Learning and Memory Flashcards
(24 cards)
HM
Henry Molaison
1953 - medial temporal lobe and hippocampus removed for epileptic seizures
Developed profound amnesia and couldn’t form new memories but had good long-term memory of events before surgery
struggled to find his way around his new neighbourhood
Treatment produced memory impairments (Anterograde amnesia)
can repeat 7 numbers if no distractions but wouldn’t remember the task if distracted/the next day
could motor learn (ie mirror drawing where one must trace outline of shape using visual cues from mirror image, got better at this everyday), and perceptually learn (ie five drawings show elephant and umbrella with discontinued lines)
had an issue with ENCODING STM to LTM
classical conditioning could be learned
Anterograde and Retrograde Amnesia
Retrograde = can’t remember events prior to brain damage
Anterograde = can’t remember events after brain damage - unable to form declarative, only nondeclarative
Sensory Memory
brief period of time that initial sensation of environmental stimuli is initially remembered
Length ranges from fractions of a second to few seconds
Short-Term Memory
info from sensory memory if it’s meaningful or salient enough
seconds to minutes
rehearsal
capacity limited to a few items (chunking)
Long-Term Memory
contains info from STM that’s consolidated
permanent
strengthened with increased retrieval
nondeclarative mem - implicit memory, includes memories that we aren’t conscious of, operates automatically and controls motor behaviours (riding a bike etc)
declarative mem - explicit memory, memory of events and facts we can think and talk about, including episodic memories and semantic memories
spatial memories?
Human Eyelid Conditioning
eyelid can be classically conditioned
US is a puff of air to eye (causes blinking) and CS is an audio tone and CR is eyeblink
Woodruf-pak delay conditioning
DWP used delay conditioning procedure - delay of 400ms between CS onset and US
CS lasted 500ms and 100ms airpuff US delivered in final 100ms of CS
90 trials in each session separated by 10-20s and were either CS-US trials or once every 10 trials there was a CS alone trial
CS alone trials ruled out possibility that eyeblink responses were URs
results: eyeblink responses on CS alone trials
DWP retested HM after a two-year interval and still found evidence of conditional responding
Hebb’s Law
hypothesis = cellular basis of learning involves strengthening of synapse that is repeatedly active when postsynaptic neuron fires
When 1000-Hz tone is presented before puff of air to eye, Synapse T is strengthened
it takes less time to stimulate an action potential in Motor neuron
puff of air to eye picked up by neuron in somatosensory system, synapse P (strong)
1000Hz tone causes neuron in auditory system that links to synapse T
causes blink
Crowell, Hinson and Seigel
1981
conditioned tolerance
saline = no reaction
alcohol elicited hypothermia
AFTER conditioning, alcohol = hypothermia (effect of alcohol) reduced due to tolerance to alcohol
Anterograde Amnesia and Memory Types
unable to form declarative memories, but can form nondeclarative memories
Maguire et al
1998
activity in right hippocampus in participants navigating around a virtual town - same region activated as rats planning routes through mazes
Maguire, Frackowiak and Frith
1997
taxi drivers talked about their routes and hippocampal activity monitored
damage to hippocampus
damage limited to right hippocampus causes spatial impairment
patient with damage to right parahippocampal gyrus only found room by counting doors from end of hall
rats and epilepsy patients with scarring caused by seizures in right hippocampus couldn’t use spatial cues to locate object
Morris Water Maze
rat in water maze trying to find hidden platform
rats with hippocampal lesions always swim random routes trying to find platform, they do not learn quick routes to platform like controls
animal examples of memory storing
hummingbirds can hold deep memory of maps and return to new flowers, ignoring ones they went to before, 20 mins after
nutcracker gathers nuts from diff areas through using mental map, learns locations of many nut locations over Grand Canyon
spatial ability
entorhinal cortex controls egocentric guidance (place is represented in relation to self)
barkas et al 2010 = epilepsy patients with lesions to right hippocampus impaired in allocentric (place is related to external cues) but not egocentric navigational task
hippocampal formation in consolidation of declarative memories
hippocampus receives and processes info about what’s going on from sensory and motor association cortex
it then modifies memories being consolidated, linking them together so we can remember relationships among elements of memories
episodic memories placed in order so they make sense
entorhinal cortex tells you direction to go but hippocampus tells you where you are in relation to things around you
how do messages travel along neuron
when threshold of excitation (-60) is met, action potential occurs up to +35ish then down, hyperpolarisation occurs slightly then depolarisation
what is action potential
the brief electrical impulse that provides the basis of conduction of info along an axon
what is threshold of excitation
the value of membrane potential that must be reached to produce an action potential
long term potentiation procedure
an electrical stimulating electrode delivers stimulation to neurons running from entorhinal cortex which synapse on dentate gyrus cells in hippocampus
rapid series of electrical impulses and record responses in hippocampal neurons with a second recording electrode - dentate gyrus region of hippocampal formation receives neural input from the peripherate pathway - electrical pulse given by stimulating electrode and electrical pulse measured with recording electrode (size and duration of EPSPs, a rapid LTP stimulation causes larger and longer lasting) - changes in EPSPs may be a mechanism to strength synaptic connections underlying learning -
if low intensity probe stimulus is applied then a small response is recorded from the dentate gyrus cells
but if probe stimulus is preceded by high frequency potentiating stimulus then subsequent responses to probe stimulus are potentiated (this lasts a long time)
intense and rapid stimulation of neural circuits = long-term increases in size of excitatory post-synaptic potentials (EPSPs) in
long-term potentiation: glutamate’s role
series of synaptic changes, LTP among glutamate synapses in hippocampus help establish conditioned responses
synaptic changes in glutamate system increase excitatory post synaptic potential (EPSP) to postsynaptic cell
glutamate bonds with receptors NMDA and AMPA in post-synaptic membrane - when post-synaptic membrane is at resting potential (-70mV) the NMDA receptors are blocked by Magnesium
Glutamate only opens AMPA which let in Sodium molecules
The positive charge of sodium molecules depolarises the neuron which unblocks the NMDA receptors allowing calcium ions into the neuron
synaptic changes in NMDA and AMPA receptors in LTP
post-synaptic dendritic spines of neurons in CA1 region of hippocampus contains NMDA and AMPA receptors
NMDA = permeable to calcium (CA2+) but is blocked by MG2+ (magnesium) at resting potential - even if glutamate is present, this can’t be unblocked - NMDA receptor shaped like a wide cylinder and a molecule of glutamate binds with the receptor - when membrane is depolarised, magnesium ion is evicted and calcium channel is unblocked - calcium ions enter dendritic spine
AMPA is sodium (NA+) and glutamate flocks this in- EPSPs occur due to influx of sodium into channel results in objecting of MG++ from NMDA - this allows calcium to flow in, causing second messenger events leading to more AMPA receptors into dendrite - therefore it responds more strongly
how does LTP lead to synaptic strengthening
calcium ions activate enzymes in the spine
these enzymes cause AMPA receptors to move into the spine
increased number of AMPA receptors in postsynaptic membrane strengthen the synapse
