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Review

ksweeney@cogsci.ucsd.edu www.cogsci.ucsd.edu/~ksweeney/psy260.html

Introduction to Physiological Psychology

n Learning and Memory n Human Communication n Emotion

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What is memory?

n Working Memory: –  Limited capacity (7 +/- 2) –  Information can be held for several minutes

with rehearsal §  (e.g. memory system you use when you have to remember a

phone number but have no place to write it down)

n Long-term Memory: –  Very large capacity –  Essentially infinite duration

§  e.g. memory system you need when you are reminiscing with friends, or taking a final exam

Forms of Learning

Perceptual Learning

Motor Learning

Stimulus-Response Learning

Relational Learning

Objects

Situations

Form new circuits in the motor system

Form connection between perception and action

Connections between stimuli

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Learning n All forms of learning involve changes in

the ways that neurons communicate.

Stimulus-Response learning n Classical Conditioning

–  An unimportant stimulus begins to elicit a similar response as an important one

–  It involves an association between two stimuli, one of which is reflexive

n Operant Conditioning (or Instrumental Conditioning)

–  A particular stimulus begins to elicit a particular response

–  It involves an association between a stimulus and a response

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Classical Conditioning

n Famous example: Pavlov’s dogs –  First, present dogs with food and measure

amount of saliva –  Then, start ringing a bell just before food is

presented (at first, saliva only occurs at presentation of food)

–  In time, salivation occurs in response to the bell

–  Conditioning has occurred

Classical Conditioning

n Unconditional Stimulus- dog food n Unconditional Response- salivation n Conditional Stimulus- bell n Conditional Response- salivation

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n Reinforcing stimulus (favorable consequences)

§ Appetitive stimulus that follows a particular behavior and thus makes behavior occur with greater frequency

n Punishing stimulus (unfavorable consequences)

§ Aversive stimulus that follows a particular behavior and thus makes behavior occur more rarely

Instrumental (or Operant) Conditioning

An association between a stimulus and a response

But what has happened in the brain? n Hebb postulated:

–  the cellular basis of learning involves strengthening of a synapse that is repeatedly active when the postsynaptic neuron fires

–  “neurons that fire together, wire together”

For LTP to occur, the postsynaptic cell must already be depolarized

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NMDA and AMPA n  Glutamate binds to NMDA receptors, which controls a

calcium (Ca2+) channel. n  So, Ca2+ rushes in, right? NO!

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NMDA and AMPA n  At rest, that same calcium channel is ‘guarded’ by a

magnesium ion (Mg2+), so calcium can’t get in through NMDA receptors.

n  That Mg2+ ion won’t budge unless cell is depolarized. n  But cell can’t depolarize unless Ca2+ can get in, right?

NO!

NMDA and AMPA n  If a weak synapse is active by itself, nothing happens… n  BUT- if the cell has just fired due to a strong synapse

somewhere else on the cell, a dendritic spike will depolarize the membrane…

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NMDA and AMPA n  Depolarization kicks the Mg2+ ion out, and NOW Ca2+

ions can enter the cell. n  … and an association between those two synapses is

formed.

We still don’t have LTP! n  Ca2+ ions entering the cell bind with the enzyme CaM-

KII n  CaM-KII causes more AMPA receptors to to move to

post-synaptic membrane. n  More AMPA receptors means it’s easier to depolarize

the cell in the future.

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We still don’t have LTP! n  Ca2+ ions entering the cell bind with the enzyme CaM-

KII n  CaM-KII causes more AMPA receptors to to move to

post-synaptic membrane. n  More AMPA receptors means it’s easier to depolarize

the cell in the future.

n For Ca2+ to enter the cell, NMDA receptors have to be activated by glutamate AND subjected to depolarization simultaneously.

n The fact that both these things must occur together means that NMDA receptors are “coincidence detectors”.

n Thus, they are crucial for LTP.

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Perceptual Learning

n  The ventral stream –  involved with object

recognition, continues ventrally into the inferior temporal cortex.

n  The dorsal stream –  involved with perception of

the location of objects, continues dorsally into the posterior parietal cortex.

n  The ventral stream is involved with the what of visual perception; the dorsal stream is involved with the where.

Instrumental Conditioning

n Circuits responsible for instrumental conditioning begin in sensory association cortices and end in motor association cortex.

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Instrumental Conditioning

n Two major pathways from sensory to motor association areas: –  Direct transcortical connections- involved in

STM, acquisition of episodic memories and of complex behaviors that involve deliberation or instruction (slow and laborious)

–  Connections via the basal ganglia and thalamus- which are involved as behaviors become automatic and routine (fast and easy)

H.M.

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What can possibly go wrong? n Anterograde Amnesia:

–  Amnesia for events occurring after the precipitating event.

n Retrograde Amnesia: –  Amnesia for events occurring before the

precipitating event.

The Medial Temporal Lobe: Crucial in the Declarative Memory System

n  Damage to these areas usually results in anterograde amnesia: patients are unable to form new declarative memories.

n  Can also result in retrograde amnesia: typically ‘graded’.

n  Non-declarative memory is not affected.

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H.M. Effects of Bilateral Medial Temporal Lobectomy

n Minor seizure beginning at age 10, major seizures beginning age 16

n Severe, persistent seizure condition- not controlled with anticonvulsants

n By mid-20’s, condition was so severe he was unable to work

n Surgery at age 27: Bilateral medial temporal lobe resection.

n  In HM, the amygdala, entorhinal and perirhinal cortices, and about two-thirds of the hippocampus were removed

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What’s wrong with H.M., and what does it tell us about functions of Hippocampus and MTL?

n What CAN he do? –  Intellect is normal –  Can remember the past (pre-surgery)

§ He has relatively little retrograde amnesia § His long-term memory is intact

–  Can carry on excellent, short conversation § His working memory is intact

–  Can learn new skills at a normal rate- and retains those skills over long periods of time § His procedural memory is intact

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What’s wrong with H.M., and what does it tell us about functions of Hippocampus and MTL?

n What CAN’T he do? –  Doesn’t retain new semantic or episodic

information

–  Can’t form new declarative memories.

What does H.M. tell us about role of Hippocampus and MTL?

n  Hippocampus is essential for the formation, but not the storage or retrieval, of long-term declarative memory

n  Memory depends on Hippocampus for a short duration

n  Hippocampus does not mediate short-term memory

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What does H.M. tell us about role of Hippocampus and MTL?

n STM and LTM are distinctly separate –  H.M. is unable to move memories from STM to

LTM, a problem with memory consolidation

n Memory may exist but not be recalled – as when H.M. exhibits a skill he does not know he has learned

Explicit vs. Implicit Memories

n Explicit memories – conscious memories

n  Implicit memories – unconscious memories, as when H.M. shows the benefits of prior experience

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Broca’s Area and Patient “Tan”

Lateralization of Function

n For many functions the hemispheres do not differ and where there are differences, these tend to be minimal

n Lateralization of function is statistical, not absolute! –  e.g. Right hemisphere has some language

abilities

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Lateralization of Function

Left Hemisphere n  “Language”

–  Even for deaf people!

n  Words, letters

n  The details

Right Hemisphere n  Emotional Prosody n  Music n  Spatial ability n  Faces, patterns

n  The big picture

Language n Language is not a unitary ability

–  Production vs. Comprehension

n Production –  Requires having something to say, being able

to associate that “thing” with words, and making the mouth move appropriately

n Comprehension –  Begins in the auditory system (detection and

analysis of sounds) but there is a difference between recognizing a word and comprehending it

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What can possibly go wrong?

n Aphasia –  A difficulty with speech (either production or

comprehension) caused by brain damage rather than, e.g. motor deficits or deafness

What can possibly go wrong? n  Broca’s aphasia

–  difficulty in language production § Comprehension is normal § Know what they want to say, but can’t say it § “expressive aphasia”, slow laborious speech,

full of disfluencies. § Although words are often mispronounced,

words that are produced are usually meaningful

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What can possibly go wrong?

n  Broca’s aphasia –  Typically function words are most compromised, with

content words being relatively spared. –  Aphasias are a spectrum

What can possibly go wrong?

n Broca’s aphasia: not ONLY a production problem! –  Although comprehension is good, it is not normal –  Agrammatism is present in production, and

grammatical clues such as word order, tense markers or function words aren’t successfully used in comprehension either.

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What can possibly go wrong?

n Broca’s aphasia: not ONLY a production problem! –  Anomia: a difficulty in finding words (in naming

things).

What can possibly go wrong?

n Broca’s aphasia: not ONLY a production problem! –  Articulation difficulties: mouth

motor movements are disfluent, so words are often mispronounced

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What else can possibly go wrong?

n Wernicke’s aphasia –  Wernicke’s area- difficulty in comprehension;

but production is generally meaningless § Unlike Broca’s Wernicke’s aphasics generally speak

quite fluently, with normal prosody, natural-sounding rhythm and apparently normal grammatical constructions.

§  “jargon aphasia”, natural sounding rhythm and syntax, but output is meaningless (“word salad”)

§ neologisms

Wernicke’s Aphasia

n Difficulty recognizing words n  Impaired comprehension (failure to grasp

the meaning of words) n Difficulty converting thoughts into

meaningful words

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Wernicke’s Area n  Wernicke’s area is

also implicated in Pure Word Deafness

n  Uncompromised recognition of non-speech sounds and intonation.

n  Caused by disruption of auditory input to Wernicke’s area, or damage to Wernicke’s area itself

Transcortical sensory aphasia n Wernicke’s aphasics can’t understand

the meaning of words or “translate” their thoughts into meaningful words.

n This seems to be due to trauma to the ‘posterior language area’.

n Damage to just this area often results in transcortical sensory aphasia.

n These patients can recognize words: they can repeat back what you say… but can’t make ‘meaning’.

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Language Areas

Conduction Aphasia

n The fact that transcortical aphasia patients can perform repetition suggests that there is a direct connection between Wernicke’s area and Broca’s area

n This is known as the arcuate fasciculus

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Conduction Aphasia

n Conduction aphasia patients –  speak fluently –  have pretty good comprehension –  Often perform well on repetition tasks, as

long as the sounds have meaning –  Often fail at longer repetition tasks,

repeating the gist of a sentence but with different words

The arcuate fasciculus

n  A bundle of axons that seems to bring information from Wernicke’s area to Broca’s area about the sounds of words (but not their meanings!)

n  Conduction aphasia patients speak fluently, have pretty good comprehension, but fail at repetition tasks… suggesting that the AF is important in STM of words and recently heard speech sounds

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Conduction aphasia

Anomic aphasia

n Speech of anomic aphasics is fluent and grammatical, and their comprehension is fine… but they appear to have difficulty finding the right words.

n Fluent anomia is caused by posterior lesions to the temporal or parietal lobes.

n Patients adopt circumlocutions: alternative ways of saying what they mean

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Next time…