Lots of exiting papers being published at the moment. Here's this Monday's stash of noticible articles from various parts of the neurosciences.
More Damasio. Together with Josef Parvizi, Gary van Hoesen, and Joseph Buckwalter, he has an interesting study of the neural connections in the postmedial cortex (PMC) in the macaque in the January 31 issue of PNAS. The PMC encompasses the posterior cingulate and the medial parietal cortices, and appears to play an role in, among other things, consciousness. It is the first brain region to show an increased activity in patients regaining consciousness from persistent vegetative state, and it is also activated in tasks where people think about how they would describe their own personality traits and physical appearence. By injecting the component areas of PMC with anterograde and retrograde traces Damasio et al. found that all PMC areas are interconnected with each others. In their conclusion they write: "Local interconnections among the components of the PMC and their connections with some of the same neural structures argue for a functional unit within the PMC. However, the fact that each of the areas within the PMC has its own particular set of connections with other neural strctures suggests the presence of distinct functional modules operating within the PMC." [Link to the paper.]
Speaking of modules, it is becoming increasingly clear that the way "nature" and "nurture" interacts is much more complex than hitherto appreciated. Case in point: In the May issue of Nature Neuroscience Marta Majdan and Carla Shatz present evidence that the critical period in the mouse visual cortex has a specific molecular logic of gene regulation. (A critical period is a time slot in development when sensory experience diretc the maturation of neurons and their interconnections within neocortex.) From the abstract: "Four days of visual deprivation regulated one set of genes during the critical period, and different sets before or after. Dark rearing perturbed the regulation of these age-specific gene sets. In addition, a ‘common gene set’, comprised of target genes belonging to a mitogen-activated protein (MAP) kinase signaling pathway, was regulated by vision at all ages but was impervious to prior history of sensory experience. Together, our results demonstrate that vision has dual effects on gene regulation in visual cortex and that sensory experience is needed for the sequential acquisition of age-specific, but not common, gene sets. Thus, a dynamic interplay between experience and gene expression drives activity-dependent circuit maturation." [Link to the paper.]
The orbitofrontal cortex (OFC) is an important part of our decision-making system. It is, however, not clear exactly what function – or rather functions – it performs. An important paper in Nature casts new light on this question. Camillo Padoa-Schioppa and John Assad had monkeys choose between two types of juice (measured in type and quatity) while recording from neurons in their OFC. The interesting thing about the study is that, by making the monkeys choose between two kinds of juice rewards, the researchers were able to relate the value accorded to each choice with neural activity in the OFC. For instance, one quantity of type 1 juice is as desirable as four quatities of type 2 juice. The recorded cells monitor the value of each choice, and thus in effect constitute a value scale or system. Also very interesting, the activity of the cells did not depend upon whether the monkey chose the juice on the left or the right. Hence, OFC neurons encode value independently of visuospatial factors and motor reponses. A highly interesting find illuminating the role played by OFC in decision-making. [Link to paper.]
Finally, Simon Fisher – whom I wrote about last week – has new review coming up in the next issue of Trends in Cognitive Science. This time he, together withe Clyde Francks, discuss the role played by the genes DYX1C1, KIAA0319, DCDC2 and ROBO1 in the development of dyslexia. [Link to paper.]