Week6

MANUSCRIPT ID

• Sleep after spatial learning promotes covert reorganization of brain activity

Pierre Orban, Geraldine Rauchs, Evelyne Balteau, Christian Degueldre, Andre Luxen, Pierre Maquet, & Phillipe Peigneux

• Abstract:

Sleep promotes the integration of recently acquired spatial memories into cerebral networks for the long term. In this study, we examined how sleep deprivation hinders this consolidation process. Using functional MRI, we mapped regional cerebral activity during place-finding navigation in a virtual town, immediately after learning and 3 days later, in subjects either allowed regular sleep (RS) or totally sleep-deprived (TSD) on the first posttraining night. At immediate and delayed retrieval, place-finding navigation elicited increased brain activity in an extended hippocamponeocortical network in both RS and TSD subjects. Behavioral performance was equivalent between groups. However, striatal navigation-related activity increased more at delayed retrieval in RS than in TSD subjects. Furthermore, correlations between striatal response and behavioral performance, as well as functional connectivity between the striatum and the hippocampus, were modulated by posttraining sleep. These data suggest that brain activity is restructured during sleep in such a way that navigation in the virtual environment, initially related to a hippocampus-dependent spatial strategy, becomes progressively contingent in part on a response-based strategy mediated by the striatum. Both neural strategies eventually relate to equivalent performance levels, indicating that covert reorganization of brain patterns underlying navigation after sleep is not necessarily accompanied by overt changes in behavior.

• Keywords:

functional MRI; hippocampus; sleep deprivation; memory consolidation; striatum

MANUSCRIPT DETAILS

   * Introduction/Aims 

Spatial learning- flexible relationships between environmental cues

• Encoding and initial maintenance = Medial temporal lobe (hippocampus) dependent
• With training/practice = also partly striatum (caudate) mediated

Sleeping brain may actively process freshly acquired memories Support role in a gradual consolidation process

Hypothesis = Sleep deprivation after spatial learning will hinder reorganization of cortical activity underlying memory consolidation

   * Method 

Subjects: 24 healthy adults (12 male, 12 female)

• Regular Sleep (RS)- 6 males, 6 females
• Total Sleep Deprived (TSD)- 6 males, 6 females

Navigation Task: Virtual environment- Walking along streets in a complex town

• 3 distinct districts- visual backgrounds, objects along streets
• 1 target (identified)
• 10 starting points (not identified)

Setup: Regular sleep group- training, immediate retrieval (day1), 3 nights normal sleep, delayed retrieval (day4) Regular sleep group- training, immediate retrieval (day1), total sleep deprivation (night1), 2 nights normal sleep, delayed retrieval (day4)

Imaging Parameters: (with standard preprocessing)

• Structural T1-weighted MR
• BOLD Echo Planar Imaging

   * Results

Navigational Performance:

• No significant main effect of group (RS vs. TSD) or session (Immediate vs. Delayed), no interaction in a 2 way ANOVA
• Both groups learned and remembered
• Total sleep deprivation did not alter delayed retrieval performance

Increased BOLD response during place finding: (both groups, both times)

• Hippocampus + surrounding cortex
• Occipital
• Parietal
• Frontal
• Cerebellar

Brain activity positively correlates with performance: (both groups, both times)

• Positive correlation- Right hippocampus activity (corrected p-value)and navigation performance (distance from target)

Changes in activation between Immediate and Delayed Retrieval: Increased activation at Delayed (vs. immediate)

• Caudate
• Superior parietal lobule
• Middle cingulate
• Temporal
• Precuneus
• Frontal

Decreased activation at Delayed

• Hippocampus complex

Sleep modifies reorganization of brain activity at delayed retrieval: RS activation > TSD activation

• Caudate
• Insula
• Precentral gyrus
• Middle temporal gyrus

Group x Performance interaction in right caudate at delayed retrieval

• RS: positive (higher activity – improved place finding)
• TSD: negative (lower activity – improved place finding)

   * Discussion and Conclusion:

Striatal activity was increased at delayed retrieval for RS versus TSD subjects Post-training sleep modulated:

• Functional connectivity- hippocampus and caudate
• Linear relationship- striatal activity and navigational accuracy

Sleep-associated changes in brain activity where accompanied by equivalent performance

   * Informatics Tool: The LONI Pipeline

http://pipeline.loni.ucla.edu/

• Features:
  • Access to LONI computational resources
  • Graphical (vs. computer programming)
  • Once submitted to server, your pipeline workflow will run independently of your personal computer

MANUSCRIPT ID

Sleep Deprivation Specifically Impairs Short-term Olfactory Memory in Drosophila

Xinjian Li, Feng Yu, Aike Guo

• Study objectives: Sleep is crucial to memory consolidation in humans and other animals; however, the effect of insufficient sleep on subsequent

learning and memory remains largely elusive.

• Design: Learning and memory after 1-day sleep deprivation (slpD) was evaluated using Pavlovian olfactory conditioning in Drosophila, and loco-

motor activity was measured using the Drosophila Activity Monitoring System in a 12:12 light-dark cycle.

• Results: We found that slpD specifically impaired 1-h memory in wild type Canton-S flies, and this effect could persist for at least 2 h. However,

alternative stresses (heat stress, oxidative stress, starvation, and rotation stress) did not result in a similar effect and left the flies’ memory intact. Mechanistic studies demonstrated that flies with either silenced transmission of the mushroom body (MB) during slpD or down-regulated cAMP levels in the MB demonstrated no slpD-induced 1-h memory impairment.

• Conclusion: We found that slpD specifically impaired 1-h memory in Drosophila, and either silencing of MB transmission during slpD or down-

regulation of the cAMP level in the MB protected the flies from slpD-induced impairment.

• Keywords: Drosophila, sleep, learning and memory, cAMP, slpD, mushroom body

MANUSCRIPT DETAILS

   * Introduction/Aims 

• Sleep plays an important part in memory consolidation, but it is unclear whether sleep is also essential for subsequent learning and memory
• Many correlates of sleep behavior can be found in Drosophila, which has the genetic tools available to dissect the interplay between sleep and memory
• Sleep deprivation in Drosophila can be used to investigate the effects of sleep on subsequent learning and memory

Therefore, sleep deprivation (slpD) may be important for subsequent learning and memory and this effect of slpD might have a molecular and cellular origin.

   * Methods 

Flies:

• Wild-type Canton-S flies
• Rut-RNAi flies (UAS-rutRNAi)

Rut flies (UAS-rut)

• dnc1 mutant flies
• shibere mutant flies (UAS-shi)
• driver lines with promoters specific for mushroom bodies (17d and 257)
• EGFP and NP6510 flies

Sleep deprivation apparatus:

• Slowly rotating apparatus containing glass tubes with flies in them. When the apparatus rotated 180 degrees, the tubes fell along their major axis and caused the flies to fall from the top of the tube to the bottom, effectively keeping them awake

Sleep test

• Drosophila Activity Monitor System (DAMS) was used to assess activity

Stress test

• Different stressors were used to test whether effects of slpD were slpD specific. Heat shock, oxidative stress, and rotation stress were conducted on the flies

Pavlovian Olfactory Conditioning

• A classic behavioral conditioning paradigm was used to assess memory/training after sleep deprivation

   * Results

Automated Rotation and drop of vials is effective for sleep deprivation

• Flies that were put in this rotating apparatus showed effects of slpD including increased day/night sleep after slpD, and a drastically decreased sleep onset latency

slpD specifically impairs short-term memory

• The setup for this test was to slpD the flies before the initial training of the olfactory conditioning paradigm, then after a few hours test them on their memory retention
• slpD flies showed no difference from controls in their learning performance index, 3-h, 7-h and 24-h performance index
• slpD flies did show a significant difference in 1-h memory
• Only when slpD occurs at night (when the flies usually sleep) do you see a significant decrease in 1-h memory
• The effects of slpD on 1-h memory last up till 2 hours after slpD ie if you sleep deprive the flies and let them rest for 2 hours they will have impairment, but if you let them rest for 4 hours post-slpD then the impairment goes away

Stress does not impair 1-h memory

• Different stressors do not affect 1-h memory, so this effect is slpD-specific

STM impairment is blocked by silencing of mushroom bodies during slpD

• The mushroom bodies are an important site for memory consolidation in flies
• Blocking the mushroom bodies from firing (using shibere transgenic flies) during slpD restores their 1-h memory
• This is not due to transgenic flies having different amounts of sleep

Down-regulation of cAMP in the MB abolished slpD-induced STM impairment

• rutabega is an adenylyl-cyclase, dunce is a phosphodiesterase.
• Using rut-RNAi specifically targeting the MB downregulates the cAMP levels in the MB. This led to a restoration of 1-h memory for slpD flies
• Upregulation of cAMP through overexpression of rut or downregulation of dunce did not restore 1-h memory
• Thus, slpD may be exerting its effects through upregulation of cAMP in the MB

   * Discussion and Conclusion:

Sleep deprivation is critical not just for memory consolidation but also for subsequent learning and memory

• This study showed that in Drosophila sleep is important for 1-h memory after learning, which is representative of short term memory
• The effects of slpD are thought to be due to upregulated levels of cAMP in the mushroom bodies
• This may be because sleep is thought to maintain synaptic homeostasis, and coupled with the cAMP finding, slpD may cause changes in local protein activity which affects plasticity