Saturday, October 27, 2007

My Amygdala Is Very Optimistic Today...

...and my rostral anterior cingulate cortex imagines a brighter tomorrow.

I don't know what all those pigs are doing in the posterior half of the brain, however. Oink.

Doesn't everyone love a forcefully-worded headline?
Source of ‘optimism’ found in the brain
Now we know! At least what counts as ‘optimism’ is put in quotes in the New Scientist headline above. Not so at Reuters:
Brain regions responsible for optimism located

By Will Dunham

WASHINGTON (Reuters) - Imagine receiving a big chunk of cash in the future. Or winning a prize.

Chances are, such optimistic thoughts are coming from two places in the brain that play an important role in enabling people to, as the old song says, accentuate the positive, New York University scientists said on Wednesday.

Pinpointing the brain regions involved in optimism and positive thinking about the future, the researchers said, may also have shed light on what might be going wrong in people with depression.
Does this count as being overly optimistic? Why yes, yes it does.

by Cory Morgan.
We Have Pie Charts.

The headlines were describing a new study on the "neural mechanisms of optimism bias" just published in Nature (Sharot et al., 2007). The amygdala! It's not just for fear any more. Now it's for optimism as well (although the current tally is 1,621 to 1). The amygdala (LeDoux, 2007) is indeed known for its role in fear conditioning.

Figure 4 (LeDoux, 2007). Auditory fear conditioning pathways. The auditory conditioned stimulus (CS) and somatosensory (pain) unconditioned stimulus (US) converge in the lateral amygdala (La). The La receives inputs from each system via both thalamic and cortical inputs. CS–US convergence induces synaptic plasticity in La such that after conditioning the CS flows through the La to activate the central amygdala (CE) via intraamygdala connections. Outputs of the Ce control the expression of emotional reactions involving behavioral (freezing) and autonomic and endocrine responses that are components of the fear reaction. Other abbreviations: B, basal amygdala; CG, central gray; LH, lateral hypothalamus; ITC, intercalated cells of the amygdala; PVN, paraventricular nucleus of the hypothalamus.

Imagining the Future

In the optimistic fMRI study (Sharot et al., 2007), participants were cued to either remember (past) or imagine (future) certain scenarios, for instance:
6. receiving a large amount of money
7. visiting a museum
8. going to a first session of a class
9. taking a day trip
10. meeting a significant other for the first time
11. car crash
Then each trial was classified as positive, negative, or neutral according to the subjects' ratings.
After scanning, participants rated their memories and projections on six factors related to their subjective experience. ... Finally, participants completed the LOT-R (Life Orientation Test-Revised) scale that measures trait optimism.

Previous studies with this sort of task have shown that remembering the past and imagining the future activate a similar network of brain regions (including medial prefrontal cortex, parahippocampal gyrus, posterior cingulate, and occipital cortex), with more extensive activity (premotor cortex, precuneus, and the cerebellum) generally observed in the future condition (Szpunar et al., 2007). The main contrasts in the current experiment are illustrated in the figure below. Four regions of interest were identified: rostral anterior cingulate cortex (rACC), posterior cingulate cortex (PCC), dorsal medial prefrontal cortex (DMPFC), and the right amygdala.

adapted from Fig 2 of Sharot et al. (2007): BOLD signals in both c, the amygdala and d, the rACC reduced while imagining negative future events [relative to positive future events and to all past events].

Still, it doesn't seem that those two areas are related to optimism per se. So the authors
...identified voxels within the four functional ROIs in which changes in BOLD signal during future positive trials relative to future negative trials were correlated with participants' optimism score on the LOT-R scale. We found a positive correlation in the rACC. No significant correlation with optimism was observed in the other ROIs. Finally, a functional connectivity analysis revealed a strong correlation between activity in the rACC and activity in the amygdala bilaterally while imagining future positive events; this correlation was weaker and less extensive when imagining future negative events.
This seems somewhat bizarre to me in light of previous studies. For example, high scores on trait rumination were associated with enhanced activity in rACC and right amygdala when participants were merely looking at negative pictures, relative to when they were trying to decrease their emotional responses, "consistent with the notion that ruminators may tend to chronically recruit medial prefrontal regions engaged in negative self-referential processing" (Ray et al., 2005). How does this relate to the optimistic rACC and amygdala in the current study? We don't really know. Nonetheless, the authors conclude:
These findings may provide insight to the mechanisms underlying depression. Depressive symptoms are associated with pessimism and with difficulties in creating detailed images of future events. It has been suggested that malfunction of a neural pathway incorporating the rACC and the amygdala may cause depression by leading to decreased regulatory affects of the rACC over the amygdala and other regions involved in emotional processing.
And how does this study really relate to rACC function in depression? Stay tuned!


LeDoux J. (2007). The amygdala. Current Biology 17: R868-R874.

Ray RD, Ochsner KN, Cooper JC, Robertson ER, Gabrieli JD, Gross JJ. (2005). Individual differences in trait rumination and the neural systems supporting cognitive reappraisal. Cog Affect Behav Neurosci. 5:156-68.

Sharot T, Riccardi AM, Raio CM, Phelps EA. (2007). Neural mechanisms mediating optimism bias. Nature. Oct 24; [Epub ahead of print].

Humans expect positive events in the future even when there is no evidence to support such expectations. For example, people expect to live longer and be healthier than average, they underestimate their likelihood of getting a divorce, and overestimate their prospects for success on the job market. We examined how the brain generates this pervasive optimism bias. Here we report that this tendency was related specifically to enhanced activation in the amygdala and in the rostral anterior cingulate cortex when imagining positive future events relative to negative ones, suggesting a key role for areas involved in monitoring emotional salience in mediating the optimism bias. These are the same regions that show irregularities in depression, which has been related to pessimism. Across individuals, activity in the rostral anterior cingulate cortex was correlated with trait optimism. The current study highlights how the brain may generate the tendency to engage in the projection of positive future events, suggesting that the effective integration and regulation of emotional and autobiographical information supports the projection of positive future events in healthy individuals, and is related to optimism.

Szpunar KK, Watson JM, McDermott KB. Neural substrates of envisioning the future. Proc. Natl. Acad. Sci. Published online before print January 3, 2007. OPEN ACCESS ARTICLE.

Flies are buzzing around my head
Vultures circling the dead
Picking up every last crumb
The big fish eat the little ones
The big fish eat the little ones
Not my problem give me some

-- Radiohead, Optimistic

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At October 27, 2007 10:17 PM, Anonymous Anonymous said...

Liz Phelps has done some very interesting work, so I don't want to second guess her before I have read the paper, but the experiment, as described, sounds a lot like the nicely described remains of a busted experiment. Also, the reliability of the LOT-R is like 0.6 to 0.8, and the construct validity, as usual, is difficult to ascertain. I am not an emotions researcher, but it's not clear to me why people do not operationalize something like optimism in a more concrete way: ask people for their predictions of outcome on (say) a Bernoulli trial and do this enough times to really have firm data. Then classify people as optimists if their predictions for success significantly exceed the true base rate, pessimists if they are significantly less than the base rate, and, uh, realists for those who seem to be well calibrated. You can, if you need to, classify single trials where people seemed to be in an optimistic state (relying on short run departures from base rate) vs. pessimistic vs. realistic, and see if brain activation during the prediction task differs due to state or trait. You don't need any of the weird trial verbiage or instruments like the LOT-R. And yet...nobody seems to do this. Oh well...

At October 27, 2007 11:07 PM, Blogger The Neurocritic said...

I agree, Realistically, that Phelps and colleagues have done some excellent work. It seems this particular result, however, is out of left field, i.e. a busted experiment. Published in Nature, how nice. It's not like any other research on the amygdala (reviewed in Phelps, 2006, for instance) would support a role in "optimism."

Your idea for operationalizing optimism is a good one. But it requires more work than just giving people a questionnaire...

At October 28, 2007 7:35 AM, Anonymous Anonymous said...

The Neurocritic writes:
Your idea for operationalizing optimism is a good one. But it requires more work than just giving people a questionnaire...

Plus the results would likely conflict with those found in an important paper published in Nature.


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