Perception and Processing of Representations of Emotional and Physical

Pain:

Does It All Hurt the Same Way?

Petra E. Pajtás

December 12, 2006

How do we experience pain?

The “pain pathway”: from input to cortex(Image courtesy of Sigma-Aldrich.com)

What is physical pain?

Provoked by noxious stimulus Designed to warn of potential harm Usually results in a motor response to

“get you out of the noxious situation” Mediators: noci-receptors or

hypersensitization of regular receptors

Breaking physical pain into components Sensory discriminative component

-location, intensity, quality “Oh my head, I feel a bad, sharp pain!”

Motivational-affective component-depression, anxiety“Oh, I feel like $*&%! I think I might die!”

Cognitive evaluation + Reflexive component

-figuring out why it hurts, responding“Someone just hit me with a hammer upside

the head; let me run away…”

Willis, 1985

What about emotional pain?

“I know it was wrong, but I got hecka suspicious about her and Charles so I went into her email one day and I saw a letter that she sent to Charles...And after I saw that, it was over. I was so [expletive deleted] mad and so [expletive deleted] hurt, mostly mad. I wanted to throw EVERYTHING and just punch everything I saw... That night that I found out, I couldn't even sleep. I thought I was just gonna die in bed that night, it was just hella hurting. I was just lying there, and the heartache was hurting so bad, it's unexplainable. It starts from the heart, and it spreads throughout your body so the whole body hurts. The heart, the mind, everything about me was dying.”

(uclamangoboy, 2003)

MacDonald, Kingsbury, & Shaw, 2005

So does this guy hurt, physically? Is there a noxious stimulus per say?

Is there a different way to characterize how he feels other than words describing physical pain?

If we asked him to describe the intensity and quality of the pain, what would he say?

The Question:Does emotional pain (which comes without

all the nociceptive processing – suppose) hurt the same way as physical pain?

Cognition?Where does the input go?

Are there any shared cortical mechanisms? The ACC? Activation in response

to painful stimuli (processing/looking for a way out?) (Davis et al., 1997)

Activation to social exclusion (Eisenberger et al., 2003)

Activation correlating with empathy ratings in witnessing the pain of a significant other (Singer et al., 2004)

What does the ACC do? Regulation of autonomic behavior (Critchley et

al., 2003)

ACC activation in conflict resolution (Cohen et al., 1999; Ochsner et al., 2001)

Activation to detect error when a response is possible (Hadland et al., 2002)

Lesions: apathetic, unconcerned, prone to mistakes (Eslinger & Damasio, 1985)

Detecting when strategic control is required (MacDonald et al., 2000)

Metabolically highly active even at rest (Raichle et al., 2001)

Problems with the ACC

Very large region; localizations for each of the references in the previous slide remains inconsistent and often the experiments have not yet been replicated.

If we’re going to look at ACC functioning, we may as well start from scratch.

Hypothesis In the event that emotional pain and the

motivational/affective component of physical pain (“physical pain”) are processed by the same mechanisms, overlapping activation of the ACC is predicted.

If emotional and “physical” pain are processed by different mechanisms – even if these overlap or are similar – only partially overlapping or distinct activation of the ACC is predicted.

Methods – Participants 16 participants (8 female) Right-handed; 18-40 years old Normal or corrected-to-normal vision No color blindness; no past or current

psychiatric or neurological conditions Participants to undergo SCID before

experiment

Methods – Task Participants will be told that they would be

presented images with both physically and emotionally painful stimuli as well as neutral pictures.

They are told that their job is to focus on identifying with the events presented in each of the images; they are also asked to evaluate the degree of pain in each presentation (without providing verbal responses).

Sets of images depicting emotional or physical pain

Sets of images of neutral matched control images

Images normalized for stim intensity; hue and saturation are similar

Images piloted for emotional vs. physical pain depiction…

Methods – Task

Methods – Image Examples

Suggests physical pain(courtesy of fotosearch.com)

Suggests emotional pain(this is debatable – but this is just an example; it’s difficult to find matching pictures)(courtesy of picsearch.com)

Methods – Design-6 functional scans + structurals-block-design, 5 blocks

-emotional p, physical p, emotional n., physical n., fixation

-10 stim per block, presented 2x-begins with fixation for 500 ms-stimulus on screen for 2.5 sec-blank screen for 750 ms

-blocks counterbalanced across scans-new set of 10 stimuli for each scan

Total scan length: 5.4 min each

One-back task 1x per block Just for attentional engagement

Methods – Design & Acquisition

Acquisition:-TR=1.173, TE=30 ms, flip angle = 90°-3 mm slice thickness, 3x3x3 mm voxel size-realignment, normalization, spatial smoothing (FreeSurfer)-HR function via gamma function + derivative(found to be best for this region)

Data Analysis – Whole Brain

Random effects analysis of variance for whole brain data to be conducted

Expected results: increased activity in the ACC for emotional AND physical pain compared to neutral picture viewing

Also, remember that we have to also separate by gender.

Data Analysis – Matched Sets

We split the data into even and odd runs: set 1 (scans 1, 3, 5) and set 2 (scans 2, 4, 6)

We perform the same analyses we do in whole brain ANOVAs, only on half the set this time (we can look at how much power we lost…)

Take the coordinates for the regions we find in set 1 and:

We do the equiv. of whole brain on set 2; then we subtract from the activation maps the coordinates for the regions found in set 1 (one set for ROI EMO, one for ROI PHYS).

What we are left with is everything outside the region of subtraction; with t-tests corrected for multiple comparisons, we can compare voxel-by-voxel activation between what we found in set 1 (including what became ROIs and what we found in set 2).

If we do a SET2EMO – PHYS_ROI and SET2PHYS – EMO_ROI, we can figure out whether the regions for EMO and PHYS overlap.

THIS IS COMPLICATED, make sure you ask me questions (it’s also a good opportunity to confuse me… )

How We Do the Analyses: SET 1:

EMO_FUL BLOCKS – EMO_NEU BLOCKS = EMO1 PHYS_FUL BLOCKS – PHYS_NEU BLOCKS = PHYS1… ANOVA EMO_ROI & PHYS_ROI

SET 2: EMO_FUL BLOCKS – EMO_NEU BLOCKS = EMO2 PHYS_FUL BLOCKS – PHYS_NEU BLOCKS = PHYS2…EMO2 – PHYS_ROI = EMO2_cleanPHYS2 – EMO_ROI = PHYS2_clean

We check if EMO2_clean and PHYS2_clean overlap… -if EMO2_clean and PHYS2_clean >0, there is a non-overlapping region in processing physical and emotional pain;-if subtraction leads a close to 0 result, the processing of physical and emotional pain is done via the same regions.

Expected Results

This says the same thing, just a bit differently; the point is still that results should look something like this with no significant diff. in ACC activity for PHY vs. EMO pain.

Percent Signal of Voxel Activity Accounted For by Each Component

0

20

40

60

80

100

EMO Pain PHYS Pain

Stimulus Separation by Pain Type

Per

cen

t S

ign

al

EMO ROI

PHYS ROI

Interpretations Is the subjective experience still different

despite the ACC being involved in both? Are there differences between women

and men in emotional reactivity? Are our findings

How can we inform the field with out findings?

What follow-ups do we need? Why aren’t these follow-ups feasible? (I’ll tell ya…)

Importance

What we find can help inform what we know about ACC lesions, disorders where emotion and empathy are compromised (alexithymia)

We learn about how the brain processes fear/pain/emotional stressors

Potential Problems Gender, individual variability in capacity to

empathize (despite self-report similarities) Task engagement (one-back task may not

be enough) Splitting into 2 sets may be decimating our

power, but … Because the lit is inconsistent it would be

silly to do ROIs based on other people’s published results…

We shouldn’t have phobics, but what if someone responds aversively to the stimuli… moving in the scanner – trashing data…

Costs

16 hrs. scan time = $8592 (+ $1500 wiggle room for data loss) $50 / subject = $800 $1000 for conference presentation Publication expenses: 5 figures x $600 = $3000 We have RAs working for free…. the beauty of dedicated

students and aspiring grad students Estimated total cost = $14,892+

Questions, Comments, Suggestions?

Thanks Yuhong for breaking down the data analysis to intelligible bits…!

Thanks everyone!