Learning, Memory, Cognition - 2

Learning, Memory, Cognition – 2

P475Consolidation of a motor sequence learning task increases sleep

spindles

A. MORIN, J. DOYON, J. PERREAULT, S. FRENETTE, M.

PARENTEAU and J. CARRIER

Psychology, University of Montreal, Montreal, QC, Canada

Growing evidence supports the role of sleep in consolidation of motor

learning tasks. However, mechanisms involved in the consolidation

process are not well understood. We investigated sleep spindles by

comparing sleep following training on a motor sequence task for which

significant overnight gains were anticipated, and sleep after training on

a control task where no such consolidation was expected. After a

screening night in our laboratory, 12 young healthy participants were

submitted to two PSG sleep recordings, separated by one week. Before

each recording night, subjects were trained in the evening on either a

specific motor sequence (SEQ), or on a control task consisting to press

the response key according to the displayed number (1–4) appearing in

a random order (CTRL). They were retested 12 h later in the morning.

The two tasks were counterbalanced across the two nights. Sleep

spindles were visually counted (frequency 12–16 Hz, duration > 0.5 s)

for the total non-REM sleep at sites FZ, CZ and PZ. Significant gains

in the number of sequences (14%, P < 0.0001) were observed at retest

for the SEQ task, but only minimal gains for the CTRL task (4%,

P = 0.02). Higher amount of sleep spindles was found in the post-

training sleep associated to the SEQ, compared to the CTRL task in all

three sites: Fz [t (11) = 4.42, P = 0.001], Cz [t (11) = 4.35,

P = 0.001] and Pz [t (11) = 3.91, P = 0.002]. Overnight gains were

correlated (r = 0.63, P = 0.03) with sleep spindles increase at site Cz

in the last third of post-training non-REM sleep. No difference was

observed in PSG sleep parameters between the SEQ and CTRL nights

including amount of sleep stages. These results demonstrate that sleep

spindles increase in post-training sleep is not simply related to the

motor activity generated by the task, but to the consolidation process

per se. More interestingly, they suggest that consolidation-based

enhancement effects are associated with enhanced sleep spindles during

the night, and show that spindles may be an efficient consolidation

indicator. We propose that sleep spindles may trigger cellular

mechanisms that initiate neuronal plasticity related to motor memory

consolidation.

P476Neuronal correlates of sleep-dependent declarative memory

consolidation

S. FISCHER1, A. ISCHEBECK2, F. KOPPELSTATTER3,

S. FELBER3, W. W. FLEISCHHACKER4 and

H. HINTERHUBER1

1Department of General Psychiatry, Innsbruck Medical University,

Innsbruck, 2Department of Neurology, Innsbruck Medical University,

Innsbruck, 3Department of Magnetic Resonance Imaging, Innsbruck

Medical University, Innsbruck and 4Department of Biological Psychia-

try, Innsbruck Medical University, Innsbruck, Austria

Sleep essentially participates in memory consolidation, a process that

converts newly acquired memory traces into a long-lasting form.

Whereas the enhancing effect of sleep on procedural memory has been

well established in humans, evidence for a similar improving influence

of sleep on declarative memory mainly derives from spatial learning in

rodents. Hippocampal ensembles modified by spatial experience during

waking have been shown to be spontaneously reactivated during

subsequent sleep. During this offline reprocessing the newly encoded

memory traces are supposed to be translated from short-term

hippocampal to long-lasting structures within the neocortex. In

humans, declarative learning likewise depends on the integrity of the

hippocampus. Here, using functional magnetic resonance imaging

(fMRI), we aimed at investigating sleep-related changes in the cerebral

representation of newly encoded declarative memories. Healthy

subjects were trained on a word-pair learning task in the evening

before a night of sleep or wakefulness. Retrieval testing took place

immediately after learning and 48 h later, after all subjects had an

additional night of recovery sleep in order to rule out effects of sleep

loss on memory retrieval. During retesting after the retention interval

subjects lay in the fMRI scanner in order to map task-related patterns

of brain activation. Our preliminary results indicate that memory

performance on the word-pair learning task was significantly enhanced

by sleep. Moreover, sleep-dependent memory improvements were

accompanied by reduced activation in the medial temporal lobe system

and increased activation in several neocortical brain sites. Our findings

suggest, that sleep enhances the consolidation of newly encoded

declarative learning material by reorganizing its brain representation

from preferential hippocampal to neocortical storing sites.

P477Investigating the relationships between sleep and memory in

Alzheimer’s disease

G. RAUCHS1, M. SCHABUS1, F. BERTRAN2, F. EUSTACHE3,

P. DENISE2, G. GRUBER4 and P. ANDERER4

1Centre de Recherche du Cyclotron, Liege, Belgium, 2Service des

Explorations Fonctionnelles Neurologiques, CHU de Caen, Caen,

France, 3Inserm-EPHE-Universite de Caen, Unite E0218, GIP Cyceron,

CHU de Caen, Caen, France and 4Department of Psychiatry, Medical

University of Vienna, Vienna, Austria

Alzheimer’s disease (AD) is characterized by an early and severe

impairment of episodic memory, but also by sleep changes including a

decrease in the amount of REM and slow-wave sleep as well as

changes in spindle activity [1]. As numerous studies indicate a

beneficial role of sleep for memory consolidation [2], we investigated

the potential link between sleep changes and episodic memory decline

in AD. Fourteen patients with mild to moderate AD (MMSE:

24.9 ± 2; age: 76.9 ± 4) and 10 healthy elderly controls paired in

age participated in the study. Episodic memory was assessed using an

adaptation of the Grober and Buschke procedure [3] and a story recall

test. Learning occurred in the evening with retrieval in the morning

after a night of sleep. Sleep was scored according to standard criteria.

Results revealed that episodic memory was significantly impaired in

AD patients compared to controls in both tasks. In contrast, classical

sleep parameters did not differ between groups. As healthy elderly

subjects showed ceiling performances, correlation analyses were only

performed for the AD group. No significant correlations were found

between sleep measures and episodic memory decline. We conclude

that in the early stages of AD, sleep architecture is not significantly

altered as compared to healthy elderly subjects. However, because

recent studies also indicated robust associations of sleep spindle

activity with measures of general cognitive abilities [4,5] and episodic

memory [6] we are currently running additionally analyses on sleep

� 2006 European Sleep Research Society, JSR 15 (Suppl. 1), 1–253

230

spindles in AD patients.GR was supported by the France Alzheimer

association.

References:

1. Petit et al. (2004), J Psychom Res, 487–96.

2. Rauchs et al. (2005), J Sleep Res, 123–40.

3. Grober & Buschke (1987), Dev Neuropsychol, 13–36.

4. Bodizs et al. (2005), J Sleep Res, 285-92.

5. Schabus et al., in press.

6. Schabus et al (2004), Sleep, 1479–85.

P478Influence of the selective serotonin reuptake-inhibitor fluvoxamine

on procedural memory consolidation during sleep

B. H. RASCH, J. POMMER and J. BORN

Neuroendocrinology, University of Luebeck, Luebeck, Germany

Sleep serves memory consolidation. More specifically, procedural

memory consolidation of motor skills has been shown to benefit

particularly from REM sleep after training. REM sleep occurs mostly

in the second part of the night and is associated with prominent

changes in neuromodulator activity: Levels of acetylcholine are high,

whereas levels of serotonin and norepinephrine drop to a minimum. In

the present study we focused on serotonin, which has been implicated

in memory processes and is known to influence the induction and

persistence of long-term potentiation. We investigated whether low

levels of serotonin – characteristically occurring during REM sleep –

are critical for procedural memory consolidation by pharmacologically

increasing serotonin during the second part of the night. Sixteen

healthy young men were tested in two experimental nights in the sleep

laboratory. Before sleep, the participants learned two procedural

memory tasks (sequence finger tapping and mirror tracing). In one

night, they received the selective serotonin reuptake inhibitor

fluvoxamine (50 mg p.o.) immediately after learning. In the other

night they received a placebo according to a double-blind cross-over

design. Retrieval was tested 36 h later. Fluvoxamine, reaching its

maximal plasma concentrations after 3–5 h, significantly reduced the

amount of REM sleep compared to placebo, whereas other sleep stages

and total sleep time did not differ between the two conditions.

However, memory retention in both tasks was not affected by

fluvoxamine. Thus, increased levels of serotonin associated with

suppressed REM sleep in the second half of the night do not influence

procedural memory consolidation, which probably relies on more

specific neuromodulatory or electrophysiological characteristics than

levels of serotonin or the amount of REM sleep per se.

P479The effect of napping on implicit and explicit memory

consolidation

C. SAUTER1, D. C. MOSER1, P. ANDERER2, G. KLOESCH1,

K. HOEDLMOSER3, W. STADLER3, M. SCHABUS3 and

J. ZEITLHOFER1

1Department of Neurology, Medical University of Vienna, Vienna,2Department of Psychiatry, Medical University of Vienna, Vienna and3Department of Physiological Psychology, University of Salzburg,

Salzburg, Austria

Aims: The present study tested whether 90 min naps in the afternoon

have a positive impact on implicit and explicit memory tasks as

compared to active wakefulness.

Methods: A total of 88 healthy young subjects (44 female, aged

23.5 ± 2.4) were either assigned to an implicit or an explicit memory

task. All subjects filled in a sleep log and were monitored by actigraphs

for 14 days. On day 7 and day 14 subjects learned to perform either a

mirror tracing task (cf. Plihal & Born, 1997), or a paired-associate

word list task (cf. Schabus et al., 2004), and a corresponding control

task (without learning component). Subjects were randomly assigned

to either a napping or an active wakefulness group (listening to radio

dramas) between 14:00 and 15:30 h. Performance was checked before

and 45 min after the nap/no-nap condition. All PSG data was

analyzed by Somnolyzer 24 x 7 and controlled visually.

Results: Mean total sleep time of naps in the learning condition was

76.3 ± 14.4 min, mean sleep efficiency was 83.3 ± 15.7%, and mean

sleep latency was 7.6 ± 10.8 min. These variables did not differ from

those of the control condition. While subjects showed no improvement

in the paired-associate list after the nap, performance of correctly

retrieved word pairs even deteriorated significantly in the active

wakefulness group (P < 0.05). Error time in the mirror tracing group

was reduced after napping, and increased in the no-nap condition

(P < 0.05). Postsleep performance did not correlate with any sleep

stage.

Conclusion: Behavioural performances were not related to any sleep

stage in the napping groups. Napping improved memory consolidation

in an implicit, but not in an explicit paired-associate list. By contrast,

active wakefulness even led to performance deteriorations in both

memory tasks.

Acknowledgment: Research supported by the Austrian �Fonds zur

Foerderung der wissenschaftlichen Forschung� (FWF), Project

P-15370-B02.

Keywords: napping, active wakefulness, memory consolidation.

P480A beneficial effect of a post-training nap: countering interference

and the evolution of delayed gains in a motor sequence-learning

task

M. KORMAN1, J. TAMIR2, J. DOYON3, J. CARRIER3,

Y. DAGAN2 and A. KARNI1

1Brain-Behaviour Research Center, University of Haifa, Haifa, Israel,2Chronobiology and sleep laboratory, Sheba Medical Center, Tel-Aviv,

Israel and 3Departement de psychologie, Universite de Montreal,

Montreal, QC, Canada

A growing body of evidence indicates a role for sleep in the post-

training consolidation of motor memory. In humans, a night’s sleep

has been shown to result in significant overnight performance

improvements (delayed, off-line, gains) while an equivalent time in

the wake state did not. Two behavioural phenomena characterize

memory consolidation: interference, a process whereby the memory of

a given experience is transformed into a robust and enduring form; and

the emergence of delayed gains in performance. Here, we report a

study aimed to test the hypothesis that the two aspects of procedural

memory consolidation – the off-line delayed improvement in

performance and the declining sensitivity to competing experience –

are functionally related to each other and that both are affected by

sleep. Four groups of participants were trained in a single session on

performing a specific sequence of finger opposition movements.

Pretraining, immediate, 12 and 24 h post-training performance tests

were recorded. Two groups were trained on a second sequence,

composed of identical component movements arranged in the reversed

order, 2 h following the initial training (interference training). No

additional training was given to the two other groups. From these

four, two groups, one with, the other without interference training,

were given 90 min day-time sleep immediately after the training

session. Without the nap, interference training prevented the expres-


Learning, Memory, Cognition – 2 231

sion of the delayed gains by 24 h post-training. However, given

afternoon post-training nap, robust delayed gains, at 24 h post-

training, were expressed even after interference training. Our results

demonstrate that the process of procedural memory consolidation is

sensitive to both sleep and interference in a time-window of several

hours post-training. Post-training day-time sleep (nap) may result in

faster memory trace stabilization.

P481Brain activity related to memory retrieval changes after overnight

sleep: a study of EEG theta frequency

W. STADLER1, M. SCHABUS1, K. HOEDLMOSER1,

C. SAUTER2, P. ANDERER3, G. GRUBER3, W. KLIMESCH1 and

J. ZEITLHOFER2

1Department of Psychology, University of Salzburg, Salzburg,2Department of Neurology, Medical University of Vienna, Vienna and3Department of Psychiatry, Medical University of Vienna, Vienna,

Austria

It is broadly recognized that sleep subserves the consolidation of

memories acquired during daytime. The present results could help to

explain how memory related brain activity is modified after overnight

sleep. EEG was recorded during a paired associate word list task

carried out before and after overnight sleep in 17 subjects. Analysis of

relative changes in activity during memory retrieval (ERS/ERD)

focused on activity in the theta frequency range. Theta rhythm is

associated with encoding and retrieval of episodic memories. In the late

afternoon before spending a night in the laboratory participants

learned a list of 160 word-pairs. After encoding only the first word of a

pair was presented in a retrieval session and the subjects were asked to

name the associate they had encoded before. After 8 h of overnight

sleep a second retrieval session was carried out. Whereas a significant

increase in reaction times was found after overnight sleep the number

of correctly retrieved words increased only slightly. Theta activity

recorded during retrieval was analysed separately for correctly

retrieved words (hits) and compared to non-remembered words

(misses). As expected on the basis of previous findings, theta activity

was generally higher for hits compared to misses. After 8 h of sleep the

theta synchronisation was further increased for hits and less extended

in time. Maximal activity was shifted from central locations (as found

in the first retrieval session) to left parietal sites. In addition, theta

activity also increased for misses which was interpreted as reflecting the

establishing of a memory trace for the cue (in cases in which the second

word was not remembered). Together with faster reaction times the

increased theta activity could point to a strengthening of the memory

trace of formerly stored words that had been achieved overnight. As a

consequence, the episodic trace can be accessed more efficiently as

reflected in shorter theta activity and faster responses.

P482EEG theta power during sleep and memory performance

K. HOEDLMOSER1, W. STADLER1, M. SCHABUS1,

P. ANDERER3, C. SAUTER2, G. KLOESCH2, W. KLIMESCH1

and J. ZEITLHOFER2

1Psychology, University of Salzburg, Salzburg, 2Neurology, Medical

University of Vienna, Vienna and 3Psychiatry, Medical University of

Vienna, Vienna, Austria

The aim of the present study was to examine the relationship of EEG

parameters during sleep – especially theta power – with memory

consolidation. 16 right handed subjects (eight male), mean age

25.0 years (SD = 2.85) had to perform a declarative learning task

consisting of 160 visually presented word pairs and were tested (cued

recall) before and after spending a night in sleep laboratory with

complete polysomnographic montage. Two performance groups (good

versus. bad memory performers) were created using a median split

according to the subject’s retrieval rate during cued recall. Quantitative

EEG analyses revealed significantly stronger theta synchronization

during REM sleep in good as compared to bad memory performers.

Theta synchronization was most prominent over visual processing

regions that are captured by occipital electrodes. It has been repeatedly

shown that theta oscillations as recorded over the human scalp,

respond selectively – usually with a phasic increase in band power – to

the encoding and retrieval of new information (e.g. Klimesch, 2001).

Memory consolidation is suggested to be based on hippocampal-

neocortical interactions (e.g. Buzsaki, 1996) taking place during

periods of quiet wakefulness or sleep. Two steps are postulated: (i)

�loading� of the hippocampus during REM and wakefulness and (2)

�storing� during slow-wave sleep. Memory for specific events is first

encoded by the hippocampus and then relayed to the neocortex. Theta

and gamma oscillations are postulated to be involved in information

transfer from neocortical to hippocampal areas. In our analysis

subjects having more theta frequency during sleep are also those

showing general higher memory performances. It is speculated that

increased theta activity during REM might be beneficial for memory

consolidation or in other words much theta throughout life might

shape more efficient networks for general memory processes.

Acknowledgment: This study was supported by the Austrian Science

Fonds (FWF; P-15370).

P483Sleep-dependent memory consolidation in patients with

schizophrenia

T. KRUPALIJA1, A. HOFER2, M. EDLINGER2,

H. HINTERHUBER1, W. W. FLEISCHHACKER2 and

S. FISCHER1

1Department of General Psychiatry and 2Department of Biological

Psychiatry, Innsbruck Medical University, Innsbruck, Austria

Impaired memory is one of the most consistently reported cognitive

disorders in patients with schizophrenia. Whereas previous studies

investigating memory function in schizophrenia primarily focused on

the stages of information encoding and retrieval, studies on memory

consolidation, a time-dependent process that converts labile memory

traces into more permanent and enhanced forms, are quite rare. Since

memory consolidation in healthy subjects is significantly enhanced by

sleep the purpose of the present study was to examine sleep-related

memory consolidation in schizophrenia. Seven patients with schizo-

phrenia in remission and seven healthy control subjects participated in

two experiments investigating (i) episodic and (ii) procedural memory

consolidation. At the time of the study patients received a second-

generation antipsychotic and were clinically stable for at least

6 months. None of them received any other concomitant medications.

Healthy control subjects were matched for age, sex and educational

level. Before and after 12 h retention intervals positioned during the

day (wake condition) or during the night (sleep condition) subjects

were tested using an episodic virtual town learning task or a procedural

visual discrimination task. Consistent with previous studies sleep in

healthy subjects significantly enhanced both episodic and procedural

memory consolidation. In contrast, patients with schizophrenia had a

greater benefit from retention intervals of wakefulness: episodic

memory performance only improved in the wake but not in the sleep

condition. With respect to the visual discrimination task, wakefulness


232 Learning, Memory, Cognition – 2

appeared to prevent a performance deterioration occurring across

intervals of sleep. Our findings indicate that different from healthy

subjects memory consolidation in patients with schizophrenia benefits

from wakefulness rather than from sleep. We speculate that the brain

processes underlying sleep-dependent memory consolidation in healthy

subjects to some extent may be active during wakefulness in

schizophrenia.

P484Motivation-dependent motor memory formation during sleep

T. KRUPALIJA1, J. BORN2 and S. FISCHER1

1Department of General Psychiatry, Innsbruck Medical University,

Innsbruck, Austria and 2Department of Neuroendocrinology, University

of Lubeck, Lubeck, Germany

There is strong evidence that sleep essentially enhances motor memory

consolidation. Here, we examined whether sleep differentially affects

this process depending on motivational cues. Young healthy subjects

were trained on two different finger motor sequences one immediately

after the other. Directly thereafter they were informed that they will be

retested on both of these sequences after a 12-h retention interval and

that any performance improvements with respect to the first (n = 30)

or the second (n = 32) sequence learned will be rewarded with extra

earnings. In both of these conditions half of the subjects slept whereas

the other half stayed awake during the retention interval. In order to

eliminate any further finger movements the left (trained) hand was

fixed. At the beginning of the retest session subjects were informed that

contrary to their expectations any extra earnings will not exclusively

depend on performance improvements with respect to one of the

sequences but on the average improvement with respect to both of

them. Sleep significantly improved performance on the sequence that

was linked with monetary reward before the retention interval

irrespectively if this was the first or the second sequence learned

(P < 0.01). Wakefulness did not provide any beneficial effect

(P > 0.4). From these findings we conclude that one feature of

sleep-dependent memory consolidation might be a selective enhance-

ment of memories that are associated with increased motivational load.

P485Sleep spindles and memory consolidation

J. ZEITLHOFER1, B. WEBER2, C. SAUTER1, G. KLOESCH1,

P. ANDERER3, M. SCHABUS4, B. SALETU3 and W. KLIMESCH4

1Neurology, Medical University Vienna, Vienna, 2Institute of Psychol-

ogy, University of Vienna, Vienna, 3Psychiatry, Medical University

Vienna, Vienna and 4Physiological Psychology, University of Salzburg,

Salzburg, Austria

Introduction: There is growing evidence that sleep spindles in stage 2

are linked to reprocessing of implicit and explicit memory traces. The

current investigation focuses on different variables of night sleep and

two learning tasks.

Subjects and methods: 45 healthy subjects (23 males, 22 female; age:

20–30a) participated in the study, 24 of them in an explicit, (word-pair

association task) and 21 in an implicit, procedural (mirror tracing)

learning task. The learning effect was tested in the evening and in the

morning after the encoding. All night sleep recordings were the basis

for the evaluation of the spindles at C3-M2 and C4-M1, which were

detected automatically.

Results: In the explicit task a positive correlation was found between

correct answers (in the morning) and spindles per epoch (r = 0.44;

P = 0.031) as well as in the spindle difference (learning versus control

night: r = 0.421; P = 0.041). The higher the number of spindles in the

night after learning the higher is the number of correct answers in the

morning. A positive correlation between stage 2 and correct answers in

the morning was found too (r = 0.452; P = 0.027). For the implicit

learning task a significant improvement was found in the morning after

the learning condition. Learning performance in the morning was

whether correlated with spindle variables (spindles per epoch, spindle

frequency and amplitude, difference) nor with sleep stages.

Discussion: Results show that memory consolidation processes are

very complex and sleep spindle activity may reflect the replay of

learned information in hippocampo-cortical networks.

Acknowledgement: The research was supported by a grand of the

Austrian �Fonds zur Forderung der wissenschaftlichen Forschung�,Projekt P-15370.

P486Slow wave sleep and recollection in recognition memory

M. TIBERGE2, A. DAURAT1, P. TERRIER1 and J. FORET3

1Laboratoire Travail et Cognition, UMR 5551 CNRS-Toulouse II

university, Toulouse, 2Service Neurologoe, CHU Rangueil, Toulouse and3INSERM 0218, CHU Caen, Caen, France

Recognition memory performance reflects two distinct memory

processes: a conscious process of recollection, which allows remember-

ing specific details of a previous event, and familiarity, which emerges

in the absence of any conscious information about the context in which

the event occurred (Yonelinas, 2002). Slow wave sleep (SWS) and

REM (Rapid Eye Movement) sleep are differentially involved in the

consolidation of different types of memory (Rauch et al., 2005). The

study assessed the effects of SWS and REM sleep on recollection, by

means of the �Remember�/�Know� paradigm (Tulving, 1985). Subjects

studied three blocks of twelve words before a 3-h retention interval

filled with SWS, REM sleep or wakefulness, placed between 3 am and

6 am (Barrett and Ekstrand, 1972). Afterwards, recognition and

recollection were tested. The proportion of retrieved items that were

given a �Remember� response (measuring recollection) was higher after

a retention interval dominated by SWS than after a retention interval

filled with REM sleep or wakefulness. The data suggest that SWS

facilitates the process of recollection in recognition memory.

Keywords: Slow wave sleep, REM sleep, recollection

Reference:

1. Yonelinas PA (2002) J Learn Mem 46:441–517.2. Rauch et al (2005)

J Sleep Res 14:123–140.3. Tulving E (1985) Can Psychol 26:1–12.4.

Barrett TR & Ekstrand BR (1972) J Exp Psychol 96:321–327.

P487Potentiating learning by potentiating slow oscillations?

H. HELGADOTTIR, L. MARSHALL, M. MOLLE and J. BORN

Department of Neuroendocrinology, University of Lubeck, Lubeck,

Germany

Introduction: Periods rich in slow-wave sleep (SWS) have been

consistently found to enhance in particular declarative memories in

humans. Slow (<1 Hz) potential oscillations predominantly arising

from the prefrontal neocortex characterize slow wave sleep. In the

present study we investigated a causative role of slow oscillations for

memory by inducing transcranially slow oscillating brain potentials in

humans during SWS.

Methods: Thirteen healthy subjects (seven women) with a mean age of

23.8 years were tested in two conditions, a stimulation condition and a

sham stimulation condition, which were balanced in order across

subjects. A standard polysomnography was recorded. The 30 min slow

oscillation stimulation, located frontolateral, began after the subject


Learning, Memory, Cognition – 2 233

had attained 4 min of stable NonREM sleep for the first time after

sleep onset. The subjects were tested on learning tasks for hippocam-

pus-dependent declarative memory (paired associate learning) and for

non-declarative memory (mirror tracing; sequential finger tapping

task).

Results: Following slow oscillation stimulation, hippocampus-depen-

dent declarative memory improvement was clearly greater than after

sham stimulation (P < 0.01). In contrast to declarative memory

performance, the overnight changes in the non-declarative memory

tasks did not differ between conditions (P > 0.05). Spectral analysis of

the EEG activity during the intervals between stimulation periods

confirmed an acute facilitating effect of stimulation on endogenous

slow oscillatory activity. Stimulation distinctly enhanced EEG power

within the 0.5–1.3 Hz band covering the range of the endogenous slow

oscillation (P < 0.01).

Conclusion: Slow oscillation stimulation increased endogenous cortical

slow oscillations, and distinctly improved retention of hippocampus-

dependent memories acquired before sleep. To our knowledge this is

the first study in which through manipulation of endogenous cortical

slow oscillatory activity a robust effect on memory performance was

induced. Our results are thus indicative of a causal role for slow

oscillations in the consolidation of hippocampus-dependent memories

during sleep.

P488Differential effects of fast and slow sleep spindles in early and late

sleep on the consolidation of an explicit memory task

G. GRUBER1, P. ANDERER2, S. PARAPATICS2, B. SALETU2, T.

MIAZHYNSKAIA5, M. SCHABUS4, W. KLIMESCH4 and J.

ZEITLHOFER3

1The Siesta Group Schlafanalyse GmbH, Vienna, 2Department of

Psychiatry, Medical University of Vienna, Vienna, 3Department of

Neurology, Medical University of Vienna, Vienna, 4Department of

Psychology, University of Salzburg, Salzburg and 5Austrian Research

Institute for Artificial Intelligence, Vienna, Austria

Introduction: A beneficial effect of sleep spindles on the consolidation

of explicit memory has been supported by recent studies. The present

study explores whether overnight improvements in a word-pair

association task is differentially correlated to characteristics of fast

(>13 Hz) or slow (<13 Hz) sleep spindles.

Methods: Twenty-four young healthy subjects participated either in a

control condition without intentional learning or in an experimental

condition (declarative memory task: paired-associate word list) 2.5 h

before sleep. Subjects performed a cued recall task after the encoding

session and after sleep in the morning. Sleep spindles were detected

automatically by means of Somnolyzer 24 x 7 in C3-A1 Spindle

features were determined for fast, slow, and all spindles in five 1.5-h

parts and in the entire night.

Results: There were no significant differences regarding sleep efficiency

and architecture as well as spindle activity between both nights.

However, there was a significant correlation between changes in

spindle density and intensity (experimental minutes control night) and

overnight changes in memory performance (r = 0.44, P < 0.05 and

r = 0.52, P < 0.01 for density and intensity, respectively). These

correlations were most prominent in the early parts of the night.

Changes in memory performance correlated significantly only with fast

but not with slow spindle measures.

Discussion: Significant correlations were observed predominantly in

the first parts of the night, which is in line with the hypothesis that

early sleep is critical for consolidation of declarative memory. The

differential effect of fast and slow spindles provide further evidence for

differential functional significances of both spindle types.

Acknowledgment: Supported by the Austrian Science Fund (P-15370),

and by Austrian Industrial Research Promotion Fund (Project

806765).


234 Learning, Memory, Cognition – 2

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