On 2014 Jun 27, Serge Ahmed commented:

The authors propose to reclassify addictive drugs, including cocaine, according to their common property of directly evoking a high frequency of de novo dopamine transients that would surpass that normally evoked by “natural” rewards. This property is particularly obvious in awake and behaving rats. This property would be necessary and sufficient to explain why “a higher reward magnitude [would be] conferred to abused drugs compared to natural rewards” and why “drug-associated cues [would acquire] the powerful ability to reinstate drug seeking and taking”.

This is an interesting hypothesis but it totally ignores recent research showing that when rats have a choice between i.v. cocaine and sweet water (a nondrug reward which is “processed by sensory systems”), most rats prefer the latter over the former regardless of the dose of cocaine available and even after a long history of cocaine self-administration (e.g., http://www.ncbi.nlm.nih.gov/pubmed/24260227; http://www.ncbi.nlm.nih.gov/pubmed/22871910; http://www.ncbi.nlm.nih.gov/pubmed/23551949; http://www.ncbi.nlm.nih.gov/pubmed/24886157; http://www.ncbi.nlm.nih.gov/pubmed/24602027; http://www.ncbi.nlm.nih.gov/pubmed/20676364; http://www.ncbi.nlm.nih.gov/pubmed/17668074; but see: http://www.ncbi.nlm.nih.gov/pubmed/23319458). Thus, it seems that the ability of a drug, like cocaine, to directly evoke a high frequency of de novo dopamine transients is not sufficient to explain its addictive potential (see also: http://www.ncbi.nlm.nih.gov/pubmed/23428657).

On 2014 Jun 27, Serge Ahmed commented:

The authors propose to reclassify addictive drugs, including cocaine, according to their common property of directly evoking a high frequency of de novo dopamine transients that would surpass that normally evoked by “natural” rewards. This property is particularly obvious in awake and behaving rats. This property would be necessary and sufficient to explain why “a higher reward magnitude [would be] conferred to abused drugs compared to natural rewards” and why “drug-associated cues [would acquire] the powerful ability to reinstate drug seeking and taking”.

This is an interesting hypothesis but it totally ignores recent research showing that when rats have a choice between i.v. cocaine and sweet water (a nondrug reward which is “processed by sensory systems”), most rats prefer the latter over the former regardless of the dose of cocaine available and even after a long history of cocaine self-administration (e.g., http://www.ncbi.nlm.nih.gov/pubmed/24260227; http://www.ncbi.nlm.nih.gov/pubmed/22871910; http://www.ncbi.nlm.nih.gov/pubmed/23551949; http://www.ncbi.nlm.nih.gov/pubmed/24886157; http://www.ncbi.nlm.nih.gov/pubmed/24602027; http://www.ncbi.nlm.nih.gov/pubmed/20676364; http://www.ncbi.nlm.nih.gov/pubmed/17668074; but see: http://www.ncbi.nlm.nih.gov/pubmed/23319458). Thus, it seems that the ability of a drug, like cocaine, to directly evoke a high frequency of de novo dopamine transients is not sufficient to explain its addictive potential (see also: http://www.ncbi.nlm.nih.gov/pubmed/23428657).