lecture 2 - noradrenaline, acetylcholine and alertness Flashcards
the brain stem
the thalamus
what are these important in
-these two areas are really important in alertness and arousal
- Basic behavioural functions: sleep/wake cycle, reflexive responses to sensory input
-areas present in much less evolved creatures
what is the ascending reticular activating system (ARAS)
-how does this system work
-which neurotransmitters are involved
-what does it result in
-ascending comes from parts of the brain that are old and lower down (in the brain)-go upwards
-reticular - type of cells
Axons of ARAS project from
brain stem to higher cortical
regions (incl. via thalamus)
-cell bodies in brainstem projecting their axons elsewhere and making synapses
- Source of major excitatory
neurotransmitters:
noradrenaline (NA) &
acetylcholine (ACh)- cause new action potentials where they arrive - Regulates general levels of
cortical arousal, alertness &
consciousness
what is the link between ARAS and extraversion
Eysenck (1967) suggested a link between ARAS & extraversion:
extraverts have low ‘resting’ ARAS activity (so they seek out more
stimulation); introverts have high ‘resting’ ARAS activity (so they avoid
overstimulation)
difference between noradrenline and acetylcholine systems and the gaba and glutamate systems
cells that produce glutamate and gaba can be found all over the brain and all over the cortex -main information system with excitation and inhibition
-however na and acy , their cell bodies are just down there in the brain stem - are not located / widely distributes across the brain, they have specific regions
what are the anterior and posterior attention systems in our cortex
- Anterior (frontal) system = ‘top-down’ (cognitive), voluntary,
controlled, task- or goal-driven attention, ‘executive functions’ - Posterior (parietal) system = ‘bottom-up’ (sensory), involuntary,
automatic, stimulus-driven attention, ‘orienting reflex’
definitions
-alertness
-attention
-arousal
- Alertness: generalised readiness to process stimuli and
respond. Measured by subjective feelings or simple
psychomotor tasks. - Attention: enhanced processing of specific/selected
stimuli. Measured by behavioural performance – e.g.,
RT/accuracy. - Arousal: physiological activation in autonomic nervous
system (e.g., skin conductance) or central nervous
system (using EEG, fMRI, etc.); sleep/wake cycle
how can we measure alertness
1) simple detection / reaction time tasks
2) vigilance (or continuous performance) tasks
-simple detection / reaction time tasks
- measuring tonic and phasic alertness
-eg ‘press when you see X’
-means reaction time depends on average alertness during task (tonic alertness)
-eg ‘press when you see the x; the dot will warn you that its about to appear
-means the rt depends on temporary increase in alertness following warning cues (‘phasic’ alertness)
vigilance (or continuous performance) tasks
-what kind of attention does this require
show people a series of letters one at a time
Respond only to pre-specified
target stimulus/sequence (E.g.
“only respond to X”;
or “only respond
if same letter is presented twice in
succession”.)
* Targets are rare (e.g. 5% of
trials); presentation is rapid
Requires sustained attention (= vigilance) & is more cognitively
demanding than simple RT task (e.g. additional demands on working
memory & response inhibition); involves anterior system
- Measures: average RT to targets, errors of omission (missed
targets) & errors of commission (false alarm; responding to non-
targets)
what are stimulants
-what do these drugs do
Drugs that increase alertness/arousal are called
stimulants – examples include caffeine, nicotine,
amphetamines & methylphenidate (Ritalin)
These drugs mimic or enhance the effects of
noradrenaline and/or acetylcholine in the brain – i.e.,
they are noradrenergic or cholinergic agonists.
what are sedatives
Drugs that reduce alertness/arousal are sedatives –
examples include GABA agonists (see previous lecture),
noradrenergic beta-blockers, & cholinergic antagonists
(e.g. scopolamine).
noradrenaline
-where is their main source
-what do they do, what does it allow for
noradrenaline comes from cells whose cell bodies are located in a particular part of the brain
Neurons in the locus coeruleus
(LC, ‘blue spot’) in the brain stem
are main source of NA. (they look blue under a microscope)
- They project to many different
‘higher’ brain areas (incl. via
thalamus) - These projections allow LC to
modulate general levels of brain
arousal & alertness
Increased activity in LC (therefore, increased release of NA) is
also associated with stress, anxiety, & panic attacks
drugs that increase NA- ergic activity (noradrenaline activity)
-how do these drugs do this
-what effect do these drugs have
Amphetamines are synthetic drugs, derived from ephedrine or pseudoephedrine (found in the
Ephedra plant)
Amphetamines increase release and block reuptake of noradrenaline (& dopamine)
imagine the synapse, having all the noradrenaline stored in the vesicles , amphetamine will cause that to be released into the synapse more than it would be otherwise. once its in the synapse they block it from being taken back up into the presynaptic cell. more of it in the synapse, and its there for longer.
These have psychostimulant (alertness-increasing)
& anxiogenic (anxiety-producing) effects
amphetamines - acute effects
-subjective effects
-effects on task performance at low and high doses
Subjective effects – feelings of alertness & energy;
increased anxiety at higher doses.
Task performance
– Low dose: improved performance in simple psychomotor & vigilance tasks
– High dose: impaired task performance; increased
distractibility
explain the inverted U relationship between arousal and task performance
-why does this effect occur?
Under-arousal (fatigue, boredom) AND over-arousal (anxiety, stress, excitement) can both impair performance
Therefore, increasing arousal with a
psychostimulant can improve
performance (if arousal low) OR impair performance (if arousal high).
- This effect may be due to arousal
narrowing the attentional focus, which can be too narrow for optimal
performance (esp. with complex tasks) (you dont want to be too concentrated or focused on something complex like driving as you have to focus on quite a few things at the same time)
