Post-traumatic stress influences the brain even in the absence of symptoms: A systematic, quantitative meta-analysis of neuroimaging studies.

Stress affects brain function, and may lead to post-traumatic stress disorder (PTSD). Considerable empirical data for the neurobiology of PTSD has been derived from neuroimaging studies, although findings have proven inconsistent. We used an activation likelihood estimation analysis to explore differences in brain activity between adults with and without PTSD in response to affective stimuli. We separated studies by type of control group: trauma-exposed and trauma-naïve. This revealed distinct patterns of differences in functional activity. Compared to trauma-exposed controls, regions of the basal ganglia were differentially active in PTSD; whereas the comparison with trauma-naïve controls revealed differential involvement in the right anterior insula, precuneus, cingulate and orbitofrontal cortices known to be involved in emotional regulation. Changes in activity in the amygdala and parahippocampal cortex distinguished PTSD from both control groups. Results suggest that trauma has a measurable, enduring effect upon the functional dynamics of the brain, even in individuals who experience trauma but do not develop PTSD. These findings contribute to the understanding of whole-brain network activity following trauma, and its transition to clinical PTSD.

Molecular analysis of the structure of the maize B-chromosome.

The overall composition of the maize B is similar to that of the standard chromosome complement (A-chromosomes). This has been demonstrated by the use of several methods including: (a) genomic in situ hybridization (GISH), (b) analysis of highly repetitive sequences by the comparison of restriction digests of 0B and +B DNA and (c) the characterization of middle-repetitive cloned sequences. By the use of the technique of random amplification of polymorphic DNA-polymerase chain reaction, we have identified a B-specific repetitive sequence family. Sequence analysis of the B-specific clone reveals a relationship to the PREM-1 family of maize retroelements, which are preferentially transcribed in pollen. These results suggest an internal origin of the B-chromosome from within the maize genome, but demonstrate also that specific sequences can evolve by rapid processes of genomic turnover. Models for the origin of the maize B are discussed in the context of the present data.

Simulation technology and the fixation phase.

Continuing advances in simulator technology have produced almost totally real instrument and aural cue systems, and a number of specialized G-cuing systems are rapidly being matched to the sensory capabilities and needs of flight crews. Intensive research in visual cuing is providing more and more realistic visual scenes and, in general, flight simulators are becoming more real, more complex, and more expensive. It is suggested that Fitts' "fixation" phase of skill acquisition does not require a flight environment, or even a reproduction of the flight environment, for effective learning and transfer. While similarity between training and operational environments appears to be essential for transfer of training to take place, the concept of similarity may not include the total complex of stimuli available in flight as perceived by the instructor or the simulator designer, but may include only the stimuli perceived by the student as he observes, practices, and validates specific tasks within the period of response fixation. It is suggested that special attention be given to the task information required and the learning functions involved in the fixation phase of skill learning.