bio 38 unit 3

ebbinghaus’ forgetting curve

• ebbinghaus taught himself nonsense words, then checked his retention for them

• he found that after a very steep slope of forgetting, there is a flattening of retention

• main findings

  • if you remember something after 2 days, you’re likely to also remember it after 30

  • most forgetting occurs immediately after learning

do memories become inaccessible or just lost?

• they likely become inaccessible, and just need the right cue to get them back

• evidence

  • people were able to match names to pictures of people from their high school from decades ago, and they were able to do it because they got the right cue

  • optogenetically activating neurons in the dentate gyrus (hippocampus) makes remote memories come back in mice

  • stimulating regions of epileptic brains made patients vaguely remember things

decay

• cause of forgetting where memories gradually deteriorate with time

• evidence = synaptic pruning makes inactive synapses smaller and less prone to activation

interference

• cause of forgetting where memories interfere with each other

• the more similar they are, the more likely they are to compete

• a memory cue leads to several memories

• ex: losing your car in a parking lot because there is too much interference in memories

change in context

• cause of forgetting where memories are less accessible when you switch contexts

• being in the same context during retrieval as you were during encoding improves retention

directed forgetting

• the DLPFC works to inhibit memory systems to help us not remember something

• evidence = participants are cued to either remember or forget something, and instruction to forget led to worse memory

memory suppression

• in the think/no think method, participants are instructed to avoid thinking of a word/to push it out of mind

• after multiple repetitions, the no-think instructions lead to a weakening of memory

retrieval-induced forgetting

• retrieval of one memory can harm retrieval for another memory

• AKA being tested for one item vs the other improves the recall for the item that was tested

• compromises testimony because being asked one question repeatedly harms the retention for other important details

anterograde amnesia

• inability to form new memories due to hippocampal damage

  • memories can’t be formed without the hippocampus

retrograde amnesia

• inability to remember recent remote memories due to hippocampal damage

  • younger memories rely on the hippocampus

• graded in time with the most remote memories remaining intact

• tested by asking about past events before the accident while gradually moving further and further back in time

amnesia primarily impacts what type of memory?

• episodic

what types of memory are intact in amnesia?

• remote declarative

• working/short term memory

  • HM could retain a 3 digit number for 15 min without interference

• nondeclarative memory (priming and conditioning)

lesions

• selective brain damage resulting in behavioral changes based on the site of damage

• pros

  • causal manipulation with animals AND humans

  • tests necessity

  • aided us in history

• cons

  • not super well controlled/exact damage

  • small sample sizes

  • not generalizable

  • brain adapts once damage occurs (compensatory mechanisms)

  • we do not always know what the person was like before the lesion

patient HM

• had bilateral hippocampal lesion during surgery for epilepsy

• intact working/short term memory and general cognition (could copy an image and improve on the mirror drawing task)

• could not draw an image later on or remember doing the mirror drawing task

patient EP

• contracted a herpes infection that caused encephalitis of the MTL

• anterograde amnesia (could not remember that he had already told a story or remember lists of words he just learned)

childhood/infantile amnesia

• inability of adults to retrieve episodic memories from before 2-4 years old and even afterwards up until about 10

• occurs in humans and animals

• caused by an immature hippocampus and cortex, and lots of hippocampal neurogensis

  • human hippocampus reaches full maturity at 3-5 years old