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“In this section, we discuss existing research into red-black trees, vacuum tubes, and courseware. On a similar note, recent work by Takahashi suggests a methodology for providing robust modalities, but does not offer an implementation...”
The above excerpt comes from a paper submitted by Philip Davis and Kent Anderson to The Open Information Science Journal. Confused by its meandering and seemingly bizarre prose? You should be. The entire paper was constructed using software that creates grammatically correct but nonsensical text. Surely such a paper would never be accepted for publication in a peer-reviewed journal, right? Wrong Read Full Article
Reconsidering the value of dopamine
Consult any introductory neuroscience text on the topic of dopamine, and you’re likely to be regaled with how dopaminergic neurons of the midbrain code for the rewarding value of a stimulus. According to this generally accepted theory, midbrain dopamine neurons increase their firing rate in response to a) an unexpected reward; or b) a stimulus that predicts delivery of reward. Conversely, firing rate decreases if reward is withheld following presentation of a reward-predicting stimulus. However, results regarding the response of dopamine neurons in response to adverse stimuli have been conflicting, with some experiments showing increased firing, and others depressed firing. In this week’s edition of Nature, Matsumoto and Hikosaka recorded from distinct classes of dopaminergic neurons that differ based on their response to adverse stimuli – in essence showing that both response patterns exist in the same animal. Interestingly, these separate populations were largely confined to distinct regions of the midbrain, with neurons excited by adverse stimuli found mostly in the dorsolateral midbrain, while those inhibited by adverse stimuli located in ventromedial regions.
While all recorded neurons showed the well-established excitatory response to rewarding stimuli, this study is the first concrete evidence that dopaminergic neurons of the midbrain may not be as homogenous as previously thought, with one population encoding the rewarding value of a stimulus (neurons excited by reward and inhibited by “punishment”), and the other seemingly encoding motivational salience (neurons excited by both rewarding and adverse stimuli).
The authors point out that, based on their location in the midbrain, these distinct populations of neurons can also be differentiated based on their primary target of axonal projection, which may account for the unique information carried by these different classes of neuron. It will also be interesting to see whether the type of dopamine receptors contacted differs by class.
Matsumoto and Hikosaka are quick to point out that their boundaries for classification are rather arbitrary, and in reality there probably exist many distinct categories based on more subtle criteria. Still, the study is a landmark in the reward signaling field, and provides fertile ground for reexamining our rather simple view of dopaminergic signaling.