Download Short-term memories

Memory Has Temporal Stages
• Iconic memories are the briefest memories and store sensory
impressions that only last a few seconds.
• Short-term memories (STMs) usually last only for up to 30
seconds or throughout rehearsal.
– Short-term memory is also known as working memory.
• An intermediate-term memory (ITM) outlasts a STM, but is
not permanent.
• Long-term memories (LTMs) last for days to years.
– Long-term memory has a large capacity.
– Information can also be forgotten or recalled inaccurately.
Stages of Memory Formation
Memory Has Temporal Stages
• Mechanisms differ for STM and LTM storage
• Demonstrate with memory experiments
• Learning lists of words or numbers
• Recall the list after a delay
• The primacy effect is the higher performance for items at
the beginning of a list (LTM).
• The recency effect shows better performance for the items
at the end of a list (STM).
• Produces a serial position curve that is sensitive to
amount of delay
Serial Position Curves from Immediate-Recall Experiments
Memory Has Temporal Stages
Working memory can be subdivided into three components,
all supervised by an executive control module:
• Phonological loop—contains auditory information
• Visuospatial sketch pad—holds visual impressions
• Episodic buffer—contains more integrated, sensory
information
A functional memory system incorporates three aspects:
• Encoding—sensory information is passed into short-term
memory.
• Consolidation—short-term memory information is
transferred into long-term storage (The Engram).
• Retrieval—stored information is used.
Hypothesized Memory Processes: Encoding, Consolidation, and Retrieval
Successive Processes Capture, Store, and Retrieve
Information in the Brain
• Multiple brain regions are involved in encoding, consolidation and
retrieval
– For recalling pictures, the right prefrontal cortex and parahippocampal cortex
in both hemispheres are activated.
– For recalling words, the left prefrontal cortex and the left parahippocampal
cortex are activated.
– These mechanisms reflect hemispheric specializations
(left hemisphere for language and right hemisphere for spatial ability).
• Different brain circuits for consolidation and retrieval of declarative
– Hippocampal damage impairs consolidation of declarative (see H.M. below)
– LTM storage in cortex not the hippocampus
– Consolidation requires processing in Medial Temporal Lobe circuits
• Perirhinal, Entorhinal, Parahippocampal and hipocampus
• After consolidation retrieval can occur without MTL circuits
Encoding, Consolidation, and Retrieval of Declarative Memories
Successive Processes Capture, Store, and Retrieve
Information in the Brain
• The process of retrieving information from LTM can cause
memories to become unstable and susceptible to disruption or
alteration.
• Reconsolidation is the return of a memory trace to stable longterm storage after it’s temporarily volatile during recall.
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Reconsolidation can distort memories.
Successive activations can deviate from original information.
New information during recall can also influence the memory trace.
Leading questions can lead to ‘remembering’ events that never happened.
‘Recovered memories’ and ‘guided imagery’ can have false information
implanted into the recollection.
Box 17.1 The Amygdala and Memory
Amnesia “Without Memory”
Deficit in memory ability
Two broad categories:
Retrograde: loss of memories for events prior to damage
Anterograde: loss of ability to store new memories
Both can occur within a patient at one time
Neurological Examination of Amnesia Patients
• Based on amnesic patient Henry Molaison (H.M.)
– Surgical damage to Medial temporal lobes and underlying structures
• Parahippocampal cortex, Hippocampus,
• play a critical role in our ability to form new memories “consolidation”
– Has functioning short-term memory so encoding is normal
– Anterograde Amnesia for declarative information but not nondeclarative
• Note also has some Retrograde Episodic amnesia
– Demonstrated that not all forms of memory are equally affected by damage to
the medial temporal lobes.
– Declarative or explicit memory (facts that can be declared) is disrupted
– Nondeclarative or implicit memory is largely intact
• allowing patients to acquire
– perceptual skills - read mirror-reversed text
– motor skills - mirror-tracing task
– conditioned responses – fear conditioning
– demonstrate repetition priming - with word list and then word stems
Brain Tissue Removed from Henry Molaison (Patient H.M.)
Henry’s Performance on a Mirror-Tracing Task
There Are Several Kinds of Memory and Learning
• Patient N.A.
• accidental damage to the left dorsal thalamus, bilateral damage to the
mammillary bodies (limbic structures in the hypothalamus), and probable
damage to the mammillothalamic tract
• Like H M, he has short-term memory but cannot form declarative long-term
memories. (anterograde declarative amnesia)
• Korsakoff’s syndrome is a memory deficiency caused by lack of
thiamine—seen in chronic alcoholism.
• Brain damage occurs in mammillary bodies and dorsomedial thalamus, similar
to N.A., and to the basal frontal cortex.
• anterograde declarative amnesia
• Graded retrograde amnesia
• Patients often confabulate—fill in a gap in memory with a falsification which
they accept as true.
Two Main Kinds of Memory: Declarative and Nondeclarative
There Are Several Kinds of Memory and Learning
• Patient K.C. (Kent Cochrane, 1951 – March 27, 2014)
• accidental damage to the cortex and severe shrinkage of the hippocampus
and parahippocampal cortex
• Graded Retrograde Episodic amnesia
• cannot retrieve personal (episodic) memory
• his semantic memory (from before the accident) is good
• Anterograde Episodic amnesia
• cannot form new personal (episodic) memory
• Can form new semantic with difficulty
• Two subtypes of declarative memory:
– Semantic memory—generalized memory, “word meaning”
– Episodic memory—detailed autobiographical memory,
• “who-where-when”
Subtypes of Declarative and Nondeclarative Memory
Preservation of musical memory in an amnesic professional cellist
• Are there special neural circuits for musical memory?
• Patient PM with brain damage following encephalitis
• lesions of the right medial temporal lobe, large portions of the
left temporal lobe and parts of left frontal and insular cortex
• Severe amnesia
• persistent anterograde and retrograde amnesia.
• Profound deficits in semantic and episodic memory.
• Lack of recall for biographical information from childhood
through adulthood including professional events
• unable to recall or recognize lyrics of well-known songs
• could not recall any famous cellist and remembered the name of
only one composer (Beethoven)
• Musical memory: good retrograde and anterograde memory
• able to sight-read and to play the cello
• normal for all aspects music perception after brain damage
Experimental Research with Non-Human Animals
• Clinical studies with amnesia patients lack control
• Experimental lesion studies with non-human animals have control
• However it is difficult to model clinical examples of amnesia
• Especially examples of declarative
• Different brain regions are involved with different attributes of
working memories such as space, time, or sensory perception.
• Different memory tasks assess the contributions of each brain region.
• The eight-arm radial maze is used to test spatial location memory.
• Only lesions of the hippocampus produce a deficit in this predominantly
spatial task.
Tests of Specific Attributes of Memory
Experimental Research with Non-Human Animals
• Early research indicated that animals form a cognitive map—a
mental representation of spatial relationships.
• The hippocampus is also important in spatial learning.
• It contains place cells that become active when in, or moving toward, a
particular location.
• Place cells remap when a rodent is placed in a new environment.
• Grid cells and border cells are neurons that fire when animal is at an
intersection and at the perimeter of an abstract grid map, respectively.
Experimental Research with Non-Human Animals
Testing declarative memories in monkeys:
• Delayed non-matching-to-sample task—a test of object
recognition memory, where the subject must choose the object that
was not seen previously.
• Medial temporal lobe damage causes impairment on the delayed
nonmatching-to-sample task.
• The amygdala is not necessary for declarative memory tasks.
• The hippocampus (in conjunction with the entorhinal,
parahippocampal) and perirhinal cortices, is important for these
tasks.
The Delayed Non-Matching-to-Sample Task
Memory Performance after Medial Temporal Lobe Lesions
Brain Regions Involved in Different Kinds of Learning and Memory