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You can find the current article at its original source at http://www.theguardian.com/science/neurophilosophy/2014/jun/01/sleep-hemispatial-neglect
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| Version 1 | Version 2 |
|---|---|
| Sleepy brains neglect half the world | Sleepy brains neglect half the world |
| (35 minutes later) | |
| Damage to certain parts of | Damage to certain parts of |
| the brain can lead to a bizarre syndrome called hemispatial neglect, in which one loses awareness of one side of their body and the space around it. In | |
| extreme cases, a patient with hemispatial neglect might eat food from only one | extreme cases, a patient with hemispatial neglect might eat food from only one |
| side of their plate, dress on only one side of their body or shave or apply make-up to half of their face, apparently because they cannot pay attention to | side of their plate, dress on only one side of their body or shave or apply make-up to half of their face, apparently because they cannot pay attention to |
| anything on that the other side. | anything on that the other side. |
| Research published | Research published |
| last week now suggests that something like this happens to all of us when we drift off to sleep each night. The work could help researchers to | last week now suggests that something like this happens to all of us when we drift off to sleep each night. The work could help researchers to |
| understand the causes of hemispatial neglect, and why it affects one side far | understand the causes of hemispatial neglect, and why it affects one side far |
| more often than the other. It also begins to reveal the profound changes in | more often than the other. It also begins to reveal the profound changes in |
| conscious experience that take place while we fall asleep, and the brain | conscious experience that take place while we fall asleep, and the brain |
| changes that accompany them. | changes that accompany them. |
| Hemispatial neglect is a debilitating condition that occurs often in people who suffer a stroke, | Hemispatial neglect is a debilitating condition that occurs often in people who suffer a stroke, |
| where damage to the left hemisphere of the brain results in neglect of the | where damage to the left hemisphere of the brain results in neglect of the |
| right half of space, and vice versa. | right half of space, and vice versa. |
| It can occur as a result of damage to certain parts of the frontal lobes, which | It can occur as a result of damage to certain parts of the frontal lobes, which |
| are involved in alertness and attention, and the parietal lobes, which process | are involved in alertness and attention, and the parietal lobes, which process |
| information about the body and its surrounding space. | information about the body and its surrounding space. |
| In clinical tests, patients | In clinical tests, patients |
| with hemispatial neglect are typically unaware of all kinds of stimuli in one | with hemispatial neglect are typically unaware of all kinds of stimuli in one |
| half of space – they fail to acknowledge objects placed in the affected half of | half of space – they fail to acknowledge objects placed in the affected half of |
| their visual field, for example and cannot state the location of touch | their visual field, for example and cannot state the location of touch |
| sensations on the affected side of their body. Some may stop using the limbs on | sensations on the affected side of their body. Some may stop using the limbs on |
| the affected side, or even deny that the limbs belong to them. Patients with neglect can usually see perfectly | the affected side, or even deny that the limbs belong to them. Patients with neglect can usually see perfectly |
| well, but information from the affected side just does not reach their conscious | well, but information from the affected side just does not reach their conscious |
| awareness. | awareness. |
| In 2005, researchers at the MRC | In 2005, researchers at the MRC |
| Cognition and Brain Sciences Unit in | Cognition and Brain Sciences Unit in |
| Cambridge reported that reduced | Cambridge reported that reduced |
| alertness dramatically alters spatial awareness in healthy people by shifting | alertness dramatically alters spatial awareness in healthy people by shifting |
| attention to the right so that they | attention to the right so that they |
| neglect visual stimuli to the left. To investigate further, they recruited 26 more healthy participants and tested their | neglect visual stimuli to the left. To investigate further, they recruited 26 more healthy participants and tested their |
| spatial awareness while they fell asleep. | spatial awareness while they fell asleep. |
| To do so, they took the | To do so, they took the |
| participants one by one into a dark room and told them to sit back in a | participants one by one into a dark room and told them to sit back in a |
| comfortable reclining chair and relax. They recorded the participants’ brain | comfortable reclining chair and relax. They recorded the participants’ brain |
| wave patterns using electrodes attached to the scalp, and measured their reaction | wave patterns using electrodes attached to the scalp, and measured their reaction |
| times, to determine exactly when they started getting drowsy, then played sounds | times, to determine exactly when they started getting drowsy, then played sounds |
| to either their left or right, and asked them to indicate which side each one | to either their left or right, and asked them to indicate which side each one |
| came from by pressing one of two buttons. | came from by pressing one of two buttons. |
| Again, the researchers saw | Again, the researchers saw |
| that reduced alertness caused a rightward shift in spatial attention. During | that reduced alertness caused a rightward shift in spatial attention. During |
| the few moments of drowsiness just before falling asleep, the participants | the few moments of drowsiness just before falling asleep, the participants |
| consistently mislocated sounds played to their left, and said that they had been | consistently mislocated sounds played to their left, and said that they had been |
| played to the right. | played to the right. |
| “This is an exciting development,” | “This is an exciting development,” |
| says Masud Husain, | says Masud Husain, |
| a clinical neurologist at the University of Oxford who studies neglect in stroke patients. “It suggests that while falling asleep the healthy brain behaves in a | a clinical neurologist at the University of Oxford who studies neglect in stroke patients. “It suggests that while falling asleep the healthy brain behaves in a |
| similar way to stroke patients who have difficulty keeping alert.” | similar way to stroke patients who have difficulty keeping alert.” |
| The findings | The findings |
| further suggest that the attentional | further suggest that the attentional |
| deficits associated with hemispatial neglect apply to sounds as well as | deficits associated with hemispatial neglect apply to sounds as well as |
| to sights and bodily sensations, and also provide clues about why, in the vast | to sights and bodily sensations, and also provide clues about why, in the vast |
| majority of cases, neglect only persists after damage to the right hemisphere | majority of cases, neglect only persists after damage to the right hemisphere |
| of the brain. “Both groups appear | of the brain. “Both groups appear |
| to have particular difficulty attending to information to their left, consistent | to have particular difficulty attending to information to their left, consistent |
| with the view that frontal and parietal regions of the right hemisphere play a | with the view that frontal and parietal regions of the right hemisphere play a |
| key role in maintaining alertness.” | key role in maintaining alertness.” |
| The study also provides clues about the brain mechanisms | The study also provides clues about the brain mechanisms |
| underlying neglect. “People don't necessarily miss items on the left as they | underlying neglect. “People don't necessarily miss items on the left as they |
| become more drowsy, but instead respond as if they had come from the right,” | become more drowsy, but instead respond as if they had come from the right,” |
| says Husain, “as if their perception of space becomes skewed to the right as | says Husain, “as if their perception of space becomes skewed to the right as |
| their alertness declines.” | their alertness declines.” |
| “The implication is that right hemisphere brain mechanisms that are crucial to representing space around our bodies also interact with | “The implication is that right hemisphere brain mechanisms that are crucial to representing space around our bodies also interact with |
| processes that keep us vigilant and alert,” he adds. “The results are | processes that keep us vigilant and alert,” he adds. “The results are |
| intriguing but need to be confirmed, perhaps with a more precise method than | intriguing but need to be confirmed, perhaps with a more precise method than |
| pressing buttons.” | pressing buttons.” |
| Reference: Bareham, C. A., et | Reference: Bareham, C. A., et |
| al. (2014). Losing | al. (2014). Losing |
| the left side of the world: Rightward shift in human spatial attention with | the left side of the world: Rightward shift in human spatial attention with |
| sleep onset. Scientific Reports 4, doi: 10.1038/srep05092 | sleep onset. Scientific Reports 4, doi: 10.1038/srep05092 |