Memory and Brain Ying Shen, Ph.D. Voice: 0571-88208240 Email: yshen@zju.edu.cn Department of...

Memory and BrainMemory and Brain

Ying Shen, Ph.D.Ying Shen, Ph.D.Voice: 0571-88208240 Email: yshen@zju.edu.cnVoice: 0571-88208240 Email: yshen@zju.edu.cn

Department of NeurobiologyDepartment of NeurobiologyZhejiang University School of MedicineZhejiang University School of Medicine

A Test

A Test (cont)

Encoding – information for each memory is assembled from the different sensory systems and translated into whatever form necessary to be remembered.

Consolidation - converting the encoded information into a form that can be permanently stored. The hippocampal and surrounding areas apparently accomplish this.

Storage - the actual deposition of the memories into the final resting places–this is though to be in association cortex.

Retrieval - memories are of little use if they cannot be read out for later use. Less is known about this process.

Composition of MemoryComposition of Memory

Implicit vs. Explicit MemoryImplicit vs. Explicit Memory

Explicit memory:

Subjects finish tasks directly by trying and usingstudy items when completing the memory test.

Implicit memory:

Without specifically directing, subjects think about the study items.

Implicit vs. Explicit Memory

Various Memories

• Also called non-declarative memory

• Information about how to perform something; it’s recalled unconsciously

• Trained, reflexive motor or perceptual skills （ drive car; get to work ）

• Patients who have bilateral medial temporal lobe lesions can learn simple reflexive skills (habituate and sensitized), i.e. learning certain perceptual tasks, recall a word learned previously in Priming test. But they deny ever having learned the word previously.

• Further classfied to associative and non-associative.

• Two well-known types of non-associative learning: habituation and sensitization.

Implicit Memory

Store of Implicit Memory

• “Fear conditioning” involves the amygdala

• Operant conditioning involves the striatum and cerebellum

Eye blink conditioning is disrupted by lesions of the dentate and interpositus

nuclei of the cerebellum

• Classical conditioning, sensitization and habituation involve the sensory and

motor systems involved in producing the motor responses being conditioned

• Perhaps surprisingly, certain simple reflexes mediated by the spinal cord can

be classically conditioned even after the cord has been surgically isolated

from the brain

• It appears that all regions of the nervous system may be capable of memory

storage

•Also called declarative memory

• Knowledge of facts (places, things and people) and the meaning of these facts

• These things must be recalled into consciousness to be used

• Patients who have bilateral medial temporal lobe lesions have an inability to learn and remember items of factual knowledge; They can’t remember people that they met the day before; They can’t remember what they did the day before

• Further parcel explicit memories as episodic (events) or semantic (facts)

• Kandel points out “…all explicit memories can be expressed by declarative statements such as “I was here yesterday” (episodic) and “The hippocampus has something to do with memory” (semantic)

Explicit Memory

Store of Explicit Memory

• “Fear conditioning” involves the amygdala

• Operant conditioning involves the striatum and cerebellum

Eye blink conditioning is disrupted by lesions of the dentate and interpositus

nuclei of the cerebellum

• Classical conditioning, sensitization and habituation involve the sensory and

motor systems involved in producing the motor responses being conditioned

• Perhaps surprisingly, certain simple reflexes mediated by the spinal cord can

be classically conditioned even after the cord has been surgically isolated

from the brain

• It appears that all regions of the nervous system may be capable of memory

storage

Processing of The MemoryProcessing of The Memory

Processing of Memory

iconic or echoic memory

short-term memory

memory

StimulusStimulus

Sensory memorySensory memory

Working memoryWorking memory

Long-Term memoryLong-Term memory

Sensory Memory 15

Sensory Memory

Often a “sensory trace” or the stimulus remains after thestimulus is gone.

These traces are termed sensory memory, and they tendto be very short-lived.

Sensory memory was most extensively studies by a cognitive psychologist named Sperling.

Sperling’s studies focused on visual sensory memorywhich he termed iconic memory … here’s how they worked.

Working Memory 16

How long do things stay in Working Memory?

If a person is allowed to rehearse, information will stay inworking memory for as long as it is rehearsed.

However, if not allowed to rehearse, Peterson & Peterson(1959) showed that information decays from working memoryfairly quickly.

In their experiment, rehearsalwas prevented by making subjects count back from some number by threes while remembering letter trios (e.g., JDK, LPD)

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Working Memory 17

How are things lost from Working Memory

So, this disappear quite quickly from working memoryif they are not rehearsed … what makes them disappear?

One possibility is that the items just decay over time.

A second possibility is thatnew items coming into working memory actually“push out” things currentlyin it.

This second possibility seemsmost reasonable given the datato the right.

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Working Memory 18

The Capacity of Working Memory

As we already discussed, working memory has a limitedcapacity. Specifically, the limit seems to be 7 plus orminus 2 chunks.

What is a chunk? Time for another memory experiment!

Hopefully the demo showed that we can greatly increaseour ability to keep things in working memory by chunkingthe information.

Amnesia

Long-Term Memory 20

Summary of Long-Term Memory So Far

So we know that there are a number of ways things can get into long-term memory, and various strategies can be used to facilitate this process.

We also know that there at least seems to be different types of long-term memory and episodic memory seems to be the most fragile of these.

Finally, we also know that the hippocampus appears critical for the formation of new long-term episodic memories, with destruction of the hippocampus leading to anterograde amnesia.

Location of MemoryLocation of Memory

Cortical Lesion and Maze Task

Cortical Lesion and Maze Task

Penfield’s Patients

H. M.’s Big ProblemH. M.’s Big Problem

H.M.’s Good News and Bad NewsH.M.’s Good News and Bad News

H.M. felt much better for controlling

However, devastating memory lost happened.

Short-term memory intact Perfect Long-term memory for events before operation Cannot transfer short-term memory to long-term memory

This condition also is a common result of a form of alcoholismtermed Korsokoff’s syndrome

H.M.’s Two Type of Memories

Amygdala and FearAmygdala and Fear

Hippocampus and Spatial MemoryHippocampus and Spatial Memory

Learning in Water MazeLearning in Water Maze

Place CellPlace Cell

Prefrontal Cortex and Working Memory (1)Prefrontal Cortex and Working Memory (1)

Prefrontal Cortex and Working Memory (2)Prefrontal Cortex and Working Memory (2)

Memory, One Structure or More?Memory, One Structure or More?

Currently, one of the debates in memory concerns whetherwe have a single, or multiple long-term memory systems.

Those who believe in multiple memory systems typicallytalk about things like the following:

Episodic Memory - Our memory of very specific eventsin our lives … tends to contain rich detailed info.e.g. - What did you do last night?

Semantic Memory - Our general world knowledge. e.g. - What city is the capitol of Manitoba?

Procedural Memory - Our memory of how to do things.e.g. - How to ride a bike, or kill without thinking.

Require Both Implicit And Explicit

Learning usually has elements of both implicit and explicit learning learning to drive an auto involves conscious execution of specific sequences of motor acts necessary to control the car; with experience, however, driving becomes automatic and nonconscious motor activity

With repeated exposure to a fact (semantic learning), recall of the fact with appropriate cluse can eventually become virtually instantaneous.

Simple Behaviors Use Many Parts of Brain

Decay of The MemoryDecay of The Memory

Decay From Long-Term Memory

Often students feel like they study hard for an examand, as soon as the exam is complete, the informationthey studied is gone!

How long does information stay in memory, and howcan we scientifically study memory decay?

This issue was first addressed by Ebbinghaus (1895)and his results and techniques are still interesting.

Ebbinghaus taught himself thirteen nonsense syllables(e.g., dax, wuj) and then tested his memory after various delays.

Ebbinghaus’ Results and Real World

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Ebbinghaus’ work suggests we retain some of the info for at least 30 days, even when it has no meaning.

Similar “real world” studies suggest that we can retain information we learned over 40 years ago or more.

Thank you

School of Medicine, B515