Somnambulists are in an irrational state during which they could harm themselves or others. Some extreme examples include the instance of the English teenager who in jumped eight metres out of her bedroom window, or the case of Kenneth Parks in Toronto, who in drove 23km and murdered his mother-in-law, all apparently while sleeping. Why do some enter into such a potentially harmful state during sleep? B ut why would our brains enter into such a mixed state, representative of neither wakefulness nor sleeping? When one considers our distant, pre-human ancestors, answers begin to take shape.
Survival mechanism definition and meaning | Collins English Dictionary
For aeons, the safety provided by the spot where our predecessors chose to lay their heads for the night was, in many ways, compromised compared with the safety of our current bedroom spaces. Other species employ such strategies as well. As I was navigating the trail in the twilight, a deer jumped out from underneath the branches of a fallen tree and bolted off into the distance. I was amazed at how close I had come to it before it sprang into furious action — only a few metres.
It likely had been asleep and, upon waking, realised the potential danger it was in. What struck me was how the deer seemed to be triggered for action, even while asleep. In fact, many animals can maintain brain activity required for survival during sleep.
For example , frigate birds fly for days, even months, and maintain flight during sleep while travelling vast distances over an ocean. The phenomenon is observed in humans too. Scientists now agree that bouts of localised wakeful-like activity in motor-related areas and the limbic system can occur without concurrent sleepwalking. In fact, these areas have been shown to have low arousal thresholds for activation. Surprisingly, despite their association with sleepwalking, these low thresholds have been considered an adaptive trait — a boon to survival.
Throughout most of our extensive ancestry, this trait may have been selected for its survival value. You need a motor system that is ready. Despite evidence of localised activity during sleep in both human and non-human animal brains, sleepwalking is, among primates, apparently a uniquely human phenomenon. It stands to reason, therefore, that the selection pressure for this trait in our ancestors uniquely outweighed the cost. Christian Jarrett.
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Photo by Wikimedia. Philip Jaekl is a cognitive neuroscientist and writer. This greatly enhanced the ability to detect where ice nucleation occurred and how it propagated. It also provided the ability to determine which, if any, tissues remained supercooled and free of ice. Relevant images were then extracted to illustrate the freezing pattern in and around buds in image plates PowerPoint, Microsoft Corporation, Redmond, USA. For cryo-microscopic investigation, twigs were exposed in the cooling compartment of the same temperature-controlled freezer as described above.
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The dissected buds could then be inspected for places where extraorgan ice masses had grown around and inside the bud and where tissues remained free of ice. Freezing resistance FR of buds was investigated by exposing whole twigs to a set of different freezing temperatures, thus simulating low temperature stresses of various degrees. Twigs bearing at least 10 buds were then put into sealable plastic bags Twigs were then removed from the plastic bags and the buds were longitudinally dissected for visual inspection of frost injury.
The logistic function was used to assess LT 50 , i. IBM Corp. Differences between mean values of different species and bud types were tested with a one-way analysis of variance ANOVA and a subsequent Duncan post hoc test, homoscedasticity provided. In the case of a negative Levene test, the Mann—Whitney U -test was used as a non-parametric post hoc test.
IDTA analysis provided the ability to directly observe the freezing pattern in and around buds, and to determine whether or not ice forms in the bud tissue. Three significantly different freezing patterns were observed. The first pattern, where ice immediately propagated from the surrounding tissue during the HTE into the bud, was observed in only four of the 37 examined species.
This freezing pattern was exhibited in Pinus cembra buds and is shown in Figure 1A Supplementary Video 1. This freezing pattern was also seen in Pinus sylvestris and two angiosperm species, Sambucus nigra , and Elaeagnus rhamnoides.
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In the majority 33 out of 37, or The initial ice wave stopped below the bud, and the bud cells remained ice-free in a supercooled state. Propagation of ice from the stem into the bud was inhibited by an ice barrier in the tissue between the stem and the bud. Two types of supercooling buds were observed. In one group, a second freezing event occurred at a much lower freezing temperature than the HTE and, in addition to the infrared observations, was recorded in the DTA as a low-temperature exotherm LTE. The LTE was triggered by an ice nucleation event inside the bud in all buds that exhibited temporary supercooling.
A breakdown of the ice barrier, i. Once ice formation was initiated in a single spot tentatively a single cell , ice spread rapidly throughout the whole bud within seconds Supplementary Video 3. In the second group of supercooled buds, no distinct LTE could be detected despite cooling the buds below the temperature at which the buds are killed.
This freezing pattern of persistently supercooled buds, without the occurrence of a distinct LTE, is exemplified by the freezing response of Betula pendula Figure 1C , Supplementary Video 4. Figure 1. Images were obtained at temperatures indicated in the upper right corner.
No further freezing process is detected, even at temperatures below the frost killing temperature. Freezing exotherm temperatures are indicated in the top right corner of each image. The time span during each freezing exotherm in seconds is indicated in the bottom right corner. Table 1. The freezing pattern around and in buds of the 37 investigated woody species could be assigned to three different types by infrared differential thermal analysis IDTA : Type A Extracellular ice formation during HTE in the bud no ice barrier , Type B Temporarily supercooled and ice-free during HTE, but killed by spontaneous ice nucleation in the bud with LTE and Type C persistently supercooled and ice-free during HTE, but no ice formation down to below the frost killing temperature no LTE.
Although DTA does not allow one to determine the location where ice forms in tissues, it is very sensitive and can detect small freezing events.
When properly configured, it also allows one to measure a considerable number of buds as replicates at the same time. The temperature of the HTE varied slightly among the tested species Table 1. Figure 2. Ice nucleation during LTE was always initiated inside the bud. The whiskers indicate at maximum the 1.
Outliers are shown as dots, extreme outliers as stars. Figure 3. Representative DTA-plots that depict the three different freezing pattern types are shown in Figure 4. Buds of S. Buds of A. LTEs in these buds were often short and pinnacle F. Lastly, buds that supercool but do not exhibit a distinct LTE are exemplified by B. Figure 4. Figure 5.
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The whiskers indicate, at maximum, the 1. In supercooling buds, formation of extraorgan ice masses was monitored by cryo-microscopy Table 1. The exceptions were four species with persistently supercooling buds Castanea sativa, L. While in DTA, no freezing exotherms were detectable during formation of translocated ice between the premature leaves, in some species in IDTA occasionally exiguous freezing processes were recorded e.
In temporarily supercooled buds, no preferential location of ice masses could be found Figure 7. In persistently supercooled buds, except for the species lacking ice masses, ice crystals mostly could be found close to premature leaves, but in Populus tremula and Corylus avellana they could additionally be found in the scales and in Viburnum lantana additionally in the stem—and only in Sorbus aucuparia was ice exclusively seen in the bud scales. Figure 6. Ice was found either in A the subtending stem J. Figure 7. In supercooled buds, translocated ice masses can be found either in S the adjoining stem, in Sc the bud scales or inside L the bud around the premature leaves.
In some buds, nd no large ice masses could be found inside or in close vicinity to the bud. Vegetative buds that freeze extracellularly, i. Interestingly, reproductive buds in Sambucus racemosa , in contrast to the many reproductive buds of angiosperm woody species Ashworth, , ; Quamme, , also did not exhibit an LTE Ishikawa and Sakai, ; this suggests that another FR mechanism exists other than deep supercooling.
With respect to conifers, the results obtained in P. Buds that only exhibit extracellular freezing with an absence of any supercooling were the most frost hardy, corroborating earlier reports on the FR of P.
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Opposed to other conifers that have buds that supercool Quamme, , in pines, ice forms in the buds at the same time when ice forms in subtending stem tissues, and no supercooling occurs Ide et al. In contrast to other Pinaceae , such as Abies Sakai, ; Ide et al. Similar to pines, the two angiosperms examined in the present study, S. Additionally, a barrier against extrinsic ice nucleation from the bud surface does not appear to exist in buds that exhibit extracellular freezing. In supercooling buds, an impermeable ice barrier can be brought about by a sophisticated bud scale architecture P.