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1

Learning

A relatively permanent change in behavior due to experience

2

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.

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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

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Determining the effects of hormones on learning and memory is difficult

......

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Learning & Memory occurs in 3 stages:

Acquisition

Consolidation/Storage

Retrieval

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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

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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

8

Hormonal effects on cognition can be examined by:

1. Observing effects of naturally occurring hormonal states:
Estrous Cycle.
Seasons.
In response to an environmental event, such as stress.


2. 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.

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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.

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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

11

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).

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Avoidance Tasks

Active Avoidance: animal must act to avoid a noxious stimulus

Passive Avoidance: animal must suppress a behavior that would otherwise be exhibited

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Active Avoidance

animal must act to avoid a noxious stimulus

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Passive Avoidance

animal must suppress a behavior that would otherwise be exhibited

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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

16

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.

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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.

18

Classical eyeblink conditioning

Tone Alone ----> No response

Eyelid shock (US) ---> Blink (UR)

Tone + eyelid shock

Tone (CS) -----> Blink (CR)

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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.

20

List the 3 Brain Areas Highly Involved in Learning & Memory

Hippocampus
Amygdala
Neocortex

21

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?

22

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.

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Stress Hormones Affect Learning & Memory

The Adrenal Glands play a large part in this.

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Adrenal Cortex

Releases Glucocorticoids (like cortisol)

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Adrenal Medulla

Releases Epinephrine and Norepinephrine.

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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.

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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.

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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

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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.

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propranolol

drug that BLOCKS β-adrenergic receptors

Memory enhancing effects of Epinephrine can be blocked propranolol in the amygdala