Algorítmica y Complejidad computacional. La complejidad computacional del cerebro de mosquito.

Redactando una entrada anterior hemos encontrado este enlace. Se trata de una entrada en un blog en la cual comentan sobre el sistema nervioso central (SNC) / cerebro de los insectos (y más en general de los artrópodos).

Además de  una descripción bastante detallada del SNC de los insectos (el SNC /cerebro de los artrópodos es bastante diferente al de los vertebrados), con algunas imágenes, hace unas consideraciones sobre la inteligencia de este linaje biológico (medida no por los ¿ inútiles desde el punto de vista evolutivo ? tests de inteligencia sino por el repertorio de comportamientos de los que son capaces)  en las que utiliza conceptos  próximos a los que se utilizan en algunos campos de la disciplina de la complejidad computacional.

Con solo entre 100.000 y unos pocos millones de neuronas, los insectos tienen capacidad de memorización y aprendizaje, y su repertorio de  comportamientos comprende, como se podrá comprobar leyendo el artículo, algunos bastante sorprendentes.

Por  su interés  hacemos una  entrada específica, ésta misma, en la que recomendamos la lectura de ese post a los lectores. El blog se llama Teaching Biology. Antes de presentar algunos extractos, una breve reflexión crítica sobre las neurociencias (cuyo sentido quedará más claro al que lea la  entrada recomendada): sorprendentemente y pese a todos los avances de las últimas décadas, todavía no sabemos “programar” con neuronas (es decir construir o modificar circuitos neuronales que generen acciones con sentido biológico), ni siquiera en organismos aparentemente tan sencillos como los insectos (esto extrapolado a humanos sería lo mismo que curas eficientes con plena conciencia de sus consecuencias). El cerebro de mosquito sigue siendo una caja negra para el cerebro del hombre.

Algunos extractos.

And even so, not all insect behaviour is just like letting a program run…The problem most people have with insect behaviour is that it’s very polarising. On the one hand, there is the characteristic very inflexible, hard-wired behaviour we all know of, but there is also the startling ability to learn.

This brings us to the concept of intelligence. What can be used as an indicator of intelligence? Whale brains weigh 9 kg and have over 200 billion neurons. Human brains weigh between 1 and 1.5 kg, with around 80 billion neurons. A honeybee brain is 1 mm³ and has less than a million neurons. Brain size, therefore, is not a good predictor of intelligence, if it’s measured by behavioural repertoire, innovativeness or sociality. In any of those examples, a honeybee will come out as more intelligent than a human or a whale.

How about learning speed? Again, a bee will beat out a human (and any other vertebrate), even when the life spans are equalised. This is an example of how difficult it is to quantify intelligence. I’m not saying bees are the most intelligent animals, but if you reduce it down to a mere statistic, they will come out on top simply because of the radically different nature of the brains in vertebrates and insects.

Is it really so surprising that insects have such advanced cognitive capabilities? No. A brain with a volume less than a millionth the size of a human’s might seem unable to perform complex operations (because of that horrible generalisation the vertebrate people have been putting out about relative brain size and cognition). In fact, insect cognition is so advanced because of the brain’s miniaturisation, not despite of it. They do not collect information by quantity, but by quality (in the visual system’s case, a greater range of light frequencies and all sorts of edge-detection and pattern recognition systems, but at the price of resolution and clarity). This requires less neurons, but gives much more flexibility and information.

Having a large brain does not add any capabilities, it just improves the resolution. Think of a computer: you can have a a dual core CPU, but it won’t bring you much if you’re only running Windows 98 and Minesweeper on it. Complexity is not a matter of power (i.e. number of neurons), but the ability to do more things. In terms of behaviour, a honeybee is in a completely respectable position, according to how ethologists classify behaviour. Insects range from between 15 to 59 (the number rising with level of sociality). Dolphins have 123. The honeybee scores 59: that means it is capable of 59 distinct behaviours…

This, however, is not as advantageous as it seems. It’s unlikely that we will find insects that have flexible tool use, that are insightful or that have some sort of theory of the mind. Then again, the 10 g brain of a corvid bird can achieve the same types of cognition of a great ape. Again, this speaks against the whole relative brain size as a measure for intelligence. But it’s important not to get too extreme in dismissing that notion. Expecting selection to produce any desirable degree of cognitive capacity independent of brain size, and dependent only on ecological factors, is a silly mindset. What I’ve been trying to say through this section is that it’s not the size of the tissue that matters, it’s the type of circuitry – and this circuitry cannot be miniaturised to an unlimited degree. 

And this leads to a realisation that every biologist interested in this field has to understand, and one that I’ve brought up several times. Correlating overall brain size and cognition is pointless, since an increase in brain size is simply an increase in processing power needed for supporting a larger organism. It will not lead to higher intelligence. A Caenorhabditis elegans worm, with its 302 neurons, is capable of learning. This is not a marvelous fact – it’s to be expected. The real surprise comes from the fact that so many animals have such large brains! All the basic components of neurons are present in vertebrates and insects, and are probably shared from their last common ancestor. Cognitive ability does not come from new types of neurons, or just more neurons. It is new links between different bundles of neurons that lead to tangible changes in behaviour: to understand the brain, we don’t look at the size of it, but at how its different components interact.

Quédese el lector con dos conceptos:

–mushroom bodies: manipulating the mushroom bodies (not allowing them to develop properly) has always resulted in loss of short- and long-term memory. There is a strong correlation between mushroom body size and memory in hymenopterans (bees, wasps, ants) as well as between size of the mushroom bodies and behavioural complexity. The reason for this is the Kenyon cells’ remarkable plasticity, in that they will readily rebuild the neural fibers, acting as a sort of neural substrate on which new memories can grow,


–central complex: In contrast to the mushroom bodies, we don’t know that much about the central complex. When central complex development is suppressed. InDrosophila, this leads to inability to fly and strange walking, indicating that while it is not necessary for initiating leg movement, it is needed for control. If only the central part of the central complex is disrupted, the fly has difficulty orienting itself and cannot deal with asymmetries: they can’t fly in a straight line, for example.

P.s. En fin, sugerimos al lector que la próxima vez que le llamen cerebro de mosquito, en vez de  ofenderse, se hinche de  orgullo…;-).

[Actualización 1 de enero 2014.

Hay división de opiniones sobre si los insectos tienen emociones. Como el concepto de emoción es algo más que borroso, es completamente difuso esto puede ser normal.

Lo digo porque no conozco ninguna definición operativa de emoción satisfactoria, aunque algunos elementos están claros: reacción somática corporal total o de algunos órganos asociada a algún acontecimiento / evento del entorno o del medio interno; la duda es  si ser consciente de la reacción, del evento y de su asociación también cuenta para ser emoción en cuyo caso  con el concepto de conciencia hemos topado, amigo lector, concepto entiendo que mucho más complicado y difuso que el de emoción… o si es suficiente con la  memorización del par reacción / evento o incluso  que la realización de dicho par tenga consecuencias observables de algún tipo al margen de la memorización o conciencia, como reacciones corporales adicionales o algún comportamiento; en cualquier caso la realización del par sin consecuencias observables, memoria ni conciencia si parece descartar la  existencia de  emoción. Y quizás de lo que se pueda hablar en vez de una dicotomía es de una graduación cualitativa. Por lo  que leo si existen consecuencias observables tras la aparición del par, pero podrían ser resultados de automatismos bioquímicos inevitables).

En fin, los extractos sobre la división de opiniones.

Most likely, insects cannot feel emotion or affection. Their brains are too simple, missing the key parts associated with emotion like in humans. Emotions would also be very useless to an insect.

Both answers so far have argued that insects can’t feel emotion. But there is good evidence, at least in fruit flies (Drosophila), that in fact they can. For instance, drosophila have a homologous limbic system – the part of the brain that deals with behavior and emotion:  the mushroom bodies.   When the mushroom bodies are ablated, flies show altered behavioral responses such as reduced centrophobism  (avoiding the center of an arena) and thiogmotaxis (the tendency to stay close to walls) Centrophobism and thigomotaxis are well established as indicators of anxiety – an emotive behavior – in mammals. Flies also respond to valium – the  first line treatment for panic and anxiety – in the way you would expect. (1)  They get angry too: intermale aggression can be exaggerated with pheromones homologous to those known in vertebrates (2) . Of course there is the caveat that flies exhibiting emotive behaviors are only assumed to be feeling emotions – but the behavioural evidence is there.

Can we draw a deeper conclusion than this? For now, no. Short of asking the bees how they’re feeling, or probing their minds with a yet un-built emotion-meter, we simply can’t know what being a bee feels like. However, Wright and her co-authors leave us with an intriguing plea for consistency, one that nudges us to think clearly on how we regard the minds and emotions of all creatures.

In other contexts, they imply, we’re instinctively willing to call a dog or a person anxious when we see behavioral evidence of pessimism. We see a “timid” but “personable” dog experience what is “quite likely” separation anxiety, test it for pessimistic biases, and upon finding these (as was done last year), conclude that dogs indeed feel anxious when left alone. “It is logically inconsistent,” Bateson and colleagues say, to conclude this “but to deny the same conclusion in the case of honeybees.”

Humans have nociceptors (also called pain receptors) that can detect uncomfortable stimulus (heat, cold, mechanical etc.) over a certain threshold. This neurological response is called nociception and a similar process has been identified in fruit flies but insects do not have nociceptors. The study I’m referencing poked hot pins in the sides of Drosophila larvae and they would uncharacteristically roll out of the way. So without nociceptors how do they exhibit a nociception response?

I learned in my undergrad insect biology class that insects can learn but they cannot think. I’ve held on to this as I progress through my graduate degree, but it’s a much more complex issue when you try to define “thinking” and “emotions” and “consciousness”. Some scientists are seriously considering if insects are conscious. On July 7th 2012 The Cambridge Declaration on Consciousness was released. It explains what some of the top scientists in relevant fields think about ‘consciousness’. Consciousness is not a definitive line, but a moving scale. 

From The Cambridge Declaration on Consciousness: 
We declare the following: “The absence of a neocortex does not appear to preclude an organism from experiencing affective states. Convergent evidence indicates that non-human animals have the neuroanatomical, neurochemical, and neurophysiological substrates of conscious states along with the capacity to exhibit intentional behaviors. Consequently, the weight of evidence indicates that humans are not unique in possessing the neurological substrates that generate consciousness. Non-human animals, including all mammals and birds, and many other creatures, including octopuses, also possess these neurological substrates.”

So where do insects fall on this scale? Probably further away from mammals and even cephalopods. But how do you KNOW? We don’t. New studies are coming out and it will be exciting to follow them. 

Fuente. Respuestas  a una pregunta en Quora. De interés también, artículo de dónde está extraído el tercer extracto. Y el cuarto y quinte están extraídos de esta entrada en un blog de otro entomólogo. Veo que también en relación a la  conciencia se ha impuesto la  idea de  graduación cualitativa. Finalmente una  posición extrema].

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