Matz Larsson

affiliated with the university

Research areas and keywords

UKÄ subject classification

  • Medical and Health Sciences
  • Natural Sciences

Keywords

  • nicotine, dependence

Research

The Swedish Smoking Cessation Project

 

The Swedish Smoking Cessation Project, modelled from the Danish smoking cessation database (DSD), aims to be implemented in Swedish health care in 2019. The county of Örebro runs a tobacco cessation unit (TPE) based on behavioural and pharmacological therapy. The unit’s response rate at follow up is modest, approx. 50%.   

Description of Objectives: The aims were to 1. test the relevance/usefulness of DSD’s methods in a cohort of Swedish smokers, 2. Assess the participant’s degree of satisfaction with the TPE programme 3. Get information about participants’ background, e.g. the amount of psychotropic drugs used, and study outcomes such as abstinence rate.

Methods/Intervention: An adapted telephone questionnaire from the DSD six months’ follow-up questionnaire was used. 100 smokers previously treated by TPE were selected to a telephone interview approx. 6 months after planned quit date.

Results (effects/impact/changes): 70 of 100 (70%), M/F 38/32, were reached/agreed to participate. The mean Fagerström score was 4.6 on a 10-degree scale; 43% were smoke-free; average satisfaction with programme was 4.4, with the counsellor 4.7 (max. score 5); 27/70 (38%) used psychotropic medication (other than for smoking cessation purpose).

Conclusions/Lessons: Compared with the unit’s normal follow up, the response rate became higherusing the modified DSD method. The unit got useful feedback and information, e.g. the participants reported a high degree of satisfaction with the program. The DSD method seems to be suitable also in a Swedish smoking cessation program.

Keywords:  smoking cessation database, psychotropic medicine

Research

The evolution of vocal learning

Did you know that people with roughly the same leg length tend to move in tandem?

This is usually done unconsciously. Between footfalls are short intervals with relatively low noise levels during which we can perceive sounds from the environment. This has less relevance in today's society, but, in the past, rhythmic movements would have helped our ancestors become aware of the pursuit of a sabre-toothed tiger, or the stealthy approach of a malicious stalker. And because behaviours that carry a positive survival benefit are selected, they will become more common within a species. This can also happen if animals (including humans) experience the beneficial behaviour as stimulating or enjoyable. This produces a surge of the "reward molecule" dopamine in the brain. Individuals – and families – with this trait will thus be more likely to walk in step. Meanwhile, less rhythmically-inclined individuals – perhaps those who were bad at paced walking - would have stomped themselves literally out of the genetic pool by being eaten!

Rhythmic behaviour could probably stimulate the production of dopamine also in safer surroundings. Clapping hands, stamping, howling around the campfire... from here, the step to dance and music was probably a small one. Dopamine definitely flows when people in the modern era are listening to music. So similar selective mechanisms may have increased the ability of early mankind to perceive, recollect and mimic sounds. Charles Darwin, and many scholars after him, have suggested that musical ability was a necessary precursor in the evolution of language. 

The so-called "motor theory" of language evolution includes the idea that it was gestures that laid the ground for the development of human language. This theory is very much about hand movements; that is, language has evolved as a result of observation and imitation of gestures. The "tool use sound theory of language", on the other hand, is a partly revamped version of the motor theory. It suggests that language development has been stimulated by the sounds of our movements. The human brain skilfully analyses the sound waves created when tools are used. These specific sounds may have played a crucial role. If early ancestors were able to mimic some tool use sound, the sound may have taken on a symbolic function. The day someone managed to imitate the sound of a cutting knife or an axe blow with the help of mouth, hands or otherwise, was an important first step. If two persons settled that a vocalization symbolised a certain subject or a particular event, the first word was in principle created. The ability to mimic the sounds of implements could only create a limited number of words, of course, but through minor changes to the sound, or a gradual change of its meaning, more words might eventually be formed.

// <![CDATA[ // ]]> // <![CDATA[ (adsbygoogle = window.adsbygoogle || []).push({}); // ]]> A new way to communicate about tools may have had selective value. Communication could take place when individuals were out of sight of each other, or in darkness. This could have resulted in increased survival of the individual and the group. Now you could talk about apparatuses. This, in turn, would have stimulated the development of tools and opportunities to transfer knowledge of them. All this may have led to increased tool use, which in turn created new types of tool use sound – and so on. Some researchers, such as Michael A. Arbib, have suggested that tool use was linked to the development of syntax, i.e. how words are joined together to form phrases, clauses and sentences. These researchers believe that the various stages in tool use have similarities with sentence structure. Implement sounds can be one piece of the puzzle here. Why? They occur in a definite succession, and shifting sounds are included in the chain of events when complex tool use is performed. Tools are usually controlled with our hands. Bass and Chagnaud have demonstrated very strong links in the vertebrate brain between vocal communication, the sounds produced by voice organ, and motion control of the upper extremities.

The idea may be valid also for language development today. Indeed many modern languages contain sound symbolism. For example, studies have shown that a nonsense word such as "baluma" will be associated with round objects, whereas the word "takiki" is associated with pointed shape. Sound mimicking – onomatopoeic – words, such as "whiz", "sweeping", "slicing" are further examples. 

Of course, early humans might have mimicked other sounds in nature too, like the "meow" of a cat, or the rushing wind. But tool use specifically enables many more senses: hearing, touch, sight and proprioception, i.e. the sense that helps us to keep track of where are fingers, arms and legs are in three dimensional space and in relation to each other. Also, the motor neurones – nerve cells that generate motion – interact when tools are used. All that stimulates the creation of association chains, which is an important component of language and language development. Spoken language is based on the human ability to create associations between complex audio information (vocalisations), and other sensations, such as sight and touch. 

There are so-called "mirror neurones" in the brain. These cells can become active when a monkey cracks a peanut, but also when a monkey sees another monkey doing the same thing. The same also applies to the sound generated when the monkey himself or another monkey cracks a peanut. So the ape doesn't even have to see the event to stimulate audio-visual mirror neurons: just hearing implement sounds is sufficient. A result of tool use training in monkeys was that more multimodal neurons had been activated. Multimodal neurons are those that can be activated by more than one type of stimulus, such as audio and visual experiences. Again, this is something that stimulates the creation of associate chains in the brain.

Which part of the brain has received most of such stimulation during evolution? Consider that about 90 per cent of us humans are right handed. When a right-hander seizes an axe or a knife, the hand works usually in the right visual field (on the right hand side of a person's body). In that situation, it is the left hemisphere neurones that are active; they are controlling the hand's movements. Similarly, virtually all sensory information about the right hand will reach the left side of brain. The left brain will therefore have large doses of multimodal stimulation during tool use. Thus, the hypothesis is consistent with the left hemisphere dominance in language processing.

Sounds created as a side effect of locomotion are labelled "incidental sounds of locomotion" or ISOL for short. Monkeys in the canopy move unpredictably and irregularly in a typically diverse vegetation. Similarly, when non-human primates are on the ground, they do not move particularly regularly. When man began to walk on two legs, one result was more rhythmic and predictable ISOL — a regularity that is likely to help individuals to keep pace. The evolution of such synchronous behaviour is far from clarified, but there are similarities with both fish in the sea and birds in the air. Basically, we are the fish that scrambled up on land. That happened more than two hundred million years ago. Although "upgrades" and adaptations to new ecological niches followed in vertebrate descendants, some basic structures of the brain are likely to be preserved. In a suitable ecological situation, synchronous behaviour may give "pay off" again. An example may be when we switched to bipedal walking.

To understand this, maybe we should turn our eyes – and ears – down to the depths. Who has not been impressed by the rapid, synchronous movements made by shoaling fish? To move synchronously may cause many acoustic advantages. Theoretical models suggest that fish and birds, swimming and flying in large groups, can use ISOL to navigate in the flock. ISOL contains potentially valuable information about the neighbour’s distance, size, speed, and frequency of wing movements. If all animals in a group stop swimming, or flapping, at the same time, a sudden noise reduction follows, and fish or birds may eavesdrop on their surroundings more efficiently. Thus, synchronous movements makes it easier to perceive acoustic information. Moreover, ISOL is likely to help the group to synchronise movements. Fin-beats, wingbeats or footsteps are clearly audible to the closest fish, bird or human and can, in theory, serve as a metronome. By listening to ISOL, nearby animals (humans) may mutually adjust their speed, distance, and pacing.

To summarise, this hypothesis suggests that schooling fish may use analogous acoustical mechanisms as a human orchestra to achieve synchronisation. The ability to synchronise movements, to listen and imitate sound is fundamental for musicality. It assumes that bipedal walking stimulated the evolution of music, which in turn may have been critical for language evolution...

 

References

 

Why do birds flock and fish shoal? - The Naked Scientists, 2017

Larsson, M. 2015. "Tool-use-associated sound in the evolution of language." Animal Cogn 18 (5):993-1005. doi: 10.1007/s10071-015-0885-x.

Larsson, M. 2014. "Self-generated sounds of locomotion and ventilation and the evolution of human rhythmic abilities." Animal Cogn 17 (1):1-14. doi: 10.1007/s10071-013-0678-z.

Larsson, M., S. R. Ekstrom, and P. Ranjbar. 2015. "Effects of sounds of locomotion on speech perception." Noise Health 17 (77):227-32. doi: 10.4103/1463-1741.160711.

Larsson M (2009) Possible functions of the octavolateralis system in fish schooling. Fish and Fish 10:344-355

Larsson M (2012) Why do fish school? Current Zool

Larsson M (2011) Incidental sounds of locomotion in animal cognition. Animal Cogn

Research

The evolution of the optic chiasm and eye hand control

In 1682, Isaac Newton proposed that the human and primate optic nerve, in terms of how it stretches from the eye to the brain, has a very particular architecture compared to that of other animals. Almost half of the nerve fibres from the human retina display hemi-decussation, that is, they project to the brain hemisphere on the same side as the eye from which they originate. In most animals, all - or almost all - nerve fibres cross to the opposite side of the brain. Newton’s theories of binocular vision provided the basis for succeeding examinations of the visual system by early anatomists and physiologists. Eventually, it led to a widely accepted concept - that the degree of optic fibre decussation in the optic chiasm is inversely related to frontal orientation of the optical axes of the eyes, which is the law of Newton-Müller-Gudden. A controversial aspect of the Newton-Müller-Gudden law is the considerable interspecific variation in ipsilateral (same sided) visual projections, particularly in non-mammalian species. This variation is not related to an overlap of visual fields, mode of life, or taxonomic position. In other words, it's an evolutionary mystery.

 

The general assumption among researchers has been that the arrangement of nerve fibres in the optic chiasm in primates and humans primarily is intended to create accurate depth perception, also known as stereopsis, i.e. the eyes perceive an object from slightly different angles and the difference in angle helps the brain to estimate distance.

 

The new eye-forelimb hypothesis challenges the idea of stereopsis as well as the Newton-Müller-Gudden law. It says that stereopsis might be no more than spinoff in a more essential evolutionary process. The eye-forelimb hypothesis suggests that the architecture of the retina, as well as the optic chiasm, is shaped to help us and other animals to steer the forelimbs (hands, claws, wings or fins).

 

 

 

With the primate variant of the optic chiasm, nerve cells that control right hand movement, nerve cells that receive sensory impressions from the hand, and nerve cells that receive visual information about the hand, will end up in the same (left) brain hemisphere. The opposite applies to the left hand. Felines (cats) and tree-climbing marsupials have similar arrangements with 30 to 45 % uncrossed nerve pathways and forward pointing eyes. Again, that aids their eyes to be in service of the paw i.e. visual information of the forelimb will reach the appropriate hemisphere.

 

There is evidence that there have been small, gradual changes to the direction of the nerve pathways in the optic chiasm. The direction of these pathways may change in either direction. Mice have lateral eyes and few crossings in the optic chiasm. Since mice’ paws mainly work in the lateral visual field, the neural architecture of mice aids the mice eye to be in service of the paw. The list of suitable examples from the animal kingdom is almost endless. The eye-forelimb hypothesis applies to essentially all vertebrates while the older theory (on depth perception) generally only applies to mammals, and even then there are important exceptions. For example, predatory dolphins have only uncrossed pathways.

 

It is commonly claimed that predatory animals generally have frontally-placed eyes to enable them to estimate the distance to their prey, while animals preyed-upon have laterally-positioned eyes, which allow them to scan their surroundings and detect the enemy in time. There are however flaws to this logic; most predatory animals may also become prey to other predators, and many predatory animals, for example the crocodile, have laterally situated eyes. The crocodile only has crossed nerve pathways, and under the new eye-forelimb hypothesis, this optic chiasm architecture would have evolved to provide short nerve connections and optimal control of the crocodile's front foot.

 

The eye-forelimb hypothesis may solve another scientific problem in the evolution of visual pathways. Snakes, cyclostomes and other animals that lack extremities have many uncrossed pathways in the optic chiasm. This can be explained by the fact that they have no hands, paws, fins or wings to coordinate for the eye. Moreover left and right body parts of such animals cannot move independently of each other; when a snake curls clockwise, the left eye will only see the left body-part and vice versa in anti-clock-wise position the left eye will see the right body-part. Hence it seems functional for snake-like animals to have some uncrossed pathways in the optic chiasm, improving visual steering of the right and left body-part. As mentioned, the direction of the nerve pathways in the optic chiasm may change in either direction. Cyclostome descendants that eventually ceased to curl and instead developed forelimbs would be favoured by achieving completely crossed pathways as long as forelimbs were primarily occupied in lateral direction. In contrast, reptiles such as snakes that lost their limbs, would gain by retaining a bunch of uncrossed fibres over their evolution. Indeed, that is what happened, providing further support for the eye-forelimb hypothesis.

 

The traditional theory on depth perception is problematic in more senses than one. For instance, birds, most of which have laterally situated eyes, have a good ability to estimate distance and they usually manage to fly through a dense wood without crashing. But wait a minute! Owls have frontal eyes and a primate-like visual system due to double crossing of neural pathways! And since owls do not use wings for manipulation of objects, their elaborate neural substrate for binocular vision appears to be at odds with the EF hypothesis. But the decussation and binocular vision of owls may in theory improve eye-lower-limb coordination. Raptors normally take prey with their feet, approaching the target with feet brought up into the visual field just prior to capture. Moreover, several owl species have been observed foraging on foot.

 

So was Newton, and others, totally wrong? The eye-forelimb hypothesis does not exclude a significant role of stereopsis, but suggests that primates evolved superb depth perception to be in service of the hand. The eye-forelimb hypothesis may provide us with a better understanding of how humans' excellent ability to estimate distance has developed. Stereopsis is an amazing aesthetical experience. It helps us to construct virtual realities, which might be more and more important in future generations. How and why stereopsis evolved in primates is another story. Most likely, the particular architecture of the primate visual system evolved to establish rapid neural pathways between neurons involved in hand coordination, assisting the hand in gripping the accurate branch and other vital objects.

 

References

Larsson M, Binocular Vision and Ipsilateral Retinal Projections in Relation to Eye and Forelimb Coordination. Brain, Behavior and Evolution, 2011 - DOI: 10.1159/000329257

Larsson M, The optic chiasm: a turning point in the evolution of eye/hand coordination. Frontiers in Zoology. 2013 - DOI: 10.1186/1742-9994-10-41

Larsson M, Binocular vision, the optic chiasm, and their associations with vertebrate motor behavior. Frontiers in Ecol. Evol. 2015 - DOI: 10.3389/fevo.2015.00089

Research

On the evolution of right handedness

Why almost 90% of humans are right handed is a mystery. The hypothesis presented here is that having your heart on the left resulted in a survival advantage for right handers in very ancient times...

 

In the 19th century, Thomas Carlyle, Scottish philosopher and essayist, proposed that right hand dominance …“probably arose in fighting; most important to protect your heart and its adjacencies...” Almost concurrently, Pye-Smith launched the warfare shield theory suggesting that, with the development of the shield, individuals carrying it in the left hand with a weapon in the right would experience mortal wounds less often than those fighting with the left hand, and hence “...a race of men who fought with the right hand would gradually be developed by a process of natural selection. Such a race would naturally use the right hand also when they discovered how to draw and to write...”

 

The first to suggest this advantage of right handers was probably the fencing master Roland (1824): “In actual combat the left-handed person labours under a serious disadvantage, as many wounds of the lungs alone have been known to do well, which, if carried to an equal depth on the left side, would immediately have produced fatal consequences by wounding the heart.” i.e. the left-handed fencer would be likely to pierce a right-handed rival’s right side, striking the right lung, usually a non-mortal wound, while the injury for the left-handed would be on the left, piercing the heart.

 

 

 

The problem with this hypothesis is that the shield was developed long after right handedness became the norm. Examination of flint implement splinters from 1.8 million years ago (mya) reveals that they were probably made by right-handed individuals (McManus 1991).

 

However, the usual argument against the warfare shield theory, that the shield is a recent invention, may be an oversimplification. The heart and the aorta are situated mainly within the left thorax. The hypothesis raised here is that, regardless of shield use, early ancestors with a preference for using the right forelimb in combat may have had reduced risk of a mortal wound.

 

The rationale is that use of the right hand or forelimb will rotate the right side of the body towards the opponent, reducing the exposure of the left hemi-thorax. This particular advantage of right-handers would not have selective value in a peaceful society, or a society without sharp implements. However, literature indicates that homicide and duels were common in early hominins. In combat with sharp implements, handedness may influence the relative level of exposure of left and right thorax. While fighting with sharp tools, a left hand unilateral grip will rotate the left hemi-thorax towards an opponent.

 

I've just published a study that attempts to quantify the degree of thoracic/cardiac asymmetry in humans and estimate the difference in risk of injury from a sharp implement attack to the left or the right human thorax. CT-scans of 37 men showed that, on average, two-thirds of the heart volume are situated in the left hemi-thorax.

 

I also asked nineteen physicians (who were unaware of the hypothesis) to estimate the outcome of weapons penetrating the left and right thorax or abdomen at random points. The difference in their estimated mortality for left and right thorax was significant, p<0.001.

 

Together, these results suggest greater vulnerability of the left side of the body in combat, and, accordingly, an adaptive value of right-handedness.

 

So we may have our hearts to thank for our handedness, it seems...

 

References

Did heart asymmetry play a role in the evolution of human handedness? - https://doi.org/10.1007/s41809-017-0009-z

Recent research outputs

Matz Larsson & Abbott, B. W., 2018 Dec, In : Evolutionary Biology. 45, 4, p. 359-373

Research output: Contribution to journalArticle

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