NA and arousal: L18 Flashcards
Noradrenaline Breakdown
- breakdown enzyme = monoamine oxidase (MAO)
2. one additional synthesis step in the adrenal gland results in the hormone adrenaline
Noradrenaline
- produced in
- controls
- Locus coeruleus (LC)
- sympathetic nervous system (flight or fight)
- arousal/vigilance
- anxiety
- exploitation vs exploration
- reward/addiction
- memory consolidation
- sympathetic nervous system (flight or fight)
Locus Ceruleus (LC)
- highest rates rapidly follow
- silent during
- a transient noxious or extremely positive stimulus/event (lots of NA released)
- rapid eye movements (REM) sleep (little NA released)
high LC/NA activity
- 4 f’s
- state of hyperarousal adapted for
- flight, fight, freeze, fornicate
2. evolutionary important situation where individual or sexual fitness is involved
high LC/NA activity =
- stress
- anxiety
- panic attacks
- experienced when LC/NA activity is sustained due to environmental factors
- excessive, uncontrolled and irrational worry (symptoms for 6 months needed for diagnosis)
- reflect spikes of LC/NA activity triggered by:
- random events
- internal thoughts
- PTSD (learnt associations)
Stress & arousal
- stress response involves
- optimal performance requires
- intricate interactions between the brain and body
2. balance. Function is impaired with too little or too much stress (inverted U)
NA function beyond arousal & 4 F’s
- moderate levels of LC activity =
- adaptive behaviour
- noradrenaline acts to consolidate decisions
- represents a tradeoff between exploiting known sources of reward and exploring the environment for alternative sources of reward (e.g. food, sex)
Exploitation vs exploration
- what is bad?
- what is needed?
- -> indecision, inaction or constant changing of decisions
- > inflexible, repetitive behaviour - balance
NA & behavioural selection
-> pattern of behaviour
- competition: behaviour A vs behaviour B
- burst of NA release “tips the balance” in favour of the winning behaviour (increases strength of activating and inhibiting signals)
- competition resolved, selection of behaviour completed
- decision is consolidated & executed
LC neurons & behavioural selection
- pattern on graph (firing rate & time)
- neurons in the LC fire when
- after they fire
- target -> response executed (increased firing rate) -> neurons inhibited after burst (low firing rate)
- a behaviour response is selected and executed
- neurons are inhibited allowing the selected behaviour to be exploited
Na & behavioural selection
- the more important/salient/arousing =
- this pattern
- one of the alternatives = the bigger the burst of LC neurons & more NA released
- (1) competition in high arousal context (preditor involved)
(2) LARGER burst of NA release “tips the balance” in favour of the winner with more strength
(3) competition resolves, selection complete
(4) decision is consolidated/executed
- > future decisions are inhibited for LONGER
LC neurons & NA during high arousal
- the larger the response of neurons in the LC =
- in highly arousing situations the chosen behaviour dominates
- the more NA released & the longer the following period of inhibition
- more for longer, “distracting” alternatives are inhibited
LC neurons & NA during low arousal
- in the absence of recent decisions or arousing events
- increased NA promotes
- how it looks on the chart
- the baseline levels of firing increase and more NA is released throughout the brain
- a switch to a new decision, promoting “exploration” of alternative behaviours
- no burst of firing -> neurons start firing more & more adding “noise/variability” to the decision
LC-NA & performance
- low levels of LC activity & NA release =
- high levels of LC activity & NA release =
- optimal performance =
- tired, vague & poor performance
- restless, stressed & poor performance
- moderate activity with large intermittent bursts
NA & the pupil
- pupil dilation reflects
- pupil constriction induced by light is caused by
- activity of LC & active amount of NA in the brain
2. ACh (atropine) & Belladonna causes dilation by blocking ACh receptors
Ambiguity & perceptual competition
- auditory streaming in study
- necker cube
- consistent bleeps, ranging in sound: 700Hz, 500Hz (sounds like they are splitting)
- ambiguous images slightly different in appearance
-> pattern of selection (previously explored) implemented between choosing 2 cubes
Question:
- is there any relationship between pupil diameter and the timing of a perceptual switch?
1. measuring pupil diameter
- recorded using stimulus presentation
- > subjects reported their perceptual switch with an immediate button press
Raw pupil trace:
1. pupil dilation recorded at the point
- before the reported switch and peaks at approximately 1 second
Motor decision
- task 1 & 2
- based on pupil dilation alone
- push button anytime between 1-10 s / select number between 1-9
= if correct win money - experimenters could predict which number would be chosen/when the button would be pressed
Mind reading: rock, paper, scissors
1. eyes dilated when
- they heard the object they would choose
Clinical uses of pupil dilation
1. possible to communicate
- with people who are minimally conscious or suffering locked-in-syndrome using pupil dilation
Experiment conclusions
- results
- theoretical implications
- pupil dilation accompanies a switch during perceptual rivalry
- pupil dilation can be used as an index of cognitive decisions
- pupil dilation accompanies a switch during perceptual rivalry
- noradrenaline & LC likely play the same role in perception & cognitive decisions as they are believed to play in behaviour (optimising a balance between exploration/stability and exploration/flexibility)
= pupil dilation can be used as an index of NA release in brain
