Modulatory and arousal systems
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What is the pathway of the specific primary visual pathway?
Retina -> thalamus -> primary visual cortex Arrows represent sensory info
Where are modulatory inputs found in the brain?
Brainstem & basal forebrain
What is happening in the primary visual pathway when one is awake?
The thalamic cells are relaying sensory info to the cortex
What is happening in the primary visual pathway when we are asleep?
Thalamic cells become insensitive to their sensory input. This is due to withdrawal of modulatory input, so the thalamic cells start to fire bursts of APs in rhythmic, regular manner but the cortex is no longer receiving the sensory input from retina.
Describe what the electroencephalogram looks like while (i) awake and (ii) asleep.
• Awake - desynchronised eeg - low amp, high freq • Asleep - synchronised eeg - high amp, low freq
Describe what happens to an EEG during the 4 stages of sleep, going from awake/relaxed to deep sleep
As you go down the stages into deeper sleep, the EEG shows the amplitude getting higher and the frequency lower. The synchronisation also increases in the thalamus and cortex.
Describe what happens in the brain and EEG during Rapid Eye Movement (REM) sleep
REM occurs following the ascent of the 4 stages of sleep. The EEG looks desynchronised, so makes it look like you are awake (low amp, high freq) but really you are in paralysis. There is an active ‘higher’ cortex, limbic and sympathetic NS -> suggests dreaming!
How does the sleep cycle change over the night?
Over the night, the REM becomes longer and the non-REM (4 stages) becomes shallower and shorter.
What are the two important centres of the cholinergic modulatory pathway, and what do they project to?
• Basal forebrain -> projects to neocortex and hippocampal complex • Pontomesencephalic tegmentum -> projects to thalamus + basal ganglia
What are the actions of the Acetycholine modulatory pathway?
• Desynchronises thalamic cells, maintains connection to outside world • Increases response strength, selectivity and plasticity • Keeps awake, attentive, increases cognition, learning, memory
What happens in dysfunction of the acetylcholinergic modulatory pathway? Example? What drug is used to treat?
• Dysfunction -> cog decline, memory issues • Eg. Alzheimer’s • Treat with AChE inhibitor (Aricept)
What are the actions of the norepinehprine / noradrenergic modulatory pathway?
• Similar to ACh • Inc response amplitde + selectivity, inc plasticity • Keep awake/vigilant, alert to novel stimuli, inc learning, memory and mood
What does dysfunction of the norepinehprine / noradrenergic modulatory pathway lead to? How can it be treated?
• Dysfunction -> anxiety, depression • Treated with NE (norepinephrine) reuptake inhibitors • Treated with MAO inhibitors • ^Drugs also boost analgesic effect down the spinal cord
What is the norepinephrine modulation centre in the brain?
Locus coeruleus
What are the dopaminergic modulatory pathways and where do they project to?
• Substantia nigra -> projects to basal ganglia • Ventral tegmental area -> projects to frontal cortex, limbic, amygdala, nucleus accumbens
What is the nucleus accumbens?
Pleasure centre
Why is the substantia nigra pathway important in dopaminergic modulation? What does downregulation lead to and how is it treated?
The pathway facilitates voluntary movement by activating the “direct” basal ganglia pathway, and reduces suppression of movement by the “indirect” basal ganglia pathway. Decreased activity -> Parkinson’s disease, treated with L-DOPA
What is important about the ventral tegmental area in dopaminergic modulation? What does increased activity lead to and how is it treated?
Involved in reinforcement of behaviour, promoting behaviour that leads to reward. Inc activity -> schizophrenia, amphetamines, treated with DA antagonists
What is the consequence of giving dopaminergic drugs, in regards to (i) anti-parkinson’s, (ii) anti-psychotics
• Anti-parkinson’s (LDOPA) can result in increased psychotic behaviour • Anti-psychotics (DA antagonists) can result in dyskinesia
What is the histamine modulatory pathway centre and where does it project to?
Hypothalamus -> thalamus + cortex
What is the role of the histamine modulatory pathway? What is a consequence of anti-histamines?
• Wakefullness, alertness • Antihistamines result in drowsiness
Where does the orexin modulatory pathway originate and project to?
From the hypothalamus to ~ everywhere
What is the role of the orexin modulatory pathway? What does dysfunction lead to?
• Wakes you up • Responds to nutritional status • Linked to reward centres • Awake + exploring, energy homeostasis Dysfunction -> narcolepsy
What is the sertonergic modulatory pathway centre and where does it project?
Raphe nuclei -> ~ everywhere