Evolution: Mirror, Mirror in the Pond

Identification of mutations in an FGF receptor gene underlying scale loss in a zebrafish mutant, as well as the domesticated mirror carp breed, emphasises the role of genetic redundancy as a facilitator of evolutionary change and has implications for the molecular basis of morphological evolution.     

Mirror agnosia.

Normal people rarely confuse the mirror image of an object with a real object so long as they realize they are looking into a mirror. We report a new neurological sign, ''mirror agnosia'', following right parietal lesions in which this ability is severely compromised. We studied four right hemisphere stroke patients who had left visual field ''neglect''. i.e. they were indifferent to objects in their left visual field even though they were not blind. We then placed a vertical parasagittal mirror on each patients'' right so that they could clearly see the reflection of objects placed in the (neglected) visual field. When shown a candy or pen on their left, the patients kept banging their hand into the mirror or groped behind it attempting to grab the reflection; they did not reach for the real object on the left, even though they were mentally quite lucid and knew they were looking into a mirror. Remarkably, all four patients kept complaining that the object was ''in the mirror'', ''outside my reach'' or ''behind the mirror''. Thus, even the patients'' ability to make simple logical inferences about mirrors has been selectively warped to accommodate the strange new sensory world that they now inhabit. The finding may have implications for understanding how the brain creates representations of mirror reflections.     

湖泊，环境状况的一面镜子

湖泊,是指在陆地表面那些能够蓄一定水量的天然洼地。据统计,中国在1平方公里以上面积的湖泊数量达到2759个,总面积91019.63平方公里。在经济高速增长的今天,已经很难见到保持自然状况的水体,全国湖泊都面临着前所未有的威胁,干旱地区的湖泊更是处在萎缩和干涸的危机之中,中科院南京地理与湖泊研究所研究员,《中国湖泊志》的编写者之一王苏民为我们揭开导致这一危机的原因。     

Mirror imagery and biological selection

Lake Tanganiyka has lefty and righty cichlid fish that show there can be natural selection for a trait over its mirror image counterpart.This raises the question ‘Can there be biological selection of a whole organism over its mirror image counterpart?’ That is, could the fitness of a fish be altered by simply changing it into its own enantaniomorph? My answer is no. I present Flatlander thought experiment to demonstrate that mirror imagecounterparts are duplicates because they only differ in how they happen to be oriented in space. The counterparts have the same intrinsic properties and are in the same environment,so there can be no difference in fitness.     

Mirror adaptation in sensory-motor simultaneity

Background

When one watches a sports game, one may feel her/his own muscles moving in synchrony with the player''s. Such parallels between observed actions of others and one''s own has been well supported in the latest progress in neuroscience, and coined “mirror system.” It is likely that due to such phenomena, we are able to learn motor skills just by observing an expert''s performance. Yet it is unknown whether such indirect learning occurs only at higher cognitive levels, or also at basic sensorimotor levels where sensorimotor delay is compensated and the timing of sensory feedback is constantly calibrated.

Methodology/Principal Findings

Here, we show that the subject''s passive observation of an actor manipulating a computer mouse with delayed auditory feedback led to shifts in subjective simultaneity of self mouse manipulation and auditory stimulus in the observing subjects. Likewise, self adaptation to the delayed feedback modulated the simultaneity judgment of the other subjects manipulating a mouse and an auditory stimulus. Meanwhile, subjective simultaneity of a simple visual disc and the auditory stimulus (flash test) was not affected by observation of an actor nor self-adaptation.

Conclusions/Significance

The lack of shift in the flash test for both conditions indicates that the recalibration transfer is specific to the action domain, and is not due to a general sensory adaptation. This points to the involvement of a system for the temporal monitoring of actions, one that processes both one''s own actions and those of others.     

Diabetic foot infections: fate of the contralateral foot

Following an initial report urging conservative management of severe diabetic foot infections, the authors have managed 45 patients with a minimum 3-year follow-up. By using standard principles for soft-tissue infection, 78 percent of the patients healed minor amputation sites and maintained biped ambulation following the initial foot involvement. Only 22 percent required a major amputation at the time of the initial foot involvement. The 45 patients were followed and 22 (or 49 percent) developed a severe infection involving the contralateral foot within 18 months. Although 15 of the 22 patients developing contralateral infection (or 33 percent of the total series) required some type of amputation on the contralateral foot, the conservative approach allowed 64 percent of the patients with severe infections in both feet to maintain biped ambulation. This included 40 percent of the patients who required amputation of some portion of both feet.     

Mirror symmetry breaking in biochemical evolution

The problem of origination of molecular asymmetry in biochemical evolution is discussed. The theoretical analysis shows that chiral purity of biomolecules has the biological significance for self-reproduction of organisms. The models of spontaneous symmetry-breaking in molecular systems are given. The aspects of various stages of biochemical evolution associated with the development of chiral polarization are analysed.     

Natural gaits of the non-pathological flat foot and high-arched foot

There has been a controversy as to whether or not the non-pathological flat foot and high-arched foot have an effect on human walking activities. The 3D foot scanning system was employed to obtain static footprints from subjects adopting a half-weight-bearing stance. Based upon their footprints, the subjects were divided into two groups: the flat-footed and the high-arched. The plantar pressure measurement system was used to measure and record the subjects' successive natural gaits. Two indices were proposed: distribution of vertical ground reaction force (VGRF) of plantar and the rate of change of footprint areas. Using these two indices to compare the natural gaits of the two subject groups, we found that (1) in stance phase, there is a significant difference (p<0.01) in the distributions of VGRF of plantar; (2) in a stride cycle, there is also a significant difference (p<0.01) in the rate of change of footprint area. Our analysis suggests that when walking, the VGRF of the plantar brings greater muscle tension to the flat-footed while a smaller rate of change of footprint area brings greater stability to the high-arched.     

Subjective Duration Distortions Mirror Neural Repetition Suppression

Background

Subjective duration is strongly influenced by repetition and novelty, such that an oddball stimulus in a stream of repeated stimuli appears to last longer in duration in comparison. We hypothesize that this duration illusion, called the temporal oddball effect, is a result of the difference in expectation between the oddball and the repeated stimuli. Specifically, we conjecture that the repeated stimuli contract in duration as a result of increased predictability; these duration contractions, we suggest, result from decreased neural response amplitude with repetition, known as repetition suppression.

Methodology/Principal Findings

Participants viewed trials consisting of lines presented at a particular orientation (standard stimuli) followed by a line presented at a different orientation (oddball stimulus). We found that the size of the oddball effect correlates with the number of repetitions of the standard stimulus as well as the amount of deviance from the oddball stimulus; both of these results are consistent with a repetition suppression hypothesis. Further, we find that the temporal oddball effect is sensitive to experimental context – that is, the size of the oddball effect for a particular experimental trial is influenced by the range of duration distortions seen in preceding trials.

Conclusions/Significance

Our data suggest that the repetition-related duration contractions causing the oddball effect are a result of neural repetition suppression. More generally, subjective duration may reflect the prediction error associated with a stimulus and, consequently, the efficiency of encoding that stimulus. Additionally, we emphasize that experimental context effects need to be taken into consideration when designing duration-related tasks.