Prof Balgrove Flashcards
Gene manipulation: Monoamine oxidase type a knockout mice
- Gene codes for an enzyme in mitochondria of cells
- Enzyme breaks down dopamine, norepinephrine and serotonin
- Enzyme is not produced in knockout mice, who have increased aggression, but no change in motor activity or sexual activity
Hormone manipulation: Lab controlled experiments
- Testosterone gel can cause men to make intuitive decisions (n=2430
- 100 mg T in a topical gel spread onto upper arms and chest (or placebo)
- T administered @9am, tested from 2pm onwards
- Took the cognitive reflection test which estimates the capacity to override incorrect intuitive judgements with deliberate correct responses
- Testosterone administered reduced CRT scores
Prenatal development stages
Germinal period:
- 0-2 weeks
- Time from conception to implantation
Embryonic period:
- 2-8 weeks
- heartbeat begins
- Recognisable body periods
- Sexual differentiation begins
Fetal period:
- 9th week-birth
- Last 3 months
- Rapid growth of body and brain
Mechanisms of neural development
- Neural proliferation
- Neural differentiation
- Neural selection and migration
- Synaptogenesis and synaptic maintenance
What is synaptogenesis/
- Creation of large numbers of synapses
- Number of synapses increases 10 times in the first year
Infancy brain growth
- 75% of adult size
- Most growth is in size/complexity of neurons
- Not addition of new neurons
- Environment affects brain development
Infancy brain plasticity
2 years - double synaptic connections than adult brain
3 years - triple synaptic connections than adult brain
Childhood brain deevelopment
First 10 years - brain twice as active as adult’s
2nd decade - growth levels off and pruning begins apart from visual cortex (less synaptic connections)
What is pruning of synapses?
- Elimination of synapses
- Number of connections between neurons are reduced
- Begins around 1 years old
- Pruning complete at 10 years of age in visual cortex
- Continues in pre-frontal cortex
- Number of synapses in adulthood 40% less than in peak during childhood
Myelination of the brain
- Baby’s brain is relatively unmyelinated
- Myelination happens in 4th week of pregnancy
- at birth spinal chord and medulla is myelinated: support basic life functions so need to be quick
- During first year there is an increase in myelination of the basic sensory and motor systems
- Later on tge connections between cortical, subcortical areas and corticortical connection are myelinated
- Increase in white matter until teens
What is grey matter
- Neuron cell bodies
- Dendrites
- myelinated and non-myelinated axons
- Glial cells
- Synapses
- Capillaries
What is white matter
- Deeper in the brain
- Fewer cell bodies
- Mainly long-range myelinated axons
What is necrosis?
- Unplanned cell death
- Assassination
What is apoptosis?
- Planned cell death
- Suicide
What is neurodegeneration?
- Related to apoptosis and necrosis
- E.g. dementias
- Can be from physical trauma e.g. stroke
- Can also be when mental go untreated e.g. depression
Atrophy of the brain due to ageing
- Neurons die with age due to irreversible damage
- No neurotransmission
- Can continue to still be alive and increase in complexity
Structural changes: Dendritic length and complexity
- Age-related regression in dendritic branches and spines of pyramidal neurons of the prefrontal superior temporal and precentral cortices
- Dendrites can continue to increase in length with age (up until a certain point), but they lose complexity
Structural changes: White matter loss
- Age effects
Diffusion tensor imaging:
- Allows for in vivo examination of white matter microstructure
- Greater difference between young and old in anterior as opposed to posterior corpus collosum
- Greater difference in frontal white matteer than in temporal, parietal or occipital suggests anterior to posterior gradient of ageing
- Greatest reduction of blood flow and loss of neural tissue in frontal region
- Decline in memory
Functional changes: Different brain activity
Reductions of activity in some brain regions and networks:
- Old may have less ability to recruit
- Old may fail to engage adequate strategies
- Dedifferentiation
Increases of activity:
- Non-specific recruitment that may have nothing to do with task performance
- Reduced inhibition due to loss of white matter?
Mechanisms of cognitive ageing: Inhibitory deficit hypothesis
- Decreased ability to suppress irrelevant information that interferes with ongoing processes
Mechanisms of cognitive ageing: Compensation hypothesis
- Increased neural activity or recruitment of additional brain regions to counteract dysfunction
What are Circadian rhythms
- Based on biological rhythms
- Biological activities that rise and fall along a 24-hour cycle
- Triggered at appropriate times by brain structures that act as biological clocks e.g. suprachiasmatic nucleus
- Set by factors in the environment, particularly light
What are ultradian rhythms?
- Biological rhythms that are less than 24 hours
- E.g. sleep cycles are ultradian and last 90 mins
Role of endogenous pacemakers and exogenous zeitgebers
- Main pacemaker for endogenous circadian rhythms is the suprachiasmatic nucleus (SCN)
- Small group of cells located in the hypothalamus
- Called SCN because it lies just above the optic chiasm, therefore it can receive info directly from the eye and the rhythm can be rest by the amount of light entering the eye.
Sleep-Wake circuitry
- Suprachiasmatic nucleus is the master clock
- If damaged the circadian rhythm is abolished
- Retina –> SCN –> pineal gland
- Pineal gland produces melatonin
What is cortisol
- Increases under conditions of stress
- Increases endogenously near the end of each night
- Increase might be related to memory consolidation
How is temp related to a circadian rhythm
- Temp follows a circadian rhythm
- Influences alertness rhythm and falling asleep and waking up
What is a zeitgeber?
- A stimulus that resets the biological clock (e.g. bright light, exercise, temperature)
How do we set our biological clock?
- Without time cues resetting the the clock each day sleep occurs a little later each day
- Natural rhythm is a little above 24 hours
- Rhythm is controlled by internal zeitgebers
- If time cues remain absent, free-running occurs
- Sleep and wake periods change greatly with each successive day
What is melatonin?
- Hormone secreted by the pineal gland that controls sleep and wake cycles
- Secreted during darkness
- Signals night time
- Leads to drowsiness and decrease in body temperature
How do we assess the circadian pacemaker
- Onset of melatonin secretion under dim light condition s( dim light melatonin onset or DLMO) is the single most accurate marker for assessing the circadian pacemaker
- DLMO is useful for determining whether an individual is entrained (synchronised) to a 24 hour light/dark cycle or is in a free-running state
- DLMO is also useful for assessing phase delays or advances of rhythms in entrained individuals
Atkinson and Shiffrin’s multi-store memory model (1968)
- Memory is a series of information that moves through different stores
- Info is detected by sensory organs and if attended to is moved to short term memory
- Info is moved to long-term memory if rehearsed
- If not rehearsed the info is lost due to decay or displacement
- Simplistic model
What is sensory memory?
- Info not immediately attended to is held briefly in a temporary ‘buffer’, making it possible to attend too some of it a bit later
What is sensory memory for vision called?
Iconic memory
What is sensory memory for audition called?
Echoic memory
What is sensory memory for touch called?
Haptic memory
Iconic memory: Capacity
That of the visual system
Iconic memory: Duration
0.3 to 1.0 seconds
Iconic memory: Processing
No additional beyond raw perceptual processing
Echoic memory: Capacity
Unknown
Echoic memory: Duration
3-4 seconds
Echoic memory: Processing
None additional beyond raw perceptual processing
Short-term memory: Capacity
7 plus or minus 2 ‘chunks’ (of information) of information
Short-term memory: Duration
18-20 seconds (average)
Short-term memory: Processing
- To hold info in STM it is often encoded verbally
- Strategies such as visualisation may also be used
- Strategies make it possible to ‘rehearse’ the info
What is a ‘chunk’ of information?
Single letters such as “GJK” are each a chunk, but recognisable words like “CAR” are a single chunk
How can information be held in short-term memory?
- Maintenance rehearsal
- Repeating the information silently or aloud so that it is recalled immediately when needed
- Does not add meaning to info
- Unlikely to be remembered when it is no longer being repeated
How is information in long-term memory represented?
- Represented as changes in brain wiring
- In the ‘conductivity’ of existing synapses, and in the formation of new synapses and destruction of old ones
Long-term memory: Capacity
Virtually unlimited
Long-term memory: Duration
Up to a lifetime