Learning & Memory (BSci 3230) PDF

NOTE ! These files are provided for the sole purpose of assisting BSci 3230 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose ot...

NOTE ! These files are provided for the sole purpose of assisting BSci 3230 students to study for exams in the class. Some of the material in these files may be copyrighted, and it is not OK for you to share these files with anyone who is not a student in this class or to use them for any purpose other than to study for BSci 3230. Thanks, Carl Johnson  Circadian Regulation of Learning and Memory featuring... “Sometimes Cockroaches are Smarter Than They Appear to Be” Mouse Memory Tests Cockroach Memory Tests  Some learning & memory terms defined Although operant and classical conditioning both involve behaviors controlled by environmental stimuli, they differ in nature. In operant conditioning, stimuli present when a behavior is rewarded or punished come to control that behavior. For example, a child may learn to open a box to get the candy inside, or learn to avoid touching a hot stove; in operant terms, the box and the stove are "discriminative stimuli." Operant conditioning is said to be voluntary: for example, the child may face a choice between opening the box and petting a puppy. In contrast, classical conditioning involves involuntary behavior based on the pairing of stimuli with biologically significant events. For example, sight of candy may cause a child to salivate, or the sound of a door slam may signal an angry parent, causing a child to tremble. Salivation and trembling are not operants; they are not reinforced by their consequences, and they are not voluntarily "chosen." (Hint: think “Pavlov’s dogs”)  Some learning & memory terms defined Novel Object Recognition (NOR) test: this is a test of how well the animal remembers a familiar object and thereafter ignores it. The "Discrimination Index" is a quantification of how much time is spent with the novel object–a high Discrimination Index means that the animal spends most of the time with the novel object and is ignoring the familiar object that is remembered well. Fear Conditioning test: an aversive stimulus (e.g. an electrical shock) is paired with a particular neutral context (e.g., the shocking cage) or neutral stimulus (e.g., a tone), resulting in the expression of fear responses to the originally neutral stimulus or context. Eventually, the neutral stimulus alone can elicit the state of fear. In the vocabulary of Classical Conditioning, the neutral stimulus or context (e.g., shocking cage or tone) is the "conditional stimulus" (CS), and the aversive stimulus (e.g., the electric shock) is the "unconditional stimulus" (US). The amydala and the hippocampus are involved in fear conditioning. Extinction: how long does it take to forget?  Learning/Memory & Clocks Memory Short-term Long-term Memory Recall Experiences Memory (hippocampus, (and/or Training) (hippocampus) cortex) Extinction 1. In some cases but not others, there is circadian suppression of memory formation at “inappropriate” times. 2. In some cases but not others, there is circadian suppression of memory recall at “inappropriate” times. 3. Disruption of circadian organization can disrupt learning and memory processes. Some History: Zeitgedächtnis (“Time Memory”) in Bees Beling, 1929 Diurnal variation in performance in learning and memory tasks are common. In humans, these rhythms have rarely been examined while subjects are held in constant conditions. So we cannot distinguish whether the rhythms are diurnal (daily) or circadian. In other species, it is possible to demonstrate that the rhythms continue when the organism is held in constant conditions, i.e. they are circadian. Gerstner et al., 2009  Mouse Memory Tests 1. contextual fear (classical) conditioning (FC) a) daily/circadian rhythms of memory acquisition, recall, and extinction b) jet-lag c) misaligned feeding 2. novel object recognition (NOR) misaligned feeding 3. novel object location (NOL) core clock gene (Bmal1) knockout Chaudhury and Colwell, Behav. Brain Res., 2002  Let’s consider a fear conditioning protocol in which context or tone is paired with foot shock Learning: in response to auditory tones followed by foot shock, mice learn to “freeze” in place (i.e., not move around) Mice were trained ZT early in the day or 0 12 24 early in the night in LD or DL; or early in LD the subjective day or DL night in DD DD Chaudhury and Colwell, Behav. Brain Res., 2002  Circadian variation in acquisition LD Training: 100 Trained in Night for Context 80 Trained in Day for Context CS = conditioned stimulus, i.e., auditory tone Freezing (%) 60 US = unconditioned stimulus, 40 i.e., foot shock just after tone 20 CS-US training cycles were 0 performed 10 minutes apart Baseline CS-US-1 CS-US-2 CS-US-3 CS-US-4 CS-US-5 CS-US-6 DD At baseline control, there was 100 no daily rhythm in freezing or 80 sensitivity to shock Testing: Freezing (%) 60 40 Mice acquire memories faster in day (or subjective day) for 20 Trained in Subjective Night for Context fear conditioning Trained in Subjective Day for Context 0 Baseline CS-US-1 CS-US-2 CS-US-3 CS-US-4 CS-US-5 CS-US-6 Chaudhury and Colwell, Behav. Brain Res., 2002  Rhythms in recall of training 80 Trained Trained in Day in Day and tested for context for CS (tone) in LD: Mice exhibit clear 60 circadian rhythms in Freezing (%) recall. 40 20 May explain why psychologists often get 0 best results if they wait 9.00 15.00 21.00 3.00 9.00 15.00 21.00 3.00 9.00 24 hrs after training to Trained Train in in Subjective Sub. Day for Day and Context access performance. 60 tested for CS (tone) in DD: Freezing (%) 40 20 (see also the early work of Kamin and Holloway & Wansley [1973ab]) 0 9 15 21 3 9 15 21 3 9 Time (CT) Chaudhury and Colwell, Behav. Brain Res., 2002 What about forgetting? “Extinction” rate also varies with time of training & testing Forgetting is highly relevant to PTSD–– trained & tested in inactive (day) phase traumatic events are more easily forgotten if trained & tested they occurred in the in active (night) phase active phase Day 1 Day 2 Day 3 Work by Spencer and Training Times: colleagues suggest that this extinction is dependent upon the prefrontal cortex (PFC) Chaudhury and Colwell, Behav. Brain Res., 2002  Mouse Memory Tests 1. contextual fear (classical) conditioning (FC) a) daily/circadian rhythms of memory acquisition, recall, and extinction b) jet-lag c) misaligned feeding 2. novel object recognition (NOR) misaligned feeding 3. novel object location (NOL) core clock gene (Bmal1) knockout Chaudhury and Colwell, Behav. Brain Res., 2002  Model 1: Rapid change in the LD cycle (jet lag) disrupts the ability of mice to recall contextual fear conditioning. 60 Control Percent Freezing Phase shifted 40 20 0 1 2 3 4 5 6 7 Phase shift after training: Days Train Test Control 24 hrs Mice forget faster if they are ΔΦ: +12hr Phase trained before but tested after Train Test 24 hrs shifted an advance phase shift !  Model 1: Phase Shifts Before Training also Impact Recall Acquisition Not Impacted: Phase shift before training: Train Test Control 24 hrs 80 ΔΦ Train Test Phase Control 24 hrs 24 hrs 60 Phase shifted shifted Freezing (%) 40 Control 20 60 Phase shifted Prior to Training Freezing (%) 0 40 Baseline CS-US 1 CS-US 2 20 0 Mice forget faster if they 1 2 3 4 5 6 7 are trained while they are Time After Training (Days) experiencing jet lag !  Mouse Memory Tests 1. contextual fear (classical) conditioning (FC) a) daily/circadian rhythms of memory acquisition, recall, and extinction b) jet-lag c) misaligned feeding 2. novel object recognition (NOR) misaligned feeding 3. novel object location (NOL) & maze escape test core clock gene (Bmal1) knockout Chaudhury and Colwell, Behav. Brain Res., 2002 Activity rhythms Sleep rhythms Model 2: Misaligned feeding schedules Loh et al., 2015 Hippocampal neurons are weak cell-autonomous circadian oscillators hippocampal slice PER2::LUC expression in vitro Loh et al., 2015 Misaligned feeding alters phase of molecular oscillations The circadian clocks in the hippocampus (HP) and liver follow the timing of food. The central clock (SCN) follows the timing of light/dark. The result is internal misalignment i.e. the loss of temporal synchrony between tissues in our body. Loh et al., 2015  Misaligned feeding interferes with memory FC Two different tests of memory recall: Top = contextual fear conditioning (FC) Bottom = novel object recognition (NOR) Training and recall tests were done at same time of day (and tested 24 h after training) The performance of both tasks varies with time of day: peak performance for negative conditioning NOR (FC) occurs during sleep (day) peak performance for positive learned tasks (NOR) occurs when the mice are normally awake (night) In both cases, misaligned feeding disrupts the time-dependent memories (possibly because the HP is no longer optimally phased to the time of day?) Loh et al., 2015  Mouse Memory Tests 1. contextual fear (classical) conditioning (FC) daily/circadian rhythms of memory acquisition, recall, and extinction jet-lag misaligned feeding 2. novel object recognition (NOR) misaligned feeding 3. novel object location (NOL) core clock gene (Bmal1) knockout Chaudhury and Colwell, Behav. Brain Res., 2002  Model 3: Targeted loss of Bmal1 in forebrain The Bmal1-”floxed” mouse line was crossed with a CaMKII-CRE driver line to delete Bmal1 from forebrain excitatory cell populations wild-type expression of Bmal1 in CTX forebrain knockout of Bmal1 expression in forebrain CTX (Bmal1 fKO) Representative IHC labeling for BMAL1 in CaMKII-CRE control mice (CRE:Bmal1(+/+)) and CRE:Bmal1(fl/fl) mice. Forebrain BMAL1 labeling in the cortex (CTX) and granule cell layer of the hippocampus (GCL) was disrupted in the Bmal1 (fl/fl) mice. Of note, the CaMKII-CRE driver does not delete in all forebrain cells, only in excitatory neurons. In line with this, expression of Bmal1 in the CRE:Bmal1 (fl/fl) mice was still detected. Snider et al., 2016 Model 3: Targeted loss of Bmal1 in forebrain Locomotor activity looks normal in the Bmal1 fKO mouse in which the Bmal1 gene is deleted in forebrain excitatory neurons Snider et al., 2016 Model 3: Targeted loss of Bmal1 in forebrain Time-of-day dependent learning using the novel object location (NOL) test. (A) Experimental design: mice were first allowed to explore an arena with two objects placed in reference to spatial cues on the arena walls (=training). (B) After a thirty minute delay, mice were returned to the arena (=test); one object was in the same location (Familiar), while the other object had been moved (Novel). (C) Discrimination index (DI*) of Bmal1 fKO and Bmal1 WT mice tested in the circadian day (CT4) versus in the circadian night (CT16); calculated as: DI = Novel—Familiar Novel + Familiar *DI = quantification of how much time is spent with the novel object Snider et al., 2016  Model 3: Targeted loss of Bmal1 in forebrain Left: Barnes Maze acquisition. Representative tracks of mice at ZT4 prior to finding the escape hole during days 1 and 3 of acquisition. Arrows indicate the escape hole locations; lighter gray is used to denote the locations of the target quadrants. Right: Long-term retention of spatial memory in the Barnes maze. Heat maps of mouse locations during the day 21 probe trial. Arrows indicate the escape hole locations. By both the NOL and maze tests, loss of Bmal1 in the forebrain disrupts time-dependent memories. Snider et al., 2016  Cockroach Memory Tests Classical Conditioning involves involuntary behavior based on the association of unrelated stimuli with biologically significant Terry Page events (e.g., salivation and bell ringing in Pavlov’s dogs). In Operant Conditioning, stimuli that are present when a behavior is rewarded or punished come to control that behavior. Operant behavior is said to be voluntary because the subject may face a choice between different responses to a stimulus. Olfactory Discrimination Test Odor Sources Testing Arena Cockroaches Naturally Prefer Vanilla Prefer Prefer Vanilla Peppermint PPI = Peppermint Preference Index (also, remember that roaches are nocturnal) Olfactory Discrimination Test Odor Sources Testing Arena Odor Preference/Discrimination Do Not Vary with Circadian Phase Cockroaches Naturally Prefer Vanilla Prefer Prefer Vanilla Peppermint  Classical Olfactory Conditioning CS US+ (reward) Peppermint + 20% Sucrose CS US- (no reward) Vanilla + 30% Saline Roaches normally like vanilla and dislike peppermint. Training: do three sets of conditioning trials over 30 min. Test 48 hours later.  Can Cockroaches Learn? Train and Test in Early Subjective Night Before training, cockroaches dislike peppermint. But after training with peppermint+sugar, cockroaches learn to prefer peppermint. YES Decker et al. 2007  Can Cockroaches Learn? Train and Test in Train and Test in Early Subjective Night Early Subjective Day YES NO Decker et al. 2007  A Circadian Rhythm in Learning and Memory Before Training 48 hours After Training Trained at CT2, CT8, CT14, or CT20 Wait Two Days Tested at the same phase they were trained above: no circadian rhythm of PPI in untrained animals Decker et al. 2007  Is the Deficit at CT 2 Due to a Deficit in Memory Formation or a Deficit in Memory Recall? There was a significant increase in PPI in animals that were trained at CT 14 and tested at CT 2, whereas there was essentially no change in odor preference for training at CT 2 and testing at CT 14. Therefore, the deficit in animals trained and tested at CT 2 was because of an inability to store new memories and was not because of an inability to recall memories already established. Decker et al. 2007  Operant Olfactory Conditioning Peppermint, Vanilla, Reward Accessible Reward NOT Accessible Peppermint, which is an aversive odor, was associated with a slice of apple as a reward. The second odor was an attractant (vanilla) that was paired with apple made inaccessible by covering it with fine mesh netting.  Does the Circadian System’s Effect Depend on the Type of Training? Operant Conditioning On the first trial roaches visit the vanilla odor 6 or more times before they go to the peppermint. After they find the apple slice at the peppermint they are much more likely to go to the peppermint Following the initial training trial, animals consistently showed a odor reduced number of visits to vanilla prior to the visit to peppermint immediately. (with the apple reward). For training at CT14 vs. CT2, little change in performance occurred in subsequent tests at e.g., 5 min, 60 min, 48 h, & 1 week after training, indicating that roaches were capable of both short-term and long-term memory at both circadian times. Garren et al., 2013  With Operant Conditioning, Recall Is Dependent On Circadian Phase 0.6 A = Trained at CT 14 B = Trained at CT 2 0.6 CT 14 CT 2 Learning Index Learning Index 0.4 0.4 0.2 0.2 0.0 0.0 -0.2 -0.2 h h h h h h h h 36 24 48 12 12 24 48 36 Hours after time of training Animals perform better when tested at the same phase as they are trained: Circadian phase is an important contextual cue for recall, reminiscent of Zeitgedächtnis in bees. Garren et al., 2013  Classical Conditioning: The Optic Lobe Clock Inhibits Memory Formation A 0.8 N=7 N = 13 N=8 N = 13 Surgical ablation of the * * * biological clock via optic lobe removal (OLX) rescues the 0.6 animal’s ability to form memories at CT 2, suggesting the circadian PPI 0.4 system inhibits memory formation in the early 0.2 subjective day (classical conditioning). OLX also abolishes the circadian 0.0 Pre-test Post-test Pre-test Post-test Pre-test Post-test Pre-test Post-test rhythm in recall in operant conditioning (data not shown here). Sham (CT 14) OLX (CT 14) Sham (CT 2) OLX (CT 2) This same effect was found for time-dependent memory formation in hamsters–lesioning the SCN allowed memories to be stored at the usually “stupid” phase (Ruby et al., 2008) Lubinski and Page, 2016  Classical Conditioning: Inhibition at CT 2 by GABA GABA is a key inhibitory neurotransmitter. Fipronil, a GABA receptor antagonist and commonly used insecticide, restores the animal’s ability to learn at CT 2 via classical conditioning, suggesting the circadian system inhibits memory formation via GABA mediated inhibition. Fipronil also abolishes the circadian rhythm in recall following operant conditioning (data not shown). This same effect was found for time- dependent memory formation in hamsters– i.p. injection of the GABA receptor inhibitor PTZ allowed memories to be stored at the usually “stupid” phase (Ruby et al., 2008) Lubinski and Page, 2016  Conclusions The circadian system has a profound effect on learning and memory. What that effect is can vary with mode of training (and possibly species). In insects, fish, and mammals the circadian clock appears to act by inhibition (possibly via GABA) of one or another aspect of learning and memory processes at “inappropriate” times of day.  Food for Thought 1. What is the adaptive advantage of being stupid at some times of day? 2. For phase dependent recall (i.e., “Zeitgedächtnis”), how would the information on phase of training be stored in the brain? (This is a much more difficult question to answer than it might initially appear to be) 3. What might all of this mean for learning and memory in humans? WHEN should you study for your BSci exam at 10:00 am ? (see Wright et al., J. Cognitive Neuroscience 18: 508-521, 2006)