Class 14:
Consciousness and Sleep
BME 2301
Session Objectives
 To explore states of consciousness
and conscious experiences
 To discuss the electroencephalogram
methodology and output
Session Outline
 States of Consciousness





State vs. Experience
EEG
Sleep
Regulation
Coma & Brain Death
 Attention
 Language
Consciousness
 Conscious state refers to levels of alertness
 Includes states of being such as being awake,
drowsy, or asleep
 Defined by two things:
 Behavior, e.g. maximum attentiveness to
comatose
 Brain electrical activity, represented by the
electroencephalogram (EEG)
 Conscious experiences are that of which we are
aware such as thoughts, feelings, perceptions,
dreams, and reasoning during any state of
consciousness
Electroencephalogram (EEG)
 Measures integrated signal of graded potentials
occurring in cortical cells (primarily pyramidal,
~105) as conducted to head surface
 Array of electrodes, often in a cap, record
electrical signal as a function of time.
 EEG waves are characteristic of brain activity
 Amplitudes 0.5 – 100 microV;
affected by synchronicity
 Frequencies 0.5 – 40 Hz
http://neurosecurity.byu.edu/wp-content/uploads/2015/01/BYUstudent-in-EEG-cap-e1424805738508.jpg
EEG
10-20
System
MEG
Sensor Array:
Magnetic Field rather than
Voltage
Can measure fields inside the
brain as well
Cannot measure fields
perpendicular to sensor
Power (μV2)
Voltage (μV)
Rhythmic Potentials
(s)
(Hz)
Fourier Transform ->
Power Spectrum
Power decays as a function
of frequency (1/f)
Normal and abnormal rhythms
α – rhythm
(Alert, eyes closed)
β – rhythm
(Alert)
Epileptic seizure
States of Consciousness
State
Behavior
EEG
Alert
wakefulness
Awake, eyes open Beta rhythm
>12 Hz
Relaxed
wakefulness
Awake, relaxed,
eyes closed
Mainly alpha rhythm
8-12 Hz
Relaxed
drowsiness
Eyelids narrow;
head droops;
momentary lapse
of attention
Decrease in alpha
wave amplitude and
frequency
State
States
NREM
(slowof
wave) sleep
– stage N1
Behavior
Consciousness
Light sleep, easily
aroused,
continuous lack of
awareness
EEG
Alpha waves  in
amplitude &
frequency;
interspersed with
theta (4-8 Hz) and
delta (<4 Hz) waves
NREM – N2
Further lack of
Alpha replaced by
sensitivity to
random waves of
arousal
greater amplitude
NREM – N3
Deep sleep;
Much theta & delta;
difficult to awaken increasing delta
REM
Greatest muscle
Beta rhythm (as if
(paradoxical) relaxation;
awake)
sleep
difficult to arouse;
rapid eye
movements
EEG Waves
Increasing
wave
frequency
~10 – 60 min REM/cycle;
each cycle 60-90 min
Increasing
wave
amplitude
Time Spent in Stages of Sleep
Awake
NREM Sleep
REM Sleep
Other neuroimaging modalities
Recap Questions
 Rhythmicity in different bands
Why We Need Sleep
 Sleep deprivation studies suggest that sleep is
a homeostatic requirement:
 Deprivation of sleep impairs the immune system;
increases risk of obesity and heart disease; causes
cognitive and memory deficits; and ultimately leads
to psychosis and even death.
 During sleep, the brain experiences
reactivation of neural pathways stimulated
during the prior awake state
 Well-rested subjects demonstrate better memory
retention, higher level reasoning, problem-solving,
and attention to detail.
 Well-rested subjects develop more immunity
following a vaccination.
Brain regions regulating states of consciousness
 RAS = reticular activating system “perks up”
the cortex
•
•
•
•
 Monoamines secreted are histamine, norepinephrine,
and serotonin; act as neuromodulators in this system
SCN is circadian
pacemaker
Orexins are neuropeptides that stimulate
the awake state.
Ach facilitates
transmission of sensory
info to / through
thalamus and up to
cortex
GABA from sleep center
is inhibitory
Regulation of States of Consciousness
In hypothalamus
Coma and Brain Death
 Coma – extreme decrease in mental function
coupled with
 sustained loss of capacity for arousal
 no outward behavioral expression of mental function
 Coma may be reversible or irreversible
 Brain Death – brain no longer functions and
appears to have no chance of functioning again;
specific though not universal criteria define this
Owen et al., 2006
Recap Questions
 Sleep Circuits
Attention
Behavioral consequences of attention



•
Enhances detection & recognition
Speeds reaction time
Gateway to memory
Neural substrates of attention
•
•
Posterior Parietal Cortex
Brain areas connected to it
Neglect
Line Bisection Test
Unilateral neglect
after brain injury on the right side
Impairment of Attention: Neglect



Once they detect a visual stimulus, patients have
normal visual acuity and are able to detect details
Much more pronounced when two stimuli are present
and compete for attention (Extinction)
Deficit does not involve only the left side of visual field,
but also left side of objects presented entirely in the
right visual field
Neglect
Facial area of primary
motor cortex
(commands facial &
tongue muscles to
speak words)
Wernicke’s
Area [in LEFT cortex] (language
comprehension; plans content of
spoken words)
Broca’s
Area [in LEFT
cortex] (programs
sound patterns of
speech)
Primary auditory cortex
(perceives sound)
4
Angular gyrus of parietaltemporal-occipital association
cortex (integrates sensory input)
2
3
Primary visual cortex
(perceives light images
as in view of written
words or speaking
mouth)
1b
1a
Wernicke’s
area
Visual cortex
Language
Language Processing Can Involve
any Sensory Modality
Language Impairments: Aphasias
 Aphasias are language deficits resulting from brain
damage
 Aphasias are diagnosed according to the patient’s
ability to understand or express language
 Broca’s Aphasia – no fluency, intact comprehension
 Wernicke’s Aphasia – no comprehension, some fluency
Recap Questions
 Attention
 Language