Lengthening of REM sleep duration consecutive to learning in the rat

Lengthening of REM sleep duration consecutive to learning in the rat

SHORT COMMUNICATIONS 319 Lengthening of REM sleep duration consecutive to learning in the rat There is increasing evidence in favour of a functional...

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SHORT COMMUNICATIONS

319

Lengthening of REM sleep duration consecutive to learning in the rat There is increasing evidence in favour of a functional relation between the REM phase of sleep and learning. Newborn animals and babies show a greater proportion of REM sleep with respect to the total sleep time than do adults 5-s, and there is a progressive decrease in that proportion as growing continues, which is paralleled by a decrease in learning ability. Mental disease in man is accompanied by alterations in REM sleep parameters whenever a learning disability exists 2,3,9,1°. Aphasic patients show an increase in REM sleep time in relation with their recoverya. In order to obtain insight on these relations, the present experiment was designed in which a polygraphic study of sleep was performed on rats that were submitted to sessions of maze learning after food deprivation, with food as reinforcement, and on control animals similarly deprived of food and exposed to the labyrinth but without a learning situation. Inbred male albino rats were used weighing between 200 and 260 g, 70-80 days old. Every animal was implanted with electrodes for the chronic recording of EEG, EOG and neck E M G under ether anaesthesia. The labyrinth consisted of a start box and bifurcating wood runways 9 cm wide and 14 cm high, painted white and covered with plexiglass, ending in 7 different goals. The whole device measured 1.8 m long by 1.2 m wide. To accomplish a learning session the animal, previously deprived of food during 24 h, was positioned in the start-box and was allowed to run until it found a small food pellet previously placed in one of the goals, and the number of errors was recorded. When the rat had finished the ingestion of the food, it was removed from the goal, positioned in the start-box and allowed to run again. The procedure was repeated, trial after trial until the animal completed 6 successive runs with no errors. After this, the food was placed in another goal (but removed from the former) and the whole procedure repeated until the animal performed 6 runs to the new goal with no errors; the position of the food was then changed again and so on. The number of choice~ that the animal had to deal with in a single run ranged from 4 to 6. The session ended when the animal no longer worked, owing to satiety. This usuallyhappened after 1.5 to 2 h. The animal was immediately transferred to a sound-proof box, 30 cm × 40 cm × 40 cm in dimensions provided with a unidirectional mirror, where it was connected to an EEG apparatus. The recording of EEG, EOG and E M G commenced immediately. The events were timed so as to complete 3 h of record from about 2 p.m. to 5 p.m. Records of sleep from the animals fed in the labyrinth with no learning were also obtained immediately after removal from the labyrinth and from 2 p.m. to 5 p.m. as well as those from the untreated controls. In order to evaluate the activity of the animals in the labyrinth, each place in it (goals and runways) was designated by a letter. The animal's trajectory during the course of every experiment was observed and codified as a succession of letters. As all the place-to-place (letter-to-letter) Brain Research, 20 (1970) 319-322

IQ

3h AFTER LEARNING,

100.48

10

21

100.08

2h (X')*

Distance run in the labyrinth in

9

No. o f experiments

P

0.09

0.09

--

0.56

0.58

<

0.16 0.001

0.49

0.48

--

0.48

S W/total time

AND NO TREATMENT

REMS/total time

0.64

Total sleep (SW + REMS)/ total time

Ratios

A SIMULATED CONDITION

* These measurements were taken during the 2 h experimental period that preceded the recording; values are given in metres.

Food deprivation followed by learning P of the difference versus untreated controls Food deprivation followed by feeding in the labyrinth without learning P of the difference versus untreated controls Untreated controls

Condition

Abbreviations: SW, slow-wave sleep; REMS, sleep with rapid eye movements.

M E A N V A L U E S O F SLEEP P A R A M E T E R S M E A S U R E D I N P E R I O D S O F

TABLE 1

<

0.16

0.15

P

0.24 0.001

REMS/total sleep

z

c Z

©

© ,..]

b~

SHORT COMMUNICATIONS

321

distances were known, the total distance run in the experiment was computed by addition of the successive translations. The following criteria were used to characterize the phases of sleep. Slew-wave sleep: animal quiet with eyes closed, synchronization spindles and slow waves in the EEG and no eye movements in the EOG. REM sleep: twitching of the extremities and vibrissa, loss of postural tone and irregular breathing. Desynchronized EEG of low voltage in frontal leads with a theta rhythm in the occipital leads. Rapid eye movements in the EOG. Disappearance of neck muscular activity in the EMG. Three sorts of experiment were performed: recording of sleep without previous treatment; recording of sleep in animals with 24 h food deprivation, after they had been fed in the labyrinth without a learning situation; and recording of sleep in animals with 24 h food deprivation, after a learning session in the labyrinth using food as reinforcement. The 3 sorts of experiment were performed in every animal of a group of 8 in different sequences and a different number of times. The results showed that, in the experiments in which the animals were submitted to learning, there was a statistically significant increase in the REM sleep duration with respect to the controls, a nonsignificant increase in total sleep time and no changes in slow-wave sleep duration (see Table I). There was no difference in the distance run in the labyrinth by the animals submitted to learning and by the control animals exposed to the labyrinth without a learning situation, that developed exploratory activity. This finding excludes the consideration of muscular exercise as a factor in the observed REM sleep changes. The increase in REM sleep time observed after incremented learning suggests that the REM phase of sleep might be involved in the processing of information acquired during wakefulness. Such processing might consist in the transformation of a labile programme acquired in the learning session, with which the animal operates in the period of wakefulness that mediates between learning and the first sleep cycles, into a more stable programme devoid of superfluous information. This interpretation is in line with Dewan's programming theory for REM sleep 1. To test the interpretation proposed, we are presently studying the effect of REM sleep deprivation on the extinction of an acquired programme and on the acquisition of a new programme.

Instituto de Fisiologia, Facultad de Ciencias Mddicas, Universidad Nacional de Rosario, Rosario (Argentina)

MIGUEL A. LUCERO

1 DEWAN, E. M., The P (programming) hypothesis for REMs, Psychophysiology, 4 (1968) 365. 2 F~INBERG,I., BRAUN,M., AND SHULMAN,E., Electrophysiologicalsleep patterns in mongolism and phenylpyruvicoligophrenia(PKU), Psychophysiology, 4 (1968) 395. 3 GREENBERG,R., PEARLMAN,C., BROOKS, R., AND HARTMANN,E., Dreaming and Korsakoff's psychosis, Arch. gen. Psychiat., 18 (1968) 203-209. Brain Research, 20 (1970) 319-322

322

SHORT COMMUNICATIONS

4 GREENBERG, R., AND DEWAN, E. M., Aphasia and rapid eye movement sleep, Nature (Lond.). 223 (1969) 183-184. 5 PARMELEE,A. H., Sleep patterns in infancy. A study of one infant from birth to 8 months of age, Actapaediat. (Uppsala), 50 (1961) 160-170. 6 PARMELEE,A. H., SCHULZ, H. R., AND DISBROW, M. A., Sleep patterns of the newborn, J. Pediat., 58 (1961) 241-250. 7 ROFEWARG, H. P., DEMENT, W. C., AND FISHER, C., Preliminary observations on the sleeppatterns in neonates, infants, children, and adults. In E. HARMS (Ed.), Problems of Sleep and Dreams in Children, Pergamon, London, 1963. 8 VALATX,J. L., JOUVET, D., ET JOUVET, M., l~volution 61ectroenc6phalographique des diff6rents 6tats de sommeil chez le chaton, Electroenceph. clin. NeuropysioL, 17 (1964) 218-233. 9 ZARCONE,V., GULEVICH,G., PIVIK, T., AND DEMEriT, W,, Schizophrenia and partial REM sleep deprivation, Psychophysiology, 4 (1968) 383. 10 ZUNG, W. W. K., Antidepressant drugs and sleep in depressive disorders, Psychophysiology, 4 (1968) 397. (Accepted March 6th, 1970)

Brain Research, 20 (1970) 319-322