Neuroscience Begins to Shine Light on the Neural Basis of Sensation-Seeking
By Brenda Patoine
Why are some people drawn to intense, even fear-inducing thrills while others shun the mere thought? How is it that the same horror movie can be entertainment to one person and tension-filled torture to another? Is something different going on in the brains of these people?
Sensation-seeking, the tendency to seek out novel experiences, is a general personality trait that has been extensively studied in psychological research, but neuroscience is just beginning to take aim at it. Beyond understanding why one person relishes the fright factor while the next studiously avoids it, scientists are asking how sensation-seeking relates to substance abuse, addiction, and anxiety disorders like Post-Traumatic Stress Disorder, areas where the clinical and public-health implications are most clear.
Some studies suggest that people who seek out high-sensation experiences even at great personal risk—so-called high-sensation seekers—are more vulnerable to drug and alcohol abuse and more likely to engage in other risky behaviors, such as sex with multiple partners. The hope is that by understanding the neural mechanisms underlying such behaviors, both at the molecular level and at the systems level, it might be possible to develop pharmacological or behavioral therapies to prevent or treat addiction or help people channel their taste for adventure toward safer pursuits.
Neuroscience is beginning to tease apart how the brain of a high-sensation seeker might be different from that of someone who generally avoids risk. Recent brain imaging studies have offered some intriguing clues, finding a direct link between the size of the hippocampus and experience-seeking behaviori and shedding light on how the brain responds differently to intense or arousing stimuli in highs vs. lows.
An Overactive ‘Approach’ System?
In a recent study using functional MRI,ii Jane Joseph, Ph.D., and colleagues at the University of Kentucky found that different brain areas are activated in high- vs. low-sensation seekers in response to strongly arousing stimuli. The subjects viewed emotionally arousing pictures—some intensely arousing, others more neutral—while researchers recorded their brain activity. Regardless of whether the pictures were pleasant (e.g., mild erotica) or unpleasant (e.g., a snake poised to strike), the high-sensation seekers showed early and strong activation in the insula. (See Figure 1a.) This brain structure acts in part as a gateway where visceral signals from the body are first received and interpreted by the brain, Joseph says, so it made sense to her team that it was active in high-arousal states.
Figure 1a: Photo courtesy of Jane Joseph, Ph.D.
In contrast, in the low-sensation seekers, insula activity barely rose above baseline levels. (See Figure 1b.) Instead, there was pronounced early activity in the anterior cingulate, a part of the cortex strongly linked to the regulation of emotions (and many other things). In high-sensation seekers, anterior cingulate activation was delayed in relation to the lows, though it eventually reached a similar peak.
Figure 1b: Photo courtesy of Jane Joseph, Ph.D.
These patterns are consistent, the researchers said, with an overactive “approach” system in high-sensation seekers and a stronger emotional-inhibitory response in low-sensation seekers.
As with any brain imaging study, the findings are correlational, and Joseph was careful not to draw conclusions at this point. One hypothesis her team will explore further is that, in lows, the anterior cingulate may be, in effect, putting the brakes on any “arousal” response in the insula. “If you look at the data, you can see that the insula response in the lows starts to rise, just as in the highs, but then the anterior cingulate kicks in and almost seems to deflect the insula response in the low-sensation seekers,” Joseph said.
Novelty and Intensity Key
These findings build on a broad base of psychological science in sensation-seeking dating back to the mid-1900’s. Psychologist Marvin Zuckerman, Ph.D., now an emeritus professor at the University of Delaware, developed the original sensation-seeking scale in 1964 as part of sensory deprivation experiments.iii He came to define the trait generally as a seeking of novel and intense stimuli, and outlined four subtypes representing the various ways sensation-seeking is expressed behaviorally:
- Thrill & Adventure Seeking: the pursuit of physical activities that are exciting, unusual and potentially dangerous (e.g., sky-diving)
- Experience Seeking: stimulation through the mind and senses; the pursuit of unfamiliar and complex environmental stimuli, as through travel or meeting new people.
- Disinhibition: sensation-seeking through engagement with other people; searching for opportunities to lose inhibitions by engaging in variety in sex, alcohol, drugs, etc.
- Boredom Susceptibility: the tendency to be easily bored by familiar or repetitive situations or people, or by routine work.
An Evolutionary Drive?
With its emphasis on novel stimuli, sensation-seeking is closely related to what scientists call “novelty-seeking,” an evolutionarily conserved trait that seems to have had a particular survival advantage in human evolution.
“Homo sapiens were the only group of early hominids to emigrate over the entire world, which entailed great risk, so I think humans as a species are characterized by novelty- and intensity-seeking,” says Zuckerman, arguing that this “must have been an adaptive trait.” Early humans also needed to hunt to survive, and those who were more willing to take risks were likely to be more successful hunters, so a certain degree of risk-taking behavior—fueled by the promise of reward—may be programmed into human DNA.
Like any personality trait, there is a normal, bell-curved distribution of sensation-seeking behavior in the population, with most people falling somewhere in the middle in terms of their appetite for intense, novel stimuli, and smaller proportions at the low and high ends. This makes sense from the evolutionary perspective because “people at either extreme are at a disadvantage,” says Zuckerman. “If you’re taking too much risk you may die before you have a chance to spread your genes around, and if you’re too cautious, you may not have the advantage of obtaining resources (like food and water) that entail some risk.”
The Dopamine Connection
Studies of identical twins suggest that heritability accounts for about 60 percent of individual variance in sensation-seeking behavior, Zuckerman says, and scientists have identified genetic variations that may explain some of these differences. For example, some studies have found that people with higher levels of a specific type of receptor (the D4 receptor) for dopamine, the primary neurotransmitter involved in reward processing, have greater sensation-seeking tendencies.
Other types of dopamine receptors that normally regulate dopamine release appear to have an opposite effect: the fewer there are, the greater the novelty-seeking behavior.iv These may act as brakes on dopamine release, so having fewer of them means that more dopamine is released in response to novelty. This may in turn drive reward-seeking behavior.
The involvement of dopamine in novelty-seeking behavior may also explain the well-established relationship between high sensation-seeking and drug use. High-sensation seekers are more likely to try drugs earlier, to become addicted, and to experiment with multiple drugs than are lows. Like drugs of abuse, exposure to novel stimuli releases a rush of dopamine in reward areas of the brain. And, high-sensation seekers often develop a sort of tolerance to high-risk activities—boredom sets in, and they are compelled to add new twists that recreate the initial charge.
“They get bored,” Zuckerman says. “Even what was initially very exciting becomes blasé when you’ve done it 100 times, so you need something more exciting, something new.”
The same is true for sex, Zuckerman adds. High-sensation seekers may get bored with the same partner, so they seek out new partners or scenarios to try to regain excitement. “You might say that sensation-seeking is the enemy of marital stability,” he says.
Weighing Novelty In Terms of Fear vs. Reward
Sensation-seeking also intersects with the fear system. Individual differences in how the brain responds to fear, balanced with how it is wired for reward, may help explain differences in sensation-seeking.
“There is clearly a component of excitement and novelty involved in thrill-seeking, but there is also likely to be a component of worry and fear,” says Kerry Ressler, M.D., Ph.D., a neurobiologist and psychiatrist at Emory University and a member of the Dana Alliance for Brain Initiatives. He points out that the amygdala, the brain region most associated with fear processing, is the same region involved in addictive and appetitive behaviors.
“Each of us, based on our genetic make-up and environmental influences, has different propensities for being drawn toward something that is attractive and appetitive, and on the opposite side, being averse to things that are dangerous or fearful,” Ressler says. “My guess is that the difference between a thrill-seeking person and someone who is not is probably a combination of the level of reward they get from novelty, thrill, or adventure and how much they’re afraid of it.”
It’s possible, for example, that high-sensation seekers may have a lower set-point for fear extinction—meaning they can more easily turn off, or at least tamp down, the physiological response to a fearful event. They may be able to more effectively engage cognitive brain regions to put a fearsome stimulus into proper context, which is pertinent to some activities.
“Thrill-seekers may be able to use cognitive parts of the brains to recognize that the scary movie or ride isn’t really going to hurt them,” Ressler says. “They can put the brakes on the flight and avoidance response and experience the emotional salience of the fear.”
This may be one reason frightening films are so popular, Zuckerman notes. “People who would never engage in high-risk activities themselves get vicarious excitement from movies,” he says. “They know that the [monsters] aren’t going to jump out of the screen and get them, so they get a little kick of fear in a safe environment.”
In an interview included on the 2004 DVD release of the horror flick The Grudge, Joseph Ledoux, Ph.D., a member of the Dana Alliance and a neurobiologist at Columbia University who studies the fear response, said: “I guess the real reason that we love to be scared so much when we go to the movies is because we get that adrenaline rush in a completely safe context. We don’t have the worry and anxiety that this will actually affect us in a personal and deep way.”
Written by Brenda Patoine, a freelance science writer who has been covering neuroscience for nearly 20 years.
i Martin SB, Covell DJ, Joseph JE, Chebrolu H, Smith CD, Kelly TH, Jiang Y, Gold BT. (2007). Human experience seeking correlates with hippocampus volume: convergent evidence from manual tracing and voxel-based morphometry. Neuropsychologia 45, 2874-2881.
ii Joseph JE, Liu X, Jiang Y, Lynam D, Kelly TH. (2008). Neural correlates of emotional reactivity in sensation seeking. Psychological Science 20(2), 215-223.
iii Zuckerman’s research is described in his recent book: Zuckerman, M. (2007), Sensation Seeking and Risky Behavior. Washington, DC: American Psychological Association.
iv See for example: Zald DH, Cowan RL, Riccardi P, Baldwin RM, Ansari MS, Li R, Shelby ES, Smith CE, McHugo M, Kessler RM. (2008). Midbrain dopamine receptor availability is inversely associated with novelty-seeking traits in humans. J. Neurosci 28(53), 14372-14378.