Wednesday, January 10, 2007

Neuroshopping

We now return to The Neuroshopping Channel!! Before the last commercial break, Brenda had placed a $7 bid on a box of Godiva chocolates. How will her brain respond when she finds out the consequences? Let's take a look.

Back to you, Bob Barker!

Yes, it's true, an fMRI study on consumer decisions was published in Neuron this month. A shopping task (with the witty and original acronym of S.H.O.P. for "Save Holdings Or Purchase") was performed by subjects in the scanner. It consisted of
a series of trials, identical in temporal structure, in which subjects could purchase products. Subjects saw a labeled product (4 s), saw the product’s price (4 s), and then chose either to purchase the product or not (by selecting either "yes" or "no" presented randomly on the right or left side of the screen; 4 s), before fixating on a crosshair (2 s) prior to the onset of the next trial.
from Knutson et al. (2007)

What were the results? Let's step back a bit. Why was this experiment done in the first place, other than to get written up in the newspaper (and to get a bunch of hits from a Google news search)?
Neuroeconomic methods offer the hope of separating and characterizing distinct components of the purchase decision process in individual consumers.
This is a consumer culture, right?

OK, so the neurogoal was to look at activity in the brain's "reward center" aka nucleus accumbens, which receives input from dopaminergic neurons in the ventral tegmental area. This mesolimbic dopamine pathway has been linked to reward, pleasure, and addiction. Other regions of interest included the medial prefrontal cortex (called mesial in the article, but that word annoys me so I'll use the synonym medial), which the authors linked to gain prediction errors, and the insula (now famous because of its spindle neurons), which was linked to loss prediction. These regions were defined in economic terms in the Introduction, which also discussed previous studies of product preferences. Thankfully, I had not heard of the study in which
men who view pictures of preferred versus nonpreferred brands of beer show increased MPFC activation, and women who view pictures of preferred versus nonpreferred brands of coffee also show increased MPFC activation (Deppe et al., 2005).
[Don't women drink beer? Don't men drink coffee?]

Since we already knew what to expect from the Introduction, the figure below comes as no surprise. Preference was correlated with activation in the NAcc, price differential (i.e., the difference between what the subject was willing to pay and the displayed price of the product) was correlated with activation in MPFC, and purchasing was correlated with deactivation of the bilateral insula.

from Knutson et al. (2007)

There were a bunch of other brain regions listed in 3 tables, but the functional significance of these activations wasn't discussed. The paper's main selling point (so to speak) was that brain activation in all three regions significantly predicted purchasing (determined by logistical regression).
Knutson B, Rick S, Wimmer GE, Prelec D, Loewenstein G. (2007). Neural predictors of purchases. Neuron 53: 147-56.

Microeconomic theory maintains that purchases are driven by a combination of consumer preference and price. Using event-related fMRI, we investigated how people weigh these factors to make purchasing decisions. Consistent with neuroimaging evidence suggesting that distinct circuits anticipate gain and loss, product preference activated the nucleus accumbens (NAcc), while excessive prices activated the insula and deactivated the mesial prefrontal cortex (MPFC) prior to the purchase decision. Activity from each of these regions independently predicted immediately subsequent purchases above and beyond self-report variables. These findings suggest that activation of distinct neural circuits related to anticipatory affect precedes and supports consumers' purchasing decisions.
Adding to the general glee surrounding the publication of this paper, the Neuron Preview article is entitled, Shopping Centers in the Brain. The author, Alain Dagher, does mention some reasons for caution in interpreting the results:
So, are there shopping centers in the brain? One must be careful in interpreting fMRI data from individual experiments. For example, although the NAcc was activated by product preference in this study, it does not necessarily follow that it encodes this value. Other fMRI studies have demonstrated a dependence of NAcc activation on novelty, unpredictability, salience (Zink et al., 2003), or a change in contingency (Cools et al., 2002), independently of reward or preference.
That's all for now. There's a 36 page supplement to the 10 page article. I really couldn't make it through all the analyses that ruled out alternate explanations of the data, such as product familiarity and price. However, a portion of the shopping list is presented below.
24 DVD Set: Season 1
256 MB MP3 Player
Big "S" Pillow
Brita Aquaview System
Catch Phrase Game
CD Wallet (224-Disc Capacity)
Collateral DVD
Color Flow Lamp
Curb Your Enthusiasm DVD
Digital Voice Recorder
Fact or Crap Game
Eternal Sunshine Of The Spotless Mind DVD
Freakonomics
Godiva Chocolate
Harry Potter Box Set
Jenga Truth or Dare
References

Dagher A. (2007). Shopping centers in the brain. Neuron 53: 7-8.

Deppe, M., Schwindt, W., Kugel, H., Plassman, H., and Kenning, P. (2005). Nonlinear responses within the medial prefrontal cortex reveal when specific implicit information influences economic decision making. J. Neuroimaging 15: 171–182.

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