Behaviour and a single neuron
From A conversation about the brain
 and, indeed, there is evidence that behaviour can be causally determined by the firing of a very small number of neurons (potentially, a single neuron). The causal argument comes from experiments in which the injection of small amounts of current to increase firing of a small number of neurons influences behaviour in a way that is consistent with the animal perceiving a change in the stimulus and responding accordingly. The figure shows two Voronoi cells corresponding to the monkey making one choice or another (making a saccade to the left or right to signal its decision). Out of n dimensions, only one separates these two Voronoi cells, i.e. the dimension determined by one neuron, the oen currently being recorded. The rest of the neurons define the context, i.e. the region in n-1 dimensional space that encompasses both the Voronoi cells shown here. The context is that the monkey is in a chair, in the lab, viewing a screen, fixating a target, motivated to concentrate, etc. In that context, the firing of this particular neuron determines the behaviour of the whole animal. Most of the time, it does not.
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- Britten, K. H., Newsome, W. T., Shadlen, M. N., Celebrini, S., & Movshon, J. A. (1996). A relationship between behavioral choice and the visual responses of neurons in macaque MT. Visual neuroscience, 13(01), 87-100.
- Dodd, J. V., Krug, K., Cumming, B. G., & Parker, A. J. (2001). Perceptually bistable three-dimensional figures evoke high choice probabilities in cortical area MT. The Journal of Neuroscience, 21(13), 4809-4821.
- Salzman, C. D., Britten, K. H., & Newsome, W. T. (1990). Cortical microstimulation influences perceptual judgements of motion direction. Nature, 346(6280), 174-177.