Emotional Learning - Limbic System and Goal Directed Behaviour

Normal, age-related cognitive decline

• Many, but not all, cognitive function decline with age

Spatial memory is one of these

• Spatial navigation task - finding objects in a maze (museum)

How does the hippocampus age

Does not appear to get smaller

• Although evidence is mixed

Retains the same number of neurons

Functional connectivity is impaired

LTP does not last as long, and is not as strong

Impaired retrieval of spatial maps

What structure does this image show?

Ventricles

Ventricular System

• Ventricles filled with cerebrospinal fluid (CSF)

Produced by ependymal cells which line ventricles

• Shock absorber

• Nutrient supply

• Waste flush

approximately 125 mL at any one time and approx., 500 mL produced per day.

Common signs of Alzheimer’s Disease

• Memory loss

• Poor judgement leading to bad decisions

• Loss of spontaneity and sense of initiative

• Repeating questions

• Trouble handling money and handling bills

• Wandering and getting lost

• Losing things or misplacing them in odd places

Alzheimer’s Disease

Loss of neurons in various brain regions

• Particularly the hippocampus, and cerebral cortex

Alzheimer’s: Cause and Treatment

Accumulation of misfolded proteins in certain brain regions

• Cholinergic nuclei, hippocampus and frontal cortex

• Beta-amyloid (amyloid plaques)

• Tau (neurofibrillary tangles)

• Accumulation is toxic - mechanisms unclear

• Some genetic risk

Memantine - slows excitotoxicity

Acetylcholinesterase inhibitors - mitigates loss of Ach

Brain cholinergic system

Key nuclei:

• Basal forebrain

• Brainstem tegmentum

Project across the brain

• Cortex

• Hippocampus

• Thalamus

Neuromodulatory functions:

• Memory

• cognition

• arousal

What structure is shown in the image?

The Limbic System

Components of the limbic system

• Hippocampus

• Amygdala

• Hypothalamus

• Fornix

• Thalamus

• Mamillary Bodies

• (Cingulate gyrus)

• (Orbitofrontal cortex)

What structure is shown by the image?

The Amygdala

What does the amygdala do?

Salience, vigilance

• Amygdalofugal pathway to/from the thalamus

Stimulation results in fear + aggression

Recognising fear in other people

Learning about cues

• best understood in fear/danger

• (more than just fear)

Amygdala - Clinical

Anxiety disorders

• Hyperactive

• Hypervigilance (PTSD)

Bilateral lesions - Kluwer-Bucy Syndrome (very rare)

• Reduced fear/docility

• Visual agnosia

• Pica

• Hyperorality and hypersexuality

• Normally caused by surgical complications or HSV

What structure is represented by this image?

The Fornix

What does the fornix do?

• Hippocampal output

• Connect left and right hemispheres

• Helps the hippocampus function

• Damage is rare

  Looks like hippocampal damage
  Anterograde amnesia

What structure is represented by this image?

Mammillary Bodies

Korsakoff’s Syndrome

Irreversible damage to the medial thymus and mammillary bodies

Most common cause is vitamin B1 deficiency

• chronic alcoholism

• Unable to absorb vitamin B1 (thiamine)

• Direct toxicity of alcohol

Anterograde and retrograde amnesia

Confabulation

Little to no recovery

precise role for mammillary bodies in learning and memory

Which structure is represented by this image?

The Hypothalamus

What does the Hypothalamus do?

Start of a physiological output from the brain

• Hypothalamus-Pituitary Adrenal (HPA axis)

• Hormonal outputs - especially stress hormones

• Also wired into the brainstem, autonomic system

• Thermoregulation

• Hunger, thirst etc.

• The rest of the limbic system is trying to persuade the hypothalamus to do what the limbic system wants

Olfactory Pathways

Don’t really go through the thalamus

• Connect to limbic/memory systems - is a very powerful memory cue

Pavlovian (Classical) Conditioning

Hungry dog → Bell → Dog food

Hungry dog salivating (unconditioned response) → dog food (unconditioned stimulus)

Amygdala and classical conditioning

Amygdala is important for learning conditioned clues

• Best understood role is learning about danger and fear

• Probably important for all cues, not just fear-inducing

• Learning about danger is really important

Extinction of Classical Conditioning

Learning about cues in our environment, that predict serious danger, is very important, and normal

This learning is very strong

Learning is when those cues are not associated with danger takes time

This ‘forgetting’ is new learning

• The old memory is not ‘lost’

• New memory is ‘stronger’, more salient

Post-traumatic stress disorder

Associated with significant trauma

• risk of death or serious harm

Sufferer ‘re-experiences’ trauma

• triggered by reminders, or reminders of reminders

• conditioned stimuli

Is normal for a few weeks, becomes PTSD if it persists

• Hyperarousal, hypervigilance (‘on edge’)

• Avoidance

• Emotional numbing

What is different in PTSD?

• Functional neuroimaging

Amygdala

• Hyperactive

Prefrontal cortex

• Hypoactive

• Smaller

Hippocampus

• Smaller?

• Impaired function

Patients exhibit behavioural signs of all of these

PTSD causes and treatments

Associated with significant trauma

Can be treated by Cognitive Behaviour Therapy

• Exposure therapy using triggers

• New learning takes time

Pharmaceutical treatment also common (SSRIs)

• Life mood

• Reduce physiological expression of anxiety

Sufferer often knows something is wrong

• Prefrontal cortex