The stick, the carrot, and the brain

Sometimes it seems easy to discern good from bad. Surviving in complex environments requires the ability to repel stimuli that might lead us to harmful consequences. Likewise, we might spend time and energy pursuing goals that maximize our benefit and pleasure. As such, we tend to choose Gondor over Mordor. Gryffindor over Slytherin. Or being a marine biologist and tracking gray whales on their migratory routes across the Pacific Ocean over becoming a neuroscientist and working the whole day sitting in front of a computer and reading about affective stuff.

Complex organisms are fully adapted for detecting and responding to positive and negative stimuli or situations. For years, researchers have addressed the neurobehavioral mechanisms that allow us to discern between good and bad, or –put in motivation-related terms– reward and punishment.

Behaviorally, reward and punishment are not processed in equivalent ways. There is a well-documented asymmetry between them: the processing of negative stimuli is prioritized over positive stimuli, a phenomenon known as the negativity bias (1,2). This means, when facing good stimuli and bad stimuli with equal intensities, bad stimuli tend to yield greater attentional and affective processing relative to good stimuli. As such, compared with positive events, negative events elicit stronger and more rapid responses, have more powerful effects on human relationships, and are recalled more accurately (1,2).

As an example of this, this Saturday I was in the city center with my BF just looking around and buying some stuff. At some point, he suggested we could sit and drink a coffee somewhere. My BF’s favorite café in Leipzig is a small cafeteria full of tourists and with a small outdoors terrace. I don’t really like it because it is always crowded, and it is more expensive that some other nice places that are not far away. Anyways, we ended there. We just sat on a table, when all the sudden, in the next table –placed less than half a meter from ours– a group of 10 Dutch girls in their eighteens sat there to have ice-cream. They spoke so loud (OMG!). We could not even have a conversation! Then, the waiter came, so I told him in my perfect German accent ‘Hallo, ich möchte ein Espresso, bitte’. The waiter just looked at me, raised his eyebrows and asked me again what I would like to have, this time in English (!!?!) I hate when this happens. Seriously. What is the German word for being grumpy because I am sitting in a place that I have not chosen by myself, surrounded by loud tourists and because, according to the waiter, my German is not good enough? Anyways, I was being totally unfair. I did not have any valid reason to be grumpy. That morning, Leipzig looked lovely, I did not have to worry about work and I was just having a great time with my awesome-and-patient BF, who just wanted to sit down and have a nice coffee with me somewhere. So, I tried to calm down and start looking at the world in a positive manner. Well, actually it also helped that another table far from the ten eighteen years old tourists got free, so we moved there, and it was sunny and lovely. Sometimes you face good things and bad things at the same time, but you can always choose where to pay attention.

So, enough anecdotes about positive and negative stimuli, an exciting paper that revolves around the asymmetry “bad > good stimuli” has been published recently. In line with previous studies, the authors found that monetary losses had 2-3 times a stronger effect on behavior than monetary gains (3). Interestingly, the authors provided further evidence that reward and punishment might guide behavior in a differential way. That is, on one hand, monetary reward was able to influence choice according to the magnitude of the event. As such, gaining 25 cents produced comparatively higher probabilities of repeating a given behavior relative to gaining 5 cents. Conversely, the effect of monetary losses on choice behavior followed a constant function. Thereby, losing money was associated with lower probabilities for repeating a certain behavior, no matter if the monetary loss was 5 cents or 25 cents (3).

This last finding is kind of cool and also kind of unexpected. Basically, it describes the fact that punishment might affect behavior, independent on the magnitude of the punishment. It is tempting to extract conclusions out of this and, for example, to recommend tram inspectors in Leipzig not to charge with 40 € bills when someone does not have a valid ticket, but rather deliver 5 € fines because the effect will be the same. Well, actually, public transport should be free for everybody! Nevertheless, it is better to be cautions by now and to see if this same effect can be detectable by using different range of monetary penalties (e.g., from 1$ to 100 $ instead of from 5 cents to 25 cents) as well as other negative stimuli that might be more biologically relevant (e.g., pain stimuli or negative social feedback).

At the neural level, and as I already mentioned in a previous post, it is known that positive/appetitive stimuli and negative aversive stimuli present huge overlapping patterns of brain activity, including the amygdala, anterior insula, and ventral striatum (4,5). However, it is plausible that, at the cellular level, these structures undergo microscopic modifications that depend on the valence of the stimuli (positive versus negative). Due to technical limitations, these changes would not be detectable with current MRI resolutions.

According to this possibility, a recent study in rodents from Namburi et al. suggests that brain circuits linking the amygdaloid complex with the nucleus accumbens might encode the valence of the stimuli (6). The authors reported that the nucleus accumbens and the centromedial amygdala contain populations of basolateral neurons that suffer opposing synaptic modifications following fear conditioning or reward learning. As such, in the centromedial amygdala projectors, fear conditioning causes increases in synaptic strengths, while reward learning is linked with decreases in synaptic strengths. Conversely, synaptic strengths onto nucleus accumbens projectors were observed to decrease following fear conditioning and to increase following reward learning (6).

There is still lot of work to be done in order to translate Namburi’s exciting findings to humans. And at a behavioral level, using Baumeister et al.’s own words, bad seems to be stronger than good “in a disappointingly relentless pattern” (1). But, nevertheless, it is also useful to remember that the asymmetry “bad > good” might provide us with the motivation we need in order to keep on searching for happiness and creating a better world.

REFERENCES         

 

  1. Baumeister RF, Bratslavsky E, Finkenauer C, Vohs KD. Bad is stronger than good. Rev Gen Psychol. 2001; 5(4):323–70.
  2. Ito TA, Larsen JT, Smith NK, Cacioppo JT. Negative Information Weighs More Heavily on the Brain : The Negativity Bias in Evaluative Categorizations has noted a tendency for negative events to result in a greater. J Pers Soc Psychol. 1998; 75(4):887–900.
  3. Kubanek J, Snyder LH, Abrams RA. Reward and punishment act as distinct factors in guiding behavior. Cognition. 2015; 139:154–67.
  4. Lindquist KA, Satpute AB, Wager TD, Weber J, Barrett LF. The Brain Basis of Positive and Negative Affect: Evidence from a Meta-Analysis of the Human Neuroimaging Literature. Cereb Cortex. 2015; 1–13.
  5. Hayes DJ, Duncan NW, Xu J, Northoff G. A comparison of neural responses to appetitive and aversive stimuli in humans and other mammals. Neurosci Biobehav Rev. 2014; 45C:350–68.
  6. Namburi P, Beyeler A, Yorozu S, Calhoon GG, Halbert SA., Wichmann R, et al. A circuit mechanism for differentiating positive and negative associations. Nature. 2015; 520(7549):675–8.
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