Input–Output Machine
A major role of the brain is to connect inputs (the environment, context, cues from the body) to appropriate outputs (physical responses, behaviours, thoughts and feelings). To change outputs, we often try to change the output itself (e.g. 'don't eat the biscuit'), but it's usually more effective to change the inputs (e.g. don't keep biscuits on the desk).
One of the most fundamental roles of the nervous system is to
So, we call this heuristic the Input–Output Machine. It takes input (stimulus, context, perception) and turns it into output (response, behaviour, action). Present certain inputs and you get the output for free. Change the inputs or retrain the pathway that connects them, and you change the output.
Let's look at the neural architecture that helps us understand this heuristic better.
What neural architecture makes this happen?
These neural systems underpin this heuristic:
The neural hardware
The underlying neural systems that make this heuristic possible
Neural Pathways
Cues in the world and in your body are processed along neural pathways and transformed into some kind of response, either in the body or in the world. The more you have the same response to a set of cues, the stronger the neural pathway connecting those things becomes. We call it a perception-action mapping, or a stimulus‑response mapping, but we could call this an input–output mapping: environmental context is the input, and the response is the output.
What this means is that certain environmental contexts, or cues from the body, automatically activate the 'action' neurons most associated with those cues---you don't activate neurons, you activate pathways. Inputs (context) imply outputs (actions or responses).
Key takeaway: to change the output, you should think about changing the input.
Circuit Reuse
Inputs are transformed into outputs, but that transformation happens on neural infrastructure that serves other input–output mappings too. The same neural circuits can support many different transformations, and so when you try to mess with one mapping, you're almost certainly messing with others. Change an input and you don't just change one output, you might change many.
Key takeaway: intervening on one transformation from input to output will probably influence many related transformations, because they'll be using the same wiring.
Plasticity & Stability
The more often a particular input produces a particular output, the faster and more likely that pathway is to run next time you come across that input. This is normal and good---it speeds up your performance---but also comes with a cost, in that it makes changing input-output mapping much more difficult. It also means that making new connections between input and output requires practice.
Key takeaway: repetition makes an input-output mapping fast and sticky.
Sources
- analects/what-are-neurons.md
- analects/making-meaning-in-the-brain.md
- analects/brain-structures-and-behaviour.md
- analects/brain-regions-to-networks.md
- analects/memory-as-neural-maps.md
- neurotypica/content/archive/anatomy-networks.md