REWARD/PUNISHMENT DOPAMINE AND MECHANISMS OF REWARD AND PUNISHMENT

Punishment is becoming a growing element in today’s political arenas. Those who support Donald Trump have been suggested by some to be an anxious lot looking for some way to PUNISH those they hate and/or fear, such as illegal immigrants. Those who support Hillary Clinton and Bernie Sanders appear to be out to PUNISH the evil rich who have more than their “fair share.” Scientific studies are discussing the rise of punitive (e.g., punishing) gods, such as those in Christianity, Islam, and Judaism, considering the existence of such gods to promote cooperation in human society. (Johnson, 2016; Purzycki, 2016.) Everywhere we see a search for somebody to do the punishing that they believe needs to be done.

What is it in the Brain of Humans that Regulates the Pursuit of Reward or Punishment?

DOPAMINE

“One hallmark of adaptive behavior is the ability to learn from the outcomes of actions, whether these results are positive or negative.” (Paton and Louie, 2012) Recent research suggests that the neurotransmitter DOPAMINE plays a leading role in this adaptive behavior by signaling the difference between a REWARD and a PUNISHMENT and selecting the physical action to be taken in response to it.

A recent paper (Paton and Louie, 2012) identified two types of dopamine receptors, D1 and D2, that are instrumental in responding to reward and punishment, respectively. D1 dopamine neurons in the medial prefrontal cortex control food intake, for example (Land, 2014). Another recent paper (Engel, 2014) reported that some hormones have been identified as playing an important role in reinforcing food intake, an inherently rewarding process. This includes ghrelin and GLP-1 (glucagon like peptide-1). (Engel, 2014) GLP-1 has also been shown to control the rewarding properties of substances such as alcohol, nicotine, amphetamine, and cocaine. In sum, the authors of this paper (Engel, 2014) suggest that the gut hormones ghrelin and GLP-1 that activate the ghrelin and GLP-1 receptors may be novel targets for development of pharmacological treatments of alcohol and drug dependence.” And also for treatment of food addiction.

Moreover, a mechanism has been identified to explain in part how these molecules foster addiction: they activate the vitally important reward system in which the cholinergic and dopaminergic nervous systems interact. Importantly, this interaction links these neurotransmitter systems to experimental findings that show that eating is initiated by a dopaminergic signal and is terminated by a cholinergic signal. (Hoebel, 2007; Rada, 2000) This hub in which the neurotransmitter systems interact is a target for the complex process of food addiction as well as other addictions.

The D1 receptors induce LTP (long term potentiation) by increasing the excitability of medium spiny neurons (a type of neuron responsive to the inhibitory neurotransmitter GABA), while the D2 receptors have the opposite effect, inducing LTD (long term depression) (Paton and Louie, 2012).

Stimulation of the D1 receptors (the “direct pathway” of dopaminergic signaling in the medium spiny neurons) “increased locomotion and decreased freezing” while stimulation of D2 receptors (the “indirect pathway”) resulted in decreased locomotion, increased freezing, and bradykinesis (slower movement). Thus, the rewarding pathway leads to movement and goal seeking of rewards, while the punishment pathway leads to signs of fear and anxiety (freezing) and depression (slower movement, less movement).

In their study, the researchers (Kravitz, 2012) reported that electrically stimulating the direct pathway in mice mimics reward, while the same treatment via the indirect pathway mimics punishment. Moreover, they found that there was an “asymmetry in the temporal longevity of stimulation effects, with positive reinforcement effects outlasting the transient punishment effects of activation.” “Overall, the results of Kravitz et al highlight a fundamental point about decision-making: selecting an action is never truly independent of reward learning (Paton and Louie, 2012).

The latter effect is interesting. People tend to pay more attention to the effect of positive information (that provides a REWARD because it supports your beliefs), as compared to negative information when they reconsider their beliefs.

References

• Engel and Jerlhag. Role of appetite-regulating peptides in the pathophysiology of addiction: implications for pharmacotherapy. CNS Drugs. 28(10):875-86 (2014).
• Hoebel et al. Accumbens dopamine-acetylcholine balance in approach and avoidance. Curr Opin Pharmacol. 7:617-627 (2007).
• Johnson. Hand of the gods in human civilization. Nature. 530:205-207 (2016).
• Kravitz AV, Tye LD, Kreitzer AC. Distinct roles for direct and indirect pathway striatal neurons in reinforcement. Nat Neurosci. 15(6):816-8 (2012 Jun).
• Land BB, Narayanan NS, Liu RJ, Gianessi CA, Brayton CE, Grimaldi DM, Sarhan M, Guarnieri DJ, Deisseroth K, Aghajanian GK, DiLeone RJ. Medial prefrontal D1dopamine neurons control food intake. Nat Neurosci. 17(2):248-53 (2014 Feb).
• Paton and Louie. Reward and punishment illuminated. Nat Neurosci. 15(6):807-9 (2012).
• Purzycki et al. Moralistic gods, supernatural punishment and the expansion of human sociality. Nature. 530:327-330 (2016).
• Rada PV, Mark GP, Yeomans JJ, Hoebel BG. Acetylcholine release in ventral tegmental area by hypothalamic self-stimulation, eating, and drinking. Pharmacol Biochem Behav. 65(3):375-9. (2000).