This continuation of earlier work by this team seems to confirm their hypothesis of the origin of timing within their behavioural task. There are a good number of cells and the animals behaviour seems to improve perhaps not as dramatically as the neuronal responses but the recorded cells can only represent a part of the timing chain that governs competent action.

They use sophisticated algorithms to analyse the results and the original records in the figures certainly tell the same story. I am a bit confused though. The ramps go on till the reward arrives even though the behavioural switch is after the 6 second expected time for the short wait situation. My analyses would be that these cells are not timing behaviour but reward expectancy, and that is not necessarily the same thing – although it might be hard to tease out of the behavioural situataion. The important time for the task is 6 seconds, by which time the animals know they are in a long trial, so why do the ‘timing’ ramps carry on regardless till reward delivery?

It would be nice to have more of a discussion of what they think the end of the ramp signifies, especially since the group of cells that increase most in experienced animals are the ones with responses to the reward as well as showing the ramping behaviour.

Nice experiments though, with lots of interesting data to play with. Did they find any fast spiking interneurons – I guess too few for this manuscript but I’m looking forward to the report of the collection when it comes.

I'm pleased with the authors comments and now think that this paper is worthy of publication.