14.5 Four areas of the brain involved in sleep

Question 1

what is encephalitis lethargica

Answer 1

a viral infection that occurred during WW1 which caused all of its suffered to sleep almost constantly.

Question 2

what was found to be the neural mechanism of action of encephalitis lethargica?

Answer 2

brains of those who died from the disorder all had damage to the posterior hypothalamus and adjacent parts of the midbrain

Question 3

did all those with encephalitis lethargica sleep too much?

Answer 3

no, some slept too little

Question 4

what brain region was typically damaged in those with encephalitis lethargica who slept too little?

Answer 4

the anterior hypothalamus in adjacent parts of the basal forebrain

Question 5

what did the findings surrounding encephalitis lethargica and its two polar symptom clusters cause baron Constantin con economo to propose?

Answer 5

that the posterior hypothalamus promotes wakefulness, while the anterior promotes sleep

Question 6

has the belief that the posterior hypthal promotes wakefulness while the ant hypthal promotes sleep been confirmed?

Answer 6

Yes, by a series of lesion and recording studies in experimental animals

Question 7

what is a cerveau isolé preparation?

Answer 7

severing brain stems between the inferior colliculi and the superior colliculi to disconnect forebrains from ascending sensory input

Question 8

what occurs in cats with cerveau isole preparation?

how long does this (stimuli) effect last?

Answer 8

cortical EEG of the isolated cat forebrains was indicative of almost continuous slow wave sleep - only when presented with strong visual or olfactory stimuli (bc these systems are preserved in this preparation) was the high amplitude slow wave activity changed to desynchronized EEG (low amp high frequency EEG)
- arousing effect barely outlasted the simuli

Question 9

what is the encephale isole preparation?

Answer 9

the transection of the brain stem located at the caudal brain stem - disconnect the brain from the rest of the NS

Question 10

what occurs in cats wit encephale isole preparation?

- what does this suggest?

Answer 10

even tho it cuts many of the same sensory fibre as the cerveau isole, this preparation didn’t disrupt normal cycle of sleep EEG and wakefulness EEG
- that the structure for maintaining wakefulness was located somewhere inn the brainstem between the two transactions.

Question 11

what two findings indicated that the reticular formation was the brainstem structure that promoted wakefulness?

Answer 11

1. partial transections at the cerveau isole level disrupted normal sleep wake cycles of cortical EEG only when they severed the reticular formation core of the brain stem - when restricted to lateral areas containing ascending sensory tracts, they have little to no effect on cortical EEG
2. electrical stimulation of the RF in sleeping cats awakened them and produced a lengthy period of EEG desynchronization

Question 12

what did Moruzzi and Magoun propose on the back of the effects of cerveau isole, encephala isole, RF lesions and RF stimulation on sleep-wake cycles?

Answer 12

slow levels of activity in the RF produces sleep and high levels produce wakefulness.

Question 13

what do we commonly refer to the RF as, and wy?

Answer 13

the reticular activating system, because the idea that high levels of RF activity produce wakefulness is so widely accepted.

Question 14

what is another important role of the RF, and what is the rational for this?

Answer 14

REM sleep, makes sense because wakefulness and REM are so similar

Question 15

what controls REM sleep?

Answer 15

variety of nuclei scattered throughout the caudal RF, each site responsible for controlling one of the major indices of REM

Question 16

what are some of the sites in the caudal RF that control for specific REM indices?

Answer 16

1. site for reduction in core muscle tone
2. site for EEG desynchronization
3. site for rapid eye movement

Question 17

what is the primary implication of the finding that different neuronal clusters in the RF cause different aspects of REM sleep?

Answer 17

the refutation father idea that there is one behaviour and an associated brain structure in the brain - but this is not the case, since REM only happens when a n network of independent structures become active together

Question 18

can the physiological changes that underlie rem and other sleep periods disconnect?
Give 2 examples

Answer 18

yes, for instance

1. during Rem sleep deprivation, penile erections which normally occur during REM begin to occur during slow wave sleep
2. during total sleep deprivation, slow waves, which normally occur during slow wave sleep, occur during wakefulness

Question 19

what does the capacity for different indices of different types of sleep to come apart indicate?

Answer 19

that REM, slow wave and wakefulness are not each controlled by a single mechanism, they arise due to several mechanisms that are capable under certain conditions of operating independently of one another.