On Snake Walking


(from reference 1)

Human beings transition between from one style of gait to another as they transition from walking to running (see figure, above). The act of walking is fundamentally one of transferring weight from one limb to another, while running is primarily an act of maintaing inertia. Furthermore, these two gaits apparently have their origin in the minimization of energy costs associated with moving at a particular speed1.


(from reference 2)

Interestingly, it seems that snakes do not make any such transition in their locomotive behavior. A study appearing in the Proceedings of the National Academy of Sciences has used theoretical modeling, friction measurements, and slithering-observations to demonstrate that snakes simply “speed-walk” at high speeds 2. Although they have no limbs, and thus no “gait” to speak of, at slow speeds, they do move about by transferring weight from one part of their body to another. In contrast to other animals, however, they do the same thing, only faster, at high speeds. It is unclear why speedwalking is not an undue energetic costs for these animals, perhaps there is simply no less-costly way to move about. Further work will be needed to more completely understand the energetics of snake locomotion.

References:
1. Srinivasan M, Ruina A. (2006) Computer optimization of a minimal biped model discovers walking and running. Nature. 439(7072): 72-75.
2. Hu DL, Nirody J, Scott T, Shelley MJ. (2009) The mechanics of slithering locomotion. Proc Natl Acad Sci U S A. [Epub ahead of print]
PMID: 19506255 [PubMed – as supplied by publisher]

On The Tree-for-the-Forest in Autism

One commonly reported feature of autism-spectrum-disorder (ASD) is the tendency to favor details over whole-object properties. That is, to notice the forest and not the trees. A study appearing in the journal Vision Research quantifies this effect experimentally1.

The authors of this study relied on a concept known as “visual crowding.” This term refers to a commonly experienced phenomenon in which objects that are spaced closely together are more difficult to individually attend to or resolve. For example, some have invoked this idea to explain why it is difficult to pick individual faces out of a crowd. It is important to note, that there is a spatial-scale, a threshold, associated with visual crowding, such that objects of a given size must be spaced within some distance limit to be considered within the crowding limit (although some objects are so large that they are immune to such effects).

from reference 1

Interestingly, the authors found that children with ASD had much lower thresholds for visual crowding than those without the disorder (see figure, above). That is: those with ASD were able to resolve and report the properties of more densely packed objects than those without ASD. Furthermore, children with ASD out-performed non-ASD children in the employed task within the crowding limit (as defined by the threshold for non-ASD children) while underperforming outside this limit.

Such a finding suggests structural irregularities in the visual-corticies of these children; while this is nothing special in and of itself, there are many different cortical areas which are affected by ASD, which leads to the intriguing possibility (suggested by many) that the disorder might be a generalized structural deficit of the cerebral cortex.

References:
1. Baldassi S, Pei F, Megna N, Recupero G, Viespoli M, Igliozzi R, Tancredi R, Muratori F, Cioni G, Search superiority in autism within, but not outside the crowding regime, Vision Research, In Press, DOI: 10.1016/j.visres.2009.06.007.

On Leanness

Although many acknowledge that some people are inherently (perhaps genetically) leaner than others, it remains unclear what the biological basis for the body’s “set-point” might be. A study appearing in the open-access journal PLoS One suggests one possible factor1.

from reference 1

Both rat and human data were collected in this work, which concludes that “the lean phenotype is characterized by high endurance capacity and high activity and may stem from altered skeletal muscle energetics.” These researchers gathered data from a population of people who they categorized as non-exercisers (less than 1 hour per week of activity exceeding 4 METS). They subjected these individuals to a treadmill test to determine their endurance (as assessed by oxygen consumption during exercise) and kept track of their average daily activity over a period of 10 days; finding that there was a significant relationship between endurance and leanness, as well as average daily activity and leanness. Furthermore, they found that there was no significant difference in the amount of food consumed by lean versus non-lean rats, and fascinatingly, that the skeletal muscle tissue of lean rats has significantly higher levels of the enzyme PEPCK-C.

Of course, it is not surprising that those individuals with higher daily activity are leaner in general, rather, this study is suggesting that there may be a fundamental, biological reason why certain individuals are more active: they simply have a greater capacity for activity. Indeed, if one fatigues more easily, it wouldn’t be surprising if they were less active; it is also conceivable that reduced activity could feed-back on behavior in the sense that an individual with lower endurance might progressively reduce the amount of physical activity they engage in so as to reserve energy for other tasks. This is especially true in contemporary society, where mental activity is often the basis for work and play.

It is unclear as yet, however, whether the differential muscle-properties found in rats extend to humans; further work will be required to clarify what the molecular-biological basis for increased human endurance might be.

References
1. Novak CM, Escande C, Gerber SM, Chini EN, Zhang M, et al. (2009) Endurance Capacity, Not Body Size, Determines Physical Activity Levels: Role of Skeletal Muscle PEPCK. PLoS ONE 4(6): e5869. doi:10.1371/journal.pone.0005869

On Feedback

One of the most fascinating questions in neuroscience, is how “high-level” cognitive properties of mind like attention feed back on and affect our biology. For example, it is known that video-game players have better visual acuity than non-video game players1. Another example of this phenomenon can be found in the result (described below) from Lee et. al., published in the Journal of Neuroscience2.

from reference 2

The authors of this study found differences in the responses of the auditory brainstems of musicians as compared to non-musicians. Specifically, these two groups (musicians and non-musicians) were presented with pairs of consonant and dissonant tones; it was found that musicians showed larger response magnitudes to certain components of consonant tones than did non-musicians (see figure, above).

The hypothesized reason for this difference is that a musician’s heightened attention to consonant tones (and their makeup or properties) leads to changes in his or her neurobiology, such that the neurons of the auditory brainstem eventually respond more strongly to certain aspects of these auditory signals. This is especially fascinating because the area of the brain that was measured was not the cortex (usually associated with consciousness and “high-level” cognitive activity), but the brainstem (the area of the brain that is evolutionarily much older; bearing greater resemblance to animal brains ).

How the conscious act of focusing on one aspect of a stimulus can lead to an enhancement of the responses of brain-regions devoted to their representation is an open question, and one with wide-ranging implications. Further research will be required to understand its basis.

References:
1. Green CS, Bavelier D. (2007) Action-video-game experience alters the spatial resolution of vision. Psychol Sci. 18(1):88-94. PMID: 17362383
2. Lee KM, Skoe E, Kraus N, Ashley R. (2009) Selective subcortical enhancement of musical intervals in musicians.
J Neurosci. 29(18):5832-40. PMID: 19420250