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Archive for April 10th, 2015

Science Notes-Sleep

Sleep has profound importance in our lives, such that we spend a considerable proportion of our time engaging in it. Sleep is Nature’s way enabling the body, to cope with outside world and with inner world as well.

Sleep works on the body as well as on behavior. For the latter the brain is a gateway. Sleep is a means for nature to allow individuals recover metabolically. Contemporary research has been moving to focus on the active rather than recuperative role that sleep has on our brain and behaviour.

Sleep is composed of several distinct stages. Two of these, slow-wave (or deep) and REM sleep, reflect very different patterns of brain activity, and have been related to different cognitive processes.

Slow-wave sleep is characterised by synchronised activity of neurons in the neo-cortex firing at a slow rate, between 0.5 and three times per second. The neo-cortex comprises the majority of the cerebral cortex in the brain, which plays a role in memory, thought, language and consciousness. In contrast during REM sleep, when most of our dreaming happens, neuronal firing is rapid and synchronised at much higher frequencies, between 30 to 80 times per second.

Such patterns of brain activity during REM sleep are reminiscent of those observed during wakefulness, and for this reason REM sleep is often referred to as “paradoxical” sleep.

Cognitive functions

There is growing evidence that slow-wave sleep is related to the consolidation of memory and is involved in transferring information from the hippocampus, which encodes recent experiences, and forging long-term connections within the neo-cortex. REM sleep has been linked to processes involving abstraction and generalisation of experiences, resulting in creative discovery and improved problem solving.

Though there are substantial similarities between wakefulness and REM sleep, numerous studies have explored differences in the activity of brain regions between these states, with the cingulate cortex, hippocampus and amygdala more active during REM sleep than wakefulness. These regions are particularly interesting to cognitive neuroscientists because they are key areas involved in emotional regulation and emotional memory.

However, which sub-regions are active within these broader cortical and limbic areas – the pathways in the brain that produce these patterns of activation – and the precise function of the activity in these regions during REM sleep is not yet fully understood.

Cortical activity in rats

A new study published in Science Advances studied the physiology and functionality of REM sleep in a group of rats and provides insight into the cortical activity and the sub-cortical pathways that result in this activity. The level of detail of this study provides a major step forward for our understanding of the effect that REM sleep has on our brain and cognitive behaviour.

(ack: the Conversation/PadraicMonaghan-leicester Univ./08-04/15)

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At Chao-cheng there lived an old woman more than seventy years of age, who had an only son. One day he went up to the hills and was eaten by a tiger, at which his mother was so overwhelmed with grief that she hardly wished to live. With tears and lamentations she ran and told her story to the magistrate of the place, who laughed and asked her how she thought the law could be brought to bear on a tiger. But the old woman would not be comforted, and at length the magistrate lost his temper and bade her begone. Of this, however, she took no notice; and then the magistrate, in compassion for her great age and unwilling to resort to extremities, promised her that he would have the tiger arrested. Even then she would not go until the warrant had been actually issued; so the magistrate, at a loss what to do, asked his attendants which of them would undertake the job. Upon this one of them, Li Neng, who happened to be gloriously drunk, stepped forward and said that he would; where- upon the warrant was immediately issued and the old woman went away. When our friend, Li Neng, got sober, he was sorry for what he had done; but reflecting that the whole thing was a mere trick of his master’s to get rid of the old woman’s importunities, did not trouble himself much about it, handing in the warrant as if the arrest had been made. “Not so,” cried the magistrate, “you said you could do this, and now I shall not let you off.” Li Neng was at his wits’ end, and begged that he might be allowed to impress the hunters of the district. This was conceded; so collecting together these men, he proceeded to spend day and night among the hills in the hope of catching a tiger, and thus making a show of having fulfilled his duty. A month passed away, during which he received several hundred blows with the bamboo, and at length, in despair, he betook himself to the Cheng-huang temple in the eastern suburb, where, falling on his knees, he prayed and wept by turns. By-and-by a tiger walked in, and Li Neng, in a great fright, thought he was going to be eaten alive. But the tiger took no notice of anything, remaining seated in the doorway. Li Neng then addressed the animal as follows: “O tiger, if thou didst slay that old woman’s son, suffer me to bind thee with this cord;” and, drawing a rope from his pocket, threw it over the animal’s neck. The tiger drooped its ears, and, allowing itself to be bound, followed Li Neng to the magistrate’s office. The latter than asked it, “Did you eat the old woman’s son?” to which the tiger replied by nodding his head; whereupon the magistrate rejoined, “That murderers should suffer death has ever been the law. Besides, this old woman had but one son, and by killing him you took from her the sole support of her declining years. But if now you will be as a son to her, your crime shall be pardoned.” The tiger again nodded assent, and accordingly the magistrate gave orders that he should be released, at which the old woman was highly incensed, thinking that the tiger ought to have paid with its life for the destruction of her son. Next morning, however, when she opened the door of her cottage, there lay a dead deer before it; and the old woman, by selling the flesh and skin, was able to purchase food. From that day this became a common event, and sometimes the tiger would even bring her money and valuables, so that she became quite rich, and was much better cared for than she had been even by her own son. Consequently, she became very well-disposed to the tiger, which often came and slept in the verandah, remaining for a whole day at a time, and giving no cause of fear either to man or beast. In a few years the old woman died, upon which the tiger walked in and roared its lamentations in the hall. However, with all the money she had saved, she was able to have a splendid funeral; and while her relatives were standing round the grave, out rushed a tiger, and sent them all running away in fear. But the tiger merely went up to the mound, and, after roaring like a thunder-peal, disappeared again. Then the people of that place built a shrine in honor of the Faithful Tiger, and it remains there to this day. (ack:englishdaily626.com)

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