Chapter 13

Amnesia: retrograde & anterograde

• retrograde amnesia - loss of memories that formed prior to an event - like surgery or trauma

  • after damage to the brain ppl have retrograde amnesia regarding events that happened a few hours, days, or year before the accident

  • unlikely that complete/longer-term retrograde memory loss has occurred

• Henry Molaison - after his surgery he was unable to form new memories after an event - anterograde amnesia

  • His case provided evidence taht short-term memory differes from long-term memory

  • Hes surgery removed the amygdala, most the hippocampus, and surrounding cortex from both temporal lobes

  • The memory deficit was caused by loss of tthe medial temporal lobe - the hippocampus

  • Henry’s type of amnesia can learn the skill of reading mirror reversed text which is a verbal task

• anterograde amnesia - the inability to form new memories after an event

Declarative memory (explicit memory)

• learned facts and information

• Memory that we can declare to others

• This memory was imparied by Henry’s surgery

Nondeclarative memory (implicit/procedural memory)

• motor procedure memories - shown by performance and not conscious recollection

• ex: mirror tracing task - Henry was able to do, riding a bike, skill of mirror reading

• delayed non matching to sample task - way to measure declarative memory in minkeys and other animals

  • a test of object recognition that requires monkeys to declare what they remember by indentifying which of two objects were not seen previously

  • monkeys with damage to the medial temporal lobe are severely impaired on this task

  • Damage to the hippocampus impairs declerative memory

Patient NA

• Had an accident wehre a miniature sword entered his nostril and injured his brain

• Showed anterograde amnesia after

• MRI shows damage to several limbic system structures in the medial diecephalon that have connections to the hippocampus

  • the dorsomedial thalamus and the mamillary bodies

  • Normal short-term memory and can gain new nondeclarative/procedural memories

  • Showed the medial temproal lobe damged in Henry’s brain and these midline regions damaged in NA are parts of a largery memory system

Korsakoff’s syndrome

• a degenerative disease in which damage is found in the mammillary bodies and dorsomedial thalamus, but not in temporal lobe structures like the hippocampus

• The mammillary bodies serve as a processing system connecting the medial temporal lobes to the thalamus and from there to other cortical sites

• Ppl with this syndrom fail to recognize their memory problems and many deny that anything is wrong with them

• They confabulate - fill a gapy in memory with a falsification that they deem as true

• Damage to the prefrontal cortex is what causes the denial and confabulation that differentiates them from other ppl who have amnesia

• Main cause of this syndrom is lack of the vitamin thiamine

• Alcoholics who get most their calories from alcohol and neglect their diet have this deficiency

  • treating them with thiamine can prevent further deterioration of memory functions but will not reverse the damage already done

• THe brain circuit that includes the hippocampus, mammillary bodies, and the dorsomedial thalamus is needed to form new declarative memories

• Established declarative memories formed before brain damage are not stored in these structures for the long term - if they were they would have been lost when the structures were damaged

Patient KC

• Some declarative memoreis are stored in the cortex

• There is a distinction between two subtypes of declarative memory

• Patient KC had a motorcyle accdient and after could no longer retreive any personal memory of his pasts - yet he still had general knowledge

• He was able to converse and played chess but couldn’t remembere where he learend to paly or who taught him

• Episodic memory - detailed autobiographical declarative memory

  • when you recall a certain episode in your life or relate an event to a particular time and place

• Semantic memory - generalized declarative memory

  • ex: knowing the meaning of a word without knowing wehre or when you learned that word

  • KC could acquire new episodic knowledge - he wouldn’t remmebre where he had learned taht new material

• Kents brain revealed extensive damage to the left frontoparietal and teh right parieto occipital cerebral cortex

• As well as shrinkage of both right and left HIppocampus and nearby cortex

• THe bilateral hippocampal damage accoutns for Kent’s anterograde declarative amnesia -

  • but it cannot account for Kents selective loss of nearly all his autobiographical memory bc other ppl with this damage are able to retain autobiographical memories

• Kents inability to recall life events from his past could be a consequence of injuries to frontal and parietal cortex

Skill learning

• The process of learning how to perform a chellenging task through deliberate repetitive practice

• Henry demonstrated that the medial temporal lobe is not required to gain skills and retain them

• Imaging studies have investigated learning and memory for different kinds of skills

  • including sensorimotor skills, percpetual skills, and cognitive skills - these skills are imparied in those with damage to the basal ganglia

  • Also those with damage to th emotor cortex and cerebellum also impair these skills

• The basal ganglia, cerebellum, and motor cortex are important for sensorimotor skill learning

Priming

• a change in the way you process a stimulus becasue youve perceived it previously

• ex: if a person shows the word stamp in a list and later asked to complete the word STA then they are more likley to reply stamp than say start

• Does not require declarative memory of the stimulus

  • those with amnesia have shown priming for words they don’t remember seein g

• Priming is not imparied by damage to the basal ganglia

• Perceptual priming ( priming based on visual form of words) -s realted to reduced activity in bilateral occipitotemporal cortex

• conceptual priming (priming based on meaning) is associated with reduced activation of the left frontal cortex

• Priming is partly a function of the cortex

Associative learning

• nondeclarative memory that involves relations between invents

• a type of learning in which an association is formed between two stimuli or. between a stimulus and a response

• Includes classical and instrumental conditioning

Classical conditioning

• A type of associative learning in which an orginally neutral stimulus acquires the power to elicit a conditioned response when presented alone

• The cerebellum are crucial for simple eyue blink conditiong - in which a tone or other stimulus is associated with eye blinking in response to a puff of air

• PPl with hippocampal lesions can acquire the conditioned eye blink response

• PPl with damge to the cerebellum on one side can acquire a conditioned eye blink response only on the side where the cerebellum is intact

Operant/instrumental conditioning

• An association is formed between the animals behavior and the consequences of that behavior

• ex: skinner box

  • the animal learns that performing a certain action is followed by a reward

  • Havent been able to pinpoint brain regions cruical for instrumental conditioning bc this type of learning taps so many different aspects of behavior

Place cells - a neuron in the hippocampus that selectively fires when the animal is in a particular location

• The hippocampus is curical for spatial learning

• The rat hippocampus contains many neurons that selectively encode spatial location

• The place cells become active when the animal is in or moving toward a particular location

• If the animal is moved to a new environment place cell activity indicates that the hippocampus remaps to the new locations

Neuroplasticity

• the ability of the nervous system to change in response to experience or the environment

• Long term memoreis may require changes in the nervous system so substatntial that they can be directly observed

Environmental enrichment/impoverishment & dendrites

• in environmental enrichment rats are randomly assigned to one of the thre conditions

  • impoverished condition - animals are housed individually in standard lab cages

  • Standard condition - animals are housed in small groups in standard lab cages

  • enriched condition - animals are housed in large social groups in special cages containing various toys and interesting features.

    • provides enhanced opportunities for learning perceptual and motor skills, social learning

Synaptic plasticity & habituation

• habituation - the simplest form of nonassociative learning

  • A decrease in response to a stimulus as it is repeated

  • the decreased response cannot be due to failure of the sensory system to detect the stimulus or due to an inability of the motor system to respond

Hebbian synapse

• A synapse that is strengthened wehn it successfully drives the postsynaptic cell

• they act together to store memory traces

• 1970 researchers discovered an impressive form of neurplasticity in the hipoocampus whcih appeared to be HEbbian synapses

Long-term potentiation (LTP): outcome, physiologically (i.e., change in firing rates)

• A stable and enduring increase in the effectiveness of synapses following repeated strong stimulation

• LTP can be generated in consicious and freely behaving animals

• LTPhas a long lasting change in synaptic strength

LTP: mechanism, structurally

LTP & NMDA receptors (TAKE MORE NOTES ON THIS)

• A glutamate receptor taht binds the glutaamite agonsit NMDA and taht is both ligand=gated and voltage-sensitive

LTP & AMPA receptors (TAKE MORE NOTES ON THIS)

• A fast acting ionotropic glutamate receptor that binds teh glutamate agonsit AMPA