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A "decision" is highly complex emergent behaviour. Looking for it in a single neuron is like asking if there's a single air molecule where a gale started. We almost certainly will never identify single neurons corresponding to single mental ideas. A "go to the cinema" neuron versus "go to the park" likely don't exist. What is more likely is that large 'flows' of neutral activity correspond to these things or to what we call 'decisions'. However when we think of more and more specific mechanical things (like lifting a finger) then it's more likely this corresponds to very small areas of neurons that controlled their activation and it makes a bit more sense to talk about that being a switch to 'decide' to move a finger. But the decision itself is actually the vast cloud of neutral activity leading into it not a single thing.
Interesting! This is what I was getting at. I'm trying to figure out at what level decisions are made and how are they made. From what I can tell so far, it seems like neurons act as nodes that either fire or not based on the information they receive from previous neurons. The information they receive from previous neurons either encourage or discourage activation, each at a different strength. Once a neuron receives enough encouragement to fire from the previous neurons, it fires and sends its signal to the neurons it is connected to, which they take as encouragement or discouragement. In a sense, decision-making is a series of very long logistic regression models. Each previous neuron serves as a predictive factor with it's own polarity (encouragement or discouragement) and coefficient (magnitude of signal). Learning is changing the values of coefficients so that predictive factors have different impacts on the outcome variable. With this in mind, then at least 2 neurons are needed to make a decision. The more neurons, the more variables can be included in the decision making process. Does that make sense?
That's how neurons work, yes. But you can't reduce a "decision" down to a single neuron. It depends what you mean by decision really. Do you mean "the smallest thing that can affect something else", in which case, yes, neurons are the smallest unit (it seems) of brain function. But not consciously so.
Or do you mean the collective input that goes into the brain generating an output? In which case, the brain appears to function more with swarms of neurons firing together. You won't find any examples of a single neuron affecting, say, the choice of going to the cinema. We don't know the brain in enough detail for that, nor does it seem possible for it to work that way (neurons die and are replaced but our behaviour and decisions seems far more stable).
Or do you mean the conscious experience of making a decision (free choice)? Which is a different thing again. The mechanics of the brain operating input and output and the conscious experience of it are not the same thing. They may be generated by distinct but overlapping parts of the brain. Often in step but not always. Conscious choice can't have elements of it reduced to single neurons, brain experiments seem to frustrated any attempt to turn up evidence for that.
Whatever it is we colloquially mean by making a conscious decision about something doesn't exist on the neuron level. It exists on the millions of neurons acting simultaneously level.
By decision, I meant anything that was more than mere chemical or mechanical reaction. Another way of separating it is the point where we can say there is a purpose or difference between dead molecules and being alive. In this case, going to the cinema is wayyy too advanced a decision to help define. More like a cell or group of cells that recognizes its environment and has the opportunity to decide to go towards one direction over another rather than respond merely because a chemical in their environment reacted with their body in a way that gave them an impulse.
But in the larger picture, it seems like there are many decisions that occur for us to commit a behavior. For example, we have to decide what we perceive, decide what our emotional state is, decide what our memories are, decide our personal taste for movies, decide our current motivational state, decide if we have enough time, etc, be fore we decide to go to the movies. All those have to happen prior to deciding on the cinema, and the majority of them occur simultaneously with a central network organizing them into a coherent process, correct? Omg, is this central network what people call executive functioning‽
I'm afraid you are not going to find anything in the brain except "dead molecules". There isn't anything in there except the laws of physics and chemistry acting out like clockwork.
But in terms of the scale of how "decisions" work. Then, yes, far simpler decisions (perhaps better to say "reactions") happen with relatively few neurons. The complete brains of small insects have been mapped by researchers, maybe several million neurons. They can detect movement reactions happening in response to stimuli.
This though is a very different thing to what people mean when referring to their conscious decision to do something.