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Monthly Archives: August 2004

Feel The Burn

I am off to the Burning Man festival with some pals. I’ll be back on the weekend of September the 11th. Until then I’ve turned off comments completely on the site and I won’t be answering emails, calls, faxes or post. But, hey, if you see me, give me a shout. Coming in September: lots about the Mind Hacks book.

Comment Spammers 2 – Tom 0

I’ve further restricted commenting on the site. You can now only post comments on entries which are less than 2 days old. (And I am feeling a variety of very negative emotions towards the people who design bots to spam my site).

Comment Spammers 1 – Tom 0

As of now it is harder to comment on my site. If the post is from more than 7 days ago and no one has been commenting on it then you won’t be able to add any comments. You’ll have to email me instead. Sorry folks, but the comment spam is getting too annoying.

Links for 23rd August 2004

Links for 12 August 2004

hello world!

Congrats to Ewan who has just launched his site, cognitivemiser.co.uk and who has also won himself a holiday job in Chiba, Japan for the next year. Well done Ewan!

While I’m at it, congratulations also to Dr Will for getting a post-doc at LSE and to Kev for getting his website set up – great stuff.

I’m going camping the day after tomorrow, so there’s nothing new likely to be here until tuesday 17th.

Links for 9th August 2004

Dolphin’s Brains

A wrinkle to add to one of my favourite neurobiology factoids: Dolphins may not sleep with one side of their brains at a time after all [1]. Or, rather, they do sleep one side at a time (unihemispherically), but they may also sometimes let both sides sleep at once, albeit very briefly.

It’s not just dolphins who sleep with one side of the brains at a time. Other sea-sleeping mammals (whales, seals and manatee), many birds and maybe reptiles, like crocodiles, sleep unihemispherically too [1].

Posture assumed by northern fur seals during unihemispheric slow-wave sleep in water. In this example, the fur seal is lying on its left side while the left flipper (connected to the awake (right) hemisphere) constantly paddles. This posture allows the fur seal to keep its nostrils above the water?s surface, while the left hemisphere sleeps. When the fur seal switches to lying on its right side, the left hemisphere remains awake while the right hemisphere sleeps. (Figure and text shamelessly stolen without permission)

So: possibly our reptilian ancestors slept unihemispherically and we lost the habit as we tripped up the phylogenetic scale. Secondly, dolphins probably wouldn’t sleep one hemisphere at a time if they weren’t sleeping in the water. If we could just convince those guys to move onto land…I mean they’re pretty smart already, think what they could do if they could let one of their hemispheres drop the functions needed for wakefulness [3]. With one hemisphere relived of the need to be self-sufficient it could develop a deeper, complementary role for the other, waking-responsible hemisphere. They could be even smarter than they already are. Lets face it, we could do with some help up here- we need the dolphins on our team!

Hmm. Anyway. I wonder if there asymmetries in the human hemispheric response to sleep? It would suggest that a similar process had happen in mammalian evolution. And did dolphins evolve from a land-based mammalian line, and when?

Refs

1. Sam H. Ridgway (2002). Asymmetry and Symmetry in Brain Waves from Dolphin Left and Right Hemispheres: Some Observations after Anesthesia, during Quiescent Hanging Behavior, and during Visual Obstruction. Brain, Behavior and Evolution 2002;60:265-274

Abstract: Studies of sleep in cetaceans (whales, dolphins, and porpoises), substantiated by electrophysiological data, are rare with the great majority of observations having been made by one group from Russia. This group employed hard-wired recording with low-noise cables for their EEG observations, whereas our report describes behavioral and EEG observations of dolphin sleep using telemetry. Marked asymmetry of the EEG was observed during behavioral sleep posture. At different times synchronized slow waves appeared in both left and right brain hemispheres concurrently with lower voltage, faster, desynchronized EEG activity in the opposite hemisphere. On the other hand, during one brief period of sleep behavior, sleep-like EEG activity appeared on leads from both hemispheres. When the animal was exposed to a loud sound, it woke with lower voltage, faster, relatively symmetrical, desynchronized EEG activity appearing from both hemispheres. Additionally, the EEG appeared relatively desynchronized and symmetrical between the two hemispheres when the animal was awake during recovery from pentothal-halothane anesthesia as well as during waking periods when one or both of the animal’s eyes were covered by an opaque rubber suction cup.

2. N.C. Rattenborg, C.J. Amlaner, S.L. Lima (2000). Behavioral, neurophysiological and evolutionary perspectives on unihemispheric sleep. Neuroscience & Biobehavioral Reviews. Volume 24, Issue 8 , December 2000, Pages 817-842

3. Incidentally dolphins do have some hemispheric specialisation – they have a left dominance for visuo-spatial cognition (ie the opposite to humans): Kilian, A., von Fersen, L., G?nt?rk?n, O. (2000). Lateralization of visuospatial processing in the bottlenose dolphin (Tursiops truncatus). Behav Brain Res 116: 211-215

Optimal neural population coding of an auditory spatial cue

My friend Nicol had his first paper in Nature come out today [1]. Well done Nicol! [2]. For any readers who care for a bit of computational neuroscience, with information theory on the side, here’s the abstract:

A sound, depending on the position of its source, can take more time to reach one ear than the other. This interaural (between the ears) time difference (ITD) provides a major cue for determining the source location. Many auditory neurons are sensitive to ITDs, but the means by which such neurons represent ITD is a contentious issue. Recent studies question whether the classical general model (the Jeffress model) applies across species. Here we show that ITD coding strategies of different species can be explained by a unifying principle: that the ITDs an animal naturally encounters should be coded with maximal accuracy. Using statistical techniques and a stochastic neural model, we demonstrate that the optimal coding strategy for ITD depends critically on head size and sound frequency. For small head sizes and/or low-frequency sounds, the optimal coding strategy tends towards two distinct sub-populations tuned to ITDs outside the range created by the head. This is consistent with recent observations in small mammals. For large head sizes and/or high frequencies, the optimal strategy is a homogeneous distribution of ITD tunings within the range created by the head. This is consistent with observations in the barn owl. For humans, the optimal strategy to code ITDs from an acoustically measured distribution depends on frequency; above 400 Hz a homogeneous distribution is optimal, and below 400 Hz distinct sub-populations are optimal.

Update: Article from BBC news Hearing more complex than thought

Refs
[1] Optimal neural population coding of an auditory spatial cue
Nicol S. Harper and David McAlpine
Nature, 05 August 2004, Volume 430, No. 7000, pgs 682-686

[2] I am immensely proud – in the it-had-nothing-whatsoever-to-do-with-me-I-just-watched-it-happen kinda way

Codename ‘Brain Hacks’

I’m writing a book, with my friend Matt, for O’Reilly, codenamed ‘Brain Hacks’

The book is a selection of 100 design quirks of consciousness – ways in which constraints from neurobiology or evolution have produced unexpected features in cognition.

O’Reilly are an American publisher who produce computer books. One series they do, the Hacks series covers tips, tricks, unorthodox methods and functional insights for well known bits of software. This book will be the same, but covering for the bugs and features of the human operating system. A selection of functional anecdotes about the construction of conscious experience and behaviour. A smash and grab on the intellectual goodies of cognitive neuroscience!

Writing the book is going really well, and we’ve got some great people contributing. It’s great fun putting together practical demonstrations of important computational and cog neuro principles, and it’s even fun being driven slightly mad as I start to notice all the ways in which my experience of the world is constructed from the raw data available to my senses, and the ways my actions are delegated to different, intermeshed, subsystems.

There’s loads more to say, but for now I’m going to get back to writing the book. Swing over to Matt’s blog if you want to read a bit more about the project – and of course check back here over the next month (until I fly to Burning Man when this blog will go a bit quiet for a couple of weeks).

Links for 4th August 2004

A group is it’s own worst enemy

Read this! Clay Shirky on ‘A Group is it’s own worst enemy’. As well as containing gems like this, on the power of out-group prejudice:

groups often gravitate towards members who are the most paranoid and make them leaders, because those are the people who are best at identifying external enemies.

And, on why geocities came before weblogs:

It took a long time to figure out that people talking to one another, instead of simply uploading badly-scanned photos of their cats, would be a useful pattern.

He also has some interesting reflections on the basic patterns groups reproduce (he says sex/flirtation, outgroup animosity and religious veneration are the top three), on why structure is needed to protect groups from themselves (it is members of the group, operating within the deliberate remit of the group’s initial intention that often cause its collapse, not ‘outsiders’) and a whole lot of other stuff about social software.

And, basically, i’m not too wrapped up in the software bit of social software, i’m more interested in the social. How can we catalyse well functioning groups?

Clay says that you need some kind of privilaged group of core users, or some kinds of barriers to entry – in an internet forum a lack of these things leads to a one-person-one-vote tyranny of the majority [please read the article before getting upset about any anti-democratic sentiments you perceive here].

However for non-internet groups, I’m wonder if our problem isn’t the lack of limits to commitment, rather than lack of barriers to entry based on a minimum level of commitment. I’ve seen a lot of social and political groups which get overly swayed by the minority that have the time to commit totally and obsessively to the group – it doesn’t make for a rounded decision making process.

I’m in danger of starting an epic string of posts on the interrelation of group structure and group function, if anyone would like to head me off at the pass and recommend some reading/ideas to get my head corrected on this first i’d welcome it…

Teen mice and anti-gravity fish

I think coming across stuff like this is one of the reasons I love science. I’d never have thought of it, but someone did and now the knowledge is available for everyone to share. Plus it means that somewhere in Germany, someone is getting paid to centifuge fish.

Risk-taking behavior in adolescent mice: psychobiological determinants and early epigenetic influence
Giovanni Laviola, Simone Macri, Sara Morley-Fletcher, Walter Adriani
Neuroscience and Biobehavioral Reviews 27 (2003) 19?31

Abstract: Epidemiological research has emphasized that adolescence is associated with some temperamental and behavioral traits that are typical of this age and that might substantially contribute to both psychological and psychobiological vulnerability. The contribution of the important developmental rearrangements in neurobiological and neuroendocrinological processes has received surprisingly little investigation. The present review summarizes recent work in animal models, indicating that adolescent rodents exhibit marked peculiarities in their spontaneous behavioral repertoire. When compared to adults, adolescents show an unbalanced and extremes oriented behavior, consisting of an increased novelty seeking, together with decreased novelty-induced stress and anxiety, an increased risk-taking behavior in the plus-maze, as well as elevated levels of impulsivity and restlessness. Age-related discontinuities in the function of monoaminergic systems, which are a main target of abused drugs, can perhaps account for such a profile. In particular, a peculiar function within reward-related dopaminergic brain pathways actually seems to underlie the search for novel and rewarding sensations, as well as changes in the magnitude of psychostimulant effects. The role played by early epigenetic factors in the shaping of novelty-seeking behavior of adolescent and adult rodents are also reviewed. Two examples are considered, namely, subtle variations in the hormonal milieu as a function of intrauterine position and precocious or delayed maturation of nutritional independence as a function of changes in time of weaning. As for spontaneous drug consumption, a prominent vulnerability to the oral intake of nicotine during early adolescence is reported. In conclusion, adolescence in rodents may represent a suitable animal model with enough face- and construct-validity. Actually, this model is able to show behavioral features that resemble those found in human adolescents, including vulnerability to the consumption of psychoactive drugs.

Neurobiology of fish under altered gravity conditions
Ralf H. Anken, Michael Ibsch, Hinrich Rahmann
Brain Research Reviews 28 1998 9?18

Abstract: In vertebrates (including man), an altered gravitational environment such as weightlessness can induce malfunction of the inner ear, based on an irregular dislocation of the otoliths from the corresponding sensory epithelia. This dislocation leads to an illusionary tilt, since the otolithic inputs are not in register with other sensory organs. This results in an intersensory conflict. Vertebrates in orbit therefore face severe orientation problems. In humans, the intersensory conflict may additionally lead to a malaise, commonly referred to as space motion sickness (SMS). During the first days in weightlessness, the orientation problems and SMS disappear, since the brain develops a new compensatory interpretation of the available sensory data. The present review reports the neurobiological responses?particularly in fish?observed at altered gravitational states, concerning behaviour and neuroplastic reactivities. Recent investigations employing microgravity (spaceflight, parabolic aircraft flights, clinostat) and hyper-gravity (laboratory centrifuges as ground based research tools) yielded clues and insights into the understanding of the respective basic phenomena. The possible sources of human space sickness a kinetosis and of the space adaptation syndrome (when a sensory reinterpretation of gravitational and visual cues takes place) are particularly highlighted with regard to the functional significance of bilaterally asymmetric otoliths (weight, size).