Memory (lecture 4) Thoth MnemosyneMinerva God/dess of learning, memory & wisdom

Memory in oral cultures  Memory was essential for passing of knowledge: person to person & generation to generation.  Memory was the fourth of the five traditional canons of rhetoric, the others being invention, arrangement, delivery, and style.  Memory aided by process of architectural mnemonic known as Cicero’s technique: parts of the speech were associated with spatial details.

Memory in literate cultures  Writing: externalized the memory.  Electronic media: provides fast access to both verbal and graphical data bases (“the virtual Cicero’s technique”).  Eric Havelock: "a modern student thinks he does well if he diverts a tiny fraction of his psychic powers to memorize a single sonnet of Shakespeare. In stead, he pours his energy into search and reading….  Memory is extended to artificial fast accessible devices (soon directly connected to brain).

Memory as a process  Cognitive Ψ: Three stages of memory.  Biological Ψ: Stages in same/different brain sites? Neuronal mechanisms of memory? Life time storage?

Duration of memory: cognitive Ψ  Sensory memory: Vast amount of sensory information in five modalities kept for very short time.  Working memory/short-term memory: Rather limited information kept for short time in conscious mode.  Long-term memory: Vast amount of information in subconscious mode.

Duration of memory: biological Ψ  Short Working-memory: different sites of frontal cortex, can we be aware of all?  Long-term memory: migration of information from hippocampus to cortex, amnesia in HM patient. Technique: experiments by nature & functional imaging.

Content of memory Cognitive Ψ:  Explicit memory: conscious recollection of events tagged with time and place.  Implicit memory: skills with no conscious recollection of details. Biological Ψ:  Explicit memory: evolution-wise recent brain structures, cortex & hippocampus.  Implicit memory: evolution-wise old brain structures.

Conclusions so far Memory is mediated by multiple brain sites. Each site:  Is governed by the three stages of memory: parallel – distributed processing.  Processes different content: memory disintegrates the environment.  Storing capacity seems to be unlimited except of working-memory.  Stores with different time constant.

Working memory (1) Encoding:  Phonological buffer in L-hemisphere.  Semantic buffer in L-hemisphere.  Spatial buffer in R-hemisphere. Identity of the letter Position of the letter

Working memory (2) Storage:  Low capacity: only 7±2 bits of information. Disappointed? Don’t despair:  LTM enables chunking and capacity increases to 7±2 chunks of information.  Many working-memory sites?  Fast forgetting due to ‘decay’ and ‘displacement’ (high throughput).

Working memory (3) Retrieval:  Easy with minimal mistakes.  Decision time increases with # of items, i.e., serial processing. Decision time paces the swiftness of conscious mental computations, slow thinking!!!

From working-memory to LTM (1) Maintenance rehearsal in WM: prevents a decay in a reverberating circuitry.

From working-memory to LTM (2) In a free recall task: elaborative rehearsal helps to encode information in LTM.

LTM (1) Encoding:  Meaning – the remembered idea.  Elaborate on meaning to add connections between items.  Exact wording.  Sensory impressions: phonological, visual, smells…

LTM (2) Storage:  Initial store in hippocampus and later migration to various cortical sites.  Hippocampus and the surrounding cortex: cross- referencing between the many store sites.  Hippocampus as a cognitive map includes the past and future (prospective) events.

The many LTM cortical sites

LTM (3) Storage: New memories are consolidated over period of months and more.

LTM (4) Retrieval:  Effortful process – on “tip-of-the-tongue”.  Retrieval cues help - recognition vs. recall.  Failures due to association of one cue with several items: * Retroactive interference. * Proactive interference.

Retrieval cues as gateways to LTM

השראת הגברה ארוכת טווח (LTP) כמנגנון שינוי סינפטי בדיקה: פולס בודד למידה: רצף פולסים

Lessons from amnesia  Hippocampus removed bilaterally.  Spared working-memory.  Anterograde amnesia for explicit-episodic memory.  Partial retrograde amnesia for explicit- episodic memory.  Other memories spared.

A variety of memories

Priming

Memory aids

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