Download Unit 11 Chapter 14

PSYC 3832
NEURAL BASIS OF LEARNING
Week 11
Chapter 14
TIAN YU, PhD
Department of Psychology
College of Liberal Arts and Sciences
Chapter Goals
Under some conditions, retrieving or reactivating a
consolidated memory can return it to an active, labile
state. The goal of this chapter is to provide an
understanding of the empirical facts and theoretical
concepts that are associated with this observation.
This will be done by discussing:
• Key empirical findings
• Active trace theory
• Reconsolidation theory
• How retrieval returns the trace to an unstable, labile
state
• How the trace is restabilized
• The concept of trace updating
Reactivated Memory Disrupted by ECS
(A) A fear-conditioning experiment was
used to study the vulnerability of a
reactivated memory—a noise CS was
paired with a shock US. In one
condition, 24 hours after fear
conditioning, the CS was presented to
reactivate the fear memory. Some
animals received electroconvulsive
shock (ECS), while others did not. In
the second condition, the fear memory
was not reactivated, but animals
received either ECS or no ECS. All
animals were tested for fear of the CS.
(B) The results of the experiment. Note
that when the memory trace was
reactivated by briefly presenting the
CS, ECS disrupted the memory for the
CS–shock experience. ECS had no
effect when it was presented in the
absence of shock.
Active Trace Theory
This figure illustrates the assumptions of active trace theory. Memories
exist in either a short-term memory (STM) active state or a long-term
memory (LTM) inactive state. (A) Novel experience can create an active
STM trace that will decay into the inactive LTM state. (B) Retrieval cues
can retrieve an inactive LTM trace and place it in the active state that
then will decay into the inactive LTM state. Memories in the active state
are more vulnerable to disruption than memories in the inactive state.
Reconsolidation Theory: Nader’s Finding
(A) The design of Nader et al.’s 2000
experiment. Rats were conditioned to
an auditory-cue–CS paired with a
shock–US. Following the reactivation
of the fear memory, the protein
synthesis inhibitor anisomycin or the
vehicle solution in which the drug was
suspended was injected into the lateral
nucleus of the amygdala. Rats were
then given either a short-term memory
(STM) test or a long-term memory
(LTM) test. (B) Anisomycin disrupted
the long-term retention of the
reactivated fear memory but had no
effect on the short-term retention of the
memory. (After Nader et al., 2000.)
Reconsolidation Theory
(A) A retrieval cue activates a well consolidated but inactive memory
trace from long-term memory. The synaptic connections linking the
neurons involved in the trace become unbound. However, retrieval
also initiates protein synthesis and the memory trace is reconsolidated.
Thus, when it returns to the inactive state it will be stable. (B) If protein
synthesis is prevented, the memory trace will be weakened or lost
when it returns to the inactive state.
Assessing Reconsolidation Theory: Only the Reactivated Trace
Needs to Be Reconsolidated
Rats acquired two fear memories. However, only the reactivated memory
(CS1) was disrupted by U0126, a drug that interferes with reconsolidation.
How Does Reactivation Destabilize the Trace? A Role for the UPS
This figure illustrates key events that destabilize the synaptic basis of a
memory trace.
Proteasomes Degrade Proteins Tagged with Ubiquitin
Proteins
PSD
Ubiquitin
Proteasome
Proteasomes Degrade Scaffolding Protein Tagged with Ubiquitin
Glutamate
Calcium
NMDA
AMPA
Scaffolding
proteins
Ubiquitin
PSD
Proteasome
The collapse of the scaffold results in AMPA receptor loss from the spine.