How do I interpret this depiction of dopamine neuron signaling?

Question

I am studying the work of Wolfram Schultz on reward signals. He depicts dopamine reward signals as shown below, which I do not know how to interpret. Each dot represents an action potential in a dopamine neuron, but is each row a different trial of the same neuron, or is each row the activation pattern of a different neuron? And are the bars at the top showing a sum of the count of the action potentials at each time step?

Schultz, W. (1999). The reward signal of midbrain dopamine neurons. Physiology, 14(6), 249-255.

Answer 1

From the figure caption for that figure:

Each line of dots shows one trial, the original sequence in each panel being from top to bottom.

The bars at top are a summed histogram. Dots mark the time of spikes (this is called a "raster"). Each line is a different single trial from the same neuron.

(also note: this type of paper is called a 'review' paper, i.e., it isn't original research, although the original research might have been done by the same author. That doesn't mean anything bad, reviews are an excellent place to start understanding a topic, but you should be aware that the figures here are just representative examples or in some cases schematic diagrams. There is a lot of other data behind the conclusions drawn besides these single examples)