Eating, having sex, and making money are rewarding pursuits that drive human behavior. The degree of motivation that compels someone to obtain edible, erotic, or economic rewards varies from person to person and fluctuates from adolescence to old age. That said, a new meta-analysis identifies how basal ganglia brain regions typically process food, sex, and money rewards.
These findings (Arsalidou et al., 2020) were published online ahead of print on January 11 in the journal Brain Imaging and Behavior. This meta-analysis of 190 different fMRI studies involving a total of 5,551 participants was conducted by researchers at the Higher School of Economics (HSE) University and the University of Toronto.
What Are the Basal Ganglia?
Basal ganglia refers to interconnected subcortical structures of gray matter (e.g., the caudate, globus pallidus, and putamen) nestled below the cerebral cortex and above the midbrain.
Historically, basal ganglia brain regions were viewed primarily as part of the motor system that facilitates the physical actions required to obtain a reward or achieve a particular goal. However, there is increasing evidence that basal ganglia brain regions are also involved in a wide range of cognitive and emotional functions.
After the cerebral cortex sends a motor command to pursue a reward, the basal ganglia orchestrate the appropriate physical actions via skeletal muscle movements. Basal ganglia brain regions play a key role in driving hard-wired habitual behaviors associated with substance use disorders and addiction.
In recent years, countless studies have shown that brain regions in the basal ganglia facilitate reward-driven behaviors. What makes this recent (2020) meta-analysis of 190 different brain imaging studies significant is that it unearths how food, sex, and money rewards engage specific clusters of neurons in the basal ganglia and favor other brain regions in slightly different ways.
"The connection between these [basal ganglia] nuclei and other areas of the brain depends on the reward type," lead author Marie Arsalidou, who is an assistant professor of psychology at HSE, said in a news release.
During every decision-making process, different brain regions work in concert to determine the size of a given reward and to make an assessment of how much sacrifice and risk are involved in obtaining the reward. Identifying how the brain processes different types of rewards advances our understanding of the human decision-making process and has significant real-world implications.
Hypothetically, readers of the Old Testament could speculate about how various regions of Eve's basal ganglia were activated in the Garden of Eden when she decided to take a bite of "forbidden fruit" from the tree of knowledge and then shared the apple with Adam.
Food and sex are classified as "primary rewards" because they've been essential for the survival of our species since the dawn of time.
Money is considered a "secondary reward" because it's a human creation that, in and of itself, isn't necessary for survival. Of course, money is required to buy food and other rewards in modern society and having financial resources can make a potential mate more desirable.
Through this quantitative meta-analysis, Arsalidou et al. were able to identify how the basal ganglia coordinates whole-brain functions by engaging distinct cortical and subcortical brain regions depending on the type of reward. The authors write:
"Common to all reward types was concordance in basal ganglia nuclei, with distinct differences in hemispheric dominance and spatial extent in response to the different reward types. Food reward processing favored the right hemisphere; erotic rewards favored the right lateral globus pallidus and left caudate body. Money rewards engaged the basal ganglia bilaterally, including its most anterior part, nucleus accumbens."
Based on these findings, the authors propose a new, multi-pronged model for reward processing in the basal ganglia that addresses the commonality of reward-driven behavior in the nuclei but also differentiates between food, money, and sex-related rewards.
Marie Arsalidou, Sagana Vijayarajah, and Maksim Sharaev. "Basal Ganglia Lateralization in Different Types of Reward." Brain Imaging and Behavior (First published online: January 11, 2020) DOI: 10.1007/s11682-019-00215-3