Other frontal areas and regions of the parietal lobe, as well as subcortical areas are also affected by marijuana exposure. Moreover, the three circuits involved in response inhibition,namely the frontal-striatal thalamic circuit, the cingulo-opercular circuit and frontal-parietal circuit, are all still under development during adolescence.Therefore,the overactive brain regions observed in this investigation may be due not only to the current marijuana use but also to the relatively long term marijuana exposure during those crucial years in adolescence.The strength of this study was the ability to control foran unparalleled number of lifestyle variables including IQ, current nicotine and alcohol use and prenatal marijuana,nicotine, and alcohol exposure. The well controlled sample strengthens the validity of the results and provides outcomes that are able to shed light on more exclusive contributions of marijuana on the response inhibition network than previous studies.
The limitations of the study include that the sample was small and a primarily Caucasian, middle-class population.Thus, these results cannot be generalized to other ethnic or socioeconomic status populations. However,this is a low risk population and these effects are significant, suggesting that a high risk population would be even more likely to show a negative impact of marijuana use given the other risk factors.The present study also used a block design rather than an event related design. Thus, an event-related study may have helped to separate response inhibition from other cognitive processes. It is also difficult to ever truly remove a drug’s effect from a BOLD study and thus it must be considered that current use of nicotine impacted the result seven after using it as a covariate. Similarly, there was no measure of alcohol consumption on the day of testing other than the self-report of each participant. Although the self-report and urine sample values were highly correlated for those drugs tested in the urine, this was an oversight for the alcohol consumption and should be rectified with the addition of a breath alcohol level assessment in future research.
Finally, there was no abstinence period for the participants of either group. However,careful statistical analyses were performed including and not including those participants who smoked marijuana on the day of testing. Even though these analyses had less power than the reported results, the same positive relationship between amount of marijuana smoked and neural activity was observed. This suggests that the reported results are indicative of the regular marijuana use and not only acute marijuana effects. Future research will test participants who have stopped using marijuana for at least 6 months.In conclusion, adolescent use of marijuana can have detrimental effects on the brain that can be observed in young adulthood. The findings in this study suggest that increase in neural activation with increased marijuana use may be due to a form of neural compensation or an altered neural development, or both. Also, this may occur not only in the prefrontal cortex but also in the extensive neural network required for inhibitory control, a cognitive process important for executive functioning and thus success in establishing and reaching appropriate goals during adulthood.
The valorization of plant biomass through the use of ligneous resources for the design and production of composite structures is a current issue in the research sector and applications in automotive, construction, goods and leisure industries are more and more observable. This visibility is demonstrated by the manufacturing of equipments such as: prostheses, tennis rackets, turbine blades, vehicle doors, shutters and roofs, etc.. Moreover, the use of products obtained from these materials is in line with the Kyoto Protocol’s requirements for sustainable development and environmental protection . Thus, the rush to substitute synthetic fibers with natural fibers in composite structures is justified.Apart from their eco-friendly aspect, biofibers stand out for remarkable specific mechanical properties and relatively low cost. However, their qualities depend on the quality of the fabrication. The choice of the manufacturing process of an ecological composite requires the knowledge of some fundamental elements. Thermal behaviours such as the maximum degradation temperature and the thermal stability range of the fiber are indispensable. Physical characteristic slike porosity, density and water absorption capacity have to be specified.In addition to these parameters,crystallinity rate and chemical composition of the fibre will be an undeniable asset.The natural fibers characteristics depend on a number of factors like the age of the plant from which the fibers are extracted, the part of the plant where the fibers are located and the fibers extraction technique used .The plant fibers most widely used as reinforcement for composite materials a reflax, sisal, hemp, jute and kenaf .