Learning, Memory, and Amnesia

• Learning and memory encompasses several key concepts
• Learning involves acquiring new information, which updates and leads to the formation of new memories
• Memory refers to the storage of information
• Retrieval consists of accessing and interpreting stored memories

Patient H.M. (Henry Molaison)

• Patient H.M. is one of the most well known patients in neuroscience
• Working with H.M. led to the establishment of fundamental principles regarding memory functions in the brain
• Patient H.M. had temporal lobe epilepsy
• He underwent experimental neurosurgery during which his amygdala, hippocampus, and some cortex were removed
• The surgery was partially successful in curing his epilepsy
• A major side effect of H.M.'s surgery was severe anterograde amnesia

Types of Learning and Memory

• Anterograde Amnesia: The inability to form new memories after the onset of a disorder; antero means forward
• H.M.'s resected hippocampus resulted in the loss of the ability to form new memories
• Retrograde Amnesia: Loss of memories formed before trauma, accident, or surgery; retro means backward
• Clive Wearing experienced damage to his hippocampus which resulted in waking up approximately every 20 seconds; this is a case of both anterograde and retrograde amnesia

Brain Regions for Memory

• Key brain regions crucial for memory formation include:

• H, hippocampus

• EC, entorhinal cortex

• PH, parahippocampal cortex

• Cer, cerebellum

• Extensive damage to the hippocampus and entorhinal cortex and cerebellum atrophy can impair memory

• H.M. could repeat digit sequences when presented, but could not study or remember a list of digits long-term, or even remember that there ever was a list

  • Short and long-term memories must have distinct processing

• H.M. and Wearing retained the ability to form new motor memories without remembering doing so

• Provided some of the first evidence that different types of memories are distinct in the brain

• Performance of H.M. on a mirror-tracking test revealed procedural memories could be formed

• H.M. (anterograde amnesia) learned to read mirror-reversed text but couldn't recall practicing the skill

• H.M. was unable to form new declarative memories, which are memories containing facts that you can tell others

Synapses in Neuroscience

• H.M.'s surgery removed substantial portions of the amygdala and hippocampus
• Patients with amygdala damage alone did not show the same memory deficits
• Each synapse is glutamatergic, meaning that LTP occurs at each synapse

Types of Memories

• There are two main types of long-term memory, declarative and nondeclarative or procedural memories
• Declarative memories include facts and events you can tell others
• Nondeclarative memories include skills and tasks you can show by doing
• Declarative memory can be tested readily in humans
• Henry Molaison was unable to form new declarative memories
• Nondeclarative memory can be tested readily in other animals as well as in humans and was present in Henry Molaison as exemplified by his mirror tracing skills

Nonverbal Subject Declarations

• The delayed non-matching-to-sample task is used to test nonverbal subjects

• Monkeys declare recognition of an old object by reaching for a novel object

• Monkeys declare if they remember an old object by reaching for the novel object not previously associated with reward

• Monkeys must learn to identify features of objects and remember them

• After training, the duration of memory retention increases

• Hippocampal lesions interrupt the ability to form working memories and impairs task performance

• Lesions to the medial temporal lobe affect memory performance

Declarative Memory

• Subtypes include:

• Episodic: Remembering an event like your first day in school

• Semantic: Knowing simple facts like the capital of France

• Early phases of memory involve medial temporal systems

• Consolidated memories don't require the hippocampus

• H.M. could recall old memories

• A patient who suffered damage to the parietal cortex (sensory processing) with an accident involving loss of consciousness for 30 minutes

• Reported that her limbs drift and fade unless she sees them

• This is unlike other patients with parietal damage, as loss of limb awareness was only over time

• Short-term memories are essential for motor control

• Loss of limb awareness occurs only after some time

• Patients are capable of sensing when weight was added to hand or when it was removed, but perception faded if hand was still

• Patients can acquire new information, but not integrate it over time

Internal Representations

• Loss of the ability to maintain internal representations of the body
• Normal grip strength is maintained with visual feedback
• Removal of visual feedback in the affected right hand leads to a loss of grip force

Body position

• Pointing movements made at normal speed are accurate

• Movements at slow speed are compromised

• Slow speed relies on fading internal representation of body state which includes position and or velocity

• Subtypes of declarative and nondeclarative memory exist

• Declarative (things you know that you can tell others) and Nondeclarative (things you know that you can show by doing)

• Subtypes of Declarative (things you know that you can tell others) include:

• Episodic (remembering your first day of school)

• Semantic (knowing the capital of France)

• Subtypes of Nondeclarative (things you know that you can show by doing) include:

• Skill learning (knowing how to ride a bicycle)

• Priming (being more likely to use a word you heard recently)

• Conditioning (salivating when you see a favorite food)

Brain Regions

• Brain regions are involved in different memory formations
• Medial temporal lobe and neocortex are relevant in episodic memory
• The striatum, motor cortex, and cerebellum are relevant in skill learning
• Reflex pathways are used in non associative learning

Physical Changes to Memory

• Memory storage entails physical changes such as Neuroplasticity

• Neuroplasticity is the ability of neurons and neural circuits to be structurally or physiologically remodeled by events

• New synapses form, microglia (immune system) prune other synapses

• Training might also lead to the reorganization of synaptic connections

• Glia plays a role in learning and synaptic activity

• Astrocytes have a critical role in marking which synapses will change in strength

• Physiological changes include neurotransmitter release and effect due to neurotransmitter-receptor interactions

• Morphological changes underlie long-term potentiation (LTP) and long-term depression (LTD)

• Synaptic changes can store memories

• Lab animals living in a complex environment show biochemical and anatomical changes in the brain

• Experiments often use three housing conditions

• Standard condition (SC)

• Impoverished (IC)

• Enriched (EC)

• A variety of plastic changes in the brain are linked to environmental enrichment

• Animals housed in enriched environments, compared to impoverished environments, often have:

• Heavier, thicker cortex

• Enhanced activity of particular neurotransmitters inlcuding actetylcholine

• Cortical neurons with more dendritic branches, especially basal dendrites

• Reduced stress and lower glucocorticoid secretion, reducing sources of hippocampal damage

• These effects have been seen in many species, including humans

• In humans, physical activity, mental activity, and adequate sleep can postpone cognitive decline in old age

• Associative memory has several forms

• In Operant conditioning, lab animals learn to press a level for food in a Skinner box

• In Classical conditioning (Pavlovian conditioning), a neutral stimulus predicts an event

• In Classical Conditioning

• Prior to condititioning, dogs salivate in response to food

• During conditioning the bell is rung repeatedly, and shortly after food is presented to the dog

• After conditioning the dog salivates in response to the bell ringing

Fear Learning

• Contextual fear learning in animals:

• The animal is placed in a novel environment and given an aversive or unconditioned stimulus before it is removed

• The animal associates the environment with the aversive stimulus

• The animal exhibits a trained response, like freezing, when put back in the conditioned environment

• Cuing of fear shows that animals placed give an aversive (unconditioned) stimulus with a conditioned stimulus cue.

• The animal asosiates the cue to stimulus

• The animals exhibit trained response with conditional resposne

• Pairing of cue and US introduces time-dependence, training depends on their timing

• In delay and cued is paired with US

• trace has a non overlapping delayed

• backward trace

• Different neural regions become involved

• Cuing learning incorporates aspects of context as cues in the environment are associated

Brain Regions and Fear

• Lesions can reduce in anyagdala and lesion the aility to conduct
• Required for trace with long intervals
• Can reduce the areas in attentional learning.

Extinction learning

• Exposure based learning reduces conditinal factors
• Animals lose asscoiation with cs and us
• Extinction is reduced
• Adolescents will reduce rates of cortical and subcordical.
• Learning will not be the loss of a memory

Fear extinction Regulated

• With high pnn it leads to a quick erasure of fear
• Otherwise with high levels. There is high levels.
• Digesting proteoglycan eliminates it.