Hippocampus + Amygdala

Hippocampus

A part of the temporal lobe which is crucial for LTM memory formation of declarative memories. And spatial memory—the physical location of objects in space.

Patient HM - 1953

• Bike accident at age 7 left him with epilepsy

• by age 27 he was having serious weekly seizures

• Scientist Schoville decided to remove his hippocampus thinking it was causing the epilepsy

• could complete physical skills (procedural) but not remember facts, figures or events as they were store in the declarative memory and rely on the hippocampus.

AMYGDALA

• A small structure located next to and interconnected with the hippocampus in the temporal lobe.

• Involved in encoding and storing memories that have an emotional component.

• The amygdala attaches emotional significance to events that provide strong emotional reactions (e.g. wedding day, car accident) and stimulates the hippocampus to encode and store the relevant emotional details.

• Because of this the amygdala has a role in forming explicit declarative memories (episodic memory).

• There are two types of specific memories associate with the amygdala.

Two types of specific memories associated with the amygdala

• Flashbulb memories

• Conditioned fear response

Flashbulb memories

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

• e.g. death of a loved one — people remember where they were, what they were wearing, who they were with at the time.

Causes of flashbulb memories

At the time of the emotional reaction increased amounts of norepinephrine (released consistently to keep you awake) is released. This provides a signal to the hippocampus from the amygdala to tag the memory of the event with important emotional details and strengthen its long term storage.

Conditioned fear responses

• The amygdala attaches significance to a neutral stimuli event when it is associated with fear. (e.g. bird attack)

• There is never any intentional recall of the event and the memory of the response is only observed through our reactions.

Cerebellum

Plays a large role in creation of implicit (procedural) memories e.g. riding a bike

Causes of memory loss

1. Neurodegenerative diseases - Alzheimer’s disease

2. Brain trauma - Chronic Traumatic Encephalopathy (CTE)

3. Drug induced - Wernicke-Korsakoff Syndrome (WKS)

Neurodegenerative diseases

• Dementia (a disorder affecting higher mental functions

• Alzheimer’s disease (a type of dementia. Gradual and severe memory loss, confusion, impaired attention, disordered thinking and depression. It affects the hippocampus (declarative memories (episodic)) and prefrontal cortex (personality, problem solving, decision making skills). It involves anterograde and retrograde amnesia.)

• Progression of Alzheimer’s disease: Remembering events from your day → forgetting names → difficulty finding correct words → repeating stories → failing to recognize family and friends

Structures effected by neurodegenerative diseases

• Amyloid plaques - proteins that form amount axon terminals*

• Neurofibrillary tangles - abnormal build-up of protein inside neurons*

• Low levels of neurotransmitters - acetylcholine*

• Hippocampus - as the cells die the brain will atrophy and the hippocampus will become isolated

• *all of these lead to death of brain cells

Wernicke Korsakoff’s Syndrome

• A form of brain deterioration caused by chronic alcoholism and a deficiency in the vitamin Thiamine (B1)

• Wernicke’s syndrome and Korsakoff’s syndrome are distinct but overlapping disorders.

• When left untreated it will progress to Korsakoff’s syndrome.

• When one syndrome progressed to the other it is now known as Wernicke’s Korsakoff’s Syndrome.

Wernicke’s syndrome is characterized by:

• inability to control voluntary movement

• vision problems (occipital lobe)

Korsakoff’s syndrome is characterized by:

• memory impairment

• making up inaccurate stories about events

• experiencing hallucinations

causes of WKS

1. the alcoholic consumes most of their calories in alcohol and suffers malnutrition

2. The alcohol reduces the amount of absorption and thiamine in the stomach.

Chronic Traumatic Encephalopathy (CTE)

A progressive and fatal brain disease associated with repeated traumatic brain injuries.

Structures effected by CTE

the protein in neurons misfolds and malfunctions causing other proteins to misfold which spreads throughout the brain, killing brain cells and causing the brain to waste away.

Symptoms of CTE

• Aggression (both)

• Mood swings (Emotion)

• Depression (Emotions)

• Paranoia (Both)

• Anxiety (Both)

• Short-term memory issues (Behaviour)

• Dementia (Both)

• Sleep problems (Both)

• Confusion (Both)

• Slurred speech (Both)