Sleep and Arousal Prof. K. Sivapalan

Electroencephalogram. It is record of potentials in volume conductor as ECG. The changes are in micro volts as opposed to millivolts in ECG. Flow towards the electrode is positive and away is negative. The recorded waves represent oscillating currents within cortex and feed back circuits between thalamus and cortex. 5/31/2019 Sleep and arousal

Electroencephalogram. 8-12 Hz. 50-100 μV Record of variations in the brain potentials recorded with electrodes on the surface of the scalp. Electrocorticogram- electrodes on the pial surface. 18-30 Hz 4-7 Hz <4 Hz 5/31/2019 Sleep and arousal

Normal EEG. Alpha rhythm: 8-12 Hz, 50-100 μV, when awake, most marked in parieto-occipital area. Beta rhythm: 18-30 Hz, lower amplitude, seen over frontal areas, may be harmonious with alpha. Gamma oscillations: when aroused and focus attention on something. Irregular fast activity replaces it on initiation of motor activity. Theta rhythm: 4-7 Hz, large amplitude, occurs in children. Delta rhythm: less than 4 Hz, large waves. 5/31/2019 Sleep and arousal

Variations in EEG. Age- Beta like activity is seen in infants but the occipital rhythm is 0.5-2 Hz. This speeds up in childhood to typical theta rhythm. The adult alpha pattern appears gradually in adolescence. Frequency of alpha rhythm is decreased by: ↓ blood glucose , ↓ body temperature, ↑ arterial PCO2, ↓glucocorticoids. Alpha block- [arousal] focusing the attention causes replacement of alpha waves by irregular low voltage waves. Atypical pattern can be seen in epilepsy. 5/31/2019 Sleep and arousal

Mechanism of arousal. Arousal occurs on stimulation of any sensory input at receptor or pathway up to midbrain. Stimulation of the specific pathways above midbrain does not generate arousal. Collaterals of all sensory input activate reticular activating system [RAS] in brain stem which sends impulse to all parts of the cortex to generate arousal. Each sensory input produces two responses in the cortex- one fast response in the sensory cortex representing the stimulated area only. Then a second diffuse response is observed. Stimuli are processed in the cortex when awake but they cause arousal when in sleep. 5/31/2019 Sleep and arousal

Sleep. Sleep is an active process controlled by certain centers in the brain. Sleep has been investigated by EEG and other observations. Dreams are associated with rapid eye movements and EEG changes. Sleep is divided into REM and NREM sleep depending on the eye movements. 5/31/2019 Sleep and arousal

Sleep Paterns. NREM [non rapid eye movement sleep] is divided into 4 stages. Stage 1- low amplitudehigh frwquency activity in EEG. Stage 2- appearance of ‘sleep spindles’ which are 10-14Hz, 50μV waves. [alpha like] Stage 3- lower frequency and increased amplitude. Stage 4- maximum slowing with large waves. REM sleep [paradoxical sleep] - rapid low voltage activity resembling stage 1 but threshold for arousal is increased. Marked reduction of tone of neck muscles and relative paralysis of skeletal muscles during REM sleep. Locus cerulus [in the floor of the fourth ventricle] seems to be responsible for this paralysis. 5/31/2019 Sleep and arousal

5/31/2019 Sleep and arousal

Slow wave sleep. The diencephalic sleep zone in posterior hypothalamus and related structures generate sleep if stimulated at 8 Hz. Faster stimuli produce arousal. Medullary synchronizing zone in the reticular formation of medulla also same. Basal forebrain sleep zone in preoptic area and diagonal band of Borca produces sleep by slow or high frequency stimuli. Stimulation of mechano receptors at 10 Hz in animals and regularly repeated monotonous stimuli in humans produce sleep. Suprachaiasmatic nuclei of hypothalamus regulate circadian sleep pattern. Reduction in vascular tone, blood pressure, respiratory rate and metabolic rate. 5/31/2019 Sleep and arousal

REM Sleep. Associated with dreaming. There is catching up after deprivation. Activity is increased in pontine area, amygdala, anterior cingulate gyrus and visual association areas. Activity is decreased in prefrontal, parietal, and primary visual cortices The mechanism that triggers REM sleep is in the pontine reticular formation. Reduced muscle tone, irregular heart beat and respiration. 5/31/2019 Sleep and arousal

Didstribution of sleep stages. In a typical sleep, the person passes through the stages 1,2 and spends about 100 minutes in stage 3 and 4. Then REM follows and the cycle is repeated in about 90 minute intervals. Towards the morning, less stage 3,4 and more REM sleep. REM sleep: 80 % for preterm babies, 50 % for term babies, and 25 % in old age. 5/31/2019 Sleep and arousal

Sleep Time 5/31/2019 Sleep and arousal

Sleep disorders. Insomnia- mental and medical conditions can cause this. Somnambulism- sleep walking-occurs during awaking from stage 4. common in children, males. Sleep apnoea- obstruction of airway in inspiration due to relaxation of muscles Narcolepsy- sleep attack during day- REM while awake- last several seconds to 30 minutes 5/31/2019 Sleep and arousal