Monthly Archives: October 2014

Nerves of endearment: how a gentle touch affects emotions

22 May 2014, 6.21am AEST

Nerves of endearment: how a gentle touch affects emotions

A soft and tender caress between two people can trigger a flood of emotions, and now we may have some idea why. Research published in Neuron today suggests that certain sensory nerve cells, known as C…

Gentle physical contact activates a special type of nerve cell linked to emotion. Jonathan McPherskesen/Flickr, CC BY-NC-SA

A soft and tender caress between two people can trigger a flood of emotions, and now we may have some idea why.

Research published in Neuron today suggests that certain sensory nerve cells, known as C tactile (CT) afferents, are involved in stimulating the emotions caused by gentle physical contact.

Francis McGlone, from Liverpool John Moores University in the UK, and colleagues argue that these cells, which are found in the skin of most mammals including humans, are critical for mediating social behaviours and even in giving beings a sense of “self”.

The senses of touch

There is a general tendency to lump all our somatic senses into a single classification: the “sense of touch”. This is inaccurate, since what we call touch actually comprises several distinct sensory systems.

Bart Everson/Flickr, CC BY-NC-SA

Mammals sense pain and temperature changes via a primordial system of nerve cells that run within the spinal cord and brain. This system can signal the temperature in the environment or the presence of harmful stimuli, and typically trigger behaviours in the search of a suitable and safe environment.

Discriminative touch, a neural process operating in pathways well separated from these primordial systems, allows us and other mammals to localise tactile stimuli on our skin.

These sensors are incredibly sensitive: they can recognise tiny details of external materials, identify the shapes of objects and allow blind people to read Braille.

Responding to a gentle touch

CT afferents are, in the neuroscience jargon, a distinct type of “unmyelinated, low-threshold mechanoreceptive unit” existing in the hairy skin of humans and other mammals.

These nerve cells belong anatomically and evolutionarily to the more primordial sensory system of the skin, together with pain and temperature sensors. Although known in humans for several decades, CT afferents continue to reveal new secrets.

The cells are stimulated by gentle pressure on the skin and what’s intriguing is they respond preferentially to stroking at a velocity similar to that of caressing.

CT afferents are also connected with those areas of the brain ‒ the insular cortex, the posterior superior temporal sulcus, the medial prefrontal cortex and the dorsoanterior cingulate cortex ‒ known to be activated by caressing and associated with feeling pleasure.

The behaviour of these sensory nerve cells suggests that the pleasure of having one’s skin stroked represents an innate, non-learned process, giving rise to the pleasures associated with social interactions.

This may explain the prevalence of social grooming (allogrooming) in many primate species.

elaine/Flickr, CC BY-NC-ND
Click to enlarge

A feeling of self

Those same areas of the brain that respond to caressing also receive sensory input from internal parts of the body (interoception). Here, internal and external signals combine to give a unique sense of body ownership, and by implication to create our embodied psychological “self”.

Over the past century, neuroscience has strived to bridge the gap between the two Cartesian worlds ‒ that is, to link the physical actions of sensory nerve cells with the subjective sensations and feelings that they produce.

Touch is one of the ways in which human and other animals establish a boundary between themselves and the external world, and these CT afferents through their stimulation may give rise to embodiment, the sense of being localised within one’s own body.

Far-reaching implications

Because CT afferents help mediate the interaction between the physical world and the internal world of the brain, hopes are high for their explanatory power.

They might even aid our understanding of such phenomena as pain perception, body image distortions, out-of-body experiences, neurodevelopmental disorders and placebo effects.

All these fascinating possibilities aside, there’s no doubt that a soft caress between two people remains among the most powerful of all emotional social signals. Our growing understanding of CT afferents is helping us explain how such deep feelings and emotions can be mediated by so gentle a touch.

More Fish in Diets of Children and Pregnant Women

Health Officials Call for More Fish in Diets of Children and Pregnant Women

The new federal recommendations noted the nutritional benefits of seafood, though not dietary supplements like fish oil.Dominic Chavez for The New York TimesThe new federal recommendations noted the nutritional benefits of seafood, though not dietary supplements like fish oil.

Federal officials on Tuesday announced that they would recommendfor the first time that women who are pregnant or breast-feeding and young children eat a minimum of two servings of low-mercury seafood every week for their health.

The recommendations represent a significant shift for the Food and Drug Administration and the Environmental Protection Agency, whose previous seafood advisory in 2004 set only an upper limit on the amount of fish that these groups should eat.

The proposed advisory, which will enter a public commenting period, recommends a weekly limit of 12 ounces — or about three servings — of low-mercury seafood like salmon, shrimp, cod, tilapia and light canned tuna for the women. But unlike the last advisory, it now encourages a minimum of two servings, or about eight ounces, which was prompted by an F.D.A. analysis that found that one in five pregnant women in the United States ate little or no fish at all.

Dr. Stephen Ostroff, the F.D.A.’s acting chief scientist, said the agency was concerned that pregnant and nursing women were missing out on the benefits of eating fish. He cited studies showing that children born to women who consume fish have higher I.Q.s and better cognitive development than children born to women who do not.

“A large percentage of women are simply not eating enough fish, and as a result they are not getting the developmental and health benefits that fish can provide,” he said. “Studies very consistently demonstrate that among women who consumed more fish during pregnancy — or at least the amounts we’re currently recommending — that there were improvements in children.”

Dr. Ostroff said the advisory did not pertain to supplements, like fish oil, that contain omega-3 fatty acids but lack a wide variety of other nutrients typically found in seafood. “We don’t believe women would accrue the same benefits in terms of health and development if they were to use supplements in place of fish,” he said.

The F.D.A. is also recommending that young children eat a weekly minimum of two fish servings, the size of which would vary depending on their age and weight.

Some environmental groups criticized the new recommendations. Michael Bender, the executive director of the Mercury Policy Project, one of two advocacy groups that sued the F.D.A. this year, demanding that it post warning labels about mercury content on packaged fish, said he was particularly concerned about tuna consumption. He said Americans get about a third of their methyl mercury exposure from tuna, and he argued that the F.D.A. should discourage pregnant and nursing women from eating it.

The latest advisory discourages pregnant and nursing women and young children from eating four high-mercury fish: shark, swordfish, king mackerel and tilefish from the Gulf of Mexico. The F.D.A. said orange roughy and marlin might be added to that list in the future.

As for tuna, the advisory lists the canned light variety as a low-mercury option. It recommends a limit of six ounces a week on albacore tuna because it has more mercury than canned light tuna.

Dr. Ostroff said tuna was not a problem as long as women did not eat it to the exclusion of low-mercury fish. “The health benefits that accrue from the consumption of fish far outweigh any risks,” he said.

Some doctors said the new advisory did not go far enough in encouraging greater fish consumption among pregnant women. By setting an upper limit on the amount of fish that should be consumed, the federal advisory has scared many women away from eating any fish at all, said Dr. Roger B. Newman, the director of the obstetrics and gynecology department at the Medical University of South Carolina and a member of the Perinatal Nutrition Working Group, which promotes seafood consumption among pregnant and breast-feeding women.

Dr. Newman said that many women in his clinical practice vowed to stop eating fish after the last advisory in 2004 because they were concerned or confused by the recommendations. “They didn’t know exactly what was wrong with fish,” he said, “but they had heard that it was bad.”

Dr. Newman said he told pregnant patients not to worry about restricting themselves to 12 ounces of fish weekly as long as they were eating low-mercury varieties. He said there were many epidemiological studies suggesting that children born to women who ate fish while pregnant have higher I.Q.s and better behavioral development.

One large study of thousands of mothers and their childrenpublished in The Lancet in 2007, for example, suggested that pregnant women needed to eat a minimum of about three servings of fish per week to get the benefits for child development.

“Seafood has multiple nutritional benefits to pregnant women, to developing fetuses and to young children,” Dr. Newman said. “I’m disappointed in the recommendations. But I do think they’re a step in the right direction.”

Colloidal Silver: Is It Safe?

Colloidal Silver: Is It Safe?
Published: 3/24/2014

Widely promoted as a cure for everything from ear infections to shingles to AIDS, colloidal silver is a solution of silver particles suspended in liquid. Promoters claim that colloidal silver is an alternative to antibiotics and can extend life and remedy mineral deficiencies that lead to a weakened immune system. Is any of this true?

I don’t think so – the claims are unproven, and colloidal silver is not a substitute for antibiotics, or any other medications. Not only does the human body have absolutely no need for silver, it can be harmful:

  1. Silver can accumulate in the body and lead to a skin condition called argyria, which causes bluish-gray skin pigmentation, especially around the nose and mouth, a color change that cannot be reversed.
  2. Long-term use of oral silver products has led to neurological problems including seizures, as well as kidney damage, stomach distress, headaches, fatigue and skin irritation.
  3. It can also interfere with the absorption of some drugs including tetracycline antibiotics and thyroid hormone supplements.

While it is true that silver is an effective germicide, it has limited usefulness in medicine. In 1999, the FDA banned the sale of all over-the-counter drugs containing colloidal silver and silver salts as these compounds haven’t been recognized as safe. However the ban doesn’t apply to dietary supplements containing colloidal silver because the FDA has no jurisdiction over such products, unless there are established safety issues. I would avoid all products containing colloidal silver.