Biology 463 - Neurobiology
Topic 20
Brain Rhythms & Sleep
Lange
Basics of Brain Rhythms:
• More technically referred to as neural oscillations
• Any rhythmic or repetitive neural activity in the central nervous system
• Neural tissue can generate oscillatory activity in many ways, driven either by
mechanisms localized within individual neurons or by interactions between
neurons.
• Neural oscillations were observed by researchers as early as Hans Berger in
1924.
Hans Berger
The Electroencephalogram
• The Electroencephalogram (EEG)
– Measurement of generalized cortical activity
– Noninvasive, painless
– Diagnose neurological conditions such as epilepsy and sleep disorders
Recording Brain Waves:
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Electrodes anchored to the scalp, low-resistance connection
Connected to banks of amplifiers and recording devices
Voltage fluctuations measured (microvolts)
Electrode pairs: Measure different brain regions
Set of simultaneous “squiggles” that indicate voltage changes between
electrode pairs
How the Electroencephalogram Measures the Voltages
• EEG records very small electrical fields generated by synaptic currents
in pyramidal cells
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Generating Large EEG Signals by Synchronous Activity
Sleep
Sleep is
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Universal among higher vertebrates
Sleep deprivation, devastating
One-third of lives in sleep state
Defined: “Sleep is a readily reversible state of reduced responsiveness
to, and interaction with, the environment.”
Three Functional Brain States of Sleep:
Why do we sleep (meaning, how does sleep help our body)?
No definitive answers. Still a highly theoretical area of study.
Major reasons suggested include:
– Recovery time for brain?
– Restoration?
• Sleep to rest and recover, and prepare to be awake again
– Adaptation?
• Sleep to keep out of trouble, hide from predators
However…..
Even though we cannot pinpoint yet how sleep HELPS, we can describe what
happens with sleep deprivation.
Functions of Dreaming and REM Sleep
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Body requires REM sleep
Sigmund Freud: Dream functions- Wish-fulfillment, conquer anxieties
Allan Hobson and Robert McCarley: Activation-synthesis hypothesis
Avi Karni: Certain memories require strengthening period REM sleep
Freud
Hobson
McCarley
Karni
Seizures and Epilepsy:
– Epilepsy: Repeated seizures
– Causes: Tumor, trauma, infection, vascular disease, many cases
unknown
– Generalized: Entire cerebral cortex, complete behavior disruption,
consciousness loss
– Partial: Circumscribed cortex area, abnormal sensation or aura
– Absence: Less than 30 sec of generalized, 3 Hz EEG waves
Generalized Epileptic Seizure
Circadian Rhythms
A circadian rhythm is any biological process that displays an endogenous,
entrainable oscillation of about 24 hours. These rhythms are driven by a
circadian clock, and rhythms have been widely observed in plants, animals,
fungi, and cyanobacteria.
Circadian rhythms
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circa = approximately; dies = a day
Daily cycles of light and dark
Schedules of circadian rhythms vary among species
Physiological and biochemical processes in body: Rise and fall with daily
rhythms
Daylight and darkness cycles removed, circadian rhythms continue
Brain clocks
Typical Human Circadian Rhythm Peaks and Valleys in a 24 hour period.
Circadian rhythms and physiological functions
Circadian rhythms of sleep and wakefulness
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