week 10-noradrenaline Flashcards
Noradrenaline Synthesis
1.Tryrosine an amino acid found in food 2.dopa 3.dopamine 4.noradrenaline
noradrenaline
Sympathetic nervous system (flight or fight) Arousal / Vigilance Anxiety Exploitation vs Exploration Reward / addiction memory consolidation Very small area of the brain with very few neurons (~30,000). (In contrast the primary visual cortex V1 estimated to have 280million neurons).
Locus Ceruleus (LC) - Neuron Firing
Highest rates rapidly follow a transient noxious or extremely positive stimulus/event (lots of NA released
Silent during rapid eye movement (REM) sleep (very little NA released).
High LC/NA activity = 4 F’s
4F’s (Fight, Flight, Freeze or F… Fornicate)
State of Hyperarousal adapted for evolutionarily important situations where “individual” or “sexual fitness” is involved
High LC/NA activity = Stress & Anxiety
High levels of LC/NA activity can lead to the following, depending on the trigger and duration
Stress: often experienced when LC/NA
Activity is sustained due to environmental
Factors (social, emotional, physical etc).
Anxiety: excessive, uncontrolled and
often irrational “worry” (diagnosis requires
symptoms for 6 months).
Panic attacks: brief intense episodes believed to reflect spikes of LC/NA activity triggered by
- apparently random events - internal thoughts - learned associations (PTSD)
NA Function beyond arousal & 4F’s
At moderate levels of LC activity, Noradrenaline acts to consolidate decisions.
Adaptive behaviour represents a tradeoff between exploiting known sources of reward and exploring the environment for alternative sources of reward (food, water, sex etc).
Exploitation vs Exploration
Indecision, inaction or constant changing decisions is BAD
………But inflexible, repetitive behaviour is also BAD. Balance is needed!!
NA & Behavioural Selection
competition Burst of NA release “tips the balance” in favor of the winner. (Increases strength of activating & inhibiting signals) Competition resolved Selection complete Decision is “consolidated”
LC neurons & Behavioural Selection
Neurons in the Locus Coeruleus (LC) fire when a behavioural response is selected and executed.
After they fire the neurons are inhibited allowing the selected behaviour to be “exploited”.
NA & Behavioural Selection
The more “important,” “salient,” “arousing” one of the alternatives the bigger the burst of LC neurons and more NA released.
NA & Behavioural Selection
in high arousal
Competition in “high-arousal” context LARGER burst of NA release “tips the balance” in favor of the winner with MORE STRENGTH Competition resolved Selection complete Decision is “consolidated
LC neurons & during high arousal
The larger the response of neurons in the Locus Coeruleus (LC), the more NA released & and the longer the following period of inhibition.
In highly arousing situations the chosen focus of attention/behaviour dominates more for longer .. “distracting” alternatives are inhibited
LC neurons & during low arousal
In the absence of recent decisions or arousing events the baseline levels of firing increase and more NA is released throughout the brain.
Increased NA promotes a switch to a new decision, promoting “exploration” of alternative behaviors.
LC-NA & Performance
Low levels of LC activity and NA release = tired, vague & poor performance.
High levels of LC activity and NA release = restless, stressed & poor performance.
Optimal performance requires moderate activity with large intermittent bursts
NA & The Pupil
In the dark dilation reflects NA levels
- Noradrenaline is released from the Locus Coeruleus
Measuring Pupil Diameter
Pupil diameter sampled at 1000/second
Stimulus presentation 5min continuous while subjects reported their perceptual switch with an immediate button press
Other types of decisions
Pupil responses should be seen with
1) motor decisions
2) cognitive decisions?
Motor Decision-Instruction: “push a button when ever you feel like it during 10 seconds, if you push the button during the lucky 1 second you win money”
cognitive decision-Instruction: “Select a number WHEN it is presented and remember it until the end of the trial. If you select the lucky number you win money”
mind reading
rock paper scissors challenge
Clinical uses of pupil dilations
Using the same basic idea we recently showed it is possible to communicate with people that are minimally conscious or are suffering locked-in-syndrome using pupil dilation
Experiment conclusions
Results
Pupil dilation accompanies a switches during perceptual rivalry
Pupil dilation can also be used as an index of cognitive decisions
Theoretical Implications
Noradrenalin and the locus coeruleus likely play the same role in perceptual and cognitive decisions, as they are believed to play in behaviour (optimizing a balance between “exploitation” / “stability” and “exploration” / “flexibility”).
lecture summary
Noradrenaline (NA) is synthesized from foods containing tyrosine and released by neurons in the Locus Coeruleus (LC).
NA is important in increasing arousal during evolutionarily important events (4 F’s).
High levels of NA/LC activity is associated with stress, anxiety and panic attacks
NA helps to consolidate decisions and find an optimal balance between exploitation and exploration of the environment and cognitive or perceptual strategies.
Pupil dilation can be used as index of NA release in brain.
