- Email: [email protected]
Sweat ducts make skin a memristor
THIS WEEK
How sweat pores give skin memory Kate McAlpine
pore. Conversely, a positive potential pushes the ions back, thinning the layer of sweat lining the pore walls and increasing the skin’s resistance to current. Whether this behaviour helps skin function isn’t clear but Yuriy Pershin of the University of South Carolina in Columbia, who has studied memristive behaviour in amoebas, describes the skin’s role in processes such as temperature regulation as “primitive intelligence”. A new understanding of skin’s electrical properties could have
a current that meets with a much higher resistance. In other words, the skin has a memory of previous currents. The finding is due to be published in Physical Review E. The researchers attribute skin’s memristor behaviour to sweat pores. Sweat contains positively charged ions such as sodium. When skin is exposed to a “The involvement of skin in negative potential, the fluid at regulatory processes can the bottom of the sweat pores is be considered a form of drawn upward. Although a thin primitive intelligence” layer of fluid always coats the inside of the cylindrical pore, this layer thickens as the sweat rises. implications for medicine. As sweat is highly conductive, Resistance to alternating current extra fluid rising to the surface is already used to diagnose skin increases skin’s surface abnormalities, says Johnsen’s conductivity and thereby lowers colleague Andrew Lütken. its resistance if a subsequent Williams, meanwhile, is potential is applied. gratified by the interest in The longer skin is exposed to a memristors. “It is very interesting negative potential, the lower the to me to see the range of the fields subsequent resistance, until it that can benefit from application maxes out when sweat fills the of memristor theory.” n
THE missing link of electronics, which evaded discovery until 2008, was at our fingertips the whole time. Ordinary human skin behaves like a memristor, a device that “remembers” the last current it experienced and varies its resistance accordingly. In 1971 Leon Chua of the University of California, Berkeley, came up with the notion of a resistor with memory. He showed mathematically that this memristor should be a fourth basic circuit element alongside the familiar trio of resistor, capacitor and inductor. But it wasn’t until 2008 that a team led by Stanley Williams, director of HP’s Information and Quantum Systems lab in Palo Alto, California, finally made one from a speck of titanium dioxide. Synapses, junctions between neurons in the brain, display electrical behaviour that depends Memristor skin on past activity and are said to Applying a current across sweat pores turns skin into a memristor, a device behave like memristors. This has that changes its resistance depending on the last voltage applied raised the prospect of using memristors as the basis of an Negative potential Positive potential artificial brain. — + from electrode from electrode Now, by re-examining data from the early 1980s on the electrical conductivity of human + + skin in response to various voltages, Gorm Johnsen and his SWEAT PORE colleagues at the University of Oslo in Norway have uncovered + + a more prosaic example of SODIUM IONS + memristive behaviour in nature. They found that when a + + negative electrical potential is applied to skin on various parts + of the arm, creating a current, + that stretch of skin exhibits a low + resistance to a subsequent current SWEAT flowing through the skin. But + + + + if the first potential is positive relative to the skin, then a Conductive fluid drawn up sweat Conductive fluid flows down sweat pore helping current to flow across it pore, increasing pore’s resistance subsequent potential produces 16 | NewScientist | 5 March 2011
Following the herd can shift your opinion ALL your friends praise a film you just watched. Instead of admitting how dull you found it, you agree. We all sometimes mute our own beliefs like this, but it seems there is more to this than a little white lie. Conforming to others’ views can cause a real shift in your own opinion. That’s the conclusion of Jamil Zaki at Harvard University and colleagues, who asked men to rate how attractive they found a series of photos of women’s faces. The men were then given the average rating for each photo, said to be determined by a previous group. In reality, these ratings were randomly generated by a computer. Thirty minutes later, the participants reassessed the same photos while having their brains scanned using fMRI. As expected, the men’s ratings changed to match the consensus scores more closely. However, Zaki’s team found that if the participant decided a woman was more attractive than they first thought, there was a spike of activity in the orbitofrontal cortex and nucleus accumbens; if they decided she was not as pretty, activity decreased in these areas. Previous research has shown that the higher the activity in these brain regions, the more a person values a certain stimulus. In other words, the researchers argue, the participants were not just modifying their appraisals for the sake of appearances: the so-called average results had genuinely changed their opinion of the photos. The work will appear in Psychological Science. “We know that we adopt the beliefs and perceptions of people around us, but one of the big issues is whether conformity represents a true shift in opinion or just a kind of a white lie,” says Zaki. “The brain regions [we studied] specifically track how you regard something and they recapitulated the shift in opinion,” he says. Ferris Jabr n
How sweat pores give skin memory Kate McAlpine
pore. Conversely, a positive potential pushes the ions back, thinning the layer of sweat lining the pore walls and increasing the skin’s resistance to current. Whether this behaviour helps skin function isn’t clear but Yuriy Pershin of the University of South Carolina in Columbia, who has studied memristive behaviour in amoebas, describes the skin’s role in processes such as temperature regulation as “primitive intelligence”. A new understanding of skin’s electrical properties could have
a current that meets with a much higher resistance. In other words, the skin has a memory of previous currents. The finding is due to be published in Physical Review E. The researchers attribute skin’s memristor behaviour to sweat pores. Sweat contains positively charged ions such as sodium. When skin is exposed to a “The involvement of skin in negative potential, the fluid at regulatory processes can the bottom of the sweat pores is be considered a form of drawn upward. Although a thin primitive intelligence” layer of fluid always coats the inside of the cylindrical pore, this layer thickens as the sweat rises. implications for medicine. As sweat is highly conductive, Resistance to alternating current extra fluid rising to the surface is already used to diagnose skin increases skin’s surface abnormalities, says Johnsen’s conductivity and thereby lowers colleague Andrew Lütken. its resistance if a subsequent Williams, meanwhile, is potential is applied. gratified by the interest in The longer skin is exposed to a memristors. “It is very interesting negative potential, the lower the to me to see the range of the fields subsequent resistance, until it that can benefit from application maxes out when sweat fills the of memristor theory.” n
THE missing link of electronics, which evaded discovery until 2008, was at our fingertips the whole time. Ordinary human skin behaves like a memristor, a device that “remembers” the last current it experienced and varies its resistance accordingly. In 1971 Leon Chua of the University of California, Berkeley, came up with the notion of a resistor with memory. He showed mathematically that this memristor should be a fourth basic circuit element alongside the familiar trio of resistor, capacitor and inductor. But it wasn’t until 2008 that a team led by Stanley Williams, director of HP’s Information and Quantum Systems lab in Palo Alto, California, finally made one from a speck of titanium dioxide. Synapses, junctions between neurons in the brain, display electrical behaviour that depends Memristor skin on past activity and are said to Applying a current across sweat pores turns skin into a memristor, a device behave like memristors. This has that changes its resistance depending on the last voltage applied raised the prospect of using memristors as the basis of an Negative potential Positive potential artificial brain. — + from electrode from electrode Now, by re-examining data from the early 1980s on the electrical conductivity of human + + skin in response to various voltages, Gorm Johnsen and his SWEAT PORE colleagues at the University of Oslo in Norway have uncovered + + a more prosaic example of SODIUM IONS + memristive behaviour in nature. They found that when a + + negative electrical potential is applied to skin on various parts + of the arm, creating a current, + that stretch of skin exhibits a low + resistance to a subsequent current SWEAT flowing through the skin. But + + + + if the first potential is positive relative to the skin, then a Conductive fluid drawn up sweat Conductive fluid flows down sweat pore helping current to flow across it pore, increasing pore’s resistance subsequent potential produces 16 | NewScientist | 5 March 2011
Following the herd can shift your opinion ALL your friends praise a film you just watched. Instead of admitting how dull you found it, you agree. We all sometimes mute our own beliefs like this, but it seems there is more to this than a little white lie. Conforming to others’ views can cause a real shift in your own opinion. That’s the conclusion of Jamil Zaki at Harvard University and colleagues, who asked men to rate how attractive they found a series of photos of women’s faces. The men were then given the average rating for each photo, said to be determined by a previous group. In reality, these ratings were randomly generated by a computer. Thirty minutes later, the participants reassessed the same photos while having their brains scanned using fMRI. As expected, the men’s ratings changed to match the consensus scores more closely. However, Zaki’s team found that if the participant decided a woman was more attractive than they first thought, there was a spike of activity in the orbitofrontal cortex and nucleus accumbens; if they decided she was not as pretty, activity decreased in these areas. Previous research has shown that the higher the activity in these brain regions, the more a person values a certain stimulus. In other words, the researchers argue, the participants were not just modifying their appraisals for the sake of appearances: the so-called average results had genuinely changed their opinion of the photos. The work will appear in Psychological Science. “We know that we adopt the beliefs and perceptions of people around us, but one of the big issues is whether conformity represents a true shift in opinion or just a kind of a white lie,” says Zaki. “The brain regions [we studied] specifically track how you regard something and they recapitulated the shift in opinion,” he says. Ferris Jabr n