Tag: Scientific American

Junk food makes rats lose appetite for balanced diet

Coverage: Scientific American, TIME, CNN, Discovery News, IFLS, Newsweek, RedOrbit

A diet of junk food not only makes rats fat, but also reduces their appetite for novel foods, a preference that normally drives them to seek a balanced diet, reports a study published in the open-access journal Frontiers in Psychology.

The study helps to explain how excessive consumption of junk food can change behavior, weaken self-control and lead to overeating and obesity.
The team of researchers, led by Professor Margaret Morris, Head of Pharmacology from the School of Medical Sciences, UNSW Australia, taught young male rats to associate each of two different sound cues with a particular flavor of sugar water – cherry and grape.

Healthy rats, raised on a healthy diet, stopped responding to cues linked to a flavor in which they have recently overindulged. This inborn mechanism, widespread in animals, protects against overeating and promotes a healthy, balanced diet.

But after 2 weeks on a diet that included daily access to cafeteria foods, including pie, dumplings, cookies, and cake – with 150% more calories – the rats’ weight increased by 10% and their behavior changed dramatically. They became indifferent in their food choices and no longer avoided the sound advertising the overfamiliar taste. This indicated that they had lost their natural preference for novelty. The change even lasted for some time after the rats returned to a healthy diet.

The researchers think that a junk diet causes lasting changes in the reward circuit parts of the rats’ brain, for example, the orbitofrontal cortex, an area of the brain responsible for decision-making. They say these results may have implications for people’s ability to limit their intake of certain kinds of foods, because the brain’s reward circuitry is similar in all mammals.
“The interesting thing about this finding is that if the same thing happens in humans, eating junk food may change our responses to signals associated with food rewards,” says UNSW Professor Morris. “It’s like you’ve just had ice cream for lunch, yet you still go and eat more when you hear the ice cream van come by.”

The World Health Organization estimates that over 10% of the world’s adult population is obese and at least 2.8 million people die each year as a result of being overweight or obesity. Overweight and obesity are major risk factors for a number of chronic diseases, including diabetes, cardiovascular diseases and cancer.

“As the global obesity epidemic intensifies, advertisements may have a greater effect on people who are overweight and make snacks like chocolate bars harder to resist,” adds Dr Amy Reichelt, lead author of the paper and UNSW postdoctoral associate.

EurekAlert! PR: http://www.eurekalert.org/pub_releases/2014-08/f-jfm082514.php

Study: http://journal.frontiersin.org/article/10.3389/fpsyg.2014.00852/full

A neurological basis for the lack of empathy in psychopaths

Selected coverage: Scientific American, WebMD

When individuals with psychopathy imagine others in pain, brain areas necessary for feeling empathy and concern for others fail to become active and be connected to other important regions involved in affective processing and decision-making, reports a study published in the open-access journal Frontiers in Human Neuroscience.

Psychopathy is a personality disorder characterized by a lack of empathy and remorse, shallow affect, glibness, manipulation and callousness. Previous research indicates that the rate of psychopathy in prisons is around 23%, greater than the average population which is around 1%.

To better understand the neurological basis of empathy dysfunction in psychopaths, neuroscientists used functional magnetic resonance imaging (fMRI) on the brains of 121 inmates of a medium-security prison in the USA.

Participants were shown visual scenarios illustrating physical pain, such as a finger caught between a door, or a toe caught under a heavy object. They were by turns invited to imagine that this accident happened to themselves, or somebody else. They were also shown control images that did not depict any painful situation, for example a hand on a doorknob.

Participants were assessed with the widely used PCL-R, a diagnostic tool to identify their degree of psychopathic tendencies. Based on this assessment, the participants were then divided in three groups of approximately 40 individuals each: highly, moderately, and weakly psychopathic.

When highly psychopathic participants imagined pain to themselves, they showed a typical neural response within the brain regions involved in empathy for pain, including the anterior insula, the anterior midcingulate cortex, somatosensory cortex, and the right amygdala. The increase in brain activity in these regions was unusually pronounced, suggesting that psychopathic people are sensitive to the thought of pain.

But when participants imagined pain to others, these regions failed to become active in high psychopaths. Moreover, psychopaths showed an increased response in the ventral striatum, an area known to be involved in pleasure, when imagining others in pain.

This atypical activation combined with a negative functional connectivity between the insula and the ventromedial prefrontal cortex may suggest that individuals with high scores on psychopathy actually enjoyed imagining pain inflicted on others and did not care for them. The ventromedial prefrontal cortex is a region that plays a critical role in empathetic decision-making, such as caring for the wellbeing of others.

Taken together, this atypical pattern of activation and effective connectivity associated with perspective taking manipulations may inform intervention programs in a domain where therapeutic pessimism is more the rule than the exception. Altered connectivity may constitute novel targets for intervention. Imagining oneself in pain or in distress may trigger a stronger affective reaction than imagining what another person would feel, and this could be used with some psychopaths in cognitive-behavior therapies as a kick-starting technique, write the authors.

EurekAlert! PR: http://www.eurekalert.org/pub_releases/2013-09/f-anb092313.php

Study: http://journal.frontiersin.org/article/10.3389/fnhum.2013.00489/full