Reading focus
Syllabus: How Do Neural Circuits Turn Sensation into Action?
Trace an example in which a changing state alters which cells participate or how their connections influence behavior.
Why you’re reading it. This provides possible mechanisms for flexible circuit operation without assuming that anatomy has been rewired.
A question to consider. Choose one state-dependent example and name what a connectome, a neural recording, and a receptor manipulation would each contribute to explaining it.
Why this reading
A wiring diagram describes possible routes of influence, but the same connected cells need not operate in the same way in every state. Bargmann uses tractable circuits to explain how neuromodulators change participation and interaction, making the relationship between structure and function a question to investigate.
Before you read
A connectome maps neural connections. Neuromodulators alter properties such as cellular excitability or synaptic influence, sometimes acting beyond a single anatomically defined synapse. The stomatogastric ganglion is a small crustacean circuit that helps organize feeding movements. The nematode C. elegans provides another relatively small nervous system in which cells and connections can be identified.
Read for
- Distinguish one neuron participating in several behaviors from one behavior recruiting different sets of neurons in different conditions.
- Use the feeding-state and sensory-response examples to ask what an anatomical map does and does not specify.
- Follow the evidence connecting a modulator, its receptors, circuit activity, and behavior. Compare that chain with merely finding the molecule in a region.
Consider afterwards
- A complete connection map predicts that removing one neuron will abolish an avoidance response, but this occurs only in well-fed animals. What should the explanation add?
- What measurement would show that a modulator changes circuit organization rather than uniformly amplifying every response?
Editorial context
The argument complements anatomical mapping: structure constrains function, while physiological state helps determine how those constraints are used. Most detailed examples come from small animal nervous systems; they do not establish a one-to-one correspondence between a human mental state and a transmitter. Descriptions of the state of connectome mapping belong to 2012. The enduring question is what additional functional evidence a structural map requires.