Measuring Sleep

Question 1

What measures muscle activity?

Answer 1

Electromyogram (EMG)

Question 2

What measures eye movement?

Answer 2

Electro-oculorogram (EOG)

Question 3

Stages of sleep

Answer 3

Awake - alpha EEG activity regular (synchronised) medium frequency
Beta EEG activity irregular (desynchronised)

Stage 1 - theta activity

Stage 2 - after 10 minutes
Contains sleep spindles and K-complexes
Sleep spindles - mechanism that disconnect brain (Steriade, 1992)
K-complexes - only occur in stage 2 triggered by noises (Niyama et al, 1996)

Stage 3 (after 25 minutes) - high amplitude (4Hz) delta activity

Stage 4 (after 50 minutes) -delta activity more than 50%

REM sleep (after 90 minutes) - desynchronised theta and beta waves, loss of core muscle tone (relaxation)
During REM cerebral blood flow high in visual cortex but low in inferior frontal cortex (Madsen et al. 1991)
Eye movements during REM related to what you see in dream (Roffwarg, 1962)
Dreams length related to real time (Dement and Kleitman, 1957)

Question 4

Sleep studies

Answer 4

Cortical mechanisms involved with movement become active when running in a dream (McCarley and Hobson, 1979)
Madsen - activity of frontal cortex associated with ordering of serial events
Roffwarg - tennis dream
Dement - 5 minutes and 30 minutes waking
McCarley - activity in motor cortex relates to what you are doing in your dream

Question 5

Adenosine - sleep promoting substance

Benington, Kodali & Heller, 1995

Answer 5

Porkka-Heiskanen, Strecker and McCarley (2000) used microdialysis to measure adenosine levels in several regions of the brain
They found level of adenosine increased during wakefulness and slowly decreased during sleep, especially in the basal forebrain

Question 6

Neuronal control of sleep

Answer 6

Areas of the brain historically associated with sleep

Question 7

Hypothalamus

Answer 7

Work by Baron Constanin von Economo
During WW1 - victims of encephalitis lethargic caused some to sleep continuously and others to sleep little
Damage in posterior hypothalamus and adjacent midbrain > excessive sleep
Damage in anterior hypothalamus or preoptic area and adjacent forebrain > wakefulness

Question 8

Activating arousal

Answer 8

Injecting of acetylcholine (ACh) increases EEG signs of cortical arousal (Vanderwolf, 1992)
Marius et al. (1995) used microdialysis probes to measure the release of ACh in the hippocampus and neocortex
Found levels of ACh in these regions were high during both waking and REM sleep but low during slow-wave sleep

Question 9

Orexin

Answer 9

The cell bodies of neurons that secrete orexin are located in the lateral and posterior hypothalamus
The axons project to almost every part of the brain and all regions involved in arousal and wakefulness (Sakurai, 2007)
Orexin has an excitatory effect in all of these regions

Question 10

Activating sleepiness

Answer 10

Baron preoptic area, anterior hypothalamus or pre optic area activates sleepiness
Damage to pre optic area suppresses sleep (Lu et el, 2000)
When preoptic neurons become active, they suppress the activity of the pons and we fall asleep (Saper, Scammell and Lu, 2005)

Question 11

Sleep waking flip-flop

Answer 11

Orexinergic neurons in the hypothalamus help stabilise the flip-flop

Question 12

What measures brain activity?

Answer 12

Electroencephalograph (EEG)