As usual, I can only play the part of the damp squibb on this subject.
Your link didn't work for me Druidus (busy perhaps ?), but the latest researchI could find is below.
From:-
http://www.newscientist.com/channel/being-human/drugs-alcohol/dn7698
Cocaine may keep users from adapting to new situations by disrupting connections between key brain regions, suggests a new study in rats. The finding may shed light on the impulsive behaviour seen in cocaine addicts, researchers say.
A team looked at the connections between two regions of the brain: one involved with learning, memory and processing information - the prefrontal cortex and hippocampus - and one involved with pleasure seeking, emotion and reward behaviour - the nucleus accumbens in the limbic system.
Normally, these two regions are held in balance with connections between the two sending information in both directions and allowing plasticity of thought, so that behaviour can be modified and adapted to different situations.
Neuroscientists Yuriori Goto and Anthony Grace at the University of Pittsburgh, US, believe that cocaine disrupts these connections and causes the limbic system to become over stimulated.
It may explain why cocaine addicts are oriented towards pleasure rather than other goals, and have an impaired ability to make decisions. It could be why addicts go back to taking more of the drug and ex-addicts often become addicted again faster than those who have never taken it, says Grace
From :
http://www.ukcia.org/research/iom1999/iom3pt2.htm
[size=+1]Amotivational Syndrome[/size]
One of the more controversial of the effects claimed for marijuana is the production of an "amotivational syndrome." This syndrome is not a medical diagnosis, but it has been used to describe young people who drop out of social activities and show little interest in school, work, or other goal-directed activity. When heavy marijuana use accompanies these symptoms, the drug is often cited as the cause, but there are no convincing data to demonstrate a causal relationship between marijuana smoking and these behavioral characteristics.23 It is not enough to observe that a chronic marijuana user lacks motivation. Instead, relevant personality traits and behavior of subjects must be assessed before, as well as, after the subject becomes a heavy marijuana user. Because such research can only be done on subjects who become heavy marijuana users on their own, a large population study such as the Epidemiological Catchment Area study described earlier in this chapter - would be needed to shed light on the relationship between motivation and marijuana use. Even then, while a causal relationship between the two could, in theory, be dismissed by an epidemiological study, causality not be proven.
[size=+1]Summary on Psychological Effects[/size]
Measures of mood, cognition, and psychomotor performance should be incorporated into clinical trials evaluating the efficacy of marijuana or cannabinoid drugs for a given medical condition. Ideally, participants would complete mood assessment questionnaires at various intervals throughout the day for a period prior to and at weekly intervals during treatment, and, where appropriate, after the cessation of marijuana therapy. A full psychological screening of research participants should be conducted to determine whether there is an interaction between the mood altering effects of chronic marijuana use and the psychological characteristics of the individual. Similarly, the cognitive and psychomotor functioning of individuals should be assessed prior to and at regular intervals during the course of a chronic regimen of marijuana or cannabinoid treatment to determine to what extent tolerance develops to the impairing effects of marijuana and to monitor whether new problems develop.
