LEARNING
Overview of Topics
Lesson Objectives
Definition and Description
Types of Learning
Neural Correlates
Orienting
Acquisition
Maintenance
Role of the Cortex
Cortex-Limbic System
Conditioning
Lashley's Research
Cortico-cortical Conditioning
Lesson Objectives
- Describe what happens in the CNS with acquisition of a new response.
- What role does the limbic system play in conditioning?
- Describe the role of the cortex in conditioning
- Describe the difference between acquisition and maintenance of a learned response.
- Describe the role of the limbic system in conditioning.
- What are Lashley's major points?
- What are the problems with some of his findings?
- How can Lashley's findings be accounted for? Subject? Task?
- What is meant by associative learning?
- Explain equipotentiality and mass action.
- What is the unique characteristic of the unconditioned stimulus with regard to the brain?
Learning -- Definition and Description
- Learning = Change in response probability, resulting from reinforced practice.
- Stereotyped genetic coding device (closed instinct)becomes impractical in complex behavior.
- Survival is enhanced by behavioral flexibility - learning
- Instinctive behaviors may be stereotyped and inflexible (closed instincts) or they may provide some stereotyped features but allow for significant elaboration or learning(open instincts).
Provides means whereby animal can develop responses appropriate to environmental stimuli.
- Behavioral C1onstruct
- CNS associations are important but are extremely complex networks.
- Involves other input (stimuli from animal, from environment other than controlled stimuli)
Conditioning - learning in simplest form is complex process involving sensory, motor input and integration, retention, coordination, activation, attention, discrimination, etc..., habituation.
- Different mechanism
may be involved in different learning situations.
- Attention, activation, and emotion
.
Behavioral flexibility
Learning versus Memory
- Learning
- a logical construct that refers to the acquisition of new information (refers to the process of acquiring)
- Memory
- the process of storage and/or retrieval of acquired information
Electrophysiological Changes with Learning
- First presentation
- Attention
- Diffuse activation
- Later presentations
- Activity in many areas becomes habituated to stimulus presentation
- Area of UCS projection, lateral hypothalamus and DTAS remains active
- UCS has the unique property of activating the limbic system.
- CS projects via sensory nuclei to cortex.
Types of Learning
- Habituation
- learning not to attend to non-changing inconsequential stimuli
- Sensitization
- increase in response probability after strong stimulus
- Classical Conditioning
- associative learning.
Associative conditioning:
where the presentation of a "neutral stimulus" (CS) is paired with the presentation of a unconditioned stimulus (UCS) until the CS comes to elicit the response which was previously made to the (UCS).
- The UCS-UCR connection
is wired into the CNS (anatomically arranged)
- E. g., withdrawal response (UCR) of a subject to foot shock (UCS); this is built into the organism.
- The number of UCS-UCR combinations of this type are limited in number.
- Instrumental Conditioning
- situation in which outcome is dependent on response
- Operant Conditioning
- response is instrumental in outcome, but animal is free to operate on his environment.
- Perceptual Learning
- learning relationships between stimuli -- sensory associations.
- Language Learning
- Motor Learning
- learning skilled actions -- non-associative learning
Neural Correlates
- Study correlations between electrical activity and learning.
- Problem
- relation between electrical activity and neural events.
- Observed correlation
- not necessarily reflecting learning.
Orienting
- Diffuse activation
.
- Behavioral adjustments
- important in initial phase of conditioning process,
- General activation
.
- Habituation
- eventually only (lost if RF lesions, H-Peon, 61) localized response. Where?
- EEG changes
- much quicker than behavior.
Acquisition
- Hippocampus response
not present early but appears and remains until
CRs begin to appear.
- Reappears in discrimination
training and extinction.
- Behavioral orientation
correlated almost perfectly with hippocampal activation.
- Hippocampal stimulation
- stimulus-bound orienting also interrupts ongoing behavior.
- Hippocampus
- may work to prevent orienting response to nonsignificant stimuli.
- Limbic system response
appears in Amygdala and Posterior Hypothalamus
- Limbic System - May be correlated with internal stimuli whereas RF may mediate external stimuli
- Cortical desynchronization appears before overt response; more persistent during extinction.
- Localized cortical desynchronization - sensory & motor cortex.
Maintenance
- For simple task
- Response in anterior thalamic nuclei, amygdala, sensory relays.
- Not in cortex (except motor), reticular formation
- As response acquires meaning
, the response shifts from specific sensory structures to nonsensory specific structures (not reticular formation, but thalamus and limbic system extinction)
- Learning not to respond
(habituation).
- Pavlov's disinhibition suggests that extinction is active process.
- Frequency-specific cortical responses can reappear in specific sensory areas.
Role of the Cortex in Learning
- Switchboard analogy
- severing association neurons between sensory-motor areas has little effect.
- Association areas
- Areas 17-18-19 tend to respond to progressively more complex stimuli.
- Information not relayed from other cortical areas (respond if other cortical areas removed).
Frontal lobes project from dorsal median nucleus of thalamus
- Lesions deficit in relayed response
- Same effect - lesions in hippocampus or caudate
- Hyperactivity
- Age important - more dramatic in old.
- Relief from pain.
Posterior Association Areas - temporal lobe
- Kluver and Bucy (1937) psychic blindness; learning-set loss. No delayed-response loss.
Connection Between Cortex and Limbic System.
- Damage to posterior hypothalamus
or connections abolishes conditioned defensive reactions
- Lateral hypothalamic lesions
reduce CR and emotion
- Light CS -- foot shock (UCS) conditioning is prevented with anterior hypothalamic or septal stimulation
- Effective hypothalamic stimulation parallels the state of conditioning
- Well-established CR -- posterior hypothalamus. Stimulation = big response
- Partially established CR -- posterior hypothalamus. Stimulation. = less response
Facilitatory influence from neocortex to hypothalamus, and the hypothalamus increases excitatory discharges to the cortex.
Increased hypothalamic activity influences motor system
Hypothalamic-cortical fibers pass, in part, through DTPS
Limbic System and Conditioning
- Cortex removal
-- CR to complex stimulus impaired; not too simple
- More severe impairment with limbic system lesions
- Limbic system to be more important in conditioning
than neocortex
Primary Connections
The major process involved in conditioning is the facilitation of connections between the cortical areas and the limbic system so that, when a CS is presented, it acquires the ability to activate the cortex and the limbic system.
Such a notion is supported by findings where posterior hypothalamic lesions and limbic system lesions impair conditioning to a greater extent than do lesions in the cortex.
Doty -- conditioning loss is greater and relearning less effective after elimination of subcortical (as compared with intracortical connection)
Conditioning
- Intercranial stimulation serves as conditioned stimulus
.
- Stimulus-conditioning may have been based on pain stimulus.
- Limbic system and conditioning
- Cortex removal
- conditioning to simple stimuli (not complex).
- Spreading depression of hippocampus
: greater impairment of conditioning than with neocortex spreading depression.
Limbic system is required for determination of reinforced properties of stimuli; if damaged stimulus may produce a conditioned response but discrimination between reinforced stimulus and an irrelevant stimulus is lost.
Lashley's research: In search of the engram
Complexity of Memory Trace
- Stimulus-Response diagram is a misleading schematic
.
- Effective stimulus presented as well as the whole background of other stimuli.
- Memories become part of the relevant information already available (part of an extensive organization).
- Memory not a single fact
but probably a reorganization of a vast system of associations.
Dunlap (1930) thought only used part of the total neutrons available; but, due to the convergence toward the cortex, probably all cells are active or actively inhibited.
Transcortical conduction
- Rats trained on task, then subjected to cortical sections did not disturb responses (only if sensory input impaired)
- Monkeys--color brightness and form discrimination task--transcortical fibers of frontal lobes leaving only projection--no loss.
Severing association fibers - no significant loss.
Conclusions about learning effects:
- Are diffuse
- Result in projection to subcortical nuclei in rat
- Do not exist in the CNS
Association areas
- Complete removal
-- no obvious loss in rat
- Almost any effect could be attributed to shorter attention span
Equipotentiality -- sensory areas. Performance of habits of the CR type is dependent on the sensory areas and upon no other part of the cerebral cortex.
- What about localization within these areas?
- As long as some part remains, animal can function.
- Lashley concludes that it is the pattern, not localization of energy on the sense organ, that determines its functional effect.
Mass action
- Amount of relearning closely proportional to amount of cortex removed.
- Complex discriminations and delayed reactions are a function of association area destruction.
Chapman & Wolff
Have replicated Lashley's findings with humans and found same effect.
Cortico-Cortical Conditioning
involves the facilitation of functional interconnections between the two areas via association neurons.
- No consistent overt behavior is conditioned; change in response probability results.
- Much conditioning involves the pairing of a neutral stimulus (NS) with a previously unconditioned Stimulus (UCS)
- The previous (NS) then becomes a conditioned stimulus (CS) after repeated pairings.
- The CS conveys information to the cortex
- Function of the cortex is to incorporate all available information into decisions; responding due to the specificity of sensory information; cortex functions to mediate complex discrimination, delayed discrimination, & to instigate, direct, and terminate behavior
- The cortex does not provide the only neural substrate for reinforcement
Reinforcement
- The act of presenting a reward or punishment appears to be a function of posterior hypothalamic-limbic system activity
- Certain stimuli are + or - due to the way the nervous system is designed anatomically.
- Pain acts on the CNS through two routes:
- Through RF-DTPS to cortex for cortical desynchronization (make perception possible and increase sensitivity)
- Through posterior hypothalamus-LS to produce behavioral arousal and to activate the autonomic nervous system (SNS division). This prepares the organism to deal with stimulus situation, and the consequences of such stimulation are aversive; therefore, they increase the likelihood that the animal will get away from the pain-producing stimulus.
Latent learning
- Latent learning is a situation where cortico-cortical conditioning has occurred, followed by the pairing of one CS with one UCS.
- Much conditioning actually involves higher-order conditioning, where a CS is paired with a stimulus that is not unconditioned, but conditioned earlier.
Positive reinforcement
- Reward - follows the same logic as negative.
- Many stimuli result from the absence of food, water, etc;
- Limbic system consequences; is aversive
- A stimulus that will abolish these stimuli is considered to be negatively reinforcing
- Sensory reinforcement or stimulus change is more difficult to account for by this theory or any other
TERMS you should know
|
Conditioning |
habituation |
sensitization |
|
Behavioral flexibility |
motor learning |
perceptual learning |
|
Learning |
Open instinct |
Associative learning |
|
Orienting |
Spreading depression |
Non-associative learning |
|
Equipotentiality |
Mass action |
Chapman & Wolff |
