Transcript Conditioned reflex

Integrative and Intellectual
Functions of the Brain
Higher nervous activity
Lecture is prepared by
EKATERINA ELISEEVA
Ass. Prof. of the Normal Physiology Department
Stavropol state medical university, 2015
Learning
is the most characteristic ability of
humans and higher animals.
 This process make an individual possible
to change his behavior according current
needs and environment changes.
 Learning and memory are the functions of
nervous system based on conditioned and
unconditioned reflexes.
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Conditioned reflex
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Is a reflex response to a stimulus which
does not elicit the response itself but
acquires after repeated application with
another specific stimulation that normally
evokes such a response.
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Conditioning = training
Unconditioned vs. conditioned
Inborn, inherited
 Stable, constant
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Activity of low nerve
centers
Adequate stimulation only
Specific (for species)
Based on the certain
reflex arch
Give certain adaptation
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Acquired during life
May be established or
abolished
Activity of cortical
(higher) centers
Any stimulus may be
conditioned
Individual
Based on temporary
connection of neurons
Give better adaptation
Characteristics
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Variability, which is the most characteristic feature of a
conditioned reflex, ensures the body’s adjustment to th
e external environment. A
conditioned signal that gives incorrect information on th
e external environment ceases to be a stimulus for re
sponsive behaviour, and the
reaction to such a signal disappears.This phenomenon i
s based on internal inhibition, which causes a
sensitive discrimination among stimuli
according to their physiological and biological
properties and which helps the body dispense with
conditioned reflexes that are no longer
biologically useful.
Characteristics
The conditioned reflex warns person about
approach of the subsequent kinds of activity and
prepares them for future kinds of activity (eating,
avoidance of danger and another).
 With the help of the conditioned-reflex mechanism
such function of nervous system as purposeful
behaviour of the person in an environment and
society, the adaptation to varied conditions of an
environment are carried out. Such activity of
nervous system concerns to the higher nervous
activity.
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Classification
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I. According to biological importance
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Nutritional
Defensive
Sexual
Homeostatic, etc.
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II. According to reflex reactions
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Motor
Visceral
Cardiac
Secretary, etc.
Classification
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III. According to base reflexes
First order reflex
 Second order reflex
 High order reflex
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IV. According to time periods
 Classic
 Traced
 Reflex for time
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Classification
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V. According to receptors
Exteroreceptive
 Interoreceptive
 Proprioreceptive
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VI. According to basal methodic
Natural
 Instrumental (Artificial)
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Characteristics & Features
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Depending on the stimulus causing the reflex,
conditioned reflexes are classified as either natural or
artificial.
Natural conditioned reflexes are
evoked by the inherent properties of an
unconditional reinforcement that have biological
significance for an animal, for example, the sight and
smell of food.
Artificial conditioned reflexes are evoked by stimuli
that are initially unconnected to a reinforcement, for
example, a bell, a light, or the sound of a metronome.
Rules for conditioned reflexes
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Combination of two stimuli: conditioned
stimulus must be the first in order and
unconditioned stimulus must follow it.
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Conditional stimulus is at first relatively
neutral (indifferent) and evokes orientation
reflex. The goal is to suppress this reaction by
applying the conditioned stimulation several
times.
The special reflex laboratory by I.V.Pavlov
The orientation reflex
has a special place among unconditioned reflexes. It is a
reflex response to novelty, elicited by any sufficiently
quick change in the external environment, and is
outwardly expressed in alertness, listening for new
sounds, sniffing, turning the eyes and head, and
sometimes the whole body toward a stimulus, etc.
This reflex facilitates best perception of an acting
agent and has great adaptive significance. As Pavlov
figuratively described it, the orientation reaction is a
"What is it?" reflex.
Rules for conditioned reflexes
Both stimuli must be more intensive than threshold.
Intensity of unconditioned stimulus must be more
than intensity of conditioned one.
 For example: Conditional nutritional reflex may be
established if the dog is hungry. Ringing (at first
neutral signal, which then becomes conditional one)
is followed by some food in a few second (strong
unconditional reinforce). Repetitive combination of
both signals provokes formation of conditional
nutritional reflex: secretion of saliva. This means
that now ringing provokes secretion of saliva
without any food.
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Rules for conditioned reflexes
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Combination of conditioned and
unconditioned stimuli must be repetitive.
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Formation of temporary connections
requires normal active state of central
nervous system.
Mechanism of conditioned reflex
Conditioned reflexes, as a rule, reproduce the structure
of an unconditioned reflex, since the conditioned
stimulus excites the same nerve centers as the
unconditioned one. Therefore the components of the
conditioned reflex are similar to those of the
unconditioned reaction. They include primary
components specific for the type of reflex and
secondary, unspecific components. In the defensive
reflex the leading role is played by I he motor
component, in the nutritional reflex by the motor and
secretory components.
Conditioned
stimulus
center
Unconditioned
reflex center
PAVLOV'S CONCEPT:
Conditional reflexes are built on the basis of unconditional ones. The
building of a conditional reflex is based on the formation of
temporary connections between two cortical centers:
(a) perceiving the conditional stimulus and
(b) perceiving the unconditional one.
Important role in the mechanism of interaction between different
cortical regions play (a) cortico-subcortico-cortical pathways and (b)
the dominant phenomenon. When conditioned and unconditioned
stimuli are combined, the excitation is summated. Nervous cells of
both cortical regions are involved in a rhythmic activity. Circulation
of impulses along the same neuronal chains ensures the formation of
temporary connections.
Functional changes are important only for brief impression of traces of
stimuli on the cortex ("short-term memory"). Long retention of
temporary connections ("long-term memory") is based on some
molecular plastic changes taking place in the synapses and neurons.
Biological importance of conditioned
reflexes:
reflex reactions appear a certain time
before actual unconditioned stimulation
thus preparing the organism. Conditioned
reflexes help to find food, to avoid
danger in proper time, to eliminate
harmful influences, etc, they are base for
habits.
Reflexes may be applied in clinical and
psychological practice.
Inhibition of higher nervous
activity
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External inhibition
– conditioned reflex
is weakened or
suppressed by
simultaneous
excitatory process
Temporary
 Permanent
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Internal inhibition –
inhibitory effects in
the cortical center of
conditioned reflex
Extinction
 Differential inhibition
 Conditioned
inhibition
 Inhibition of delay
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Temporary inhibition
Inhibitory effect arises in a new cortical
center, not in centers involved into
conditioned reflex.
 E.g., orientation reflex – any new
stimulation suppresses current
conditioned activity.
 Importance – readiness to give response
to a stimulus
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Extinction
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If the conditioned stimulus is repeated
without unconditioned base for several
times, reflex becomes extinct, suppressed.
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Importance – brain does not keep
reflexes and habits which are not
necessary.
Extinction
Example of extinction: a dog has been previously
conditioned to come when he hears a bell because
he knows he will get food. But the previous handful
of times the dog did not receive food so no longer
comes when he hears the bell.
The figure is another example, applied on mouse.
Differential inhibition
Firstly conditioned response may be given
to different stimuli rather similar to
conditioned stimulus (generalization
period in reflex activity).
 After several repetitions response in given
accurately to certain stimulus only, other
are inhibited in differential manner.
 Importance – the base for learning.
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Inhibition of delay
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If unconditioned base is delayed the
established conditioned reflex is inhibited.
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Importance - organism gives response
only to stimulus applied in proper time.
Type of nervous system
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determines the rate at which conditioned
reflexes are built, the strength and
stability of these reflexes, the rate of
irradiation and concentration of nerve
process, greater or lesser susceptibility to
various influences causing pathology in
higher nervous activity.
Nerve processes are
characterized through:
Strength of
excitation and
inhibition
Equilibrium in
excitation and
inhibition
Mobility of
excitation and
inhibition
How much time is required for
building conditioned reflex and
for how long time period
Excitatory or inhibitory
reactions prevail
How easily organism changes
one reflex complex to the
other if necessary
Types of nervous system
Choleric
Strong but unbalanced nerve
processes characterized by
predominance of excitation
Sanguine
Strong, well-balanced, highly mobile
nerve processes
Phlegmatic
Strong, well-balanced, low mobile
nerve processes
Melancholic Extremely weak development of
both excitation and inhibition,
unbalanced, low mobile
This figure is an application of the four types:
Human’s types of nervous system
(1) Thinking type - with dominant left
hemisphere
(2) Art type - with dominant right
hemisphere
(3) Mixed type - with equally developed
functions of left and right hemispheres
(4) Genius type – with equally
overdeveloped functions of left and right
hemispheres
Emotions
Emotion is a kind of psyco-physiological
phenomenon, it is a multifaceted form of
behavior, involving:
 Different somatic reactions (smiling,
laughing, running, etc.);
 Variety of autonomic responses (heart
rate changes, paleness, fainting, etc.)
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Aspects of emotions
Cognition determines the emotion that
in its type and degree is appropriate to
given situation
 Expression in form of somatic and
autonomic activity during emotional state
 Experience is the subjective aspect, basis
for pleasant and unpleasant emotions
 Excitement may be delight or distress
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Nerve control of emotions
Hypothalamus is often considered as
the seat of emotions. It is the principle
center where various components of
emotional reactions are organized into
definite pattern.
 Stimulation of different parts of
hypothalamus shows different emotional
reactions.
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Nerve control of emotions
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Thalamus – anterior nuclei, dorsomedial
nucleolus, posteroventral nucleous are part of
limbic system.
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Cerebral cortex and limbic system –
amygdaloid nucleous complex, hyppocampus,
hypothalamus, thalamus, ancient cortex – form
“circles” making possible prolonged analyzes
of information, base for behavior and
emotions.
Behavioral program
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