the contextual brain Flashcards
what is peripersonal space?
peripersonal space is the region of space immediately surrounding the body in which objects can be grasped and manipulated
what is hemi-spatial neglect in the peripersonal space?
tactile stimulus can be detected when it is presented on contralateral side alone
when stimulus is presented on both sides, contralateral side cannot be detected
the further away the stimulus is presented from peripersonal space, the more accurately is can be identified
what is the hand-blink reflex and how is it effected by peripersonal space?
HAND BLINK REFLEX = shows existence os defensive per-personal space
painful stimuli is delivered to hand, resulting in a motor response at eye mediated by brainstem
when hand is close to face, reflex increases (compared to hand far from face)
HOWEVER blink reflex is only increased when hand starts far away and moves closer to face
no change in blink reflex when hand starts close to face and moves further away
when screen is placed between hand and face, there is no difference when hand changes proximity
shows there is a fast and dynamic association with reflexes
is periperonal space modualted by bottom-up or top-down processing?
strong ‘top-down’ influence as brainstem-mediated reflex can be dynamically modulated.
what is the difference between placebo hypoalgesia and placebo hyperglesia?
placebo hypoalgesia = reduction in pain attributed to treatment context
placebo hyperalgesia = nocebo = increase in pain attributed to treatment context
what are three ways to induce placebo hypoalgesia?
verbal suggestion:
explicit statement re. effectiveness of a treatment
response conditioning:
associate a cue with a biased input in an induction phase to create the expectation of effectiveness
e.g. associate inert cream with high-intensity stimulus and treatment cream with low-intensity stimulus
pharmacological conditioning:
associate a cue (inert treatment) with an active drug in induction phase to create an expectation of effectiveness
how is the endogenous opioid mechanism implicated in placebo hyperalgesia
placebo hypoalgesia engages the the endogenous opioid system
evoked pain with thermal stimulus delivered to hand, presented stimuli at different strength to modify perception
dose given of radioactive tracer has no physiological effect
—> able to measure binding of receptors
—> does not activate opioid receptors
reduction in binding potential = less sites available = endogenous opioids taking up space
high binding potential = more sites available = reduction of opioid production
found increase in opioid binding and release in frontal areas (anterior cingulate, orbital) as well as nucleus accumbens, amygdala, thalamus
how is the PAG-RVM-spinal cord axis implicated in placebo hyperalgesia
as part of the descending pain modulatory system:
peri-aqueductal grey (PAG) → rostro-ventromedial medulla (RVM) → spinal cord
involved in reduced pain processing and fear aversion
MODULATION OF AMYGDALA (implicit):
• input from amygdala to PAG depends on endogenous opioids
• implicated in pre-cognitive placebo (conditioning phase)
MODULATION OF FRONTAL AREAS (explicit):
• frontal cortical areas disinhibit PAG to inhibit pain signal
• relies on mental schema of context
