Sharks have this incredible ability to pick up nanoscopic currents while swimming through "a blizzard of electric noise," researchers say. Photo / Clinton Duffy/DoC
Imagine having superhuman hearing.
You're at a noisy party and yet your ears can detect normally inaudible sounds made by your friends' muscles as they lean in to dish the latest gossip.
But, unlike normal hearing, each of these sounds causes your ears to react in the same way.
There is no difference between the quietest and loudest movements.
To your superhuman ears, they all sound loud, like honking horns.
According to a new US study, that may be how a shark's electro-sensing organ reacts when it detects tiny electrical fields emanating from nearby prey.
"Sharks have this incredible ability to pick up nanoscopic currents while swimming through a blizzard of electric noise," Professor David Julius, of the University of California, San Francisco, said.
"Our results suggest that a shark's electrosensing organ is tuned to react to any of these changes in a sudden, all-or-none manner, as if to say, 'attack now'."
The team showed that the shark's responses may be very different from the way the same organ reacts in skates, the flat, winged, evolutionary cousins of sharks and sting rays, and this may help explain why sharks appear to use electric fields strictly to locate prey while skates use them to find food, friends, and mates.
They also showed how genes that encode for proteins called ion channels may control the shark's unique "sixth sense".
"Ion channels essentially make the nervous system tick," co-author Nina Schor explained.
"They play a major role in controlling how information flows through a nervous system."
Mutations in ion channels could be devastating, and have been linked to a variety of disorders, including cystic fibrosis and some forms of epilepsy, migraines, paralysis, blindness and deafness.
"Studies like this highlight the role a single ion channel can play in any nervous system, shark, skate, or human."
US scientists have shown in mice how to erase the brain's underlying desire for sweet and its distaste for bitter.
Their new study in the scientific journal Nature also showed that removing an animal's capacity to crave or despise a taste had no impact on its ability to identify it.
The findings suggest that the brain's complex taste system - which produces an array of thoughts, memories and emotions when tasting food - are actually discrete units that can be individually isolated, modified or removed altogether.
The research points to new strategies for understanding and treating eating disorders including obesity and anorexia.
"When our brain senses a taste, it not only identifies its quality, it choreographs a wonderful symphony of neuronal signals that link that experience to its context, hedonic value, memories, emotions and the other senses, to produce a coherent response," study author Dr Charles S Zuker, of Columbia University, said.
He and colleagues had previously demonstrated that when the tongue encounters one of the five tastes - sweet, bitter, salty, sour or umami - specialised cells on the tongue send signals to specialised regions of the brain so as to identify the taste, and trigger the appropriate actions and behaviours.
To shed light on that experience, the scientists focused on sweet and bitter taste and the amygdala, a brain region known to be important for making value judgments about sensory information.
"Our earlier work revealed a clear divide between the sweet and bitter regions of the taste cortex," co-author Dr Li Wang explained.
"This new study showed that same division continued all the way into the amygdala.
"This segregation between sweet and bitter regions in both the taste cortex and amygdala meant we could independently manipulate these brain regions and monitor any resulting changes in behaviour."
The scientists performed several experiments in which the sweet or bitter connections to the amygdala were artificially switched on, like flicking a series of light switches.
When the sweet connections were turned on, the animals responded to water as if it were sugar.
And by manipulating the same types of connections, the researchers could even change the perceived quality of a taste, turning sweet into an aversive taste, or bitter into an attractive one.
In contrast, when the researchers turned off the amygdala connections but left the taste cortex untouched, the mice could still recognise and distinguish sweet from bitter, but now lacked the basic emotional reactions, like preference for sugar or aversion to bitter.
"It would be like taking a bite of your favourite chocolate cake but not deriving any enjoyment from doing so," Wang said.
"After a few bites, you may stop eating, whereas otherwise you would have scarfed it down."
Regrets, we've probably all had a few, to paraphrase Sinatra.
But the most enduring ones are those that stem from our failure to live up to our ideal selves.
Cornell University researchers have found people are haunted more by regrets about failing to fulfill their hopes, goals and aspirations than by regrets about failing to fulfil their duties, obligations and responsibilities.
Their study, just published in the journal Emotion, builds on the idea that three elements make up a person's sense of self: the actual, ideal and the ought selves.
The actual self is made up of the attributes a person believes they possess; the ideal self is the attributes they would ideally like to possess, such as hopes, goals, aspirations or wishes; the ought self is the person they feel they should have been based on duties, obligations and responsibilities.
Psychologist Tom Gilovich and former Cornell graduate student Shai Davidai surveyed hundreds of participants through the course of six studies, describing the differences between the ought and ideal selves, and asking them to list and categorise their regrets based on these descriptions.
The participants said they experienced regrets about their ideal self far more often (72 per cent versus 28 per cent).
More than half mentioned more ideal-self regrets than ought-self regrets when asked to list their regrets in life so far.
And when asked to name their single biggest regret in life, 76 per cent of participants mentioned a regret about not fulfilling their ideal self.
Why do ideal-self failures spark such enduring regret?
The expectations of the ought self are usually more concrete and involve specific rules - such as how to behave at a funeral - and so are easier to fulfil.
But ideal-related regrets tend to be more general: be a good parent, be a good mentor.
"Well, what does that mean, really?" Gilovich said.
"There aren't clear guideposts. And you can always do more."
The research had practical implications, he said.
First, we often assume we first need inspiration before we can strive to achieve our ideals.
But a significant amount of psychological research showed that was not true, Gilovich said.
"As the Nike slogan says, just do it. Don't wait around for inspiration, just plunge in.
"Waiting around for inspiration is an excuse. Inspiration arises from engaging in the activity."
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