TYPES OF MEMORY

Short term memory

• Short-term memory (STM): Short-term retention of information measured in seconds to minutes; limited

capacity (about 7 chunks of information); the ‘brain's post-it note’.

• Working memory: short-term retention in which information can be maintained (contents remain

accessible) or manipulated (can perform mental operations over contents). Ex: You’ll need to retain in

memory some numbers, and perform logical/arithmetic operations on them.

• PFC is responsible for refreshing information in the stores and manipulating that information

• The main storage of information is not within the frontal lobes, but in the posterior cortices.

o of information retained for a short time.

Long-term forms of memory (LTM): information retained for a long time measured in days to years.

• DECLARATIVE memory (EXPLICIT memory): knowledge to which we have conscious access, and we

can report verbally

o Episodic memory: memory of past events in our lives (what, where, when, with whom),

associated with context (source memory); personal and subjective

o Semantic memory: memory of world knowledge (e.g., facts, physical laws) that does not

relate to our lives, not associated with the specific context in which such knowledge was

acquired; objective. Ex: you know that Paris is the capital of France, but you can’t

remember exactly when, where, how, with whom you learned it.

o Episodic memory is more severely affected by MTL lesions

• NONDECLARATIVE memory (IMPLICIT memory): our behavior is influenced by previous experiences

without conscious recollection of those experiences → we cannot verbally report such memories.

• Procedural memory: Ex: knowing how to ride a bike, inflexible. Mediated by the striatum

THE ANATOMY OF MEMORY

MEDIAL TEMPORAL LOBE (MTL) structures

• Hippocampus (horse-shaped, blue color) and interconnected structures: entorhinal cortex, perirhinal cortex,

parahippocampal cortex. BINDS the representations of items with their context!

• Amygdala (red): encodes affective qualities of an experience.

PREFRONTAL CORTEX (PFC) – see below

• Working memory; Long term memory – working with memory

MEMORY STAGES

• Encoding: the process of organizing and transforming incoming information that

creates memory traces to be stored.

o Each aspect of an event activates the cortical areas involved in perceiving the

different aspects of the event. The hippocampus stores a summary

representation of the whole event, with pointers to the location of the traces

distributed over the cortex.

• Storage: the process of retaining information in memory.

• Consolidation: the process that stabilizes a memory over time. Impaired episodic memory in

amnesia may be a deficit in consolidation.

o Standard Model of Consolidation: initial rapid consolidation (hippocampus) followed

by a slower permanent consolidation (memory finally stored in the neocortex).

o Hippocampus essential for the rapid consolidation and initial storage of episodic and

semantic memories

o Neocortex important for the permanent consolidation of semantic information

▪ Over time, binding no longer needed -- these memories become independent of

hippocampus → hippocampus damage did not affect remote LTM.

▪ → explains why recent memories were more affected following MTL damage.

• Retrieval: the process of accessing information stored in memory.

o Types of retrieval

▪ Recall (with no cues); Recognition: with cues

▪ Recollection: consciously retrieve events with source memory; with a higher level of

certainty

▪ Familiarity: the feeling of knowing, without source memory (kind of know, but don’t know

for sure)

▪ Hippocampus involved in encoding and retrieval for recollected episodic memories

Areas outside the hippocampus (especially the perirhinal cortex), support recognition based on familiarity.

Medial PFC PFC

PFC’S INVOLVEMENT IN MEMORY

• Both STM and LTM engage PFC, involved in online maintenance & manipulation of information

• Frontal lobes do not store information long-term, but can temporarily hold information and

manipulate it (working memory) → acts as a temporary buffer.

• The PFC also plays an important role in long-term memory, namely in ' working with memory',

contributing directly to encoding, retrieval, and evaluation of information stored in long-term

memory.

MEMORY DEFICITS: AMNESIA

Two types of amnesia

• Retrograde amnesia: problems with remembering past memories (retro-past)

• Anterograde amnesia: problems forming new memories (antero-forward), but consolidated past memories

are not affected

• Amnesic patients usually suffer from both types.

Amnesia is caused by damage to the MTL

Case study: H.M., who had most of the hippocampus and connective MTL cortices surgically removed in order to

treat epilepsy.

• Severe, global anterograde amnesia and temporally limited retrograde amnesia (intact

remote memories) with intact short-term memory. Can’t form new declarative memories,

but shows signs of procedural learning

• Preserved perceptual, motor & cognitive functions.

o Insights from H.M.: MTL is essential for the ability to form new declarative

memories, but not for STM or the ability to form new non-declarative memories. MTL is not likely

the site for LTM storage, as his retrograde amnesia only affected more recent LTMs.

Hyperthymestic Syndrome

A kind of autobiographical memory syndrome in which a person:

1) Spends an abnormally large amount of time thinking about their personal past; and 2) Have an

extraordinary capacity to recall specific events from their personal past.

MALINGERING

The intentional production of false or grossly exaggerated physical or psychological problems.

Motivation for Malingering: usually external (e.g., avoiding military duty or work, obtaining financial

compensation, evading criminal prosecution, or obtaining drugs)