Lecture 29: Sleep, Consciousness, and Attention

Fatal familial insomnia

inherited prion disease (mutation of PRNP gene)

onset in middle-age

death within 1-3 years

Changes in sleep with age

sleep more lightly, for shorter durations, and with less time spent in REM sleep

Circadian rhythm

photosensitive RGCs contain melanopsin

project to suprachiasmatic n. (SCN) of hypothalamus

SCN activates paraventricular n. (PVN) of hypothalamus

PVN activates pineal gland via sympathetic stimulation

pineal gland synthesizes melatonin

melatonin affects activity cycle

Circadian Rhythm and Sleep Deficit

The drive to sleep depends on two

main components: Circadian rhythm and Time since last full period of sleep (sleep deficit)

Toward evening, sleep deficit continues to increase, while circadian rhythm of arousal begins to wane, producing a sleep drive

Although the SCN is the “master clock” it does not generate sleep or arousal

With sleep deprivation, drive to sleep is at maximum when circadian rhythm is at a minimum

Sleep Stages

During Sleep

Initial descent into slow-wave sleep

Rapid ascent into REM sleep

Rapid descent into slow-wave sleep

Repeat ~4 times

As the night progresses, duration of slow wave sleep shortens while duration of REM sleep increases

Characteristics of REM sleep

Rapid eye movement

REM atonia: paralysis of large muscle groups (except diaphragm &

extraocular mm.) and twitching of small muscles

Pulse and respiration reach waking levels

Sexual arousal

Ascending reticular activating system

Lateral hypothalamic n

Lateral hypothalamic n

Lateral hypothalamic n

Lateral hypothalamic n

small population of cells produce orexin (hypocretin)

active during wakefulness

stimulates tuberomammillary n.

suppressed during SWS & REM

Lateral hypothalamic n

Tuberomammillary n

Tuberomammillary n

source of histaminergic projections

stimulated by orexin-producing neurons of the lateral hypothalamic n.

active during wakefulness

suppressed during SWS & REM

Ventrolateral preoptic n

Ventrolateral preoptic n

GABA-ergic

inactive during wakefulness

active during all stages of sleep

initiates the sleep cycle by suppressing the ARAS and TMN

Initiation of Sleep

Narcolepsy

REM sleep attacks: individual enters REM sleep directly

Cataplexy: sudden loss of muscle tone

Human narcolepsy: autoimmune destruction of orexin-producing neurons in the lateral hypothalamic nuclei

REM cycles: The Reciprocal Interaction Model

Dreaming

primarily during REM sleep

Dreaming may occur near the onset of sleep (hypnagogic) or just prior to waking (hypnopompic)

Characteristics of REM dreams

intense emotions

bizarre/illogical content

rich sensory perception

uncritical acceptance

memory deficit (acquisition suppressed)

Increase in limbic activity, coupled with suppression of the dlPFC, may explain the emotionality of REM dreams and our acceptance of their illogical content

REM atonia

Binocular Rivalry

When a particular stimulus is presented to one eye while a discordant stimulus is presented to the other, the visual perception is of either one stimulus

or the other, alternating every few seconds, with only transient blending of both eyes’ view

The activity of neurons in visual association cortex can be associated with a preferred stimulus

The fusiform face area (FFA) becomes active when perception shifts to faces

The parahippocampal place area (PPA) becomes active when perception shifts to houses

Activation of dlPFC and parietal association cortex are correlated with shifts in perception for a variety of

visual rivalry tasks- executive-cognitive

control of perception

Attentional Blink

Attentional blink refers to a deficit in

reporting a second target

Due to attentional (not sensory) limitations b/c blink does not occur when subjects ignore T1

While Target 1 and Target 2 both elicit the same early EEG response, a late-stage “P3” component is present only when the subject successfully perceives Target 2

The P3 activity consists of prefrontal association cortex (P3a) followed by parietal association cortex (P3b)

The P3 component is thought to represent the neural process by which selective attention brings a target into conscious awareness

Consciousness

Coordinated activity of frontal and parietal association allows stimuli to reach conscious awareness

Frontoparietal “filter” provides coherent, seamless experience of the world

Forms part of the central-executive network of cognition

Anti-reductionist/Integrated

Information Theory- Consciousness is not reducible to (cannot be entirely explained by) the physical workings of the brain

Reductionist/Computational-

functionalist hypothesis- Consciousness can be reducible to (could be explained by) the physical workings of the brain; Monism: the brain and the mind are a singular phenomenon