Brain Maturation and Ageing

How does the brain mature in the neonate?

The degree of myelination increases, the number of dendrites and synapses increase.

How does cerebral blood flow change throughout life

Low at birth

Higher than adult during childhood

What is developmental learning?

The fact that the brain depends on the external environment of the animal and experiences to alter its structure and function.

What cellular processes occur during maturation of the brain?

• Mitosis & apoptosis of neurones

• Development & pruning of synapses

• Increased myelination

• Strengthening of connectivity.

What are sensitive periods?

Certain times of development in which the brain is more susceptible to developmental learning.

What are critical periods?

When certain pathways in the brain require certain types of experience to occur before a certain time in order to develop e.g. if social behaviour is not learnt within this time, it will never be learnt

What is imprinting?

The process by which certain animals form attachments during a critical period very early in life.

What occurs to the brain during adolescence?

Brain undergoes significant synaptic pruning, reduction and refinement of grey matter, increased myelination and enhanced connectivity.

Describe the brain just after sexual maturity

Sensory and motor cortices are fully developed. The rest of the cerebral function develops in a region-specific manner.

(In humans, the association cortex and impulse control develop much later than those regarding emotion and reward-based behaviour).

What does learning occur as a consequence of and what does it require?

Occurs as a consequence of experience

Requires motivation & attention

Relies on ability to form memories

How is learning displayed?

As a change in behaviour

What are the two types of memory?

Declarative and procedural.

What is declarative memory?

Memory of facts and events.

i.e. knowing that something is the case

What is procedural memory?

Motor skills resulting from repetitive training.

i.e. knowing how to do something

What are the two types of memory storage?

Short term memory & long term memory

Short-term memory vs long-term memory

Short term:

• Seconds to hours

• Electrical memory trace only

• Limited storage capacity

Long term:

• Days to years

• Physical memory trace

• Infinite capacity

• Constantly refined in light of new related short-term memories

• Can take longer to retrieve info

Compare how short-term memories vs long-term memories are forgotten

• Short term must be rehearsed to be consolidated as long term (easily forgotten if not rehearsed)

• Forgetting long-term memories often just temporary

How is a short term memory consolidated to long term memory?

Needs memory traces which are neuronal changes whereby new synapses (and new dendrites) form that retain the memory in electrical pathways.

i.e. animals with greater learning opportunites have longer, more branched dendrites —> more potential for synaptic connecctions

What structures in the brain are involved in memory and how?

• The hippocampus and other limbic structures, which are important for STM formation and consolidation to LTM

• The cerebellum and relevant cerebral cortical regions —> important for storage of procedural "how to" memories.

What are the two types of non-associative learning?

Habituation and sensitisation.

What is habituation?

Natural response to a stimulus reduces over time (e.g. startled animal to a loud noise will reduce if the loud noise is repeated with no consequences).

What is sensitisation?

The natural response to a stimulus increases over time (e.g. an animal becomes more and more distressed by fireworks over time).

Is non-associative learning forming short term or long term memories?

Short term.

Is associative learning forming short term or long term memories?

Long term.

What are the main types of associative learning?

Operant and classical conditioning.

What is operant conditioning?

Where an animal learns to associate a behaviour with an outcome.

(e.g. a cat meowing then getting fed)

What is classical conditioning?

Where an animal learns to associate two stimuli (conditioned & unconditioned) that produces a desirable behaviour.

(e.g. Clicker training —> conitioned stimuli = clicker, unconditioned stimuli = treat)

What needs to be done for classical training to be effective in e.g. clicker training?

• Replace the treat with a click and stop giving the treat gradually, but keep giving treat as an incentive if dog begins to learn no longer getting the treat

• Incentive should be given promptly (motivation)

What is incentive learning?

The animal must be motivated in order to learn.

What is required for associative learning to work?

Incentive, motivation.

What memories can be completely forgotten?

Short term memories (if unrehearsed)

Why are long term memories sometimes apparently lost?

• If the conditioned stimulus is presented with no unconditioned stimulus

• Context = testing under different conditions may yield apparent loss

• Conflicting information = e.g. recalling a dog in an angry voice

correcting the error will usually reinstate the behaviour i.e. not forgotten at all

What negative things can occur to the brain due to ageing?

Increased likelihood of and susceptibility to certain disease processes e.g. immune impairment, degenerative processes (BUT AGEING IS NOT A DISEASE)

What is cognitive dysfunction syndrome (CDS)?

Loss of the ability to think, process information and manipulate knowledge through learning, memory and planning.

Which type of animals is cognitive dysfunction syndrome more obvious in?

Highly trained performance / working animals

recognised by changes in behaviour BUT loss of learning & memory starts occurring long before visual behaviour changes

What are the main neuropathological changes of CDS (and Alzheimer's disease)?

• Brain atrophy (wider sulci, narrower gyri)

• Senile plaques

• Oxidative damage

• Neurofibrillary tangles

What occurs during brain atrophy in CCD?

• Widening of the sulci

• Thinning of the gyri

• Dilation of the ventricles

• Reduced neuronal density

What occurs during senile plaque formation in CDS?

• Abnormal accumulation of protein plaques (esp. beta-amyloid protein) within and around neurones impairs synaptic function

• Deposition of these plaques often occurs in grey matter of the prefrontal cortex, temporal cortex and hippocampus, & blood vessels supplying brain

What happens when the brain experiences oxidative damage in CCD?

Free radicals cause damage to proteins, lipids, and nucleotides in neurones —> affect their function.

What happens when the brain in a CDS case has neurofibrillary tangles?

Phosphorylation of tau protein causes disintegration of neuronal microtubules —> unbound tau proteins forms clumps

What is the common presenting sign of CCD?

Aggression in a previously non aggressive animal.

What are the main clinical signs of CDS?

Disorientation

Interaction and social behaviour changes (esp. aggression)

Sleep-wake cycle alterations

House soiling

Activity level changes

(DISHA)

Clinical signs of CDS reflect loss of what?

Learning

Imbalances in which two neurotransmitters are particularly associated with the aggression sometimes seen in CDS?

Acetylcholine & serotonin