Memory and Brain Ying Shen, Ph.D. Voice: Department of Neurobiology Zhejiang 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 Memory

Implicit vs. Explicit Memory

Explicit memory: Subjects finish tasks directly by trying and using study 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 Memory

Processing of Memory iconic or echoic memory short-term memory memory Stimulus Sensory memory Working memory Long-Term memory

Sensory Memory15 Sensory Memory Often a “sensory trace” or the stimulus remains after the stimulus is gone. These traces are termed sensory memory, and they tend to be very short-lived. Sensory memory was most extensively studies by a cognitive psychologist named Sperling. Sperling’s studies focused on visual sensory memory which he termed iconic memory … here’s how they worked.

Working Memory16 How long do things stay in Working Memory? If a person is allowed to rehearse, information will stay in working memory for as long as it is rehearsed. However, if not allowed to rehearse, Peterson & Peterson (1959) showed that information decays from working memory fairly quickly. In their experiment, rehearsal was prevented by making subjects count back from some number by threes while remembering letter trios (e.g., JDK, LPD)

Working Memory17 How are things lost from Working Memory So, this disappear quite quickly from working memory if they are not rehearsed … what makes them disappear? One possibility is that the items just decay over time. A second possibility is that new items coming into working memory actually “push out” things currently in it. This second possibility seems most reasonable given the data to the right.

Working Memory18 The Capacity of Working Memory As we already discussed, working memory has a limited capacity. Specifically, the limit seems to be 7 plus or minus 2 chunks. What is a chunk? Time for another memory experiment! Hopefully the demo showed that we can greatly increase our ability to keep things in working memory by chunking the information.

Amnesia

Long-Term Memory20 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 Memory

Cortical Lesion and Maze Task

Penfield’s Patients

H. M.’s Big Problem

H.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 alcoholism termed Korsokoff’s syndrome

H.M.’s Two Type of Memories

Amygdala and Fear

Hippocampus and Spatial Memory

Learning in Water Maze

Place Cell

Prefrontal Cortex and Working Memory (1)

Prefrontal Cortex and Working Memory (2)

Memory, One Structure or More?

Currently, one of the debates in memory concerns whether we have a single, or multiple long-term memory systems. Those who believe in multiple memory systems typically talk about things like the following: Episodic Memory - Our memory of very specific events in 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 Memory

Decay From Long-Term Memory Often students feel like they study hard for an exam and, as soon as the exam is complete, the information they studied is gone! How long does information stay in memory, and how can 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 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