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What is it with scientific conferences and horrible WiFi connectivity? Either they don't have any connectivity at all, or only in the hallways between the lecture rooms where the science is actually happening, or the access points are so few that the net is just just breaking down constantly. ICN2010 here in Salamanca, Spain is no exception. In a lot of ways it's even worse. Here, they have only some connectivity in the hallways and whenever there's a break in the program, people flock there, occupying all seats and power outlets as well as of course bringing down the net, forcing people to miss sessions if they want or need to go online. So I'm sitting here in the afternoon session of the first day, typing my post into notepad only to paste it later onto my blog. Pathetic. Most likely, I'll not be blogging any more from this otherwise wonderful event, if circumstances don't become more favorable.

This symposium was about "Neuroeconomics and decision in small neuronal circuits" and features Karli Watson, William Kristan Jian Jing and Rhanor Gillette.

Karli Watson kicked the symposium off with her talk on "The Neuroethology of primate social decision making". Her data was all from Rhesus macaques. She started by telling us about the serotonin transporter length polymorphism region (5-HTTLPR). The gene for this serotonin (5-HT) transporter comes in two alleles, a long one and a short one. The variant affects several long-term personality traits in humans and macaques, particularly by making carriers susceptible to certain environmental stressors. She showed us data from her macaques, that short-carriers (s-carriers) look less at faces than non s-carriers. More specifically, they look less at eyes than non s-carriers. S-carriers also have greater pupil dilation in response to high status faces. In another experiment, the data indicated that s-cariers gamble less than non-carriers after seeing a high status face. Collectively, these experiments can be interpreted as genetic variation in the 5-HT transporter modulating the monkeys' vigilance after social threats.
The next part of her talk was about orbitofrontal cortex (OFC). She recorded from single units in this brain area of the macaque brain, while they were performing behavioral tasks. The neurons from which she recorded responded both to juice reward and to images of conspecifics. Interestingly, these neurons showed differential responses to juice alone as opposed to juice together with a social image. Karli could also differentiate between different social categories by looking at the firing rate of the OFC neurons. She concluded this part of her talk by stating that OFC neurons encode social value. Linking the two parts of her talk, she told us that s-carriers have smaller a grey matter area in OFC.

Next up was Bill Kristan telling us about "Multiple mechanisms of behavioral choice in the leech". I'll be doing some related experiments in Bill's lab starting next week, so I was particularly looking forward to this presentation. Bill introduced his talk by recounting Nico Tinbergen's concepts about decision-making in animals. The central point here was that different behaviors are mutually exclusive, entailing that animals need to make a decision, which of them to initiate. Rapidly progressing to the neuronal level, he recounted the old model that sensory input reaches command neurons which trigger central pattern generators (CPGs)which generate the behavior. Importantly, reflecting Tinbergen's notions, command neurons have been thought to be mutually inhibitory. Bill's model system is the leech and he went on to tell us about some leech behaviors, like local bending, swimming, crawling, shortening and feeding. While complex interactions occur between swimming and crawling, feeding inhibits all other behaviors. This latter interaction means that you can do almost anything to these animals while they're feeding, even dissecting them, so strongly inhibited are all other behaviors. In a reduced preparation, then graduate student Quentin Gaudry (now postdoc in Rachel Wilson's lab at Harvard)found out that the behaviors are shut down by presynaptic inhibition of the tactile sensory terminals and that it is the release of serotonin which is mediating the effect via MOD-1 receptors. Thus, in contrast to the postulation above, the interaction between these behaviors is not mediated by inhibition at the level of command neurons, but already, in a top-down fashion reminding of attention-like processes, on the sensory level.
Next, Bill talked about the interaction between swimming and crawling. In this project, they used voltage-sensitive dyes to image the activity of the neurons in the leech ganglia while they're generating swimming or crawling behaviors. Then graduate student Kevin Briggman optically recorded from 140 neurons in experiments where exactly the same electrical nerve stimulation elicits either swimming or crawling in an unpredictable sequence. His results indicate that this decision between swimming and crawling is also not negotiated between command neurons, but rather remind of a process of collective decision-making among groups of shared interneurons. Interestingly, there is almost a complete overlap between the neurons active during crawling and those active during swimming, suggesting that the swim CPG is a subset of the crawl CPG and evolved from it.

The penultimate presentation was by Jian Jing telling us about “Modulatory neurons and behavioral sequences”. His talk was about the marine snail Aplysia, a model system on which I have worked before, also in the lab of Klaude Weisz at Mount Sinai School of Medicine in New York, where Jian is working. He started by explaining how behavioral sequences, prompted by changes in an animal's internal state, are an important consequence of decision-making. The first example was the transition from hungry to sated in Aplysia. Aplysia feed by grasping food with their radula (a tongue-like organ)and then pushing the food down their esophagous. In case they ingest inedible food, they can reverse the movement of the radula and egest the inedible item. This distinction between ingestive and egestive motor programs was essential for the rest of the talk. The CPG generating these motor programs sits in the buccal ganglia. The esophageal nerve releases two neuropeptides onto the buccal ganglia which change the network properties of the CPG, promoting egestive pattern generation. Feeding leads to activation of the esophageal nerve which reconfigures the buccal CPG via the neuropeptides to stop responding to stimuli which would lead to ingestive behaviors in the hungry animal.
The second part of his talk concerned the neural mechanisms underlying arousal. Jian distinguished between specific arousal, elicited, e.g. by food and general arousal, elicited by tail-pinch. Specific arousal only enhances specific behaviors, i.e., ingestive behaviors after food, while general arousal also enhances non-specific behaviors such as feeding after tail-pinch. Does general arousal activate the specific arousal centers, or is it a separate arousal mechanism? Jian presented elaborate electrophysiological data suggesting that general arousal acts on local downstream arousal elements, leading to an enhanced response to food, depending on the prior history of the animal.

Finally, the organizer of this symposium, Rhanor Gillette presented his work on “Value, risk, reward and decision in a simple nervous system”. He talked about the neural toggle between approach/avoidance behavior in the marine mollusk Pleurobranchia. In its simplest form, one can think of approach/avoidance decisions as modulated by the internal appetitive state.
See their great video of single trial avoidance learning!
In this slug, if you dissect the nervous system of a hungry animal, it will spontaneously generate feeding motor programs, compared to a nervous system from a sated animal: the appetitive state of the animal is conserved in the isolated nervous system. The fictive avoidance turn is also conserved in the isolated nervous system. With these prerequisites, Rhanor and his colleagues can study the neural toggle between approach and avoidance. For instance, the nervous system of a sated animal will respond to oral veil nerve stimulation with an avoidance turn, but if the feeding command neuron is depolarized experimentally and fires, the same stimulation leads to an approach program. Rhanor went on to show that serotonin modulates this appetitive state and can switch avoidance to orienting.
Posted on Tuesday 03 August 2010 - 21:12:24 comment: 0

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