Recent research published in Mapping the human brain The study sheds light on the neural mechanisms of associative learning related to Internet use behaviors, with a particular focus on online gaming and pornography. The study found that pornographic stimuli are more strongly associated with reward responses in the brain than monetary and gambling stimuli in healthy men.
Although appetitive conditioning—a process by which neutral stimuli are associated with rewards—has been widely studied with traditional rewards like money and food, there is little research on how it works with Internet-related stimuli.
Appetitive conditioning is a learning process in which a neutral stimulus is paired with a rewarding unconditioned stimulus, leading to conditioned responses such as increased pleasure and arousal. For example, a neutral sound (conditioned stimulus) may be repeatedly paired with food (unconditioned stimulus) until the sound alone elicits salivation (conditioned response).
Pornography and video games are two of the most common activities linked to Internet addiction, but the neural mechanisms underlying their conditioning processes are not well understood. Previous research has shown that specific brain areas, including the orbitofrontal cortex, anterior cingulate cortex, insula, amygdala, nucleus accumbens, and thalamus, are involved in reward processing.
However, how these areas respond to Internet-related rewards versus traditional rewards remains unclear. In their new study, the researchers sought to fill this gap by studying how the brain learns to associate rewards with these stimuli in a healthy, non-disease context.
The study involved 31 healthy, right-handed male participants, aged 19 to 38, who were specifically selected to control for gender differences in reward processing. Before the main experiment, participants were asked to choose their favorite images from three categories: pornographic photographs, game screenshots, and images of money. This personalized selection process ensured that the stimuli were truly rewarding for each participant.
The experimental procedure was performed using a classical conditioning paradigm in an MRI scanner. Conditioning consisted of repeatedly associating geometric figures (conditioned stimuli or CS) with chosen rewarding images (unconditioned stimuli or UCS).
Four types of CS were used: one for each type of reward (pornography, gambling, and money) and one control. Across 68 trials, the CS+ (conditioned stimuli associated with rewards) was followed by the UCS 62.5% of the time, while the control CS- was never followed by a reward. This setup allowed the researchers to observe how the brain learns to associate neutral stimuli with rewarding outcomes.
To measure responses, the researchers used three different methods. Subjective ratings were collected to assess the pleasure and arousal of each CS before and after the conditioning process. Skin conductance responses (SCRs) were recorded to measure physiological arousal by tracking changes in sweat gland activity, providing an objective measure of participants’ autonomic nervous system responses. Finally, functional MRI (fMRI) scans were used to record brain activity, allowing the researchers to observe how different brain regions responded to stimuli and map the neural correlates of reward processing.
The study found significant differences in how participants responded to the different stimuli. In terms of subjective evaluation, all three types of CS+ (pornography, money, and gambling) were rated as more pleasant and arousing than the control CS- after the conditioning process.
Pornographic stimuli were rated significantly more arousing than gambling stimuli, indicating a stronger affective response to pornography. SCR data confirmed these findings, showing higher levels of physiological arousal during presentation of CS+ for pornography, money, and gambling compared to the control group, demonstrating successful conditioning.
The fMRI results provided insight into the brain’s response to these stimuli. The anticipation of pornographic rewards led to increased activity in key brain areas associated with reward processing, including the bilateral nucleus accumbens, right medial orbitofrontal cortex, and right ventral anterior cingulate cortex. These findings suggest that pornographic stimuli have high reward value and can significantly activate the brain’s reward circuitry.
In contrast, despite the increase in subjective ratings and SCR, monetary stimuli did not elicit significant brain activity compared to the control group, indicating a weaker neural response. Similarly, gambling stimuli did not significantly activate reward-related brain areas in fMRI scans, even though subjective ratings and SCR data indicated successful conditioning.
The study results suggest that pornographic stimuli have a higher reward value and stronger conditioning effects than monetary and playful stimuli. This is evidenced by the significant neural activation observed during the anticipation of pornographic rewards, as well as the increased subjective evaluations and physiological responses. These findings are consistent with previous research indicating that pornography has a high addictive potential due to its strong affective and arousal properties.
In contrast, the weaker neural responses to monetary and playful stimuli, despite successful conditioning in both subjective and physiological measures, suggest that these rewards may be less effective in activating brain reward systems in non-pathological users. This highlights the complexity of reward processing and suggests that different types of rewards may engage distinct neural mechanisms.
The study, “Appetitive Conditioning with Pornographic Stimuli Elicits Stronger Activation in Reward Regions Than Monetary and Gambling Stimuli,” was authored by Kseniya Krikova, Sanja Klein, Miriam Kampa, Bertram Walter, Rudolf Stark, and Tim Klucken.