NEURO2O20 WEEK 11

AMNESIA 

Retrograde 

• Backward acting 

• Deficits in memory prior to surgery/trauma 

Anterograde 

• Forward acting 

• Deficits in the ability to form new memories after surgery/trauma 

  • deficits in storing new memories in short-term memory 

  • deficits in transfer of information to long term storage that can be retrieved after attention has been diverted from it 

CASE OF H.M

H.M. 

• Severe epilepsy and seizures resulted in removal of medial temporal lobes, hippocampus and amygdala 

• Surgery reduced his seizures but caused amnesic effects 

DIGIT SPAN +1 TEST

• test of long-term memory 

• 5 digits read to patient at a rate of 1 per second 

• Next trial – same 5 digits + 1 more at the end…etc

• H.M.'s best performance was 7 digits after 25 trials 

• Most people can do 15 digits after 25 trials 

BLOCK TAPPING TEST

• 9 blocks spread out on a board 

• The psychologist taps the blocks in the order numbered on their side of the block  

• Patient repeats sequence 

• H.M could not match the normal performance of about 6 taps  

MIRROR DRAWING TEST

• Implicit memory  

• Trace boundaries of a star without going outside the track 

• Patient has to watch their hand in the mirror 

• Trace the pattern 10 times per day for 3 days 

• Reduction in the number of errors indicated H.M. retained something from the task 

• He did not have explicit memory of doing the task the previous day 

INCOMPLETE PICTURES TEST

• Implicit memory  

• five sets of pictures – containing 20 objects, but the sets differ in their degree of completion 

• Step 1 = determine the level of completeness required to reliably identify the pictures 

• Wait 1 hour and test again 

• Non-impaired people identify pictures at a lower level of completeness on the second run – as did H.M. 

PAVLOVIAN CONDITIONING TEST

• A tone played just before puff of air administered to his eye 

• Trials repeated until the tone elicited the eye blink 

• H.M.'s rate of learning was slower than normal and lasted two years.  

SCIENTIFIC CONTRIBUTIONS OF H.M

• Revealed the role of medial temporal lobes in memory 

• Provided support for the theory that there are modes of storage for short term, long term and remote memory 

• First to reveal that an amnesic patient might report no memory of an experience but demonstrates memory by showing improved performances 

• Lead to distinction between two memory types: 

  • Explicit – conscious, long-term memory. Allows flexible use of information. 

  • Implicit – long-term memory demonstrated by improved performance without conscious awareness. Simpler and likely older.  

H.M DEFICITS IN…

Explicit memory

MEDIAL TEMPORAL LOBE AMNESIA

• Refers to patients who have preserved intellectual functioning with evident damage to the medial temporal lobe  

• Difficulty forming explicit memories 

• Retain ability to form implicit memories  

• impair long delay (long -term memory)

SEMANTIC VS EPISODIC MEMORY

• People with temporal lobe damage have difficulty with episodic memory 

Semantic 

• Explicit memories for general facts or information 

Episodic 

• Explicit memories for specific moments in one's life  

AMNESIA OF KORSAKOFF’S SYNDROME

• Memory disorder in people who consume large amounts of alcohol for a prolonged period (>35 drinks per week for 5-10 years) 

• Associated with Thiamine deficiency 

• In advanced stages: 

  • Confusion 

  • Personality change 

  • Organ dysfunction 

  • Damage to medial thalamus, neocortex, hippocampus, cerebellum 

• Amnesia is similar to medial temporal lobe amnesia 

• hard to specify the structure that is responsible for observed deficits, but damage to mediodorsal nuclei of the thalamus is nearly universally observed

WORD STEM IMPROVEMENT IS AN EXAMPLE OF…

Working memory

X KNEW FACTS ABOUTY THE WORLD BUT NOT WHO HE HAD BREAKFAST WITH, THIS SHOWS:

Impaired semanic memory

AMNESIA OF ALZHEIMERS

• As disease progresses, deterioration to dementia where the patient cannot recognize family, speak, eat, etc.  

• Deficits in tests of anterograde and retrograde explicit memory 

• Short term memory deficits 

• Degradation in implicit memory for verbal and perceptual information 

POST-TRAUMATIC AMNESIA

• Closed head traumatic brain injury is most common cause 

• Stages: 

  • Coma: state of unconsciousness following head blow 

  • Retrograde amnesia for events leading up to head blow 

  • Confusion and Anterograde amnesia for events that occurred during the state of confusion 

ELECTROCONVULSIVE SHOCK AND CONSOLIDATION

• Brief but intensive seizure inducing current administered to the brain via electrodes on scalp 

• Tests memory consolidation because it disrupts Hebb's reverberation 

• Erases memories that have not undergone consolidation 

• Squire et al. Showed consolidation can last several years  

HIPPOCAMPUS AND ISCHEMIA

• Patients that suffer global cerebral ischemia (interrupted blood flow to the entire brain) often suffer from medial temporal lobe amnesia 

• Damage to the pyramidal cell layer of the hippocampus 

• Suggests the hippocampus was important in memory (PARTICULARLY SPATIAL MEMORY + EPISODIC MEMORY)

DELAYED NON-MATCHING TO SAMPLE TEST

• Tested the idea that amnesia due to temporal lobe damage is entirely due to hippocampus damage 

• Easier to test in rats because the hippocampus is easier to isolate 

• The tested proved not true  

Instead: 

• The hippocampus's role seems to be less thought of for object recognition memory and more for performance on tasks that involve memory for spatial location 

HIPPOCAMPAL PLACE CELLS

• Cells that respond only when an individual is in a particular place/location 

• Each place cell has a place field that corresponds to a different part of each environment 

JENNIFER ANISTON NEURONS; CONCEPT CELLS

• One neuron was discovered that fired in response to images of Jennifer Aniston.  

• Concepts cells are cells that are found to respond to more than one object that are similar 

• Related concepts are thought to trigger activity in circuits of concepts cells in the medial temporal lobes 

ENGRAM CELLS

• Neurons that undergo a persistent change in response to experiences, such that when they are activated/inhibited, the retrieval of the original experience is triggered or suppressed.   

• Structures that are active during encoding of memories are also active during recall.  

FIVE BRAIN AREAS IN MEMORY

INFEROTEMPORAL CORTEX 

• Is responsible for complex visual function 

• Responsible for memories of visual input 

AMYGDALA 

• Encodes emotionally charged memories 

• Does not store memories itself, but strengthens emotionally charged memories 

PREFRONTAL CORTEX 

• Memories for tasks that involve a series of responses 

• Ex. Recipes 

CEREBELLUM 

• Memory for sensorimotor tasks 

STRIATUM 

• Memory for relationships between stimuli and their responses 

• Changes gradually over time 

• Thought to be the basis of habit formation 

LONG TERM POTENTIATION

• Occurs when two or more neurons are excited at the same time 

• The synapse is repeatedly activated and the chemistry of the synapses changes such that the connection is strengthened 

• 'neurons that fire together, wire together' 

• Long term learning based on the development and growth of further synaptic connections 

STAGES OF LONG TERM POTENTIATION

1. Induction 

   • If the postsynaptic neuron is depolarised when glutamate binds to its receptors, the NMDA receptors permits the entry of many calcium ions and a LTP is induced 

2. Maintenance 

   •  Ensuring those preferential links are sustained 

3. Expression 

   • Using links to recall your memories 

   • LTP causes structural changes such as increase in the number + size of synapses, number of dendridic spines, changes in pre and post-synaptic membranes, and changes to dendritic branching 

MYELINATION

Myelination 

• Oligodendrocytes modulate the myelination of axons in response to experience 

• Myelin sheath is not static, rather dynamic and ongoing throughout lifespan 

FIVE MECHANISMS THAT CHANGE MYELINATION

• Unmyelinated axons can be myelinated by oligodendrocytes 

• Myelinated axons can have their myelin sheaths removed 

• Myelin can be replaced when it degrades 

• Myelin sheaths can be thinned or thickened 

• Myelin sheaths can be lengthened or shortened 

INFANTILE AMNESIA

• Lack of explicit memory during infancy  

• Children were shown photos of their preschool classmates. They reported remembering a low number, but they had heightened skin response to classmates vs control photos.  

SPACING EFFECT

Memory is better with repeated spaced learning than massed learning. Over time retention and length of retention increases.

LEITNER SYSTEM

• Flashcards are sorted by difficulty

• promoted or demoted based on performance

• lower numbers studied more frequently

• spaced repitition

NEUROSCIENCE OF SPACED LEARNING

• increase in volume and no. of postsynaptic dendritic spines recruited

• long term potentiation relies on mechanisms that take time to recover

• therefore, LTP has a refractory period where effects are diminished during massed learning

• Molecular refractory period theory

LEVELS OF PROCESSING

Deeper processing at encoding leads to better retrieval.

STRUCTURAL - spelling/visual qualities of word

PHONEMIC - Phonetic/auditory qualities of word

SEMANTIC - meaning of word

Shallowest to deepest.

TRANSFER-APPROPRIATE PROCESSING

• recall is determined by match between encoding processes and recall processes

• semantic does not always equal best recall

SERIAL POSITION EFFECT

Recall of items are influenced by order.

PRIMARY EFFECT - remember things @ start better

RECENCY EFFECT - remember things @ end better

SERIAL POSITION EFFECT COGNITIVE EXPLANATION

SINGLE STORE MODEL

• effect best explained by a single memory process

• early items recieve more attention

• late items are temporally closer to recall test

DUAL STORE MODEL

• effect best explained by short and long term memory

• earlier items are quickly encoded into long term because there are fewer competing items

• late items are still active in short term memory at recall

DRM FALSE MEMORY PARADIGM

Using a series of related words to produce a false memory/report of the ‘lure’ word.

FALSE MEMORY COGNITIVE EXPLANATION

FUZZY TRACE THEORY

• people develop two types of memory traces

• gist, verbatim

ACTIVATION-MONITORING THEORY

• words spread activation to lure the word through semantic associations.

Semantic vs episodic memories are predictive of more vs less false memories respectively.