Memory and Behavior in Roaches and Mice

BSci 3230 Study Notes

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Circadian Regulation of Learning and Memory

• The presentation discusses how circadian rhythms affect learning and memory, particularly comparing mice and cockroaches.
• "Sometimes Cockroaches are Smarter Than They Appear to Be," highlights the presentation's focus.

Learning & Memory Terms

• Operant Conditioning: Stimuli present during reward or punishment control behavior; voluntary. Examples include a child learning to open a box for candy or avoiding a hot stove.
• Classical Conditioning: Involuntary behaviors based on associations with biologically significant events; not based on consequences. Examples include salivating at the sight of candy or trembling at a door slam that signals an angry parent.

Novel Object Recognition (NOR) & Fear Conditioning

• NOR test: Measures how well an animal remembers a familiar object and ignores it. A high Discrimination Index means the animal spends more time with a new object.
• Fear Conditioning test: Pairing an aversive stimulus (e.g., shock) with a neutral context (e.g., cage) or stimulus (e.g., tone) creates fear responses to the originally neutral stimulus.

Learning/Memory & Clocks

• Circadian suppression of memory formation/recall can occur at "inappropriate" times.
• Disruptions in circadian rhythms affect learning and memory processes.

Zeitgedächtnis ("Time Memory") in Bees

• Bees in the experiment by Beling (1929) showed time-dependent memory.
• The bees continued to visit a sugar source at the same time each day, even when the sugar was removed.

Diurnal Variation in Learning and Memory

• Diurnal variation (daily rhythm) in learning and memory is common across species.
• Humans, while showing circadian rhythms, often haven't had their learning and memory studied under consistent conditions in the laboratory.
• Other species continue showing these rhythms even in constant conditions. The example studied suggests this regularity in rhythm is circadian.

Mouse Memory Tests

• Contextual fear conditioning (FC): Studies daily/circadian rhythms of memory acquisition, recall, and extinction.
• Novel object recognition (NOR): Tests recognition of objects and how misaligned feeding affects mice memories.
• Novel object location (NOL): Studies novel object location in the lab environment, related to time of day, and the effects of core clock gene knockout (Bmal1).

Fear Conditioning Protocol

• Mice conditioned to fear stimuli at specific times show circadian related learning based on the time of day the conditioning or testing happened.

Circadian Variations in Acquisition

• Training mice in different circadian phases influences how quickly they learn fear conditioning responses.
• Some tasks are faster in the day (or subjective day) for fear conditioning. Circadian variation in responses to fear conditioning was clear in the tests.

Rhythms in Recall of Training

• Mice show clear circadian rhythms in recall responses. Memory recall best in a particular period after training.

Forgetting ("Extinction")

• The rate of forgetting varies with training and testing times, more forgetting when trained in the inactive phase or when the cycle was shifted.
• Memory forgetting is related to the time of day traumatic events happened for the studies. This is relevant to PTSD in humans.

Mouse Memory Tests (Repeated Section)

• Contextual fear conditioning: Evaluates circadian rhythms in acquiring, recalling, and forgetting memories. Includes jet lag and misaligned feeding effects.
• Novel object recognition (NOR): Studies recognition of objects.
• Novel object location (NOL): Examines how time of day affects memory of object locations in the lab.
• Core clock gene (Bmal1) knockout: Investigate how removing or altering core clock genes impacts learning and memory.

Model 1: Rapid Change in the LD Cycle

• Rapid changes in the light-dark cycle disrupt the ability to remember contextual fear conditioning (recall) in mice.

Model 1: Phase Shifts Before Training

• Mice were trained during testing, demonstrating the phase shift can inhibit recall.

Model 2: Misaligned Feeding Schedules

• Misaligned feeding disrupts activity rhythms, resulting in various physiological effects.

Hippocampal Neurons

• Hippocampal neurons are weak circadian oscillators.

Misaligned Feeding Alters Phase of Molecular Oscillations

• Misaligned feeding affects the phase of molecular oscillations (the molecular, cellular, and systemic timing of the 24-hour cycles) in the SCN (Suprachiasmatic Nucleus), hippocampus, and liver. Misalignment disrupts the temporal synchrony of those tissues.

Misaligned Feeding Interferes with Memory

• Misaligned feeding disrupts memory formation, especially in contextual fear conditioning and novel object recognition (NOR) tasks.

Model 3: Targeted Loss of Bmal1 in Forebrain

• Removing the Bmal1 gene in the forebrain (part of the brain) shows a normal circadian activity rhythm for mice.
• Researchers used specialized methods (CaMKII-CRE driver) to target loss of Bmal1 to specific cell types in the forebrain.
• Removing or altering core clock genes impacts learning and memory.

Time-of-day Dependent Learning

• Time of day affects learning and memory in mice, and appears to interact with circadian systems as a vital component for recall.

Cockroach Memory Tests

• Classical Conditioning: Involuntary behaviors based on stimulus associations.
• Operant Conditioning: Voluntary behaviors based on reward or punishment association.

Olfactory Discrimination Test

• Cockroaches prefer vanilla to peppermint naturally.
• In olfactory discrimination, odor preference and discrimination don't change with circadian phase.

Classical Olfactory Conditioning

• Conditioning roaches to associate odors with rewards or punishments.
• Roaches prefer vanilla and dislike peppermint.

Can Cockroaches Learn?

• Cockroaches can learn to associate an odor (peppermint) with a reward (sugar) in the early subjective night.
• The association with the reward may modify the odor preference in the training period. Early subjective night training has a stronger association with learning.

A Circadian Rhythm in Learning and Memory

• Rats/Cockroaches trained and tested at the same phase of their circadian cycle show improved learning and memory.
• When the time of learning and recall is different from the circadian cycle, memory performance varies.

Is the Deficit at CT 2 Due to a Deficit in Memory Formation or a Deficit in Memory Recall?

• In a recall test, memory is not stored well and recall is poor when tested during the early subjective day; however, this deficit is an inability to store new memories, and not in recalling already established memories.

Operant Olfactory Conditioning

• Pairing an unpleasant odor (peppermint) with an inaccessible reward (apple) to change the cockroach's behavior patterns.

Does the Circadian System's Effect Depend on the Type of Training?

• Whether circadian rhythms affect learning and memory depends on the type of training used (e.g.; operant methods). In some cases, the circadian time of the training had little effect on performance in the test. Recall was still possible.

With Operant Conditioning, Recall Is Dependent On Circadian Phase

• Operant training at different circadian phases affect whether roaches can recall, showing time of training is a critical factor.

Classical Conditioning: The Optic Lobe Clock Inhibits Memory Formation

• Optically-induced ablation to the circadian timing system impacts the ability to establish new memories, especially with classical conditioning.
• Circadian-timed memory formation, especially the creation of new memories, is diminished during the early subjective day.

Classical Conditioning: Inhibition at CT 2 by GABA

• GABA (a neurotransmitter) can affect memory formation in a circadian dependent manner.
• In classical conditioning tests using insects (roach), GABA neurotransmitters, which are involved in inhibition, are critical to inhibiting memory formation in a certain time window.

Conclusions

• The circadian system heavily influences learning and memory.
• The impact varies with the method of training and among species.
• Inhibition in the circadian system, possibly by GABA, seems to be a widespread mechanism affecting learning and memory at particular times of the day.

Food for Thought

• What evolutionary benefits does being less effective at learning/remembering at certain times of day provide?
• How does the brain store and retrieve information related to memory phases?
• When is the ideal time for human learning/memory studies?

This quiz explores the memory and behavioral responses of roaches and mice under various experimental conditions. Questions cover topics such as memory capacity, contextual fear conditioning, and the effects of feeding schedules on recall performance. Test your understanding of how these factors influence memory in different species!