Deconstructing Insight: EEG Correlates of Insightful Problem Solving

Background: Cognitive insight phenomenon lies at the core of numerous discoveries. Behavioral research indicates four salient features of insightful problem solving: (i) mental impasse, followed by (ii) restructuring of the problem representation, which leads to (iii) a deeper understanding of the problem, and finally culminates in (iv) an “Aha!” feeling of suddenness and obviousness of the solution. However, until now no efforts have been made to investigate the neural mechanisms of these constituent features of insight in a unified framework. Methodology/Principal Findings: In an electroencephalographic study using verbal remote associate problems, we identified neural correlates of these four features of insightful problem solving. Hints were provided for unsolved problems or after mental impasse. Subjective ratings of the restructuring process and the feeling of suddenness were obtained on trial-by-trial basis. A negative correlation was found between these two ratings indicating that sudden insightful solutions, where restructuring is a key feature, involve automatic, subconscious recombination of information. Electroencephalogram signals were analyzed in the space×time×frequency domain with a nonparametric cluster randomization test. First, we found strong gamma band responses at parieto-occipital regions which we interpreted as (i) an adjustment of selective attention (leading to a mental impasse or to a correct solution depending on the gamma band power level) and (ii) encoding and retrieval processes for the emergence of spontaneous new solutions. Secondly, we observed an increased upper alpha band response in right temporal regions (suggesting active suppression of weakly activated solution relevant information) for initially unsuccessful trials that after hint presentation led to a correct solution. Finally, for trials with high restructuring, decreased alpha power (suggesting greater cortical excitation) was observed in right prefrontal area. Conclusions/Significance: Our results provide a first account of cognitive insight by dissociating its constituent components and potential neural correlates

Tolerance, toxicity and transport of Cd and Zn in Populus trichocarpa

Metal inputs to terrestrial ecosystems are of great concern due their toxicity to biota, especially for elements with no biological function such as cadmium. Fast-growing trees such as poplars may have potential in phytoremediation schemes. We assessed accumulation, metal partitioning, gene expression (Pt-HMA4) and overall tolerance to, and interaction between, cadmium (Cd) and zinc (Zn) in Populus trichocarpa ‘Trichobel’. We predicted that Zn would have an antagonistic effect in Cd accumulation and anticipated some level of tolerance to these metals. Poplars were grown in sandy substrate under different metal applications, ranging from 1 to 243 mg kg−1 Cd; or 30 to 7290 mg kg−1 Zn; and also two combined treatments: 27 mg kg−1 Cd with 90 or 270 mg kg−1 Zn. Growth parameters and metal contents in shoots and roots were determined. Transcriptional levels of the Pt-HMA4 gene were assessed in roots and leaves. P. trichocarpa showed a surprisingly high tolerance to Cd, with root biomass being affected only at the highest doses applied. Metals accumulated mainly in roots (up to 6537 mg kg−1 Cd and 21,500 mg kg-1 Zn), root-to-shoot translocation peaked at the 9 mg kg−1 dose for Cd (41%) and 90 mg kg−1 for Zn (40%). At high Cd/Zn applications, expression of Pt-HMA4 in roots decreased significantly. Contrary to the initial presumption, Zn addition increased Cd uptake, reaching hyperaccumulator-like concentrations in shoots (≥100 mg kg−1 Cd). Differential root-to-shoot partitioning has a major role in Cd tolerance in P. trichocarpa; partly by down-regulating the Pt-HMA4 gene in roots. Zn addition promoted high Cd uptake without any detriment to plant growth. P. trichocarpa was tolerant to extreme Cd concentrations, offering a great potential to be used in phytoremediation techniques for stabilization/extraction of Cd from soils contaminated by both Cd and Zn

Measurement of the diffractive cross-section in deep inelastic scattering

Diffractive scattering of $\gamma^* p \to X + N$, where $N$ is either a proton or a nucleonic system with $M_N~<~4$~GeV has been measured in deep inelastic scattering (DIS) at HERA. The cross section was determined by a novel method as a function of the $\gamma^* p$ c.m. energy $W$ between 60 and 245~GeV and of the mass $M_X$ of the system $X$ up to 15~GeV at average $Q^2$ values of 14 and 31~GeV$^2$. The diffractive cross section $d\sigma^{diff} /dM_X$ is, within errors, found to rise linearly with $W$. Parameterizing the $W$ dependence by the form d\sigma^{diff}/dM_X \propto (W^2)^{(2\overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} -2)} the DIS data yield for the pomeron trajectory \overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} = 1.23 \pm 0.02(stat) \pm 0.04 (syst) averaged over $t$ in the measured kinematic range assuming the longitudinal photon contribution to be zero. This value for the pomeron trajectory is substantially larger than \overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} extracted from soft interactions. The value of \overline{\mbox{\alpha_{_{I\hspace{-0.2em}P}}}} measured in this analysis suggests that a substantial part of the diffractive DIS cross section originates from processes which can be described by perturbative QCD. From the measured diffractive cross sections the diffractive structure function of the proton F^{D(3)}_2(\beta,Q^2, \mbox{x_{_{I\hspace{-0.2em}P}}}) has been determined, where $\beta$ is the momentum fraction of the struck quark in the pomeron. The form F^{D(3)}_2 = constant \cdot (1/ \mbox{x_{_{I\hspace{-0.2em}P}}})^a gives a good fit to the data in all $\beta$ and $Q^2$ intervals with $a = 1.46 \pm 0.04 (stat) \pmComment: 45 pages, including 16 figure