Sleep & Biological Rhythms

sleep is a…

behavior and change in consciousness

ultradian rhythms

patterns of biological variation occurring on cycles less than 24 hours

measuring sleep

• electroencephalogram (EEG; neural)

• electro-oculogram (EOG; eye movements)

• electrocardiography (EKG, heart rate)

• electromyogram (EMG; muscular)

EEG measuring

• looks at changes in postsynaptic potentials

• record many neurons all at once, reporting on the sum of their electrical activity

• if cells are active, at about the same time, electrical messages are synchronized and appear as a large, clear wave in the data

• amplitude: how many neurons doing this at same time

• frequency: firing rate/sec

action potentials

voltage spikes beginning in axon hillock down the terminals

postsynaptic potentials

• voltages in the postsynaptic membrane when NTs bind to receptors

• the neurons are primarily pyramidal neurons (which are most abundant in the cortex)

adrenergic

• dopamine, serotonin, norepinephrine

• associated w/ arousal and stress during wakefulness

• many mood disorders are associated w/ disrupted REM sleep

• adrenergic NTs are typically reduced during REM

  • some anxiety disorders assoc. w/ elevated levels during sleep

  • this might underly hyperarousal and axaggerated amygdala activity during wakefulness in ppl with anxiety disorders

decreased adrenergic NT levels

associated with decreased gamma EEG activity, which can be used as a proxy

sleep in the amygdala

• decreased amygdala activity in response to emotional stimuli during wakefulness — probably due to stronger connections that form between the amygdala and ventral medial prefrontal cortex (vmPFC)

• activity in vmPFC anticorrelated w/ activity in amygdala (vmPFC can tell amnygdala to calm down)

• vmPFC supports inhibition of emotional, impulsive R’s

REM sleep depotentiates amygdala activity to previous emotional experiences

• subjects completed two-day study protocol

• day 1: view and rate (scale 1-5) the emotional intensity of each image (fMRI recorded)

• 12 hours of restfulness (sleep w/ EEG rec) or wakefulness

• day 2: same viewing task (fMRI rec)

• people able to sleep → tendency to lower valence ratings (ex. if rate as a 4 at beginning, more likely to rate as a 3 after sleeping)

• people awake → not much change in valence ratings for emotional pics

• ppl who slept showed decreased amygdala activity but increased vmPFC activity

• ppl who slept who showed lowest gamma activity during REM also showed greatest reduction in amygdala activity

alpha waves

• regular, medium-frequency waves

• 8-12 Hz

• produced when person resting quietly and awake

beta waves

• irregular, mostly low-amplitude waves of 13-30 Hz

• person awake and alert, attentive, or actively thinking

theta waves

• stage 1 sleep

• firing of neurons in neocortex becoming more synced

• transition stage between sleep and wakefulness

• 3.5-7.5 Hz, early stages of slow-wave and REM sleep

sleep spindles

• short bursts of waves 12-14 Hz that occur between 2-5 times a minute in stages 1-3 of sleep

K-complexes

• sudden, sharp waveforms only found in stage 2 sleep

• spontaneously occur at rate of about 1 per sec

slow-wave sleep

a non-REM stage of sleep characterized by delta waveform activity in an EEG record

delta waves

• less than 3.5 Hz

• regular, synchronous electrical activity during deepest stages of slow-wave sleep