Posts Tagged ‘memory’
the best kind of sleep
Canto: So Dr Seheult tells us that the most important sleep is in the earliest period. This is called slow-wave sleep or N3 sleep. It doesn’t last long, maybe half an hour…
Jacinta: Why is it called N3 sleep?
Canto: Well, here’s the detail – you have three stages of this early sleep. N1 is when you fall asleep. It lasts no more than ten minutes generally until you’re really there, in sleep. Then there’s N2 of course, which lasts from 30-60 minutes, your muscles relax and you begin to enter this slow-wave, also called delta-wave or delta brain activity sleep. That’s the deepest sleep of the night, at its deepest in the N3 period.
Jacinta: Well that explains the 1-2-3, sort of, but what about the N?
Canto: I haven’t been able to find that out specifically, but these are all phases of NREM (non-rapid eye movement) sleep, which are followed by the REM phase. So I think the N is just short for NREM. Anyway there are two types of sleep for maintaining good health – slow wave sleep and REM sleep towards the end of the night…
Jacinta: But don’t those two make up the whole of the sleep cycle?
Canto: Let me tell the story. Slow wave sleep is when you secrete valuable growth hormone, vital for children, in the time before midnight, according to the good doctor.
Jacinta: But I virtually never sleep before midnight.
Canto: Well you’re not alone there. In cities now, which are growing ever larger, we’re going to bed later and getting up earlier, and so sleeping less…
Jacinta: But generally living longer. So what’s the problem? I’ve heard that Hong Kong, which is about as urban as it gets, has the longest life expectancy on Earth – but that was probably measured before the China crackdown haha.
Canto: Well it’s no joke that China’s thugocracy will jeopardise everything in HK’s future, but good public healthcare and a very low infant mortality rate helps. People today can still live well with diabetes, obesity and slow-developing cancers, but they’d be even better with good sleep habits, if the rat-race allows them. But cities present us with a kind of eternal daylight, at great cost, not only in electric lighting, but in lack of sleep. Not to mention brightly lit screens that we take to bed with us…
Jacinta: Okay so what are the other benefits of slow wave and REM sleep, however delayed?
Canto: Dr Seheult describes a study showing that general sleep deprivation actually reduces the levels of antibodies produced after influenza vaccination. That’s to say, vaccination is less effective for the sleep-deprived. Another study used rhinovirus, a common cold virus. They paid students to be infected and found that those with good sleep efficiency, that’s to say, a high ratio of in-bed time to sleep time – their risk of being infected was reduced five to seven-fold, an extraordinary result. Actually this ‘extraordinary result’ finding comes up again and again in Matthew Walker’s book.
Jacinta: Yes, but it’s surely good to be awake sometimes too. But again, what is it about slow-wave and REM sleep that provides such benefits. What are the mechanisms?
Canto: Well, we’re talking about N3 sleep, the deepest sleep. This sleep phase is particularly important for memory consolidation, the stabilisation of a memory trace once it’s been acquired – meaning presumably the event itself, or its impact. It’s also called sleep-dependent memory processing. Now, how this precisely works is still being researched, but it appears to have much to do with interactions between neurons or neuronal complexes in the neocortex and the hippocampus. So here I should introduce sleep spindles, which are essential to all mammalian species.
Jacinta: They’re brainwaves, aren’t they?
Canto: Neural oscillations, indeed. They’re generated in the thalamic reticular nucleus (TRN), in richest quantities during N2 and N3 sleep. Wikipedia tells me this:
The density of spindles has been shown to increase after extensive learning of declarative memory tasks and the degree of increase in stage 2 spindle activity correlates with memory performance.
This is confirmed in experiments described in Why we sleep, showing that people who slept for a night between being asked to memorise certain data, like putting a name to a face, did a significantly better job than those who tried to remember the data after eight hours without sleep (from morning to evening). During the sleep period, subjects’ brain waves were recorded, and this is Dr Walker’s account:
The memory refreshment was related to lighter, stage 2 NREM sleep, and specifically the short, powerful bursts of electrical activity called sleep spindles… The more sleep spindles an individual obtained during the nap, the greater the restoration of their learning when they woke up. Importantly, sleep spindles did not predict someone’s innate learning aptitude. That would be a less interesting result, as it would imply that inherent learning ability and spindles simply go hand in hand. Instead, it was specifically the change in learning from before relative to after sleep, which is to say the replenishment of learning ability, that spindles predicted.
Jacinta: So they were correlating the number of spindles with their memorising performance, and memory here is being equated with learning. Is that right? I mean, is learning really just memorising?
Canto: Well, no, but it helps. I’m trying to memorise Newton’s inverse square law for gravity, but I know that even if I can reel it off like a favourite poem that doesn’t mean I fully understand it. Let me see G = m1.m2 over r². I’m not sure if that’s right.
Jacinta: Yeah, basically you have to know that the gravitational attraction between two bodies is equal to the product of their masses divided by the square of the distance between their ‘centres of mass’. I think. Though why that happens to be the case I have no idea. Does anyone?
Canto: Because… the universe? I’m beginning to feel sleepy…
References
M. Walker, Why we sleep, 2017
https://www.uofmhealth.org/health-library/hw48331
How to get the best sleep for your immune system | Roger Seheult (video)
https://www.oal.cuhk.edu.hk/cuhkenews_202101_life_expectancy/
reading matters 9
New Scientist – the collection: mysteries of the human brain. 2019
- content hints – history of neurology, Galen, Hippocrates, Descartes, Galvani, Thomas Willis, Emil Du Bois-Reymond, Santiago Ramon y Cajal, connectionism, plasticity, mind-maps, forebrain, midbrain, hindbrain, frontal, parietal and occipital lobes, basal ganglia, thalamus, hypothalamus, amygdala, hippocampus, cerebral cortex, substantia nigra, pons, cerebellum, medulla oblongata, connectome, action potentials, axons and dendritic spines, neurotransmitters, axon terminals, signalling, ion channels and receptors, deep brain stimulation, transcranial direct current stimulation, hyper-connected hubs, 170,000 kilometres of nerve fibres, trains of thought, unbidden thoughts, memory and imagination, the sleeping brain, unconscious activity, the role of dreams, brainwaves during sleep, sleep cycles, traumatic stress disorder, Parkinsons, ADHD, dementia, depression, epilepsy, anaesthesia, attention, working memory, first memories, rationality, consciousness, von Economo neurons, the sense of self…
the autodidact story 1: family and authority
When I was young I was somewhat troubled about myself. I was unhappy at home, I hated school, I felt I had no-one to talk to, and my only solace was the ‘rich inner life’ that, much later, I read about in an essay by the philosopher Hilary Putnam. That’s to say, he wrote an essay in which he happened to mention that some outwardly nondescript people might have cultivated a rich inner life, or words to that effect, and this fairly mundane observation was the only thing I took from Putnam’s essay.
I had a difficult time with friendship, and still do. On my birthday – I was probably fourteen – I received a card from another boy I knew well. It read ‘to my best friend ever’. I read it with shock. It made me feel somehow ashamed and miserable. I felt that this friend of mine was deluded, and I’d been the cause of his delusion. Perhaps there was some arrogance in this – I felt that my ‘rich inner life’ was almost completely hidden from him, and everyone else, so how could he think he knew me well enough to consider me his BFF? However, when he left for England with his family a few months later I felt more alone than ever.
I’ve never felt seriously suicidal, but I do recall a particular moment, when I thought, ‘this is who I am – a loner. I have to learn to live with it’. I cried myself to sleep, and went on.
Of course, all autobiographies, whether short or long, are mostly lies, beautiful or otherwise, so don’t take any of this too seriously. My parents didn’t get on too well, to put it mildly, and my siblings were – rivals. We lived in one of the most thoroughly working-class regions of Australia, in the newly created town of Elizabeth, built around the manufactory of holden cars, now deceased. My father worked there for a brief time, but he didn’t like working in factories, and I don’t blame him, having worked in quite a few myself. Unfortunately he couldn’t think of anything else to do, so he didn’t do anything much, and my mother was the nagging, harried breadwinner. My relationship with both of them during my teen years could fairly be described as toxic.
We did have books however. Encyclopedias, classics, and surprisingly modern fare, especially in the new feminist line, such as The female eunuch, Patriarchal attitudes, The feminine mystiquue and The second sex. I don’t know where all these books came from, they just always seemed to be there. My mother insisted on getting us to the library regularly, for which I’ll always be grateful, but I rarely saw her reading anything. She had a higher-up job in the nursing profession and when she got home she’d always flip the TV from the ABC to her favourite sit-coms, I love Lucy or The Dick Van Dike show. As for my father, I often wondered if he knew how to read. But these people bestowed upon me their genes, more or less equally, and that was a source of wonder. Was I smart?
We had come to Australia as ten pound migrants, and I had flickering memories of the boat trip – a camel train on the banks of the Suez, being saved from drowning in the ship’s pool, sitting with a group of kids while my mother, seconded as an educator, taught us spelling or something.
Education. I became a teenager in 1969. It was a fantastic time for music, and the culture that came with it. I looked out the window at my brother and his friends and they were all wearing levis and it looked so cool. My older siblings were buying records – the Beatles, the Kinks, the Stones, and some now-embarrassing singles like ‘Little Arrows’ by Leapy Lee. Not long afterwards came Dylan and Cohen and I loved all that cool verbiage. Was I smart? I didn’t like school. I couldn’t talk to the teachers like other kids. I didn’t like the inequality, that they might know more than me. I didn’t like being told what to do. I liked to read, to learn stuff in my own way. I didn’t have an imaginary friend exactly, but I was always talking and arguing in my head, and felt the lack of the real thing.
One day I was somehow invited to some kid’s house whose older sister was visiting from university. Did she live in the university? There was a crowd of kids and I could just see glimpses of the girl-woman through arms and legs. She was sitting on a stool as on a pedestal and she was slim and pretty with neat blonde hair and lipstick and a neat plaid skirt and heels, and I was shocked at this first ever sight of a university student. They were supposed to wear jeans and sandals and tie-dyed t-shirts and be beautifully scruffy and hairy. Disappointing.
Anyway, I left school because I was always in trouble for not doing my homework, inter alia, and I had horrible fights with my mother when she wasn’t having horrible fights with my father, and my father had fist fights with me, which wasn’t much fun as he’d been a boxer in his past and I could see him eyeing me for maximum damage with his dukes up. I would stay at friends’ houses here and there, and I got my first job on an assembly line making Wilkins Servis washing machines. The one shown is of course a much earlier model than the ones I tended to stuff up when I worked there.
And so my first experience of formal education was botched, and maybe I should blame myself, I don’t know. I continued to read of course, and to argue with myself. A rich inner life.
I read novels, mostly, in those days. I developed an obsession with Thomas Hardy. This was in my fifteenth year, I think. The Return of the Native was my first, and I think I read every single novel except A Laodicean, which critics said was his worst. I wanted to read it, for completeness, like Two Gentlemen of Verona, which I did read. I also wanted to know why it was considered so bad. I loved Thomas Hardy, he was so kind, it seemed to me, and so sad somehow.
(to be continued)
the latest on dolphin language
I wrote, or semi-podcasted, on the brain of the dolphin a while back, and much of my focus was on language, often described as the sine qua non of cerebral complexity and intelligence. In that piece, posted about eight months ago, I reported that there there was little clear evidence of any complex language in dolphins, but there had been some interesting research. Allow me to quote myself:
Dolphins do sometimes mimic the whistles of other dolphins too, particularly those of their closest relatives, but signature whistles as a form of recognition and differentiation, are a long way from anything like language. After all, many species can recognise their own mates or kin from the distinctive sounds they make, or from their specific odour, or from visual cues. However, a clever experiment carried out more recently, which synthesised these whistles through a computer, so that the whistle pattern was divorced from its distinctive sound, found that the dolphins responded to these patterns even when produced via a different sound. It seemed that they were recognising names. It’s undoubtedly intriguing, but clearly a lot more research is required.
So it was with some interest that I heard, on a recent SGU podcast, an account of what seemed an elaboration of the experiments conducted above, further confirming that dolphins recognised names. Or were they just reporting the same experiments? Having re-listened to the SGU segment, I find that they didn’t give any details of who did the study they were talking about, the only mention was to a news article. So I’ll just report on anything I can find, because it’s such a cool subject.
There’s a nice TED talk, from February 2013, on dolphin language and intelligence here, which is about researches over many years in the Bahamas with Atlantic spotted dolphins. As always, I suggest you listen to the talk and do the ‘research on the research’ yourself, as I’m not a scientist and I’m only doing this to educate myself, but hopefully I can also engage your interest.
Dolphins have a brain- to-body ratio (a rough but not entirely reliable guide to intelligence) second only to humans, they pass the mirror self-awareness test (another standard for intelligence that’s been questioned recently), they can be made to understand very basic artificial human language tests, and they’re at least rudimentary tool users. But the real interest lies in their own, obviously complex, vocal communication systems.
I probably misrepresented the information on signature whistles before: they’re only what we humans have been able to isolate from all the ‘noise’ dolphins make, because they’re recognisable and interpretable to us. Denise Herzing, in her TED talk, refers to ‘cracking the code’ of dolphins’ communication systems. She and her team have been working with the dolphins over the summer months for 28 years. They work with underwater cameras and hydrophones to correlate the sounds and behaviours of their subjects. This particular species is born without spots, but is fully black-and-white spotted by age 15. They go through distinct developmental phases making them easy to track over the years (dolphins live into their early 50s). The distinctive spotted patterns make them easy to track individually. Females are sexually mature by about age 9, males at around 15. Dolphins are very sexually active with multiple partners, so paternity is not always easy to determine, so this is worked out by collecting fecal matter and analysing its DNA. So, over 28 years, three generations have been tracked.
What really interests me about the dolphin communication question is their relation to sound and their use of sound compared to ours. Herzing describes them as ‘natural acousticians’ who make and hear sounds ten times as high as humans do. They also have highly developed vision, so they communicate via bodily signals, and they have taste and touch. Sound is of course a wave or vibration which can be felt in water, the acoustic impedance of tissue in water being much the same as on land. Tickling, of a kind, does occur.
Signature whistles are the most studied dolphin sounds, as the most easily measured. They’re used as names, in connecting mothers and calves for example. But there are many other vocalisations, such as echo-location clicks (sonar), used in hunting and feeding, and also socially, in tightly-packed sound formations – buzzes, which can be felt in the water. They’re used regularly by males courting females. Burst-pulse sounds are used in times of conflict, and they are the least studied, most hard to measure of dolphin sounds.
Interestingly, Herzing notes that there’s a lot of interaction and co-operation in the Bahamas between spotted and bottle-nose dolphins, including baby-sitting each others’ calves, and combining to chase away sharks, but little mention is made, in this talk at least, of any vocal communication between the two species. When she goes on to talk about synchrony, I think she’s only talking about within-species rather than between species. Synchrony is a mechanism whereby the dolphins co-ordinate sounds and body postures to create a larger, stronger social unit.
As I’ve mentioned, dolphins make plenty of sounds beyond the range of human hearing. Underwater equipment is used to collect these ultrasonic sounds, but we’ve barely begun to analyse them. Whistle complexity has been analysed through information theory, and is highly rated even in relation to human languages, but virtually nothing is known about burst-pulse sounds, which, on a spectrogram, bear a remarkable similarity to human phonemes. Still, we have no Rosetta Stone for interpreting them, so researchers have developed a two-way interface, with underwater keyboards, with both visual and audible components. In developing communication, they’ve exploited the dolphins’ natural curiosity and playfulness. Dolphins, for example, are fond of mimicking the postures and vocalisations of humans, and invite the researchers into their play. Researchers have developed artificial whistles to refer to dolphins’ favourite toys, including sargassum, a kind of seaweed, and ropes and scarves, so that they can request them via the keyboard interface. These whistles were outside the dolphins’ normal repertoire, but easily mimicked by them. The experiment has been successful, but of course it isn’t known how much they understand, or what’s going through their minds with all this. What is clear, however, is that the dolphins are extremely interested in and focused on this type of activity, which sometimes goes on for hours.
This research group has lately been using an underwater wearable computer, known as CHAT (cetacean hearing and telemetry), which focuses on acoustic communication. Sounds are created via a forearm keyboard and an underwater speaker for real-time Q and A. This is still at the prototype stage, but it uses the same game-playing activity, seeking to empower dolphins to request toys, as well as human game-players, through signature whistles. It’s hoped that the technology will be utilisable for other species too in the future.
All of this is kind of by way of background to the research reported on recently. This was really about dolphin memory rather than language – or perhaps more accurately, memory triggered by language. Dolphins recognise the sounds of each others’ signature whistles, but would they recognise the whistle of a dolphin they’d not been in contact with for years. And for how many years? Researcher Jason Bruck tested this by collecting whistles of dolphins in captive facilities throughout the US. Dolphins are moved around a lot, and lose contact with friends and family. Sounds a bit like the foster-care system. Bruck found that when dolphins heard the signature whistles of old companions played to them through an underwater speaker, they responded with great attention and interest. One dolphin was able to recognise the whistle of a friend from whom he was separated at age two, after twenty years’ separation. As biologist Janet Mann put it, this is a big breakthrough but not so surprising, as dolphins are highly social animals whose lives, like ours, are criss-crossed by profound connections with others, with effects positive, negative and equivocal. It’s important, too, for what it suggests – the capacity to remember so much more, in the same coded way. in other words, a complex language, perhaps on a level with ours. Will we ever get to crack this code? Why not. Hopefully we won’t stop trying.