Week 4 Flashcards
(34 cards)
Patient HM - What did they do?
Had debilitating seizures
Seizure medication would not curve his seizures
Exploratory seizure operation- cut out his hippocampus and parts of his medial temporal lobe
What were the effects of HM’s surgery?
*No more seizures
*But, severe impact on memory retention.
*Unable to create any new memories - anterograde amnesia - explicit memory was gone
*Forgetting events as fast as they occurred.
*Memories prior to the surgery were easily accessible.
*Offered opportunity to study the brain
What did Scoville and Milner find out about MTL and LTM from HM?
- MTL and hippocampus are primarily connected to memory
- IQ and language were intact
- MTL involved in memories that can be consciously recalled but not memories for actions or other memories that cannot be consciously recalled
4.MTL is not necessary for short-term memory
HM retained…
Maintained his higher IQ
His intellect, personality, procedural memory and perception were intact
Was able to learn and retain new motor skills
Implicit memory was in tact
No deficits in language - could hold a conversation
Training for him was retained in procedural memory
Different parts of the brain were involved in different types of memory processes
What conclusion did HMs surgery ultimately lead to?
The understanding that complex functions such as learning and memory are tied to discrete regions of the brain
What is long term memory and what are the types?
Enduring and can last a lifetime in theory
Different types of long-term memory
Explicit and implicit long term memory
Episodic and autobiographical long-term memory
Fact - based generic long-term memory - semantic memory
What is Hebbian Plasticity?
- the notion that synapses are created by metabolic changes resulting from the simultaneous firing of neurons
What is Hebb’s Postulate?
The strength of synaptic connections changes as a result of repeated simultaneous activation
The more times you activate - the stronger the connection
Simultaneous firing will cause the presynaptic neuron to more frequently activate the postsynaptic
How does Hebbian plasticity explain classical conditioning?
hebbian plasticity suggests that the learned association is the result of auditory system neurons firing at the same time as neurons in the digestive system - axons form the auditory system being located near receptors for the digestive system
What is Long term potentiation?
A persistent strengthening of a synapse based on recent patterns of activity
baseline strength of perforant path in a rabbit - pulses of electricity and measuring activity in the cell-body layer of the DG - denate gyrus
Baseline: pop spikes were small - few dg neuron were firing
Second tetanus: increased and continued to increase over time
Last high frequency burst: continued to increase for another 3 hrs
Hippocampus
complex and receives input from many parts of the brain - ventral, dorsal visual streams and entorhinal complex EC
Info passing through hippo path: EX > dentate gyrus (perforant path) > through CA fields and back out the neocortex
Receptors and role in LTP
Glutamate binds to both - AMPA opens sodium channel entering the ion and depolarizing the hippocampal neuron
NMDA blocked by magnesium but depolarization opens - calcium enters
Calcium causes hippocampal neuron to create silent receptors along the postsynaptic membrane - strengthens - potentiates the synapse - respond faster to glutamate
Activated NMDA receptors influence LTP through short and long term mechanisms:
Short term - influx of Ca into receptor - more AMPA gluta receptors active - increases prob of glutamate binding
Long term - Ca ions initiate the synthesis of new proteins that are needed for the development of new synapses
Evidence that NMDA Receptors are Necessary for Learning
Rats learned to find an invisible platform
Swim directly to the platform after 10 trials
To test whether NMDA receptors were necessary for the formation of long-term spatial memory in rats - Rats injected with AP5 to block NMDA receptors show no indication of learning this task
Will not learn the location of platform - no memory for where the platform was located
Strongly indicates that NMDA receptors are required for spatial learning in rats
2 Roles of Hippocampus in Long-term memory
Main role of hippocampus to learn the relationship btw items in the environment and create cognitive maps - A cognitive map is an animal’s internal representation of the spatial relationship among objects in the environment
—Taxi - greater grey matter volume in the posterior hippocampal region - anterior volume and grey matter density decreased with years of experience
Relational Binding - process by which different memories of the same object are linked together - object can be recognized from any viewing angle - hippocampus HC study
What is the stability plasticity dilemma
Stability plasticity dilemma - problem concerning how it is possible for the brain to keep existing memories stable while integrating new memories
Two-stage model of memory was developed to explain
Two Stage Model
Concentrates on explaining the formation of explicit memories - evidence for sleep-dependent consolidation for implicit memory
Developed to explain both the time limited role of the hippocampus on LTM and the stability plasticity dilemma
Temporary Store
Relies on the hippocampus and adjacent temporal
lobe structures
Learns quickly and holds onto
information briefly
Long-term store
Relies on the neo cortex
Learns slowly but holds onto info for long
periods of time
New info gathered while awake - goes in temporary and long term
Consolidate during sleep - new info is reactivated repeatedly - slowly organized and integrated into the long term store
Same processes needed for reactivation and initial processing - have to perform reactivation and redistribution during sleep - no encoding demands
Multiple Trace theory
When memory is retrieved the hippocampus creates a new memory trace each time a memory is retrieved
Over time one memory can be stored as multiple traces
Episodic memories remain stored in the hippocampus
With multiple learnings the face will now be accessible as a context-free generic memory outside of the hippocampus
Stored in two different places simultaneously
Multiple-trace theory suggests that individual episodic memories remain stored in the hippocampus and thus that damage to the hippocampus will impair an individual’s access to episodic information
Compare and Contrast two stage and multiple trace
multiple-trace model suggests that only context-free information, such as information gleaned from multiple encounters with the same fact, will come to be stored outside of the hippocampus, while the two-stage model suggests that all episodic memories eventually become represented in the cortex through processes that take place during SWS.
Reconsolidation
After consolidation, reactivating a memory makes that memory malleable again - reconsolidation must occur after reactivation for the memory to be retained
Change lots of your memories - add in false info
What happens during retrieval in the brain?
*Polyn et al. (2005) found that brain activity associated with a certain category during the learning phase matched brain activity while participants were recalling items for that category
*Successful, intentional retrieval of information involves configuring brain activity into the same state that it was in during encoding
Categorization - short cut but less attention paid too it
What is the purpose of sleep in relation to memory
Research suggest that the primary purpose of sleep is to consolidate memories and that this process is only possible if external stimulation is cut off
How long to cycle through 5 stage of sleep?
Cycle through 5 stages of sleep in roughly 90 minute cycles
Wakefulness
High-frequency beta waves while alert
Lower frequency alpha waves when relaxed
