November 26, 2014 | David F. Coppedge

Let's Get [Thankful for the] Mental

Wonders of the human brain and sensory systems continue to pour forth from scientific research, providing more reasons to give thanks.

Skull integrity:  All the talk about concussions in football games raises a question: How do the brain and skull stay together?  Scientists at the University of Miami asked these questions. “Think about the way our bodies are assembled during early development and ask: How do neighboring cells know that they are supposed to become a nerve or a bone cell and how do these tissues find the correct place and alignment?”  Their research uncovered “a network of tissue communication events that ensure that the brain stays in the skull and the spinal cord in the spinal column.”  They found that cells in various areas communicate information about their locations and developmental identities.  It’s like knowing not only the blocks, but the home addresses in a city.

How does anesthesia work?  If you’ve had surgery, you are certainly thankful that the anesthesiologist could put you to sleep before they cut you open.  This began in the 19th century with James Simpson‘s discovery of chloroform, that turned surgery from a horror to a nap.  Neurologists are still unsure how it works.  Medical Xpress shows that it has something to do with deactivation of ion channels.

His brain, her brain?  Science Magazine is still trying to figure out what most people know intuitively, that men and women are “essentially” different, not only in anatomy, but in neurophysiology.  Scientists in this PC world are trying to navigate a fine line, teasing out actual measurable differences without becoming guilty of (gasp!) “neurosexism.”

Conservative brain:  A new paper in PNAS finds that natural selection does not account for brain size.  It’s a working-out of a “conserved” (unevolved) developmental program” Features of the cortex long thought to be the result of special selection are revealed as the necessary product of a conserved mechanism.”

Optic flow aftertaste:  Ever stop moving, then feel like you still are in motion?  This is a real phenomenon: a mental aftereffect of “optic flow.”  There’s a reason for it; your brain becomes accustomed to the constant motion flowing all around you, for “coding efficiency” to reduce redundant signals.  It takes a few seconds to compensate for stillness again.  This is described in Current Biology by Cuturi and MacNeilage, who ran perception experiments on human subjects.

We propose that crossmodal aftereffects can be understood as an example of contingent or contextual adaptation that arises in response to correlations across signals and functions to reduce these correlations in order to increase coding efficiency.  According to this view, crossmodal aftereffects in general (e.g., visual-auditory or visual-tactile) can be explained as accidental manifestations of mechanisms that constantly function to calibrate sensory modalities with each other as well as with the environment.

Seeing the unexpected:  Your eyes see what they expect to see.  This phenomenon, called “adaptive self-coding,” is explored in Current Biology; it’s a complex, neural program for visual efficiency: “The influence of recent perceptual history on the present reflects the action of efficient mechanisms that exploit temporal redundancies in natural scenes.”  But what if the unexpected happens?  That’s why optical illusions are so much fun, like the cafe wall illusion posted by Medical Xpress.  Thanks to our “plastic brain,” our visual system is highly trainable.

Rod repurposing:  In the human retina, rods are for low light, cones for bright light.  That’s what we learn in school, but the rods don’t go to sleep during the daytime.  The retina “repurposes” the rods in bright light to enhance contrast information, Medical Xpress says, “to increase the amount of visual information about the environment.”  Johns Hopkins researchers were fascinated by results from experiments with their lab mice:

During bright light conditions, the cells of the inner retina receive therefore information through two pathways: First through the well-established cone pathway, and second through this newly identified rod pathway. “We think that the surround information relayed to the inner retina through the rod pathway has different functional properties than the information obtained through the cone pathway,” comments Roska. “In any case it is fascinating to see how the retina repurposes the rod cells during bright light conditions to increase contrast information, at times when they are not directly sensing light.”

Reach out and touch:  Transplanted hands can regain a near-normal sense of touch.  Just ask Donald Rickelman, who received a hand transplant in 2011.  He and 84 others have received hand transplants, and are experiencing how the brain can re-map itself to understand the new nerve impulses.  Emily Underwood writes for Science Magazine:

Rapid changes unfold in the brain after a person’s hand is amputated. Within days—and possibly even hours—neurons that once processed sensations from the palm and fingers start to shift their allegiances, beginning to fire in response to sensations in other body parts, such as the face. But a hand transplant can bring these neurons back into the fold, restoring the sense of touch nearly back to normal, according to a study presented here this week at the annual conference of the Society for Neuroscience….

After surgery, studies have shown that it takes about 2 years for the peripheral nerves to regenerate, with sensation slowly creeping through the palm and into the fingertips at a rate of roughly 2 mm per day, says Scott Frey, a cognitive neuroscientist at the University of Missouri, Columbia.  [See also Science Daily.]

Skin so soft:  Touching is such a major part of human experience, it’s amazing how little is known about it.  Science Magazine describes the “gentle touch receptors of the skin” in a paper by 3 neuroscientists from the Howard Hughes Medical Institute.  There’s more going on in a gentle touch than we can imagine.  Watch for anchors, balancing acts, and codes:

The skin is our largest sensory organ, transmitting pain, temperature, itch, and touch information to the central nervous system. Touch sensations are conveyed by distinct combinations of mechanosensory end organs and the low-threshold mechanoreceptors (LTMRs) that innervate them. Here we explore the various structures underlying the diverse functions of cutaneous LTMR end organs. Beyond anchoring of LTMRs to the surrounding dermis and epidermis, recent evidence suggests that the non-neuronal components of end organs play an active role in signaling to LTMRs and may physically gate force-sensitive channels in these receptors. Combined with LTMR intrinsic properties, the balance of these factors comprises the response properties of mechanosensory neurons and, thus, the neural encoding of touch.

Skin so functional:  In a separate paper in Science Magazine, Fiona M. Watt of Kings College reviews other recent findings about the skin organ.  “Live-cell imaging, optogenetics, and cell ablation experiments show skin cells to be remarkably dynamic,” she says.  “…. integrative biological analysis of human skin disorders has revealed unexpected functions for elements of the skin that were previously considered purely structural.”  For example, integrins not only maintain skin integrity, but “control initiation of terminal differentiation.”  Another example: “Proteins that mediate keratinocyte intercellular adhesion also play an active role in regulating proliferation and differentiation.”  One more: “In the same way as integrins and desmosomes have functions that extend beyond cell adhesion, keratin filaments have roles in cell proliferation, apoptosis, and inflammation.”

There are more wonders going on inside us than we can imagine.  The more the detail, the more incredible to think they are the result of blind, unguided natural processes.  We hope you will be thankful for your equipment this season, and treat it with care.



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