1. Ch 11: Learning, Memory & Amnesia
Part 2

2. Amnesia after Concussion
Concussions are the #1 cause of amnesia
Posttraumatic amnesia (PTA)
Coma: pathological state of unconsciousness
Can last seconds to weeks…
After regaining consciousness, there is a period of confusion
Usually there is permanent retrograde amnesia for events just prior to the blow to the head & permanent retrograde amnesia for the subsequent period of confusion
With amnesia, there are sometimes surviving memories for isolated events: islands of memory

3. Memory Consolidation
The fact that concussions disrupt recent memories more than older ones suggests that the older ones have been strengthened
Hebb’s theory of consolidation
Memories are stored in STM by reverberating in closed circuits
If this is disrupted ex: by a blow to the head, the memory can be lost
But normally the recirculating STM will cause structural changes in the synapse, providing stable place to store it as LTM
Electroconvulsive shock (ECS) used to study consolidation by interrupting this reverberation
Mixed results; doesn’t explain long gradients of amnesia; consolidation can continue potentially indefinitely

4. Hippocampus & Consolidation
Standard consolidation theory
Memories are temporarily stored in the hippocampus until they are transferred to cortical storage
Multiple-trace theory
Hippocampus & other memory storage areas store the memories as long as they exist but over time, they become more resistant to disruption
Each time a similar experience occurs, the original memory is recalled & creates a new engram (change in the brain that stores a memory), which is linked to the original engram, making it stronger
Accounts for long gradients of retrograde amnesia

5. Reconsolidation
Theory that each time a memory is retrieved from LTM, it is temporarily held in STM and is once again susceptible to amnesia until it is reconsolidated
Some evidence suggests not all types of memories are susceptible to reconsolidation

6. Neuroanatomy of Object-Recognition Memory
Lesion studies to determine neuroanatomy of memory
Object-recognition memory tested with delayed nonmatch-to-sample test
Rhinal cortex: cortical area adjacent to the hipppocampus & amygdala; one of the 3 major temporal lobe structures
Lesions of this area caused serious deficit in object recognition memory
2 areas: entorhinal cortex & perirhinal cortex
Hippocampal lesions only caused moderate deficits
Pyramidal cells of the CA1 region seem to be the key to hippocampal involvement in this kind of memory

7. Hippocampus & Spatial Memory
While hippocampal lesions have little/no effect on general memory, they consistently impair memory of spatial location
Many hippocampal neurons are place cells
Neurons that respond only when a subject is in specific locations
Grid cells: neurons in the rhinal cortex that have an array of evenly spaced place fields

8. Hippocampus & Spatial Memory
Birds that cache food have larger hippocampi than other species
Cognitive map theory
There are several systems in the brain each specialized in memory for different kinds of info; the hippocampus is for spatial memory
There are criticisms of this theory

9. Where are memories stored?
While the hippocampus & rhinal cortex are involved in memory, memories are not necessarily stored there
Memories are stored diffusely in the brain
Can survive the destruction of one specific area
Memories become more resistant to disruption over time
Memories appear to be stored in the brain areas that participated in the original experience that created the memory

10. Where are memories stored?
So far we’ve discussed 4 brain areas with some memory storage
Hippocampus (spatial)
Perirhinal cortex (object)
Mediodorsal nucleus (Korsakoff’s)
Basal forebrain (Alzheimer’s)
5 more to discuss
Inferotemporal cortex
Amygdala
Prefrontal cortex
Cerebellum
Striatum

11. Inferotemporal Cortex
Involved in visual perception of objects & thought to participate with the perirhinal cortex in storing memories of visual patterns
In general, areas of 2ndary sensory cortex play a role in storing sensory memories

12. Amygdala Role in memory for the emotions tied to an experience
Ex: the fear that goes along with a foot shock
Doesn’t seem to store the memory itself
It is involved in strengthening emotionally significant memories stored elsewhere
Explains why you are better at remembering emotion-provoking experiences

13. Prefrontal Cortex
Damage to this area does not cause major amnesia & patients often perform well on traditional memory tests
However, damage to the PFC does seem to impair 2 episodic memory abilities
The order of events
Working memory (ability to maintain relevant memories while a task is being completed)

14. Cerebellum & Striatum
Implicit memories of sensorimotor learning presumed to be stored in the sensorimotor circuit associated with first experiencing them
Cerebellum involved in Pavlovian conditioning
Striatum stores memories of consistent relationships between stimuli & responses; habit formation
Both also seem to be involved in non-motor memories

15. Synaptic Mechanisms of L&M
Long-term potentiation (LTP)
Based on Hebb’s hypothesis about reverberation & STM to LTM
Facilitation of synaptic transmission following high- frequency electrical stimulation applied to presynaptic neurons
Can last for a long time (months) after multiple stimulations
Only develops if both the pre & postsynaptic neurons fire
One of the most widely studied phenomena in neuroscience

16. LTP 3 part process Induction Maintenance Expression
High-frequency stimulation induces LTP (learning)
Maintenance
Changes responsible for storing LTP (memory)
Expression
Changes that allow it to be expressed during the test (recall)
NMDA receptors (glutamate) play a large role in LTP
Still more questions than answers

17. Infantile Amnesia We remember essentially nothing from our infancy
But we do show there are implicit memories for experiences from this time
When kids are later shown pictures of themselves with preschool classmates, they remember almost none of them; however, they do exhibit a skin conductance response associated with seeing familiar individuals