|'Zombie walk 2010' |
under a CC license
The story was based on a paper of Cryan et al. in PNAS, which describes the effect on the behaviour of mice when fed with feed supplemented with Lactobacillus rhamnosus; altogether, mice became more relaxed. Although that's not the first time that gut bacteria have been shown to have an effect on the mood of mice in vivo, this time the impact to the public seems to be higher.
Symbiotic relationships in living organisms is nothing too uncommon. That applies to both mutualistic and parasitic symbiosis. Although 'mind control' cases have been known, especially in parasitic symbiosis, it wouldn't have been easy for me to imagine that the same would apply to a mutualistic symbiosis, especially if that was taking place in the gut.
The 'mind control' cases one would imagine that they should involve an organism with direct access to the brain or, at least, to the bloodstream. The infection of the bullet ants from cordyceps is an example. The fungus forces the infected ant to climb upwards and firmly grab itself. There, the ant will eventually die and the ascocarp (the fruiting body of the fungus) will come out of the ant's head.
'Mind control' can be used by insects which want to lay their eggs on their ideal host, too. For the orb spider, for instance, the nemesis is the pompilid wasp, which temporarily immobilises the spider, lays an egg on it and let the larva do the rest. The larva sucks nutrients from the spider and, when the time comes, chemically instructs the spider to alter its web in such a way that it can support the cocoon that the larva will later on make for itself. Needless to say that the orb spider doesn't survive the process and becomes dinner, after all. (the video below shows the process - the action starts from about 03:00)
An even spookier approach is practiced by the Ampulex compressa wasp. That uses cockroaches to lay its eggs onto. To manipulate the cockroach, the wasp injects, in series, firstly a temporary numbing agent in the cockroach's brain and, then, a chemical that blocks its escape reflex. After the process, the cockroach is alive and well (not for too long though) and follows the wasp's will. The end is bitter in this case, too, as the larvae will consume the cockroach in the process, starting from its non-vital organs.
Snails, too, can host parasites. (I found a link to the video below at http://primesurrealestate.com/2010/04/mind-altering-parasites/).
For humans, the list of parasites is not too short, either. But I am not aware of any zombie-like mind control bugs. Yes, toxoplasma gondii can alter the behaviour and behavioural characteristics of people, affecting males and females in different ways but not in the grotesque way that bullet ants are controlled by the fungus. Still though, the effect from toxoplasma might be responsible for the macroscopic properties of societies around the world, taking into consideration how widespread toxoplasmosis is, although other factors are likely to exercise far higher influence (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1635495/).
A number of diseases are also known to affect the mental processes, usually messing with the brain tissue (e.g., Alzheimer's, syphilis, etc.) but such changes - I suppose - are non-reversible.
Going back to the story with the mice and lactobacillus rahmnosus, the beauty in it is that the effect is 'subtle'. Measurable and real but mild and reversible. And that shows a lot of potential to be explored on the use of probiotics not only for the protection of the gut's normal function but also for the delivery of 'brain-related' interventions. What makes things even more interesting is that living bacteria are adaptable and 'intelligent' in the sense that they may be able to perform their 'mind-controlling action' (e.g., excreting a cocktail of chemicals) only under the right conditions. Just imagine mitigating the stress feeling by adopting a diet rich in probiotics - e.g., within fermented food - with the ability to respond to in-gut stress markers. It is so much easier than having to take pills and the fact that their action is subtle may allow individuals to also train themselves to feel less stressed.
It seems, after all, that diet does have the potential for an even greater impact on our lives...