habituation, sensitization and familiarization psyc 414

habituation

decrease in the strength or occurrence of a behavior after repeated exposure to the stimulus that produces that behavior

simple examples of habituation

often involve a single, easily controlled stimulus

and a single easily measurable response

acoustic startle reflex

a defensive response (jumping/freezing) to a startling stimulus (loud noise)

orienting response

an organism’s innate reaction to a novel stimulus

habituation to one event does not cause

habituation to every other stimulus in the same sensory modality

in some cases, presenting a novel stimuli

can lead to recovery of responses after an individual has habituated to familiar stimuli

renewal of responding after a new stimulus has been presented

dishabituation

habituation is

stimulus specific

not a result of fatigue

how rapidly a response habituates and how long the decrease in responding lasts depend on several factors

• how arousing the stimulus is

• the number of times it is experienced

• the length of time between repeated exposures (massed vs spaced)

short-term habituation

lasts a few minutes or several hours

long-term habituation

lasts a day or more

spontaneous recovery

a stimulus-evoked response that has habituated reappears after a period of no stimulus presentations

sensitization

phenomenon in which an arousing stimulus leads to stronger response to a later stimulus

fewer presentations of stimuli required

not stimulus specific

novel object recognition task

an animal is allowed to explore two objects

after some delay the animal is presented with one copy of the original object and one novel object

amount of time spent exploring each object is measured

less time spent exploring original object interpreted as

recognition of or familiarity with the original object

priming

phenomenon in which prior exposure to a stimulus can improve the ability to recognize that stimulus later

priming in humans is often studied using a word-stem completion task

participants are asked to fill in the blanks in a list of word stems (eg, MOT_) to produce the first word that comes to mind; in a priming experiment, participants are more likely to produce a particular word (ex- MOTEL) if they have been exposed to that word previously

priming in blue jays

they eat moths, but moths have evolved patterns to effectively blend into the background

asked to indicate whether a virtual moth is present

prior detection of a “species” increased speed and accuracy

priming occurs in the absence of

any feeling of familiary/recognition that the stimulus was previously experienced

perceptual learning

repeated experiences with a set of stimuli make those stimuli easier to distinguish

statistical learning

form of perceptual learning that occurs without explicit training

percepts that individuals learn the most about

are those that are experienced most frequently and consistently

perceptual learning is similar to priming

in that it leads to more effective processing on subsequent encounters with the stimuli

perceptual learning occurs even if

the learner is not aware of changes to perceptual sensitivities

cognitive map

an internal psychological representation of the spatial layout of the external world

latent learning in rats

rats must make a series of left/right choices

curtains block view of door

rats can only pass through each door in one direction

goal is to reach the “food box" in as few turns as possible

never rewarded rats

allowed to wander through the maze until they reached the “food box”, but it did not contain food

always rewarded rats

“food box” contained a food reward every time

rewarded starting on day 11 rats

“food box” did not contain a food reward for the first 10 days, but then a food reward was provided in the “food box” starting on the 11th day

latent learning

unconnected to a consequence and remains undetected until explicitly demonstrated at a later stage

familiarity

the perception of similarity that occurs when an event is repeated

subregions of hippocampus

• dentate gyrus (DG)

• Cornu Ammonis 3 (CA3)

• CA1

• Subiculum (Sub)

firing rate (Hz)

#of action potentials/duration of time

spatial ratemap

firing rate of a neuron is represented as a function of space

small area of increased activity

place field

place cell

neuron with spatial coding, when it spikes we know where the rat is in the environment

each square

is a spatial ratemap for one neuron

different place cells

code for different locations

all together there are place fields covering the entire open field

place map or cognitive map

place fields are created regardless of

task demands

stimulus specificity

habituation to one stimuli does not cause habituation to other stimuli

aplysia (sea hare) have

20,000 neurons

as simple as aplysia are, however, they are still capable of adapting their behavior in response to experience

aplysia show habituation, sensitization, and several other forms of learning just as rats and humans do

habituation of gill-withdrawal reflex

1st touch of siphon results in large amplitude gill withdrawal

subsequent touches of siphon result in smaller gill withdrawal (spontaneous recovery)

habituation to siphon contact

new stimuli in form of neck contact (dishabituation)

gill-withdrawal reflex/siphon-withdrawal reflex

when danger threatens, the aplysia reflexively retract its siphon and gills in order to protect them from damage

neural circuits in aplysia gill-withdrawal reflex

somatosensory input to the siphon (or tail or mantle) will activate respective sensory neurons

sensory neurons release the neurotransmitter glutamate at synapses onto motor neurons

motor neurons innervate muscles that retract the gill

in the aplysia gill-withdrawal reflex there are a limited number of points for system to change

to cause change in behavior

since each individual neuron involved in the gill-withdrawal reflex have been identified

change at each point can be investigated

with subsequent touches

there is less glutamate

touching siphon

stimulates sensory neuron S similarly

sensory neuron S releases less glutamate with each action potential

causing less excitation of motor neuron M (membrane potential is not moved toward threshold as much)

less excitation of motor neuron M means

the gill muscles are not activated as much and the gill is withdrawn less

fewer vesicles containing glutamate are positioned at presynapatic release site

form of synaptic depression (reduction in synaptic transmission)

number of action potentials remains the same

but each spike has less effect on the postsynaptic neuron

homosynaptic plasticity

specific to synapses involved in habituation

tail and mantle sensory neurons remain unchanged

stimuli coming into tail and mantle still elicit normal gill withdrawal (stimulus specificity)

longer term habituation requires

structural change

spaced presentation of stimuli over multiple days

results in change in number of synapses

number of presynaptic terminals onto sensory neurons

is reduced , thus reducing excitatory drive onto motor neurons

sensitization in Aplysia

an aversive shock to the tail results in an exaggerated gill-withdrawal response to a siphon or mantle touch

shock stimulates the tail sensory neuron

but some change happens in the processing pathway of the other sensory neurons

interneuron excited by tail sensory neuron synapses

on siphon and mantle sensory neurons (axo-axonic synapse)

releases serotonin (neuromodulator)

due to sensitization

siphon and mantle sensory neurons now have more glutamate vesicles available to be released

heterosynaptic plasticity

occurred at the siphon and mantle sensory neuron synapses onto the motor neuron (different pathways)

process of altering synaptic transmission at synapses not involved with processing the initial stimulus

more glutamate

results in greater excitation of motor neuron

greater gill withdrawal