Bi/CNS 163

Bi/CNS 163. Sleep and Dreams

Sleep and Memory

General Comments on Memory

Animal Experiments

Human Experiments

Problems with Memory Experiments

Memory Consolidation Theory

Unresolved issues: Hot topics for a Ph.D

References

General Comments on Memory

Why do we dedicate a whole class to Learning and Memory ?

It is interesting.

We will be doing experiments on sleep and memory.

Important function for animals now ?

Interesting applications ?

There is no one single type of memory

Memories can be distinguished by many behavioral, anatomical and physiological characteristics:

How long they last (iconic , working, short-term , long-term)
Acquisition time (one shot, repetition, associative)
Acquisition mechanism
Anatomical correlates (e.g. hippocampus dependendent or not)
Kinetics

How are memories acquired ?

Sensory Processing. Consolidation. Storage. (nont true for all kinds of memory).

Synaptic modifications. LTP/LTD (Long term potentiation/ Long term deppression).

Neural Networks. Hopfield associative Networks.

Gene Expression, Neurogenesis. Neural death.

Animal Experiments

Three basic strategies :

Record changes in sleep stages following or preceding learning.

Sleep Deprivation.

Correlation of diurnal and nocturnal neuronal activity.

REM sleep levels increase after learning complex tasks.

Type of experiments :

Y-maze shock-avoidance task.
Shapes discrimination (electric shock feedback).
Morris Water Maze .

f(type of animal, strain, number of training trials per session,task).

Most prominent increases in first night.
REM increases start 6 hrs. after training.
REM increases as predictor of learning !
Bigger increases in "faster-learning" animals.
Rats that do not show the REM increases do not learn the task.
Latency to onset of REM increases > 3 hr.
Persistence : several hours.

Correlation between "Enriched Environments" and REM sleep.

Gross Measurements

Correlations between enriched environments and dendritic branching, thicker cortex, synaptic contacts, animal weight.

Increases in REM sleep. Some studies also claim increases in SWS (slow wave sleep).

Sleep Deprivation Experiments

"REM Windows".

Increases in Ach/AchE parallel REM increases. Anisomycin / Scopolamine experiments.

Even when severely REM sleep deprived, rats seem to learn normally if they are allowed to have normal sleep during this PSW.

Human Experiments

Looking for increases/decreases in sleep stages after learning.

Results are controversial. The answer, lies in the details.

Sleep Deprivation.

Declarative explicits tasks, not affected by sleep ?

No REM window found in humans.

Karni et al. To be discussed in class.

Problems/Comments

Impoverished environments are very impoverished.

Method : "pedestal" technique.

Some Non-REM sleep is also removed.

Not all REM sleep is removed (80-90 % is).

Stress differences. No blood cortisol measured.

Falling into the water.

Movement restriction

Humans, little additional stress in REM-deprived subjects.

Sleep length increases in many cases as well.

No REM increases in learning because tasks are unimportant ?

Memory Consolidation Theory for REM sleep

Definitely not the only theory about REM sleep.

"Systematic Program Clearance".

Dreams are composed of throw-out products.

Crick-Mitchison "Reverse-Learning" hypothesis.

Age and REM sleep.

2 months premature 80 %

1 month premature 67 %

newborn 50 %

adults 20 %

True in most mammals and in chicks

f(birth developmental stage)

Precocious animals, little REM sleep. (e.g. walking in a few minutes). vs. altricial.

Almost all mammals show REM sleep.

Caution : But ... What is REM sleep ?

REM sleep deprivation --> REM rebound.
Dream recall : transfering short-term memory into long term memory.
Condensation in Dreams and spurious states
Echidna, mammal with no REM sleep : large neocortex (relative to its size).
Dolphins, no REM sleep detected. Seals do show REM sleep.

No experimental support so far.

Autism and sleep

No identified etiology.

Spectrum of autistic-like emotional disorders. E.g. Asperger’s syndrome, Rett Syndrome, Early infantile autism (EIA), hereditary progrssive dystonia (HPD).

Autism

abnormal social behaviour.

abnormal language skills.

echolalia

inadequate eye contact.

repetitive or stereotyped behaviour

unreasonable insistence on precise routines.

Asperger’s syndrome

Pedantic, socially obtuse, long-winded speech.

Impaired non-verbal communication.

Odd, egocentric social interaction.

Resistance to change, repetitive activities.

Clumsy motor movements, odd posture and gait.

Good rote memory.

Unresolved issues: Hot topics for a Ph.D

Sleep and LTP/LTD.

Effects of REM sleep deprivation in newborn animals?

Synaptic plasticity and sleep deprivation ?

Appropriate controls (e.g. stress ) for the animal sleep deprivation studies. For example, using the Rechstchaffen apparatus.

Learning disabilities, memory problems and REM sleep.

Neurogenesis, neural death and sleep.

References

This is a partial list; for a complete list of references, please go to the Bibliography page

Crick, F. and G. Mitchison (1983). "The function of dream sleep." Nature 304: 111-114.

Hobson, J. (1995). Sleep. New York, Scientific American Library.

Karni, A., D. Tanne, et al. (1994). "Dependence on REM sleep of overnight improvement of a perceptual skill." Science 265: 679-681.

Kavanau, J. L. (1997). "Memory, sleep and the evolution of mechanisms of synaptic efficacy maintenance." Neuroscience 79: 7-44.

Lavie, P. (1996). The enchanted world of sleep. New Haven, Yale University Press.

Skaggs, W. E. and B. L. McNaughton (1996). "Replay of neuronal firing sequences in rat hippocampus during sleep following spatial experience." Science 271: 1870-1873.

Wilson, M. A. and B. L. McNaughton (1994). "Reactivation of Hippocampal Ensemble Memories During Sleep." Science 265: 676-679.

Gabriel Kreiman

Gabrielk@caltech.edu

Last modified, 01/11/2000