Lecture - learning and memory Flashcards
learning
Changes in our nervous system as a result of experience
memory
How these changes are maintained over time and how they are expressed (recall)
amnesia
incapacity to remember
retrograde amnesia
Inability to remember events prior to injury (i.e., some sort of damage to your brain). Can’t remember the past.
anterograde amnesia
Inability to remember events after injury. Incapacity to form new memories.
Bilateral Medial Temporal Lobectomy (HM case)
Removal of the medial temporal lobe (MTL) bilaterally to alleviate serious epilepsy (1953). included the hippocampus, amygdala, rhinal cortical areas. Epilepsy improved, but had devastating amnesic effects.
after surgery (HM case)
Intellect was above average, IQ actually improved from 104 to 118. Normal perceptual and motor abilities and a well-adjusted individual. but, he was left with very poor memory abilities. Mild retrograde amnesia (~ 2 years prior to surgery) and profound anterograde amnesia.
HM
- HM is the most famous patient in the history of neuroscience research.
- He has made a valuable contribution to research on the neurobiology of memory. He has been extensively tested for over 50 years.
- Demonstrated that the medial temporal lobe is critical for forming new memories.
what can HM do
Remember a list of 6-7 digits.
- Digit-Span + 1 Test
- Performance in normal range.
Tap a sequence of 5 blocks
- Block-Tapping Memory Span Test
- Performance in normal range.
So, HM has relatively intact short-term memory.
HM can learn new behavioral skills
Mirror-Drawing Task and Rotary-Pursuit Test:
- HM’s performance improves with training sessions. Normal sensory-motor learning. He has no conscious recollection of ever performing it before.
HM can show normal priming
More likely to use a word if you have heard it recently. Repetition Priming Test: He has no conscious recollection of the words on the original list.
HM can learn conditioning tasks
Pavlovian Conditioning: HM’s performance improves with training sessions. He has no conscious recollection of ever performing it before.
what HM has taught us
- Evidence that there are different kinds of memory.
- Different brain regions are more important for some kinds of memory, but not others.
- Consolidating episodic memories depends on the medial temporal lobe.
- Evidence for two parallel memory systems.
how long does short term memory last
seconds - minutes (okay in HM)
how long does long term memory last
hours - years (sort of okay in HM; can form some kinds of long-term memories).
working memory
active maintenance (okay in HM)
declarative (explicit) memory
things you know that you can tell others
episodic (explicit)
impaired in HM
semantic (explicit)
okay in HM
procedural (non-declarative, implicit)
things you know that you can show by doing.
skill learning (implicit)
okay in HM
priming (implicit)
more likely to use a word you heard recently. okay in HM
conditioning (implicit)
okay in HM
Although subjects with MTL amnesia can form procedural (implicit) memories
they can not transfer that memory to a new or different context (situation)
The conscious (explicit) system may have evolved to confer
flexibility, that is, ability to use implicit learning in different ways or contexts.
memory storage equals
memory consolidation.
storing (consolidating) memories
Change the memory from a labile/vulnerable state to a stronger, more permanent state.
Concussion or Coma (closed head trauma)
Usually results in amnesia for events occurring just after regaining consciousness. Failure to convert short-term memories to long-term memories. Permanent retrograde amnesia for events just prior to the injury. Older memories are spared! Suggests that these memories have been protected by some mechanism and are stronger than newly formed memories.
Hebb (late 1940’s)
Postulated that memories are held in a short-term reverberating circuit until they are consolidated to last a long period of time.
Electroconvulsive Shock (ECS)
Used to study memory consolidation with the assumption that disrupting neural activity would erase the memories that had not been consolidated yet.
One-trial learning
- Thirsty rats allowed to discover the location of water spout.
- ECS applied more than 1 hour after training did not disrupt memory for the location of a water spout.
- Suggests that consolidation takes place within 1 hour.
Human studies show that ECS (used to treat severe depression) can
disrupt memories up to 3 years old. Suggests consolidation is a longer, ongoing process that takes more time than a short-term reverberating circuit would allow. Therefore, Hebb’s reverberating circuit hypothesis is unlikely.
reconsolidation
recalling a memory seems to put that memory into a more labile state that can still be disrupted before it is consolidated again.
misinformation effect
Loftus, Miller, and Burns; Subjects watched a video of a car accident. A sports car stopped at a yield sign. Subjects were then interviewed 20 min – 1 week later.
- Consistent Condition: “Did another car pass the sports car while it was stopped at the yield sign?”
- Neutral Condition: “Did another car pass the sports car while it was stopped?”
- Inconsistent Condition: “Did another car pass the sports car while it was stopped at the stop sign?”
Subjects then shown pictures of a stop sign and a yield sign. Subjects had to point to the sign they saw in the video.
Loftus, Miller, and Burns
Consistent questions reinforced the correct memory. Inconsistent question deteriorated the correct memory, which biased subjects towards reconsolidating the incorrect memory!
HM had some retrograde amnesia and severe anterograde episodic amnesia which
Suggests that hippocampus and related cortical areas are important for consolidating episodic memories for long-term storage in other cortical areas.
Over time, memories are stored in distributed networks of cortical areas and become
less and less connected to the hippocampus.
engram
the change in the brain that represents a memory.
Delayed Nonmatch-to-Sample Task: monkey version
test of object recognition memory. Monkey results are inconclusive. Damaged hippocampus, amygdala, and rhinal cortex. Rodent studies only damage small portions of parietal cortex, leaving rhinal cortex intact.
Delayed Nonmatch-to-Sample Task: rodent version
Mumby Box; test of object recognition memory. Rodent studies suggest that rhinal cortex is necessary for normal recognition memory for objects, while hippocampus and amygdala are not.
hippocampus is important for
spatial memory.
Morris Water Maze
normal rat learning the location of the hidden platform. Hippocampal lesions impair rats’ ability to learn the location of the platform.
reference memory
the type of task being performed. General principles and skills needed in the task.
working memory
ability to maintain relevant memories while a task is being performed.
Eight Arm Radial Maze
Hungry rats will learn which arms contain rewards (reference memory). Rats will learn to not enter an arm more than once on a given day (working memory). Hippocampal lesions produce major deficits on reference and working memory measures.
place cells
Cells that fire when the subject occupies a particularr location in the environment. seem to represent a cognitive component of the environment. example, if the cells fire in a certain pattern, the rat will behave a certain way.
Cognitive Map Hypothesis (theories of hippocampal function)
Hippocampus contains a cognitive map of allocentric space that serves as spatial context useful for acquiring and recalling memory of any episode.
Configural Association Theory (theories of hippocampal function)
Hippocampus is critical for learning the significance of combinations of stimuli (e.g., you will be learning about biopsychology in this room, not any other topic).
Allocentric map
space represented by the relation between external landmarks, as opposed to “egocentric”.
Hippocampus is important for spatial memory in many species
Birds that store seeds have larger hippocampi than non-food caching birds. In humans, there is hippocampal activation during performance of virtual navigation tasks. Hippocampal activity was measured with PET (positron emission tomography) .
memories are stored in
areas that contribute to the acquisition of the memories.
Inferotemporal cortex
object recognition
amygdala
learned fear. plays a role in memory for the emotional significance of experiences. Rats with amygdala lesion fail to associate shocks with fear.
cerebellum
implicit sensorymotor tasks (eye blink response)
prefrontal cortex
temporal order of events, as in cooking
striatum (basal ganglia)
habitat formation
Korsakoff syndrome and Alzheimer syndrome
Mediodorsal nucleus of the thalamus, and the basal forebrain (a midline area, rich in Ach, located just above the hypothalamus), appear to be damaged in patients with Korsakoff syndrome (often due to alcoholism) and Alzheimer syndrome (a terminal condition including progressive amnesia and dementia.
Hebb
changes in synaptic efficiency are the basis of long term memory.
long-term potentiation (LTP)
enduring facilitation of synaptic transmission caused by high frequency (100/sec) stimulation of presynaptic neuron. mimics normal neural activity.
cooperativity (implicates LTP in learning and memory)
affferents that cooperate become facilitated.
associativity (implicates LTP in learning and memory)
pairing a weak and a strong input enhances later responses to the weak input
LTP is consistent with
Hebb’s postulate for learning
Hebb’s postulate for learning:
The synaptic efficacy between A and B will increase when A causes B to fire consistently. LTP requires co-occurrence of firings in pre- and post-synaptic neurons.
NMDA receptors are normally blocked by
Magnesium ions (Mg++) at resting membrane potentials (-70 mV).
NMDA receptors do not respond unless
glutamate binds to the receptor and the neuron is already partially depolarized (which repels Mg++).
Ca2+ does not flow into cell unless
both conditions are met. Ca2+ influx may activate protein kinases that induce changes necessary for LTP.
LTP begins in the
postsynaptic neuron, which provides feed-back signals to the presynaptic neuron through soluble gases such as Nitric Oxide (NO).
Pre- and post-synaptic changes:
- Insertion of glutamate receptors in post-synaptic membrane
- Increase of of glutamate release in pre-synaptic neuron
NMDA receptors are needed for
inducing LTP, but not for maintaining it.
LTP effects are greatest in
brain areas involved in learning and memory.
Learning can produce
LTP-like changes
Blocking LTP interferes
with learning. Mice with abnormal NMDA receptors did not have LTP and could not learn a spatial task.
