Background: It is well known, since the pioneristic observation by Jenkins and Dallenbach (Am J
Psychol 1924;35:605-12), that a period of sleep provides a specific advantage for the consolidation
of newly acquired informations. Recent research about the possible enhancing effect of sleep on
memory consolidation has focused on procedural memory (part of non-declarative memory system,
according to Squire’s taxonomy), as it appears the memory sub-system for which the available data
are more consistent.
The acquisition of a procedural skill follows a typical time course, consisting in a substantial
practice-dependent learning followed by a slow, off-line improvement. Sleep seems to play a
critical role in promoting the process of slow learning, by consolidating memory traces and making
them more stable and resistant to interferences.
If sleep is critical for the consolidation of a procedural skill, then an alteration of the
organization of sleep should result in a less effective consolidation, and therefore in a reduced
memory performance. Such alteration can be experimentally induced, as in a deprivation protocol,
or it can be naturally observed in some sleep disorders as, for example, in narcolepsy.
In this research, a group of narcoleptic patients, and a group of matched healthy controls,
were tested in two different procedural abilities, in order to better define the size and time course of
sleep contribution to memory consolidation.
Experimental Procedure: A Texture Discrimination Task (Karni & Sagi, Nature 1993;365:250-2)
and a Finger Tapping Task (Walker et al., Neuron 2002;35:205-11) were administered to two
indipendent samples of drug-naive patients with first-diagnosed narcolepsy with cataplexy
(International Classification of Sleep Disorder 2nd ed., 2005), and two samples of matched healthy
controls. In the Texture Discrimination task, subjects (n=22) had to learn to recognize a complex
visual array on the screen of a personal computer, while in the Finger Tapping task (n=14) they had
to press a numeric sequence on a standard keyboard, as quickly and accurately as possible. Three
subsequent experimental sessions were scheduled for each partecipant, namely a training session, a
first retrieval session the next day, and a second retrieval session one week later. To test for possible
circadian effects on learning, half of the subjects performed the training session at 11 a.m. and half
at 17 p.m. Performance at training session was taken as a measure of the practice-dependent
learning, while performance of subsequent sessions were taken as a measure of the consolidation
level achieved respectively after one and seven nights of sleep. Between training and first retrieval
session, all participants spent a night in a sleep laboratory and underwent a polygraphic recording.
Results and Discussion: In both experimental tasks, while healthy controls improved their
performance after one night of undisturbed sleep, narcoleptic patients showed a non statistically
significant learning. Despite this, at the second retrieval session either healthy controls and
narcoleptics improved their skills. Narcoleptics improved relatively more than controls between
first and second retrieval session in the texture discrimination ability, while their performance
remained largely lower in the motor (FTT) ability.
Sleep parameters showed a grater fragmentation in the sleep of the pathological group, and a
different distribution of Stage 1 and 2 NREM sleep in the two groups, being thus consistent with the
hypothesis of a lower consolidation power of sleep in narcoleptic patients. Moreover, REM density
of the first part of the night of healthy subjects showed a significant correlation with the amount of
improvement achieved at the first retrieval session in TDT task, supporting the hypothesis that
REM sleep plays an important role in the consolidation of visuo-perceptual skills.
Taken together, these results speak in favor of a slower, rather than lower consolidation of
procedural skills in narcoleptic patients.
Finally, an explanation of the results, based on the possible role of sleep in contrasting the
interference provided by task repetition is proposed.
| Identifer | oai:union.ndltd.org:unibo.it/oai:amsdottorato.cib.unibo.it:1007 |
| Date | 28 April 2008 |
| Creators | Campi, Claudio <1973> |
| Contributors | Cipolli, Carlo |
| Publisher | Alma Mater Studiorum - Università di Bologna |
| Source Sets | Università di Bologna |
| Language | Italian |
| Detected Language | English |
| Type | Doctoral Thesis, PeerReviewed |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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