Two distinct neuronal networks mediate the awareness of environment and of self

Evidence from functional neuroimaging studies on resting state suggests that there are two distinct anticorrelated cortical systems that mediate conscious awareness: an "extrinsic" system that encompasses lateral fronto-parietal areas and has been linked with processes of external input (external awareness), and an "intrinsic" system which encompasses mainly medial brain areas and has been associated with internal processes (internal awareness). The aim of our study was to explore the neural correlates of resting state by providing behavioral and neuroimaging data from healthy volunteers. With no a priori assumptions, we first determined behaviorally the relationship between external and internal awareness in 31 subjects. We found a significant anticorrelation between external and internal awareness with a mean switching frequency of 0.05 Hz (range: 0.01-0.1 Hz). Interestingly, this frequency is similar to BOLD fMRI slow oscillations. We then evaluated 22 healthy volunteers in an fMRI paradigm looking for brain areas where BOLD activity correlated with "internal" and "external" scores. Activation of precuneus/posterior cingulate, anterior cingulate/mesiofrontal cortices, and parahippocampal areas ("intrinsic system") was linearly linked to intensity of internal awareness, whereas activation of lateral fronto-parietal cortices ("extrinsic system") was linearly associated with intensity of external awareness.

Reasoning versus knowledge retention and ascertainment throughout a problem-based learning curriculum

CONTEXT

Since 2000, problem-based learning (PBL) seminars have been introduced into the curriculum of medical studies at the University of Liège. We aimed to carry out a cross-sectional investigation of the maturational increase in biomedical reasoning capacity in comparison with factual knowledge retention throughout the curriculum.

METHODS

We administered a factual knowledge test (i.e. a true/false test with ascertainment degree) and a biomedical reasoning test (i.e. an adapted script concordance test [SCT]) to 104 students (Years 3-6) and a reference panel. The selected topic was endocrinology.

RESULTS

On the SCT, the students obtained higher scores in Years 5 and 6 than in Years 3 and 4. In Year 3, the scores obtained on SCT questions in a new context indicated transfer of reasoning skills. On the true/false test, the scores of Year 3 students were significantly higher than those of students in the other three year groups. A positive correlation between SCT scores and true/false test scores was observed only for students in Years 3 and 4. In each group, the ascertainment degree scores were higher for correct than for incorrect responses and the difference was calculated as an index of self-estimation of core knowledge. This index was found to be positively correlated to SCT scores in the four year groups studied.

CONCLUSIONS

Biomedical reasoning skills are evidenced early in a curriculum involving PBL and further increase during training. This is accompanied by a decrease in factual knowledge retention. The self-estimation of core knowledge appears to be related to reasoning capacity, which suggests there is a link between the two processes.

False Memories: Young and Older Adults Think of Semantic Associates at the Same Rate, but Young Adults Are More Successful at Source Monitoring

Two experiments explored whether the higher vulnerability to false memories in the DRM (J. Deese, 1959; H. L. Roediger & K. B. McDermott, 1995) paradigm in older compared to young adults reflects a deficit in source monitoring. In both experiments, adding together the number of falsely recalled critical lures and the number of critical lures produced on a post-recall test asking participants to report items that they had thought of but did not recall, indicated that the critical lures were activated during the experiment equally often in young and older adults. However, older adults were more likely than young adults to say that they had actually heard the lures. When strongly encouraged to examine the origin of memories (Experiment 2), the warning substantially reduced false recall in young but not older adults. These results are consistent with the idea that older adults have more difficulty later identifying the source of information that was activated as a consequence of intact semantic activation processes.

Children's interpretation of referential ambiguities and pragmatic inference

The verbal responses of 22 second graders, 24 fourth graders and 22 sixth graders to ambiguous and clear messages were recorded. Children's referential choices were analysed. After the ambiguous messages, children (from the age of seven years) chose preferentially a referent with only the feature described in the message rather than a referent with this feature plus another one. The results support the Jackson & Jacobs' hypothesis (1982) that children use an interpretative strategy based on a presupposition about the speaker's co-operation. But the results may also support a hypothesis that children use an information-processing rule not necessarily related to a presupposition about the speaker's co-operation.

[Hemineglect after right lesion. A report on three cases (author's transl)]

This paper is concerned with the observation of three cases of hemineglect after right frontal lesion. A review of cases indicates clear predominance of that semiology in subjects with right hemispheric damage. The observations are discussed with regards to facts and theoretical interpretations about the role of frontal areas in the determinism of hemineglect.