Neuroimaging in Pain Flashcards
What is the specificity hypothesis in the context of pain, and who proposed it?
- René Descartes in 1664
- Specificity hypothesis of pain = suggested that pain is specific sensation that occurs independently of other sensory modalities & that there are specific receptors for pain
- theory primarily focused on peripheral input w/o much emphasis on the role of the brain
What is episodic analgesia, and how does it challenge the specificity hypothesis?
- where injury occurs without the experience of pain (indicates brain prioritizes survival over pain perception)
- it demonstrates that pain does not always correlate directly with injury
How does the concept of congenital analgesia challenge the specificity hypothesis?
- refers to individuals who are genetically born without the ability to feel pain
- challenges specificity hypothesis bc pain is considered a protective mechanism necessary for survival. If pain were a specific, peripheral response as suggested by the specificity hypothesis, individuals with congenital analgesia shouldn’t exist.
What is phantom limb pain, and how does it challenge the specificity hypothesis?
- individuals experience pain in limb that has been amputated (there is no actual injury in the affected area)
- challenges specificity hypothesis bc shows that pain can occur w/o associated peripheral injury, indicating that brain plays significant role in pain perception
What is the current definition of pain according to the International Association for the Study of Pain (IASP)?
- an unpleasant sensory & emotional experience associated with actual or potential tissue damage, or such described in terms of such damage” (IASP 1994).
- definition acknowledges both bottom-up & top-down influences on pain perception
What are the research goals related to the understanding of pain?
- To understand how cognitive and affective states can alter the response to nociceptive input.
- To understand who is capable of using these mechanisms to cope successfully with pain.
How does MRI (Magnetic Resonance Imaging) work as a medical imaging technique?
- a medical imaging technique that uses strong magnetic fields and radio waves to create images of the body
- works by taking advantage of the different magnetic properties of various biological substances
What can be inferred from the presence of oxygenated blood in MRI images, and how does it relate to studying brain activity?
- Areas w/ more oxygenated blood in MRI images indicate activity in those areas
- can deduce info about time course of oxygenated blood, allowing them to account for a short delay after a stimulus is presented
- can help map regions of brain activated in response to stimuli - often referred to as BOLD (Blood Oxygen Level Dependent) response
How does MRI use voxel-based analysis to study brain activity?
- MRI divides the brain into voxels each containing a BOLD signal
- Researchers model the stimulus-induced change in the signal and then search for voxels with signals that match the predicted response model
- good match implies activation in relation to the stimulus
- different tissues with varying fat-to-water ratios contribute to contrasts observed in MRI imaging
How can the magnetic field be manipulated to optimize sensitivity to the contrast of interest in fMRI?
- By adjusting the parameters of the magnetic field
- they can enhance the ability to detect and visualize specific contrasts in brain activity
What is the typical resolution of fMRI, and what is the minimum duration of a stimulus for effective fMRI analysis?
- fMRI measures brain activity with a resolution of about 1mm.
- at least 2 seconds to capture meaningful data
Why are mock scanners used in fMRI studies, and what is their purpose?
- used to help patients or participants become familiar with the MRI environment
- purpose = acclimate individuals to scanning experience & reduce potential anxiety or discomfort when undergoing an actual fMRI scan
What is the “pain matrix” ?
- set of brain areas commonly associated with perception & processing of pain
- areas often light up in response to painful stimuli
which brain areas are commonly associated with “pain matrix” ?
- anterior cingulate cortex (ACC), insula, thalamus, and S2 region of the brain
- note: the validity of pain matrix and its components is an area of ongoing research and debate in the field
How does the brain respond to the transition from innocuous to painful stimuli, and what type of curve characterizes this response?
- Non-linear Response: The brain’s response to this transition is characterized by non-linear curve.
- Perceptual Shift: This curve represents point where brain activity intensifies, reflecting transition from innocuous to painful sensations
Which brain regions respond in a non-linear fashion during the transition from innocuous to painful stimuli, and how well does this non-linear curve explain people’s pain perception?
- insular cortex, anterior cingulate cortex (ACC) & Periaqueductal Gray (PAG)
- non-linear sigmoidal fit of signals from these regions can explain up to 85% of the variance in individuals’ pain perception, shedding light on how the brain processes and perceives pain
What is perceived control in the context of pain?
- refers to the belief that one can influence the aversiveness of a painful event
What are the behavioural responses to prolonged uncontrollable stress?
- Reduced motivation.
- Impaired learning.
- Increased negative affect.
What is the concept of learned helplessness?
- It’s an animal model where animals experience inescapable stress.
- Results in giving up and learning difficulties.
- Relates to the experiences of some chronic pain patients
Do all animals exposed to uncontrollable stress respond the same way?
- No, responses vary.
- Two groups of animals emerge: those displaying learned helplessness and those continuing normal responses.
- Research investigates factors influencing these different responses.
Why is understanding variability in responses important in clinical settings?
- It helps comprehend different reactions in chronic pain patients.
- Offers insights into potential interventions and treatments
What are the effects of low perceived control over pain?
- Increased depression.
- Increased pain severity.
- Increased functional disability
What are the research goals regarding perceived control and pain processing?
- Understand how perceived control alters pain processing.
- Explore who can effectively cope with uncontrollable pain
Describe the Salomons 2004 study on perceived control of pain.
- Subjects manipulated their perception of controllability using cues.
- In the controllable condition, they could reduce the hot stimulus duration.
- Response time had to be below a “response threshold.”
What factors were manipulated in the Salomons 2004 study?
Perception of controllability.
Hot stimulus duration.
Response time to cues.
What were the implications of the Salomons 2004 study?
- The study explored how perceived control over pain affects pain processing.
- It investigated factors that influence coping with uncontrollable pain.
What were the conditions in the Salomons 2004 study regarding perceived control over pain?
-Controllable condition: Subjects could reduce the hot stimulus duration.
- Uncontrollable condition: Subjects were asked to respond but were told their response would have no effect.
- Both conditions had the same 5-second shock; the difference was in perceived control
What brain regions respond to pain in both controllable and uncontrollable situations?
- Insula & dorsal ACC respond to pain in both conditions.
- these regions process sensory input (bottom-up) and the perception of control (top-down).
How does the activation of the pain matrix differ in controllable and uncontrollable pain situations?
-pain matrix seems to be more activated in uncontrollable pain, but self-reported pain ratings do not differ significantly
How does perceived control over pain influence pain tolerance and anticipatory anxiety?
- Perceived controllability over pain increases pain tolerance.
- It decreases anticipatory anxiety.
- The effects on self-reported pain perception vary among individuals based on the meaning of control.
What were the prefrontal responses to uncontrollable pain and how did they influence pain ratings?
-In anticipation of pain, activation in ventral lateral prefrontal cortex leads to lower pain intensity ratings.
- Activation in ventral medial prefrontal cortex during pain associated with higher pain intensity ratings
What strategy did individuals who had anticipation responses to pain use, and how did it influence their emotional response?
- individuals with anticipation responses used an emotion-focused coping strategy, meaning they coped with consequences of pain & limited their emotional response
What brain regions underlie individual differences in coping with uncontrollable pain?
- Emotion regulation regions, including the ventral lateral prefrontal cortex (vlPFC) and ventral medial prefrontal cortex (vmPFC), underlie these differences.
- these regions involved in pain & other emotional responses
How do brain regions involved in the pain matrix respond to cognitive context?
- Pain matrix regions are sensitive to cognitive context of pain experience - not just the pain itself but also the context in which it occurs (controllable/uncontrollable)
What are the limitations of using imaging studies with small sample sizes?
- Small sample sizes may not be representative.
- Long-term effects after the study completion are unclear.
Why is it important to study the emotional responses of chronic pain patients in terms of how they respond to uncontrollable pain?
- Chronic pain patients often experience uncontrollable pain, which influences their emotions.
- Understanding emotional responses in such individuals requires designs where one group experiences only uncontrollable events and vice versa
How did the study by Salomons and colleagues use fMRI to explore the effects of perceived control over pain?
- study involved 52 healthy subjects exposed to either prolonged controllable or uncontrollable pain.
- goal was to examine the impact of perceived control on neuronal and affective responses to pain.
What were the conditions in the study regarding perceived control over pain for the two groups?
- controllable group: Received pain stimuli & feedback on their responses; believed they could control pain duration.
- uncontrollable group: Received same stimuli but told their responses had no effect; believed they couldn’t control pain.
How did the controllable and uncontrollable groups differ in terms of anxiety levels before and after the experiment?
- controllable group had less anxiety after the experiment, while the uncontrollable group had increased anxiety.
- perception of control reduced anxiety in the controllable group
What brain regions were involved in regulating emotional responses to pain, and how did they relate to the perception of control?
- Amygdala & nucleus accumbens played role in regulating emotional responses
- amygdala associated with fear & emotional responses, while the nucleus accumbens was linked to reward & pleasure
- perceived control reduced anxiety & was considered rewarding.
- these regions involved in other emotional regulation tasks
What did the study find regarding functional connectivity in brain regions related to emotional regulation?
- study observed functional connectivity between the amygdala & nucleus accumbens with the ventrolateral prefrontal cortex (vlPFC).
- Functional connectivity between these regions correlated with reduced anxiety and emotional regulation
- Similar patterns found for the ventromedial prefrontal cortex (vmPFC)
How did the prefrontal cortex (PFC) regions, vlPFC and vmPFC, impact emotional responses in the context of perceived control over pain?
- The PFC regions regulated affective centers in the striatum & amygdala, essentially helping control the limbic & emotional areas
- Individuals who could recruit vlPFC and vmPFC to regulate these regions benefited from having control.
- controllable group as a whole exhibited more functional connectivity in these areas
In patients with temporomandibular disorder (TMD), what is the relationship between brain structures and self-reported helplessness?
- The study aimed to explore gray and white matter structural correlates of self-reported helplessness in TMD patients.
- Three regions were found to be associated with the degree of perceived helplessness: supplementary motor area (SMA) thickness correlated with higher helplessness, while middle cingulate cortex (MCC) thickness was inversely correlated.
- These correlations were specific to the patient group and not observed in healthy controls
How did the study examine connectivity patterns related to helplessness, and what was the outcome?
- study examined white matter tracts connecting SMA and MCC, using water diffusion measures.
- found that these regions were connected to a network across the brain, including the medial prefrontal cortex (mPFC), thalamus, putamen, and the brainstem, particularly the PAG.
- White matter structure along the corticospinal tract (CST) adjacent to the premotor cortex, in brainstem adjacent to the pons & other regions predicted individual differences in perceived helplessness
How do brain structures impact individual differences in coping with chronic pain and perceived control?
- structure of control motor planning & salience regions like the middle cingulate cortex (MCC) & associated white matter tracts were linked to differences in perceived control & helplessness in TMD patients
- Perceived control over pain reduces activation in cortical salience regions commonly activated in pain (e.g., anterior cingulate cortex, insula)
- the ventromedial prefrontal cortex (vmPFC) and ventrolateral prefrontal cortex (vlPFC) modulate the response to perceived control, helping control primary affect regions like the amygdala & nucleus accumbens
- Individuals who can use vmPFC and vlPFC-mediated regulation strategies cope better when behavioral control is unavailable (connected to limbic circuits)
How are motor areas involved in pain processing and emotional responses?
- Motor areas implicated in pain along with sensory regions
- an individual who had significant damage to brain regions e.g. amygdala, insula, vmPFC, and ACC was still able to show emotional responses to pain and regulate them in certain situations.
- this suggests that brain plasticity or limitations of neuroimaging tools may affect the specificity of our understanding
What are some limitations of the study, and how do they affect the interpretation of the results?
- A limitation of fMRI is that subjects cannot move, restricting their responses to pain as they would occur naturally.
- Brain plasticity may allow brain to rewire & perform important functions even when specific regions are damaged
- Neuroimaging tools may not capture relationships as specifically as desired
Is activation in specific brain regions necessary for pain or pain modulation? Is it sufficient?
-s tudy involved a ball-throwing game where subjects experienced social exclusion, leading to anterior cingulate activation, which was initially considered part of the pain matrix.
- interpretation was that social exclusion was painful due to overlapping circuitry, highlighting risks of inferring function from brain activation
What is reverse inference in functional neuroimaging research, and why can it be problematic?
- Reverse inference = use of brain activation data to identify mental processes engaged during a task.
- relies on logical errors (affirming the consequent), assuming that activation in a brain region implies a specific mental state.
- this approach can be problematic bc brain regions may activate in response to multiple mental processes, making it challenging to attribute activation solely to a specific mental state
How specific is activation in the “pain matrix” for pain?
- cognitive control, negative affect, & pain are all associated with anterior cingulate activation
- Activation in the anterior cingulate region does not exclusively indicate pain, as it is activated in response to various stimuli and tasks
What was observed in an fMRI study involving non-painful tactile stimuli, loud noises, and attention-grabbing visual stimuli?
- “pain matrix” activated in response to all these stimuli, suggesting that highly attention-grabbing stimuli requiring a response can lead to activation in pain matrix
- the pain matrix may not be specific to pain but instead responsive to salient or emotionally engaging stimuli
How can multivariate pattern analysis (MVPA) be used to differentiate between different mental states in brain activation?
- MVPA examines spatial patterns of activation to distinguish between distinct mental states
- this approach aims to identify specific patterns of brain activation associated with different mental states, potentially allowing detection of pain (or other conditions) based on unique patterns.
