2 - Studying Sleep and Circadian Rhythms Flashcards
In 1938, a couple people went into Mammoth cave (total darkness and constant temperature) for 30 days.
First reference of daily rhythms are in the ____
Bible, song about life during night/day
Carl Linnaeus describe sleep movements in the mimosa plant, what was the significance of this?
First to describe activity pattern governed by a biological rhythm
Reported that he took the sensitive plants and put them in a darkened closet and left them there for many days. Peaked in periodically to see position of leafs. Concluded that plant continued to have sleep movements regardless of lack of sunlight, said that it could sense the sun (dead wrong)
Experiment repeated with constant light, movements remained.
Eventually discovered that this was due to an internal biological clock.
Kurt Richter invented running wheel to measure rats activity without disturbing them. What was his findings from this (1920s)?
That rat’s period activity fluctuated. If blinded, their period was not 24 hours. Same with drosophila.
Intensity of lighting makes what different to biological rhythms?
Produces different rhythm periods (longer/shorter)
What are circadian rhythms?
Rhythms that are generated near a 24 hour period (though not exactly). A dian rhythm is exactly 24 hours.
When a rhythms is being expressed in constant environmental conditions, it is called a?
Free running rhythm
A period slanting leftwards on a 24 hour time scale is less than, or greater than 24 hours?
Less than
Leftward slant demonstrates the animal waking up earlier and earlier
Humans have a free running period at about ___?
24.1-24.3 hours
Why is the free running period important?
Internally generated circadian rhythm is synchronized to light/dark cycle (entrained)
What is entrainment?
An organism with an internal clock by synchronized to an external cycle (eg. light and dark)
How do we know we are observing entrainment and not a 24 hour free running period?
Leaving everything constant except for one variable, shifting to a new external cycle (phase shift). If the animal adapts to a new light/dark cycle, that is entrainment.
What is a zeitgeber?
An entraining agent (a ‘time giver’)
What is the limit of entrainment?
Animals can only be entrained to cycles close to their biological cycle
Species differ by how much they can deviate from their biological cycle (humans very conservative and resist change - NASA 25 hr experiment failure)
A brief light pulse administered during a free run has what consequence?
A permanent phase shift to synchronize to the new period indicated by the light (phase delay or phase advance)
Your clock is reset every day by what two factors?
Internal clock and external cues cause unique entrainment for each individual
Organisms with short periods (short oscillator) have what 24 hour position?
Early phase (leading) relative to external cycle
Organisms with long periods (long oscillator) have what 24 hour position?
Late phase (lagging) relative to external cycle
How do circadian rhythm phase lead and phase lag change from childhood to adulthood?
Shift from childhood to adulthood of late phase (lagging - late riser - long periods) to early phase (leading - early riser - short periods)
EEGs need a reference electrode, where are these usually placed?
Behind the ear
What does submental mean?
Under the chin
An EEG site starting with C denotes?
Central central
What is a polysomnogram (PSG)
Set of measures that gives you a comprehensive physiological overview of a sleeping person.
What are the 6 components of a PSG?
- brain (EEG),
- Eye movements (EOG),
- Muscle activity or skeletal muscle activation (EMG) and
- Heart rhythm (ECG) during sleep
- Airflow
- Leg movement
When are intracortical recordings of humans made?
Seizure patients undergoing surgery. Electrodes are implanted and cortical activity monitored for a few days to detect source of seizures.
What is the 10/20 system for EEG montages?
Each electrode positions are done with respect to distance percentages from anatomical features of the skull. Distances between left and right and nasion (eye socket) and inion (bump on back of head)
Why are action potentials difficult to detect by EEG?
Very rapid
What are EEGs mostly picking up on?
The summation of all the excitatory and inhibitory postsynaptic potentials under the electrode
what layer of the cortex are EEGs mostly measuring from?
The densely soma-populated fifth layer of the cortex is the main source of electrical activity.
If neurons are desynchronized from each other and you record from many neurons that perform individual tasks where they are stimulated by a specific sensory input. What type of activity are you recording with EEG? What is this called?
You wind up with an EEG recording very close to zero (very short peaks oscillating around zero line) because different neurons are getting excited and inhibited and some are inactive.
Called a desynchronized cortex
Where does the cortex receive its synchronizing signals from?
The thalamus
What is the function of a synchronized cortex?
To prevent the processing of sensory information. Seen during sleep (esp gamma waves)
What is Fourier analysis?
Taking a waveform and reducing it to simple sine waves. Any arbitrary waveform can be analysed as a series of pure sine waves added together.
The accurate weighting (aka power, frequency) of each simple sine is added to achieve the original waveform
Fourier analysis also tells you what the fundamental signal frequency is (power strectrum)
What frequency is dominant for wakefulness?
Beta (over 13 Hz)
What is stage 1 sleep frequency?
Alpha frequency (8-13 Hz)
Relaxed wakefulness achieved in meditation
What is the sigma frequency range?
13-30 Hz