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Figure 1

From: Information capacity and robustness of encoding in the medial prefrontal cortex are modulated by the bioavailability of serotonin and the time elapsed from the cue during a reward-driven task

Figure 1

Firing rate profile of neural population recordings in mPFC of behaving rats executing an operant conditioning task. (a) Extracellular electrical activity of the neural population was recorded introducing electrodes in the mPFC along the dorso-ventral axis. Rats were implanted with a fixing device in order to maintain the head fixed during the training sessions. An auditory tone, generated by computer, was implemented as a cue. Thirsty animals received a drop of water as reward to a conditioned response. On the top an example of a recording channel is displayed. Electrical signal was high-pass filtered at 300 Hz. (b) Training procedure of the operant conditioning task. The auditory cue (tone) was presented for 1 s (yellow bar), followed by an opportunity window of 2 s, in which the rat had to execute the conditioned response (lick) to obtain a drop of water as reward, otherwise the reward was omitted. Both situations were followed by a fixed inter-trial time interval of 10 s. (c) Percentage of operant responses per session for each rat (n = 5). Performance of each rat is shown in a different color. Dashed thin lines represent performance in non-recording sessions. Recording sessions of control conditions are shown in thick lines, while recording sessions of fluoxetine condition are shown in dashed thick lines. All rats performed higher than 80% during recording sessions (performance of 80% is marked by a horizontal dotted line). (d) Mean percentage of operant responses (± SEM) averaged across all recorded sessions (from all rats) throughout the duration of a session, divided into 5 intervals of equal number of trials. A significant difference was found between the last interval (80–100%) and the previous one (60–80%) (*** p < 0.001, Mann–Whitney U test). (e) Top: raster plot illustrating examples of spiking activity of 3 neurons recorded in mPFC during 40 consecutive trials. Bottom: average firing rate (spikes/s) for the same cells. Notice that the first neuron (left) showed an increment in the firing activity with respect to the basal around 3 s after the tone, while the second neuron (middle) showed a decreased firing activity between 3 and 4 s. The third (right) is a neuron with non significant changes in the firing rate. (f) Firing rate histograms across the population of recorded neurons under control (left) and fluoxetine (right) treatment. The firing rate of a single neuron was calculated considering only the rewarded trials.

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