Chapter 14: Remembering Relationships Flashcards
Procedural learning
physical type of learning that facilitates the phenomenon of muscle memory ex/ memory of riding a bike
episodic memory
memory of a specific event, part of declarative memory
semantic memory
aka declarative memory (along with episodic memory), memory of facts
Describe HM’s amnesia.
he suffered from severe epilepsy and got a bilateral temporal lobe ressection that took out the hippocampus and amygdala. seizures stopped but he faced severe anterograde amnesia that extended across all sensory modalities and affected memories for faces, places, events, facts and words. he did not suffer from retrograde amnesia; he remembered old facts and childhood events. points to the fact that the hippocampus is probably not as involved in long term storage.
T/F people with superior autobiographical memory have enhanced forms of other types of learning such as procedual memory and learning
false. they remember a lot about their own experiences but have relatively normal other forms of memories and learning. ex/ they perform average in school and in number remembering tasks.
seizures themselves are thought to arise from an imbalance of ___ and ___. Explain this mechanism.
excitation and inhibition. the imabalnce is created by the DEATH of tonically active neurons that normally excite inhibitory neurons in the DENTATE GYRUS. without this tonix excitation of inhibition, the inhibitory neurons fall silent, causing the rest of the hippocampus to become overly excitable.
evidence that hippocampus is involved with medio-temporal epilepsy
1) hippocampus is overly excitable because of the death of neurons that normally excite inhibitory neurons in the hippocampal regions 2) initial trauma causes dentate granule cells in the HC to sprout abnormal connections that create an excitatory intrahippocampal FEEDBACK LOOP. LEADS TO EXCITOTOXICITY. medial temporal epilepy is a progressive, degenerative disease.
treatment for medio-temporal epilepsy
remobing the hippocampus and adjacent cortices on the side of the brain where the seizure begins. eliminates seizures in 80% of cases.
genetic component of developing epilepsy
if your twin has epilepsy, there is a 40-50% chance you’ll have it. this is a result of a genetic mutation that affects the voltage gated Na+ and K+ channels. Other mutations may affect GABA receptors.
hippocampusvolume ___ with epilepsy duration on the side of:
DECREASES with epilepsy duration but ONLY ON THE SIDE OF THE SEIZURE. Shrinkage does not occur on the contralateral side.
There was severe anterograde amnesia experienced by HM, however, what kind of learning was spared?
procedural learning. HM could learn new motor skills (ex/ mirror tracing task- he improved over the course of several days, even though he had no memory of having done the task before).
He also could learn new cognitive skills. ex/ he got betetr with practice at recognizing objects from incomplete, fragmented drawings.
How did researchers study HM’s amnesia (anterograde amnesia) in non humans? Outline the process
using the delayed non-matched to sample task.
1) sample phase. monkeys (no HC, inferior temporal cortices (entorhinal or perirhinal cortex), or amygdala) are shown a single object
2) delay.
3) monkeys (no HC, inferior temporal cortices (entorhinal or perirhinal cortex), or amygdala)) are shown the same object again, as well as a novel object.
4) over the course of many trials, the monkeys are trained to always lift up the novel object, the one that does nto match the sample, in order to retrive food hidden underneath
because the trials involve different objects, the monkeys can solve the task only if they remember on each trial which object they saw during the corresponding sample phase. they must recognize which of the two objects seen in the test phase is old and which is new.
5) monkeys with large bilateral lesions in the medial temporal lobe are SEVERELY IMPAIRED in the DNMTS task because this involves OBJECT RECOGNITION MEMORY, and is not a procedural task.
3 regions of the medial temporal lobe that were adjcent to the hippocampus whose direct lesioning most likely memory impairment. proof?
1) enterorhianl cortex
2) perirhinal cortex
3) parahippocampal cortex.
When these areas were removed, monkeys demosntrates amnesia compared to that of HM. If you lesioned these areas but kept the amygdala and hippocampsu, monkeys performed the DNMTS task at a SEVERELY IMPAIRED LEVEL.
monkeys with large bilateral lesions of the amygdala dn hippocampus, including the dentate gyrus, the CA fields and the subiculum, but had INTACT entorhinal and perirhinal cortices performed JUSTA S WELL ON DNMTS TASKS, indicating that these cortices play a salient tole in memory and learning.
spontaneous novel recognition tasks in rats have shown that rats still exhibit a reliable preference for novel rather than familiar object. HOwever, whhen the ___ and ___ cortex was removed but NOT the hippocampus, nocel stimulus recognition was not demonstrated.
when the perirhinal and post rhinal cortex was lesioned, novel stimulus preference was not demonstrated. This indicates that the peri and post rhinal cortices, but NOT THE HIPPOCAMPUS, are needed for OBJECT RECOGNITION.
explain the double dissociation phenomenon in memory
hippocampal lesions affect spatial and temporal relationships (ex/ memory needed to navigate around a city, time patterns) but not object recognition memory, and perirhinal lesions affect object recognition but NOT spatial memory.
relational memory hypothesis
the proposal that the perirhinal and postrhinal cortices may be sufficient for forming memories of individual objects, but the hippocampus is needed to CONNECT those objects to one another, through space and across time.
aka the HC is involved in learning about SPATIAL, TEMPORAL OR LOGICAL relationships.
long term potentiaion
persistent growth or strengthening of synapses that were active just before or during post synaptic depolarization.
4 components of the hippocampus
1) dentate gyrus
2) CA1
3) CA3
4) subiculum.
information generalyl flows from the higher order neocortical areas, through the ___ and ___ cortices into the hippocampus and back out
through the perirhinal and entorhinal corticices into the hippocampus and back out.
neurons in the enothinal cortex project into the hippocampus’s ____ ___, whose output cells project to the ___ fields of the cornu ammonis, which projects to the ___ field. Where does this field project into?
neurons in the enothinal cortex project into the hippocampus’s DENTATE GYRUS, whose output cells project to the CA3 fields of the cornu ammonis, which projects to the CA1 field. THE CA1 field then projects into the SUBICULUM.
after receiving input from the CA1 field, the subiculum projects out of the hippocampus to the ___ ___, and to several subcortical targets, including:
projects to the entorhinal cortex and to several subcortical targets, including the amygdala and hypothalamus
what is the perforant path of the hippocampus? What is the mossy fiber pathway? How does the CA3 project to CA1?
the projection from the entorhinal cortex to neurons in the dentate gyrus and CA3
The mossy fiber pathway connects the dentate gyrus to CA3.
the neurons of CA3 project to CA1 AND TO OTHER CA3 NEURONS via recurrent collaterals.
what’re the three major input pathways that hippocampal CA3 neurons receive?
1) from entorhinal cortex
2) from the dentate gyrus
3) from other CA3 neurons.
T/F mossy fiber connecions between CA3 and dentate gyrus is seen to undergo LTP
false. in this connection system, the boost in synaptic strength is not dependent on post synaptic depolarization and therefore not LTP
Which connections of the hippocampus exhibit LTP (following hebbs rule)
LTP is observed at synapses connecting CA3 to CA1, as well as the synapses that connect CA3 neurons TOGETHER. synpases onto CA3 neurons can be strengthened by applying a strong, high-frequency stimulus (a long tetanic stimulus) to the axons of other CA3 neurons.
this hebbian plasticity might be a reason that allows certain neurons to be capable of storing info about their own patterns of activity.
the CA3 neurons in the hippocampus exhibit Hebbian plasticity and become more strongly connected to one anotehr. Eventually, all the activated CA3 neurons becoem capable of activating each other. These interconnected neurons form a ___ ___
CELL ASSEMBLY.
each cell assembly of CA3 neurons is a potential ____, a memory trace.
ENGRAM
in the CA3, what happens when only a subset of the neurons in a fully fromed cell assembly are activated by some external input? What’s this process known as?
as a result of prior LTP, the activated CA3 neurons have become strongly connected to the other neurons in the same assembly. through these previously strngthened connections, neural activity spreads from the initial subset of active neurons to the entire assembly, even to the neurons in the assembly that weren’t first excited by the initial external stimulus. this is known as PATTERN COMPLETION. See the “cued recall” diagram
how is LTP involved in learning and rememboring TEMPORAL SEQUENCES
the key notion here is that LTP preferentially stengthens not only synapses that were active simiultaneously, but also synapses that were active a few milliseconds earlier.
this temporal asymmetry in LTP (spike timing dependent plasticity) makes sequence learning possicle. Ex/ if neuron A is consistenyl active 10 ms before neuron B fires and AP, then the synapse from A to B will be strengthened, whereas the synapse from B to A will remaine weak. Afterwards, activation of A can trigger a spike in B, but B activation cannot trigger a spike in A.
Therefore, this 2 neuron network has stored info about the TEMPROAL SEQUENCE of the original firing pattern.
autoassociative networks with spike timing-dependent LTP are capable of storing sequences.
why is cell assembly segregation so important?
each cell assembly represents different experiences, and must remain segegated from one another. Although individual neurons may participate in multiple cell assemblies, the overlap between different assemblies must be MINIMAL or else we would not be able to separate memories.
to counteract this problem, we ensure that even similar experiences activate different sets of CA3 neurons from the outset during the intiial encoding of the memory
it is seen that each individual CA3 cell assumbly represents one memory. is activation of CA3 sufficient to generate a full blown memory experience?
actually no. there is neocortical involvement. it was found that recalling images activates a subset of neocortical areas that were involved in the INITIAL PERCEPTION (ex/ asking to recall a sound a dog makes activates the auditory cortices).
thus, memory recall appears to reinstate at least part of the neocortical activity pattern that existed when the memory was formed.
NOTABLE< it was found that the entorhinal cortex responds selectively when the clips of movies are initially displayed, and then JUST BEFORE the clips are remembered. Activation of entorhinal cortex prior to recall impries that memory recall involves at least some neocortical neurons.
In diagram:
One entorhinal neuron (A) increased its firing rate whenever the patient was watching brief (5-sec) clips of a Simpson’s episode.
The graphs in (B) show the same neuron’s activity when the patient was later asked to recall which clips he viewed.
Remarkably, the neuron increased its firing rate just before the patient reported remembering “the Simpsons.”
Similar recall-related activity has also been recorded in the hippocampus.
electrical stimuluation of area ___ of the perirhinal area and the ___ ___, but not of either area by itself, allows activity to spread into the ___ ___ an the ___ ___.
electrical stimuluation of area 35/36 of the perirhinal area and the LATERAL AMYGDALA , but not of either area by itself, allows activity to spread into the ENTERHINAL CORTEX AND THE DENTATE GYRUS
This demonstrates the the Lateral amygdala stimulation opens the “gate”
for information flowing into the hippocampus
diagram: show that electrical stimulation of area 36 and the lateral amygdala, but not of either area by itself, allows activity to spread into the entorhinal cortex and dentate gyrus.
what are the the three unconditioned fear pathways that reach the central nuclei of the amygdala. what does this allow for?
the central nucleus receives input from the 1) Parabrachial nuclei, the 2) dorsal thalamus, and 3) from the basolateral complex.
the multiplicity of the uconditioned fear pathways make the system fault tolerant.
where specifically does auditory info enter the unconditioned fear pathway, and where does the synaptic strengthening take place?
single neurons in the lateral nucleus respond to sounds as well as to foot chock, and their auditory responsees are strengthened by training. auditory info converges with pain info in the CENTRAL NUCLEUS of the amygdala and in the dorsal thalamus, both of which exhibit synpatic plasticity. therefore, auditory fear conditioning involves synaptic strengthening in multiple brain aea.
