lecture 6 Flashcards
aversive stimulus applied AFTER habituation results in
reflex responsiveness/vigour Is RESTORED
Dishabituation undoes the effects of prior habituation
what happens to reflex responsiveness / vigour after aversive stimulation if is has NOT previously been habituated
responsiveness and vigour increases= reflex sensitisation
sensitisation occurs mainly in
defensive reflexes , avoidance and related reflexed like orienting and startle reflexes
sensitisation is the opposite effect
to habituation and is responsible for dishabituation - undoing the effects of habituation
sensitisation differs from habituation
occurs quickly - reaches maximum quickly and fewer stimuli are needed
non specific - effects of habituation are confined to the elicited response but sensitisation affects all defensive avoidance and relatedness
sensitisation exhibits both
short and long term forms
short term
a SINGLE aversive stimulus may be sufficient to produce a short term sensitisation effect that lasts from a few minutes to a few hours
more aversive stimuli are needed to produce a
noticeable effect
long term
repeated sessions separated by several hours produce a long term effect that can last days/weeks
dual process theory
2 simultaneously active process - habituation and sensitisation
opposite effects -
habituation - reduces reflex responsiveness
sensitisation - increases reflex responsiveness
the dual process theory proposes that
habituation is always engaged by an eliciting stimulus
sensitisation process may be engaged- depends upon how aversive/arousing the stimulus is
when an eliciting stimulus is presented both processes
are engaged , depend on which process has the larger effect
if the eliciting stimulus is NON AVERSIVE
the habituation process proceeds and the responsiveness of the reflex declines
if the eliciting stimulus is AVERSIVE
habituation process is still automatically engaged but its effects are COUNTERACTED by a STRONGER SENSITISATION process- so responsiveness INCREASES
No stimulation
neither process is engaged
non aversive
habituation engaged
sensitisation weakly engaged
aversive
sensitisation is strongly engaged
habituation weakly engaged
what happens if both processes have equal strengths
both processes engaged but CANCEL each other out
reflex responsiveness does not change
what is the neural basis of reflex habituation
habituation effects are observed in very simple neural circuits in simple animals like sea slugs and worms
gill withdrawal reflex
reflex mediated by a simple neural circuit
connectivity is both mono and disynaptic
Sensory neuron connects
monosynaptically with the motoneuron
interneuron disynaptically
a brief tickle of the siphon elicits a
rapid gill withdrawal
a few tickles repeated with an ISI inter stimulus interval will
quickly habituate the response
what changes in the circuit as a result of repeated tickling
the effectiveness (strength) of the synaptic connections
the synaptic terminals of the SN’S release
less transmitter substance in response to the arrival of AP’S - So less excitatory effect on interneuron and motor neuron
this strength change only happens if the effects of the
previous transmitter are PRESENT when the next release occurs
a short inter stimulus interneuron is needed if its too long
the effects of previous stimulus have worn off - no change
long term habituation
if sessions of repeated tickling with short inter stimulus interneurons are repeated a long term effect is produced
structural changes of habituation
reduced number of changes - pruning
reduction of efficacy/strength - homosynaptc depression
gill withdrawal reflex
short term sensitisation
presynaptic connections cause increased neurotransmitter release - increase in withdrawal response strength
opposite of short term habituation
long term sensitisation
produced by a series of sessions of shock delivery
associated with structural changes in the synaptic connections - increased in the number of connections
short term sensitisation undoes the
changes associated with short term habituation but not long term habituation
are all learned changes a result of habituation or sensitisation
no
person standing on an horizontal platform
it unexpectedly and rapidly tilts through- toes up direction - produces a quick stretch of the calf muscle
the stretch will evoke a stretch reflex response
what happens when you make tilts a random intervals -
habitual protocol but it is not
why is it not an habituation effect
reduction is only present if the person continues to stand up
if they sit or lie down , response is back to normal
in a sitting position stretches of the calf muscle produces
no change in reflex response amplitude
reduction cannot be
dishabituated by presenting aversive stimuli
decline in calf muscle stretch reflex was due to
a contraction of the calf muscle when standing in this posture PULLS you backwards - destabilising effects on upright posture
associative learning g
animal learns to suppress a reflex response that has unwanted consequences
non associative learning
habituation and sensitisation = no consequences
