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Lecture 18

PSYO 2470 Lecture 18: Memory II

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PSYO 2470
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Memory II Information processing in MTL - - Hippocampus doesn’t receive info directly from striate cortex o A lot of processing before the cortex ▪ Association areas, then to parahippocampal and rhinal cortical areas, finally reaching hippocampus • Feedback mechanisms important for reconsolidation • Connections from hippocampus by fornix to thalamus and hypothalamus that can add emotion context - Hippocampus thought to be seat of epileptic convulsions o Stimulate hippocampus and associated areas when showing images of the same character ▪ Fires action potentials with images of a character as well as images associated with that character as well as that character’s name • Information going to hippocampus is highly processed Patient HM findings published by Milner and Scoville - HM o Sustained head trauma very young ▪ Began getting seizures later on – seizures became almost incapacitating • Doctors tied hippocampus to seizures – removed hippocampus from both left and right hemisphere as well as parts of other structures including amygdala o Was no longer able to form new long term memories – anterior grade amnesia ▪ Had some things he could remember, and some he could not • Working memory remained in tact o Suggested hippocampus was crucial for long term memory formation, which required consolidation • Difficulty with episodic and declarative memory • Procedural memory remained in tact o Still had ability to develop new motor skills ▪ Appearing independent of medial temporal lobe ▪ Shows improvement of skills he learned earlier – got better at skills he didn’t remember already learning how to do • Not all memory stored in the same area o Brenda Milner and HM ▪ Milner spent 30 years working with HM after the surgery – he doesn’t remember her Testing declarative memory in animals - Also called explicit memory o Able to declare memories – done to show evidence the memories exist - Episodic memory o Memory of episodes and events ▪ Tied to time and place o Memory most effected by damage and stroke - Looking at ability for an animal to keep something in their mind o Delay non-matching to sample ▪ Presented with an object, then a delay, then have to select the object out of the two that is different from the one presented on it’s own – have to remember the previous object and select a new one - Take out medial temporal lobe in a monkey and see what happens in delayed non-matching to sample task o Normal animal – perform at about 90% correct ▪ Doesn’t seem to matter how long delay is • Delay anywhere from 8-10 seconds to 2-10 minutes o Can still make right choice at roughly 85-90% of the time ▪ Can encode memory then retrieve it o Lesioned animal – performs same as normal animal with a short delay ▪ Shows working memory is in tact • Performance declines to essentially just guessing after long delay o Allows researchers to determine where in medial temporal lobe that they should be looking at to see what is involved in laying down new episodic memories ▪ Take out amygdala – no deficit on task – amygdala doesn’t appear to be involved ▪ Hippocampus removed • Small effect • Involved in encoding new explicit memories ▪ Perirhinal cortex removed • See the largest effect on task • Important for taking episodes that happen and applying them later on Memory functions of the hippocampus - Binds sensory info for memory consolidation o Consolidation – enhances encoding ▪ Makes memories stick ▪ Sleep is important for consolidation - - Hippocampus found in most anterior section o On the dorsal surface underneath corpus callosum under the cortex o Shape and size changes as you go anterior to posterior ▪ Moves more ventrally and laterally as you move anterior to posterior - Supports spatial memory of location of objects that are important to us o Episodic memory tied to location - Lesion hippocampus to test function o Radial arm maze ▪ ▪ Each arm on maze is baited with food • In normally behaviour animal – visits all the arms efficiently o Never revisited an arm that they just got food from – remembers an event from the recent past • In hippocampal lesioned rats – don’t get food efficiently – will revisit arms where they already got food o Can’t use spatial location efficiently ▪ Only some arms baited • Both normal and lesioned animals will only go down baited arms o Don’t just use a random search – don’t go none baited arms o Lesioned animals will go down arms that were previously baited where they got food ▪ Forget recent events o Morris water maze ▪ ▪ Hidden platform in the pool – rat swims around and eventually finds the platform • Eventually, rat learns where platform is and quickly goes to platform o Good memory means short escape time – finds the platform quickly ▪ Does task efficiently with in tact hippocampus • Unable to lay down spatial location of hidden platform when the hippocampus is lesioned o Time to find platform doesn’t improve ▪ Glutamate also involved in pr
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