1. The suprachiasmatic nucleus (SCN) in the hypothalamus acts as the brain's master circadian clock, controlling daily rhythms. It receives light input from the retina and synchronizes circadian rhythms throughout the body. Lesions to the SCN eliminate circadian rhythms. 2. Delayed sleep phase syndrome involves a later-than-normal circadian rhythm, making falling asleep very difficult before midnight or later. It is treated with light therapy and strict sleep schedules. 3. Sleep has two types - NREM and REM sleep. NREM sleep has four stages, with the deepest being stage 4. REM sleep involves rapid

1. Biological Rhythms
Dr. Zahiruddin Othman

2. Biological Rhythm
• Biological Rhythm
– Inherent rhythm that controls or initiates various
biological processes
– Linked to the cycle of days and seasons produced by
the Earth’s rotation around the sun
– Animals living near the poles of the Earth are more
affected by seasonal changes than animals living in
equatorial regions
– Human behavior is governed more by daily cycles
than by seasonal cycles

3. • Biological rhythms cause us to sleep and
wake at certain times.
– Examples include a 90 minute cycle of activity
and drowsiness in humans and a 28 day
menstrual cycle in females.
– Circadian cycle—A change in biological and
behavioral functioning that occurs over a 24
hour period.
– Circadian rhythm—The intrinsic process that
controls the circadian cycle.

4. • Rhythms are endogenous (control comes
from within)
• Biological Clock
– Neural system that times behavior
– Allows animals to anticipate events before
they happen
• Example: Birds migrate before it gets cold

5. • Circannial Rhythm
– Yearly cycles
• Infradian Rhythm
– Cycles longer than a day
• Circadian Rhythm
– Daily cycles
• Ultradian Rhythm
– Cycles less than a day (e.g., eating cycle)

6. Role of the Suprachiasmatic
Nucleus
• Suprachiasmatic nucleus (SCN)
– Shows circadian cycles of electrical and
biochemical activity, controls neural structures
responsible for activity
• Greater activity in the day than in the night, even in
diurnal animals
• Lesions that separate the SCN from other CNS
structures affect the circadian cycle; however, the
SCN maintains its cycle.

7. • Transplantation of SCN from hamsters with
a 20 hour cycle into hamsters with a 24
hour cycle changed the 24 hour cycle
animals to 20 hour cycles.
• Rats with damage to the SCN have no
circadian rhythms, i.e., they sleep the same
total amount, but polyphasically for random
lengths at a time

8. Indirect Visual Pathway via LGN

9. • Free running rhythm—
25 hour (or more)
sleep-wake cycle that
develops in the
absence of natural
light dark cycles.
– Zeitgebers—German
for “time givers” (e.g.
position of the sun,
outdoor temperature)
serve to reset the
biological clock every
24 hours.
– Seems that broad
spectrum light is the
zeitgeber that resets
our circadian rhythm.

10. Type I & II Rhythms
• Type I – directly connected to clock
mechanism
• Type II rhythms - are directly connected
with the expression of behavioral rhythms
that are driven by those clock mechanism

11. Behavioral and Biological
Changes in a 24 Hour Period

12. Melatonin
• SCN influences secretion of melatonin by
the pineal gland. SCN activity (in response
to light) inhibits melatonin release; lack of
SCN activity (in response to dim light)
increases release. Melatonin promotes
sleep and also alters the circadian
pacemaker.

13. Sunrise and Sunset
• Two coupled oscillators model
– entrained to sunset
– entrained to sunrise
– Photoperiod
– Bimodal pattern

14. • Seasonal affective disorder (SAD)
– A form of depression caused by reduced
daylight during the winter months.
– Light therapy is used to treat SAD

15. • Ramelteon
– A new class of sleep agent (agonist) that
selectively binds to the MT1 and MT2
receptors in the suprachiasmatic nucleus
(SCN)
• Agomelatine
– It is classified as a norepinephrine-dopamine
disinhibitor (NDDI) antidepressant
• 5-HT2C antagonist
• Melatonin agonist

16. Phase-Sequence Problems
• Phase-advance shift—A schedule that shortens
the day by requiring a worker to start on the late
shift and then rotate to an earlier shift the
following week.
• Phase-delay shift—A schedule that lengthens
the day by requiring a worker to rotate to a later
shift each week.
• A phase-delay shift results in greater job
satisfaction, fewer health problems, etc.
• A phase-advance shift is associated with less
job satisfaction, more health problems, etc.

18. Circadian Rhythm Sleep Disorders

19. Jet Lag
phase-advance
phase-delay

20. Wakefulness and Sleep:
Levels of Arousal

21. Brain Mechanisms
Controlling Arousal
• Reticular activating system—network of
nuclei and pathways beginning in the
hindbrain and extending through the
midbrain.
– Locus coeruleus—involved in control of
cortical activity, behavioral alertness, and
REM sleep.
• Transmitter substance is NE.

22. Levels and Stages of Sleep
• NREM
– Stage 1-4
• SWS
– Stage 3-4
• REM

23. Levels and Stages of Sleep
• REM (rapid eye movement sleep)—EEG
patterns resemble the waking state; eyes move
behind closed lids, and muscle tone is absent
– REM is also called paradoxical sleep because the
brain waves resemble waves that are present in
waking patterns of EEG.
– Dreaming is reported during REM sleep.
– PGO waves—begin in the pons, continue to the LGN
of thalamus, and end in the occipital cortex. PGO
waves may provide the foundation for visual imagery
we experience during dreams.

24. The Function of Sleep
• The function of sleep—Three views:
– A restorative function
– A learning and memory function
– Evolutionary function

25. The Function of Sleep:
A Restorative Function
• Valuable substances manufactured during
sleep:
– Growth hormones during deep sleep.
– Protein synthesis during REM sleep.
• Sleep deprivation produces:
– Tardiness (students)
– More feelings of depression
– Greater daytime sleepiness
– Impaired cognitive ability and inability to recognize the
impairment

26. The Function of Sleep:
Sleep Deprivation
• REM sleep deprivation
– Produces fatigue, lack of concentration, and irritability
as compared to no REM deprivation.
– Produces REM rebound (a greater proportion of sleep
time spent in REM sleep after a period of REM sleep
deprivation).
• Randy Gardner’s sleep deprivation (11 days)
– Produced no severe or permanent impairment.
– Sleep rebound after deprivation with a higher
percentage of recovery for stages 3 and 4; suggests
they may be important in a restorative function.

27. Sleep

28. The Function of Sleep:
Sleep Deprivation
• Three or more days of sleep deprivation
may produce microsleep periods
– People appear to be awake but the EEG
indicates stage 1 sleep.
– Particularly dangerous for truck drivers or
other equipment operators.

29. The Role of Sleep in Learning and
Memory
• REM sleep deprivation impairs memory of
episodic events.
• REM increases after training experiences in both
animals and humans indicating a role in learning
and memory.
• Counter to these findings are results from
people who take antidepressant drugs (reduce
REM sleep) and people with brain injuries that
abolish REM sleep who do not have learning or
memory problems.

30. Sleep: An Evolutionary Perspective
• Sleep evolved to help animals conserve energy
when they are less efficient in obtaining
resources and to protect them from predators
• Animals sleep for short periods if:
– They high metabolic rates so need to be constantly
eating.
– They are likely to be eaten.
• Animals sleep for long periods if:
– They have low metabolic rate so eat less and
therefore have more time available to sleep.
– They have no natural predators.

31. Sleep As a Biological Adaptation
• Basic Rest-Activity Cycle
– Recurring cycle of temporal packets, about
90-minute periods in humans, during which an
animal’s level of arousal waxes and wanes
– Examples:
• School classes, work periods, meal times, coffee
or snack breaks, NREM-REM cycles

32. – So fundamental that it cannot be turned off
even at night, so the body is paralyzed during
REM sleep to prevent interruptions throughout
sleep

33. Developmental Changes
(ontogeny) in Sleep Patterns
• REM is at higher levels during infancy and
decreases through adulthood.
• Total daily sleep decreases with age.
• REM may assist with brain development during
infancy. Children born premature show higher
levels of REM. Animals with more fully
developed brains at birth show less REM that
animals with less developed brains.

35. Brain Mechanisms Controlling Sleep
• NREM sleep
– Raphé nuclei — located in a thin strip that
runs along the midline in the caudal part of
the reticular formation.
– Damage to raphé nuclei produces insomnia.
– Serotonin is one of the transmitters in the
raphé nuclei.

36. Brain Mechanisms Controlling Sleep
• NREM sleep (cont.)
– Serotonin agonists enhance sleep.
– Serotonin antagonists decrease sleep, e.g.,
parachlorophenylalanine (PCPA).
– Findings also indicate that stimulation of the
raphé nuclei do not produce sleep. It seems
the raphé nuclei may be involved in activation
of the brain.

37. Brain Mechanisms Controlling Sleep:
NREM Sleep
• Basal forebrain region—an area anterior to the
hypothalamus.
– Has been shown to induce sleep when stimulated.
– Damage to this area produces sleeplessness.
– Research indicates that GABAergic neurons are
responsible for sleep induction in this area.
– This area is also sensitive to temperature (has
thermoreceptors) and warming the neurons promotes
sleep.

38. Brain Mechanisms Controlling Sleep:
NREM Sleep
• Locus coeruleus stimulation significantly
reduced REM sleep and produced REM sleep
rebound post stimulation.
• Decreased locus coeruleus activity removes
inhibition from the caudal reticular formation
which initiates REM sleep.
• Dreaming is closely associated with REM but
may be controlled by a different brain
mechanism, i.e., dopaminergic pathways and by
stimulating the forebrain.

40. Short Notes
1. Write short notes on the neurobiology of
circadian system in human with help of a
diagram
2. Write short notes on delayed sleep phase
syndrome
3. Write short notes on stages of sleep
* Read the topics first. On different day, sit down and
write the answer within 15 minutes for each questions.
Then discuss the answer with your friend or supervisor