Sleep and Memory: Overview Rachel Miriani Neural Systems Nov 29, 2004

Introduction to Memory “The mental faculty of retaining and recalling past experiences; the ability to remember.”1 Has many different forms of classification The most common being divided into declarative & non-declarative memories.

Introduction to Memory Declarative Non-Declarative “Consciously accessible memories of fact-based information”- The What. Non-conscious Declarative: things you consciously learn: mathematics, football games, your parents and their names, the first time you are learning dance steps. *Non-Declarative: things you learn and recall subconscously: walking, word articulation.

Introduction to Memory Declarative Non-Declarative What. Non-conscious Episodic Semantic Not event specific general knowledge Experiences and events from ones past. This declarative “what” category can further be broken into Semantic and Episodic learning. Episodic: Thanksgiving dinner this year, your 16th birthday, your family vacation to Disney World. Semantic: Calculus, vocabulary

Introduction to Memory Declarative Non-Declarative What. Non-conscious Episodic Semantic Non declarative: Explicit: Procedural Skills: Implicit learning: Conditioning Non-associative: Priming: Procedural Skills Conditioning Non-associative Priming

Introduction to Memory Declarative Non-Declarative What. Non-conscious Episodic Semantic Although the definitions are relatively clear cut it is very rare that a situation/experience would only utilize one or the other Ex: Language learning Non-declarative: procedural- motor programs to speech articulation (how to shape your lips and tongue to form the “oooo” sound); **-grammatical rules and structure. Declarative: Semantic- word selection Procedural Skills Conditioning Non-associative Priming

Introduction to Sleep: REM NREM REM: Rapid Eye Movement Muscle tone decreases. EEG oscillations are desynchronized Gamma waves appear- 30-80Hz synchronous activity is similar to being awake. Periodic bursts of rapid eye movement. PGO waves appear- Phasic endogenous waveforms expressed in the pons (P), lateral geniculate nuclei of the thalamus (G), and the occipital cortex (O). Stages 1 2 3 4 Picts of gamma waves PGO REM bursts Locale and wakeful function of pons lateral geniculate nuclei of the thalamus

Introduction to Sleep Sleep REM NREM Stages 1 2 3 4 Stage 2 characteristically has phasic electrical events: *K Complexes- Large electrically sharp EEG waves *Sleep Spindles- Short 7-14 Hz synchronized oscillations in the EEG Stages 1 2 3 4 *Increasing depth of sleep *EEG frequency slows down Pict and better descript of Kcomplexes and sleep spindles

Introduction to Sleep Sleep REM NREM Stages 1 2 3 4 Stages 3 and 4 are typically grouped together and dubbed Slow Wave Sleep (SWS) due to the low frequency waves (0.5-4 Hz and <1Hz) caused by cortical synchrony Increasing depth of sleep EEG frequency slows down Picts and a bit more physiological desc. Of deep sleep Picts of SWS

1 Cycle of REM and NREM takes ~90mins Ratio of REM to NREM changes with each cycle Initially 3&4

Sleep Cycles One cycle of NREM and REM sleep takes ~90 mins Ratio of NREM/REM per cycle changes during the night Initially Stages 3 and 4 of NREM sleep dominate Near the end of the night REM and stage 2 sleep dominate the cycles

Sleep Stages Beta waves:+14Hz Alpha waves: 7.5-13Hz Symmetrical distribution and most apparent in the frontal lobe. Rapid, irregular, and low voltage Alpha waves: 7.5-13Hz Best seen on the posterior sides the head but stronger on the dominant side. Stops when eyes open or alerting by any mechanism (thinking) Theta waves: 3.5-7.5Hz Sleep Spindles: 7-14 Hz Short bursts of high frequency activity Assumed to be responsible for keeping the individual asleep K-complexes: short burst of high amplitude activity Probably the precursors to delta activity Delta waves: <4Hz Highest amplitude, slowest waves PGO waves: Associated with increased visual system excitability but arise spontaneously Influenced by auditory and somatosensory stimuli Generated in the pontine brain stem

Neurochemistry Neurochemistry changes with sleep stages NREM Significant drop in activity of subcortical cholinergic systems Reduction in firing rate of aminergic populations REM Significant increase in activity of subcortical cholinergic systems Significant inhibition of aminergic populations REM sleep is dominated by acetylcholine and essentially absent of aminergic modulation Aminergic populations: serotonergic raphe neurons and noradrenergic locus coeruleus neurons

Developing a Memory Integration: associating new info with past experiences and knowledge Translocation: anatomical reorganization Memory consolidation (MC): memory becomes more stable Stabilization Enhancement Erasure: active removal of memory representations Both sleep and memory are composed of several different stages/groups as does the development of a memory Similar to sleep it also develops over time Acquisition: initially formed by engaging with an object or performing an action, leading to the formation of a representation of the object or action. Fragile until first sleep period Most common MC: memory consolidation refers to a process whereby a memory becomes increasingly resistant to interference from competing or disrupting factors in the absence of further practice, through the simple passage of time Stabilization: occurs during wake Enhancement: primarily if not exclusively duing sleep restoring previously lost memories producing additional learning  Active retention instead of its decay or the enhancement of it over ts simple maintenace

Sleep and Declarative MC Subtleties of task alter results post training REM sleep. Old supportive De Koninck: foreign language learning; % increase in REM Sleep ~ degree of successful learning Old contradictory Meienberg: unrelated word pairs; No evidence of altered post training sleep architecture Different behavioral measures may be more/less sensative to identifying these consolidation processes same task diff index of learning diff results REM sleep plays an active role in memory consolidation and that posttraining increases reflect a homeostatic response to the increased demands for REM-dependent consolidation. New supportive Born: Related word pairs; Improvement in association test and increase in SWS and alterations in sleep characterization

Sleep and Declarative MC Subtleties of task alter results for post training REM sleep. Old supportive De Koninck: foreign language learning; % increase in REM Sleep ~ degree of successful learning Old contradictory Meienberg: unrelated word pairs; No evidence of altered post training sleep architecture Nature of learning stask is shifted form retaining completely novel assaociations to the strengthening of well formed preexcisting associations for recall at testing New supportive Born: Related word pairs; Improvement in association test and increase in SWS and alterations in sleep characterization

Differences in studies Level of difficulty Emotional saliency Index of learning Episodic learning Semantic learning Consideration of effects from lack of sleep (stress, alertness, attention span)

Associative memories Are altered in a state dependent manner REM- Selective facilitation of accessing weak associations Enhancement of flexible creative processing of acquired information Sleep can trigger insight to a problem and thus improve performance strategy

Take Home Message SWS and REM sleep contribute to the consolidation of complex, emotionally salient declarative memories embedded in networks of previously existing associative memories

Procedural Memories: Motor Tasks Retention impaired with loss of Stage 2 NREM sleep Full night of sleep significantly increases the speed and accuracy Sleep on first night of training critical for delayed performance improvements of rotary pursuit task of tapping task.

Procedural Memories: Visual Task Performance benefits are completely dependent on the first night of sleep after the training period

Procedural Memories: Auditory Regardless of morning or evening training improvements only occurred across a full night of sleep Sleep deprivation inhibited the normal changes in brain evoked response potentials Subsequent nights of sleep can restore performance to post training levels Suggests a process of sleep cxependent copnsolidation capable of reestabliushing previously learned complex auditory skil memory

Neuroimaging: Not so Instant Replay

E-Physiology Sleep spindles (Stage 2 NREM) Phasic REM and PGO waves Increase amplitude Phase locked with theta waves Induced stimulation at the troughs of theta waves yields to LTD

Gene Expression

Objections and Contradictions Importance of considering differences in study protocol Brief memory test Affects of Drugs

Untouched areas Stabilization Association Translocation Reconsolidation

Bibliography The American Heritage Illustrated Encyclopedic Dictionary; Houghton Mifflin Company, Boston, 1982.