Chapter 12: Learning & Memory Flashcards
Learning
A relatively permanent change in behavior due to experience
Memory
the means by which past experience is drawn on to guide or direct behavior or thoughts in the present, necessary for learning to take place.
Learning and Memory endow us with the ___ to ___ to an ever-changing environment
Learning and Memory endow us with the flexibility to adapt to an ever-changing environment
Determining the effects of hormones on learning and memory is difficult
……
Learning & Memory occurs in 3 stages:
Acquisition
Consolidation/Storage
Retrieval
Timing of hormone administration is critical to the learning process:
Prior to first exposure to task:
acquisition
At a point between learning & retest:
storage/consolidation
Immediately before retest: retrieval
Hormones may also affect nonmnemonic factors which could indirectly affect learning & memory:
attention, motivation, sensory responsivity, motor capabilities
These performance factors must be ruled out
Hormonal effects on cognition can be examined by:
- Observing effects of naturally occurring hormonal states:
Estrous Cycle.
Seasons.
In response to an environmental event, such as stress. - Manipulating hormonal state of the subject:
Remove hormone producing gland.
Pharmacologically altering hormone synthesis.
Blocking receptors.
Using genetically altered animals that have no receptors for a hormone or no ability to produce particular hormone.
Cognitive Tasks
Use tasks for which the underlying neural circuitry has been partially or fully elucidated .
Advantage: if the hormone does modify performance on the task then the likely site of hormonal action can be identified & examined.
Radial Arm Maze
Spatial task.
Advantages:
Easy to perform
Easy to vary memory load by varying food site or inserting delay between choices.
Can monitor memory retention or strategies for solving task.
Disadvantages:
Many training trials are required to achieve steady performance so hormonal effects must be assessed over days, sometimes weeks, which makes it difficult to isolate the effects of hormones to one stage of learning & memory
Morris Water Maze
Spatial tasks
Makes use of the rodents’ natural tendency to escape to dry land if it is placed in water
Advantages:
Easy to perform
Quickly learned
Disadvantages:
Its an aversively motivated task so that stress of training and testing may activate other hormonal system not under study.
Because it’s easy to learn, hormonally induced improvements in memory may be difficult to detect unless task difficulty is increased (i.e. longer delay between trials, lengthening delay prior to probe trail, vary platform location each day).
Avoidance Tasks
Active Avoidance: animal must act to avoid a noxious stimulus
Passive Avoidance: animal must suppress a behavior that would otherwise be exhibited
Active Avoidance
animal must act to avoid a noxious stimulus
Passive Avoidance
animal must suppress a behavior that would otherwise be exhibited
Fear conditioning
Advantages:
Easy to perform.
Quickly learned and memory retained for many days, therefore used extensively to examine stages of memory when hormones may be acting.
Disadvantages:
Its an aversively motivated task so that stress itself activates other hormonal systems that may confound interpretation
Social Recognition
Makes use of the animals’ natural tendency towards olfactory investigation of novel conspecifics
Procedures:
2 rats allowed to interact and smell one another for several minutes.
After a delay in which they are separated from one another, they are returned for a second meeting.
If recognition occurs, then subject spends less time investigating familiar stems animal.
If no memory present, then subject investigates stimulus more than otherwise, as if it were novel.
Social Recognition:
Pros and Cons
Advantages:
Easy to perform.
Quickly learned and memory retained for many days.
Easy to increase memory demands of task by varying delay between learning and testing.
Disadvantages:
Hormones can affect olfactory processing so it is necessary to be careful that hormones are altering cognitive and not just sensory mechanisms.
Classical eyeblink conditioning
Tone Alone —-> No response
Eyelid shock (US) —> Blink (UR)
Tone + eyelid shock
Tone (CS) —–> Blink (CR)
Neural Basis of Learning & Memory
Many of the tasks & procedures used in studies of hormones and cognition depend upon neural pathways involving the hippocampus, amygdala, and various neocortical regions.
Critical for learning, memory, and emotion.
Contain receptors for several different hormones.
Receive input from other brain regions (i.e. septum) that express hormone receptors.
List the 3 Brain Areas Highly Involved in Learning & Memory
Hippocampus
Amygdala
Neocortex
Stress affects learning and memory
Emotionally charged events are more easily and vividly remembered
Suggests that the hormonal systems activated by stressful experience may directly or indirectly aid learning and long-term memory
Why do we often feel that stress blocks memory?
Yerkes-Dodson law
There is a “Goldilocks” region that’s just the right amount of stress to have the best possible effect.
Represented by a bell curve of performance vs. arousal.
Too much arousal or too little results in less than ideal performance.
Stress Hormones Affect Learning & Memory
The Adrenal Glands play a large part in this.
Adrenal Cortex
Releases Glucocorticoids (like cortisol)
Adrenal Medulla
Releases Epinephrine and Norepinephrine.
Epinephrine
Aka adrenaline.
Generally enhances performance on a variety of learning & memory tasks.
Effects are dose & time dependent.
Inverted U-shaped curve: moderate doses more effective than low or high doses
Greatest enhancement observed shortly after training than before, during or long afterwards
Suggests that epinephrine may be acting on MEMORY STORAGE.
Epinephrine:
Details, Details
Influences memory by making NOXIOUS STIMULI more salient
Evidence:
Animals perform better in avoidance tasks if receive moderate rather than mild shock.
If a mild shock is paired with Epinephrine treatment, then the animal exhibits optimal learning.
How does epinephrine affect learning & memory?
Epinephrine must act in the brain to affect learning & memory, but Epinephrine released from adrenal doesn’t easily cross blood brain barrier.
Epinephrine must affect some processes outside of the brain that subsequently influences learning & memory
Two hypotheses:
Peripheral Receptor Hypothesis
Glucose Hypothesis
Peripheral Receptor Hypothesis
Epinephrine activates peripheral receptors (β-adrenergic receptors) that interact directly with the brain
Peripheral Epinephrine
- –> β-adrenergic receptors on the vagus nerve
- –> vagal afferents project noradrenergic neurons in the nucleus tractus solitarius (NTS)
- –> NE release in the amygdala
- –> affect memory
Evidence:
Memory enhancing effects of Epinephrine can be blocked propranolol (drug that blocks β-adrenergic receptors) in the amygdala.
Blocking any part of this pathway prevents the memory enhancing effects of Epinephrine.
propranolol
drug that BLOCKS β-adrenergic receptors
Memory enhancing effects of Epinephrine can be blocked propranolol in the amygdala
β-adrenergic receptor activation is critical for arousal-induced performance in humans.
Experiment 1:
Control subjects: boy and his mother walk through town, pass several stores, cross the street, enter a hospital, where the boy’s father works and while they are in the hospital they see an X-ray machine
Experimental subjects: boy crosses the street, is hit by a car and taken to the hospital where his father works and brought to the X-ray room
After a delay, experimental subjects recalled the story better but just the final stressful part not the whole story
Experiment 2:
Half the subjects given propanolol, other half given saline.
Those that received the drug and were read the arousing version of the story had poorer recall for the study details that subjects given saline
Glucose Hypothesis
Epinephrine affects memory via its effects on blood glucose, which increases glucose availability to the brain
Evidence:
Glucose enhances memory in rodents & humans.
Just like Epinephrine, the memory enhancing effects of glucose follow an inverted U-shaped curve and are time dependent.
Memory enhancing effects of Epinephrine can be blocked by blocking peripheral Epinephrine receptors, but these have no effect on memory enhancement produced by glucose treatment
How does glucose affect memory?
Elevated blood glucose permits more glucose to enter neurons, which stimulates release of Acetylcholine (ACh) into synapses
Ach from BASAL FOREBRAIN enhances memory (degradation in Alzheimers)
Glucocorticoid: Ideal Range
The ideal range of CORT for optimal learning and memory is an inverted U-shaped curve (i.e., bell curve) again…
Glucocorticoids
In general, acute stress/glucocorticoids enhance learning & memory while chronic stress/glucocorticoids impair learning & memory.
However, the effects of stress/glucocorticoids on learning & memory are more complex than this, and depend on a variety of factors including type of stressor, dose of corticosterone, task, timing of stressor/glucocorticoid administration relative to training/testing, sex, etc…
Acute glucocorticoid administration facilitates memory consolidation
Single injection of natural or synthetic (dexamethasone) glucocorticoids mimic acute stress and enhances performance of inhibitory avoidance learning when administrated immediately after training
Memory enhancing effects involve the basolateral amygdala
Single injection of dexamethasone mimics acute stress and enhances learning & memory.
