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5. Noradrenaline (How does LC activity affect performance (LC (Modes…
5.
Noradrenaline
How does LC activity affect performance
SNC
Suprachiasmatic nuclei of hypothalamus
Affect sleep wake cycle
LC
Locus coeruleus
Plays role in regulation of circadian sleep-wake cycle
cluster of norepinephrine neurons in dorsorostral pons
Projects to
cerebral cortex, hippocampus, thalamus, midbrain, brainstem cerebellum and spinal cord
Especially related to attentional processing
Parietal cortex and superior colliculus
related to attention
Extra NE
Cognitive/behavioral functions
aking and alertness
Modes
tonic
long lasting
behavioral flexibility
task disengagement
scanning attentiveness
Poor performance on task
Phasic
short lasting
During waking
selective, focused attention
Facilitates descision making
Good performance on task
Balance between selective and scanning attentiveness
Responds both transiently to novel stimuli and in a maintained fashion during vigilance
fits temporal demands of info processing
Reduced in automatic activity, innatentive to environment
DMH
Dorsomedial hypothalamic nucleus
Modulates circadian rythme
Circuit
SCN
DMH
LC
Thalamus/cortex
Hypocretins (orexin)
Activate arousal neurons such as LC
Released in high levels in active waking
Experimen (aston 1999)
LC neurons phasically acivated only by target stim.
Inhibited by distractor
especially when reward available
Shorter LC response related to shorter behavioral response to cue
Might facilitate behavioral responses to target
related to meaning of stimuli io physical attributes
more tonic LC = more false alarm but same misses/hits
Inverse relationship between fixation and LC
Focussed attention highest with intermediate LC
Tonic
#
for target stimuli
intermediate activity and excellent performance
elevated
decreased attention and decreased phasic activation
more false alarms
Intermediate
more visual fixation
clonodine lowers tonic and improves performance
Inverted U
How does clonidine affect alertness
Clonidine
Alpha2 adrenergic receptor agonist
suppresses sympathetic nervous system
Treats hypertension
low dose
increased REM, decresed non-REM
Affects alpha2 receptors
presynaptically
decreases noradrenaline release
Medium dose
Reduced REM, increased non-REM
postsynaptically
Experiment ()
Smith
number of lapses of attention was greatest in clondine quite condition
effect reversed by idazoxan and noise
noradrinaline maintains attention
Increases NE
2 choice reation time
Leapses of attention
1500 ms
Selective attention
Witte
Clon. reduced alerting produced by peripheral cues
Increased RT to double cue
Changed overall RTs
slower in clonodine
2 explanations of no alteration of RT with increasing CTI (cue target interval)
Reduced preparedness equally for valid and invalid trails
impairment due to decrease in general preparedness
spatial information is processed rapidly, processing advantage over response preparedness??
drug-induced reduction of preparedness minima/absent in valid or invalid trails
Article favours this explanation
Validity effect
difference invalid valid
Orienting
stayed the same
2 drugs had opposite effect on arousal
no differences in CTI
Broadens attentional focus
impairs sustained attention
Decreases Validity effect
difference in reaction time between invalid and valid cue condition
What is the function of noradrenaline on types of attention
Regulates states of neurons in thalamus and cerebral cortex between 2 modes
transmission/spike mode
Waking
NE release
Oscillatory mode
NE abscence
Sleep
NE
Inhibits basal activity of cerebellar and hippocampal neurons
Decreased sponaneous impulse activity more than sensory reaction
Augments evoked activity while decreasing sponaneous activity in same neuron
Enhances signal to noise ratio
NE involved in control of attention
facilitates behavioral responses to subsequent sensory cues
Active during high arousal
Spaitial and sustained attention
Noradrenergic System
Receptors
Alpha
Second messenger
Usually inhibitory (alpha 2)
Negative feedback loop
Beta
Usually exitatory
Sympathetic nervous system
Agonist
activates receptor
Antagonist
block activity of agonist