Lecture 18- Higher Brain Functions Flashcards
What do we typically define as consciousness?
- Alert, aware, able to respond immediately to environmental cues.
- Can be defined in terms of patterns of activity in the brain
What is altered consciousness (what do commonly refer to it as)?
-Sleep: complex pattern of brain states, able to be roused but typically not aware of surroundings.
What are the two types of unconscious states? How do they differ?
-Coma: prolonged absence of wakefulness or awareness, no
response to external stimuli, unable to be roused, lacks
normal sleep-wake cycle. Usually caused by dysfunction of cortex and/or reticular activating system.
-Vegetative state – may show signs of wakefulness, but no
signs of awareness. May have sleep-wake cycles, some degree of autonomic function intact but no cognitive function. May be classified as “persistent” if vegetative state lasts >4 weeks.
What are disorders of consciousness? What’s a common example?
- Patterns of activity arising in the brain that didn’t arise from normal sensory information. For example hallucinations: activity in the visual cortex, but not from real stimuli in the world.
- Hallucinations/ other forms of disordered thinking is known as psychosis and this is integral to the definition of schizophrenia.
In terms of neurotransmitters what is believed to be the cause of schizophrenia? Why do we believe this?
-Due to hyperactivity in brain dopamine system
-Stimulants such as amphetamines & cocaine (esp. with extended
use) act via dopaminergic systems & can trigger schizophrenia-like
psychotic episodes. Effective drug therapies include specific D2 receptor blockade
Is it possible to have non psychotic hallucinations? How are these different?
Yes, they tend not to be as forceful in urging a specific action
Other than schizophrenia what is another disorder of consciousness? How is it characterised?
Epilepsy:
- Excessive abnormal synchronized activity of cortical neurons, may result in loss of consciousness and may be associated with aberrant sensory perceptions
- A period of epileptic brain activity is known as a seizure
- Seizures may be accompanied by an “aura” (patient has visual, auditory, or olfactory sensation) and may be convulsive or non convulsive depending on which part(s) of brain involved.
How are seizures diagnosed using ECGs?
- Areas of high synchronized activity= epileptic event
- Usually starts in one area and then spreads to others (focal initiation)
What does the treatment of epilepsy/ seizures involve?
Treatment usually involves drugs that interact with ion channels to modulate neuronal excitability (eg Phenytoin – V-dependent block of V-gated Na channels)
What are the two drivers of sleep?
-Homeostatic variables (controlled by hypothalamus: Long periods of
wakefulness build up “homeostatic pressure” to sleep. Possibly due to
accumulation of adenosine. Adenosine has a broad inhibitory effect on CNS activity.
-Circadian (controlled by suprachiasmatic nucleus)
Circadian rhythm?
-Sleep typically occurs with circadian (“about a day”) periodicity
-“Natural” cycle is about 25-26 hours, but is entrained by exposure to sunlight
-Specific photoreceptors in eyes respond to sunlight exposure & signal to cells in suprachiasmatic nucleus (SCN)
-Activity of SCN neurons modulates release of melatonin from pineal
gland
-Melatonin release increases as light levels fall, promotes sleep
-Melatonin peaks around 3am, & then falls so we become more wakeful in the morning
What are the different stages of slow wave sleep as presented in an ECG?
Stage I -theta waves (~5Hz)
• Stage II -theta waves interrupted by 12 Hz bursts (sleep spindles) and large slow spikes
(K complexes)
• Stage III – delta waves (~1Hz) with spindles
• Stage IV – delta waves
This cycle takes around an hour and is then followed by REM sleep
What is REM sleep/ how does it present in an ECG?
-REM = Rapid Eye Movement
-EEG resembles awake state (“Paradoxical sleep”)
-About every 90 minutes, after about 10 mins of REM, brain
cycles back thru SWS, but cycle typically omits stage 4 after 2 rounds.
-Muscle tone lost during REM, but phasic contraction of eye muscles becomes pronounced
-Intermittent fluctuation of homeostatic variables
-Most dreaming occurs during REM
What is wakefulness modulated by?
- RAS & Thalamus modulates throughput of sensory information to cortical regions
- A small group of neurons in the lateral hypothalamic area release a neuropeptide called orexin that strongly promotes wakefulness (orexin neurons inhibited by melatonin)
- Some RAS neurons release histamine, which enhances excitatory synaptic activity
What happens in people with narcolepsy?
People with defective orexin neurons suffer from narcolepsy (abnormal sleep- wake cycle and excessive daytime sleepiness)
