Shopping Centers in the Brain

That is Alain Dagher’s clever name for brain centers involved in buying decisions (2007). If you’ve had that urge to buy something, but then decided it was too expensive, or you already had too many CDs with that particular rock band, you’ve had the experience. The question is: What brain regions are involved? Do they contribute to conscious experiences or not? Surely a lot of our buying decisions are partly unconscious.

In a recent issue of Neuron, Knutson et al (2007) “support the theory that the decision to purchase involves the integration of emotional signals related to the anticipation of both obtaining the desired product and suffering the financial loss of paying for it.”

What are the brain centers for shopping? One of them has been described as the node in the brain that converts motivations into actions. It is the “nucleus accumbens” (the clump of neurons that looks like its leaning, as the early anatomists called it in their Latin vocabulary). It’s a tiny structure that is part of the basal ganglia, the giant output hub of the brain. Nucleus Accumbens (N Acc) plays a role in reward, pleasure, and even addiction. According to Wikipedia, “In addition to cocaine and amphetamine, almost every drug abused by humans has been shown to increase dopamine levels in the nucleus accumbens.” Knutson and coworkers looked at fMRI activation in the N Acc while subjects were looking at something to buy. N Acc activity predicted their buying decision.It is also the famous “pleasure center” of the brain, studied by Olds and Milner in the 1950s by inserting a tiny electrode in this area and allowing rats to press a bar to receive a small electrical zap. Rats preferred self-stimulation in N Acc to eating, and some are said to have come near starvation to pursue their addiction to electrical stimulation in the pleasure center. Knutson and coworkers looked at fMRI activation in the N Acc while subjects were looking at something to buy. N Acc activity predicted their buying decision.

But most pleasurable goods cost money – what brain structures evaluate whether the promised reward is worth the cost? In humans, voluntary decisions usually involve the prefrontal cortex, the most distinctively human part of the brain. Conflicts between gains and losses usually activate the midline portion of the prefrontal cortex – on the inside of each of the hemispheres. This is the Medial Prefrontal Cortex.

So, as Dagher asks, does that mean that Knutson et al. have found the shopping centers in the brain? Not so fast –

“One must be careful in interpreting fMRI data from individual experiments. For example, although the N Acc 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 N Acc activation on novelty, unpredictability, salience … independently of reward or preference. We must remember that the BOLD (fMRI) signal is dependent on the activity of neural inputs into an area … brain activity here may also be related to attention … or anxiety …” (Dagher, 2007)

So car dealers shouldn’t rush out to buy an fMRI machine yet. And for SCR we want to ask an additional question: Is N Acc activity conscious? Most scientists would say that the basal ganglia do not contribute directly to conscious contents. But there are plenty of ways for the N Acc to activate cortical regions that may yield conscious experiences, like the insular cortex.

So there are lots of unanswered questions. But then, five or ten years ago, few people would have predicted that we could observe even this much about an everyday experience like shopping.

References

1. Dagher, A. (2007) Neuron 53, January 4, 7-8.
2. Knutson, B., Rick, S., Wimmer, G.E., Prelec, D.,and Loewenstein, G. (2007). Neuron, 53, 147–156.