached by a snarling dog and to recognise fearful expressions in others from their facial expressions before they even say a word. It is involved in the encoding and storage of memories that have a significant emotional component. People with amygdala damage show reduced ability to acquire conditioned (learned) emotional responses and to interpret or express a variety of emotions. One reason is that the amygdala attaches emotional significance to this type of experience and stimulates the hippocampus to encode and store the relevant emotional details.

Norepinephrine (NE)

A substance that occurs as both neurotransmitter and 'stress hormone'; as a stress hormone it is secreted from the adrenal medulla during times of hightened emotional arousal; as a neurotransmitter, it influences formation of emotional memories and has roles in attention, alertness, states of arousal. It effects memory by influencing the activities of the amygdaalaand hippocampus, two adjacent brain structures with crucial roles in memory formation. It is believes that level of emotional arousal during the time of encoding influences the strength of the long-term memory of that event. Structural change essentially involves the growth and strengthening of synaptic connections. When a new memory is being formed,the numberof dendrites spines increases and the dendrites therefore become 'bushier'.

Alzheimer's disease

A type of dementia characterised by the gradual widespread degeneration of brain neurons, causing memory loss, a decline in cognitive and social skills, and personality changes. There is no single or simple diagnostic test for Alzheimer's disease (or any other dementia). Both the loss of past memories (retrograde amnesia) and difficulties in retaining newly learned information (anterograde amnesia) distinguish Alzheimer's disease from many other disorders involving amnesia. Both declarative and procedural memories are also impaired, gradually eroding as the disease progresses. Characterised by abnormally high levels of protein called amyloid, not normally found in the brain, neurotoxic, can't be metabolised by the brain, resulting in plaques, dense deposits of the protein and other materials in and around the neuron; hippocampus and related areas of midbrain most affected (up to 3/4 neurons lost). Also reduced levels of neurotransmitters acetylcholine, used by clusters of neurons enable transmission of messages, especially areas associated with memory and learning.

Flashbulb memory

A vivid and highly detailed memory of the circumstances in which someone first learns of a very surprising, significant or emotionally arousing event.

Brain trauma

An 'unbrella' term that refers to any brain damage that impairs, or interferes with, the normal functioning of the brain, either temporarily or permanetly.

Dementia

An unbrella term used to describe a variety of symptoms of a large group of neurodegenerative disease and other disorders that cause a progressive decline in mental functioning, behaviour and the ability to perform everyday tasks. One of the main symptoms of dementia is memory loss. A person with dementia may lose their sunglasses and then forget what they're used for. Other common symptoms include a decline in mental abilities such as reasoning, problem - solving and decision making, as well as behaviour and personally changes such as becoming assertive, more withdrawn or less flexible, losing interest in things that have mattered perviously becoming absent-minded or repeating the same story or question. Dementia is often described as progressing in stages, with memory loss typically being one of the first signs of its onset. Memory loss is persistent rather than occasional and worsens is the dementia progresses.

Research on consolidation theory

Evidence in support of consolidation come from studies of people who have experienced brain trauma resulting in memory loss; for example, after being knocked unconscious as a result of an accident, after acquiring certain diseases affectign the brain (such as encephalitis) or after receiving electroconvulsive therapy (ECT) as part of the treatment used in severe cases of depression. These people are frequently unable to report any memory of the events immediatly before the accident or treatment, and in many instances they cannot remember anything that occurred during a period of about 30 minutes.

Memory decline over the lifespan

If a decline in memory is experienced through ageing, effects are more likely to be experienced in short - term (working) memory and explicit declarative memories (mainly episodic).

Reconsolidation

It has been proposed that after a memory is activated and retrieved from LTM, it needs to be consolidated again in order to be stored back in LTM.

Anterograde amnesia

Loss of memory only for information or events occurring after the trauma that causes amnesia. People with anterograde amnesia lose the ability to form or store new memories. They can talk about the things that happened before the onset of their amnesia, but they cannot remember what has happened since. They have difficulty learning new information such as the names of people they subsequently meet.

Retrograde amnesia

Loss of memory only for information or events occurring before the trauma that caused the amnesia. The memory loss may extend back a few moments, days, weeks or sometimes years. Retrograde amnesias are usually of a temporary nature and are often caused by a blow to the head.

Amnesia

Loss of memory, either partial or complete, temporary or permanent.

Changes in function and structure of neurons

Research findings indicate that significant changes occur in the function and structure of brain neurons involved in memory formation. These changes do not occur independently of each other and both are required to process newly learned information for memory and enable long-term storage. Change in the function of neurons is evident in: an increase in the amount of neurotransmitter produced and released by the presynaptic neurons, and/or greater effects of neurotransmitter at its receptor sites on the postsynaptic neurons.

Effects of ageing on long - term memory

Some long - term types are more affected, especially episodic. Older people take longer to learn new information and skills (stored as semantic and procedural memories), new information is not encoded as precisely or with as much detail as young people. Speed and fluency of semantic memory retrieval can also decline. explanations for the memory changes that tend to occur as people age are lack of motivation, less self - confidence, measure of retention. The slowing of central nervous system functioning , cognitive slowing as frontal lobes reduce size (normal part of ageing), thought responsible for many cognitive changes as people age, including memory decline, difficulties in maintaining attention.

Soma

The cell body that integrates the neural information received from dendrites and sends it to the axon. It contains the nucleus (which houses the cell's genetic code), organelles (other structures) and cytoplasm (liquid gel) that maintain the neurons and keep it functioning.

Effects of ageing on short - term (working) memory

The impact of age on STM depends on the nature of the task. If the task is relatively simple, such as remembering a list of words, STM is not affected by age. If the task is more complicated, requiring simultaneously storage and manipulation of information in working memory, or when attention must be divided between tasks, then age - related factors may impact on effective STM functioning. Beyond 60 years of age, the activation of areas of the frontal lobes of the brain believed to be involved in STM decreases. The nervous system of older people are less efficient at receiving and transmitting information, and therefore the rate or speed at which information is processed in short - term (working) memory is slower.

Long-term potential (LPT)

The long - lasting strengthening of the synaptic connections of neurons, resulting in the enhanced or more effective functioning of the neurons whenever they are activated. The effect of LTP is to improve the ability of two postsynaptic neuron - to communicate with one another at the synapse. LTP strengthens synaptic connections in a way that enables the postsynaptic neurons to be more easily activated. The postsynaptic neurons become more and more responsive to the presynaptic neurons as a consequence of repeated stimulation. The more you use the information being remembered, the more the LTP process strengthens the memory circuit, making it easier to retrieve.

Consolidation theory

The proposal that structural changes occur at the neural level after learning, and these require time to transfer from short-term to long-term memory and become stable and enduring. Consolidation theory also proposes that if memory formation is didrupted during consolidation, information may not be embedded in LTM and may therefore be lost. If disruption does not occur, the information will be permanently stored, at least until it is retrieve. Information being remembered is vulnerable to disruption forat least 30 minutes, although consolidation of memories can proceed for as long as several years in people

Synapse

The site of communication between adjacent neurons.

Dedrites

The thin extensions of a neuron that receive information from other neurons and transmit it to the soma.

Synaptic gap

The tiny space between the axon terminal of a presynaptic neuron and the dendrite of a postsynaptic neuron.