Consciousness and how it got to be that way

Wednesday, November 28, 2012

Toxoplasma - Suicidal Rats and Suicidal Humans

In 2009 I posted an admittedly long-shot theory about suicidality in rodents and maladaptive (violent) behavior in humans, namely serial murder. Along comes a very interesting piece in Archives of General Psychiatry by Pedersen et al, Toxoplasma gondii Infection and Self-directed Violence in Mothers.

Toxoplasma is that bug that infects rodents and somehow makes them approach cats. The parasite then goes through the next stage of its life cycle in the cat's gut, and is defecated out, at which point it infects another rodent. Another long-shot but interesting possibility is that the "cat lady" phenomenon is actually a toxoplasmosis infection: if you're an animal so big that the cats can't eat you, you just know you want to be around cats, so you get more and more. We do know already there are definite effects in humans, although so far they could just be explained as boring motor retardation effects: in a U.S. military study, people who totaled their vehicles in accidents were significantly more likely to have Toxo antibodies.

I think we're eventually going to learn that Toxoplasma is able to manipulate the behavior of humans in very specific uncomfortable ways vis a vis rabies, which is itself an amazing pathogen. Humans and tox have a long history together. In fact, the Rh factor on red blood cells is a subunit of an ammonia channel that's implicated in resistance to tox, and it's not surprising that the only part of the world with appreciable Rh negativity is Europe (where until recent times there wasn't much cat feces around). The closer you get to Basque country, the higher the Rh negativity; interesting since the Basques have been in (barely) post-glacial Europe longer than any other population.  For a system that could result in immunized Rh- mothers that after their first child can produce very sick anemic kids, it has to be doing something important.

Sunday, November 25, 2012

Leapfrogging the Failures of C. elegans Connectomics

An argument against the present utility of trying to do brain emulations is that we cannot predict or simulate the behavior of Caenorhabditis elegans, despite having a complete connectome map of its simple nervous system. So why do we think replicating the much more complex human connectome computationally would be any more useful? These criticisms have not stopped some groups from forging ahead. Theodore Wong and team at IBM has now published preliminaries on the most ambitious brain simulation to date, with 10^14 synapses.

Certainly simulating a human nervous system is the end goal of all this, but it seems a lot of money and work is going toward projects when there is a very glaring failure at an earlier level of the same enterprise. As long as your project is being funded by a large institution with deep pockets, you probably don't have to address this question; at least not yet. But if a counterargument exists to "simulating C. elegans doesn't give us anything useful so simulating H. sapiens is also unlikely to do so", I haven't yet seen it.