Sodium appetite appears to be an excellent model to study the neural mechanisms of motivation. In this issue of Chemical Senses, experiments by St John (2016) challenge 2 hypotheses for how a systemic sodium deficit guides an animal to find and ingest more Na+ ions in the environment. Both hypotheses deal with modifications of the sensory neural code produced by Na++ ions on the tongue. One envisions a change in the Na++ signal amplitude. A reduction could make the strong Na++ signals less aversive; an increase, weak signals more noticeable. The other hypothesis requires no changes in the identity or amplitude of the Na++ signal, but a shift in its hedonic tone toward sweetness or reward. The results of the 3 behavioral experiments render both explanations unlikely but fail to suggest alternatives.
All Science Journal Classification (ASJC) codes
- Sensory Systems
- Physiology (medical)
- Behavioral Neuroscience