Interesting Papers 24 April 2009

Dual-process theories distinguish between intuition (fast and emotional) and reasoning (slow and controlled) as a basis for human decision-making. We contrast dominance-solvable games, which can be solved by step-by-step deliberative reasoning, with pure coordination games, which must be solved intuitively. Using functional magnetic resonance imaging, we found that the middle frontal gyrus, the inferior parietal lobule, and the precuneus were more active in dominance-solvable games than in coordination games. The insula and anterior cingulate cortex showed the opposite pattern. Moreover, precuneus activity correlates positively with how “effortful” a dominance-solvable game is, whereas insula activity correlates positively with how “effortless” a coordination game is.

How a cell integrates multiple signals into an all-or-none decision is the fascinating subject of a new study by Justman et al. Maturation of Xenopus oocytes is progesterone-induced, and Oocytes treated with a sufficient concentration of progesterone undergo maturation, whereas those treated with a lower concentration do not. Authors explain how oocytes specify the progesterone concentration that initiates M-phase entry of the cell cycle (Tuning the Activation Threshold of a Kinase Network by Nested Feedback Loops).

Determining proper responsiveness to incoming signals is fundamental to all biological systems. We demonstrate that intracellular signaling nodes can tune a signaling network’s response threshold away from the basal median effective concentration established by ligand-receptor interactions. Focusing on the bistable kinase network that governs progesterone-induced meiotic entry in Xenopus oocytes, we characterized glycogen synthase kinase–3β (GSK-3β) as a dampener of progesterone responsiveness. GSK-3β engages the meiotic kinase network through a double-negative feedback loop; this specific feedback architecture raises the progesterone threshold in correspondence with the strength of double-negative signaling. We also identified a marker of nutritional status, L-leucine, which lowers the progesterone threshold, indicating that oocytes integrate additional signals into their cell-fate decisions by modulating progesterone responsiveness.