In Synthetic Forager, an EU FP 7 financed project, the single overarching goal of the SF consortium is to identify the neuronal, cognitive and behavioral principles underlying optimal foraging in rodents and to implement these principles in a real-world foraging artefact or the Synthetic Forager. For the identification of the neuronal, cognitive and behavioral principles we analyze EEG data and ECG data, both measured with the g.USBamp biosignal amplifier, with respect to the position measurements collected with the g.AnTS tracking system. The combined analysis of these measurements yields interesting results regarding the correlation of the theta power band in the EEG data, the speed and the heart rate.

The recordings of EEG, ECG and the position via the tracking system are performed in the rapid prototyping environment under Matlab/Simulink (see Figure 1). The EEG signals are measured with a g.HEADstage and are connected via g.SPIKEsens driver box to the g.USBamp. The ECG signals are recorded using an electrode belt and connected to the g.USBamp as well. The EEG and ECG signals are sampled with 256Hz while the position was sampled with 50Hz.

Data offline processing

For the ECG data first the QRS complexes are detected applying the offline analyzing tool g.BSanalyze as shown in Figure 2. In order to calculate the heart rate and the heart rate variability the outliers and/or artifacts have to be removed.
The EEG recordings are mainly used for analyzing the theta band, which is between 6 and 10 Hz in rats with two interesting subintervals: 6 - 7 Hz whenever the rat is motionless but alert and 7 - 10 Hz when the rat is moving. The preprocessing of the position signal consists of outlier detection and low pass filtering and is then used to calculate the speed of the rat.

Results

In the following the data are analyzed of one trial in which the rat was recorded for 720sec. The recordings were performed at IDIBAPS in Barcelona under the supervision of Maria Victoria Sánchez Vives.
Figure 3 shows the position of the rat tracked with a video camera and g.AnTS (developed together with SPECS, UPF, Paul Verschure). Furthermore Figures 4, 5 and 6 show the dwell time (cumulated sum of time spent at a specific position), the speed and the heart rate respectively. Note that for analysis we classify the position into a 64x64 array so that one single field contains the information of a 1.56 x 1.56cm region.

Figure 3: position map (in meters)	Figure 4: dwell time map
Figure 5: speed map	Figure 6: heart rate map
Figures 7 and 8 show the band power in the theta band inside the frequency band 1 (6-10Hz) and frequency band 2 (6-7Hz). Figure 9 depicts the heart rate variability and Figure 10 the correlation between band power and speed.
Figure 7: Theta band 1 (6 – 10 Hz)	Figure 8: Theta band 2 (6 – 7 Hz)
Figure 9: Heart rate variability (RMSSD)	Figure 10: Correlation between theta band and speed

Conclusion

Considering the heart rate and the dwell time one can see that there is one preferred position (called home base) in which the heart rate is small the heart rate variability is high. Furthermore the power in the theta band 2 is also high. It is worth mentioning that it is quite untypical for rats to have the home base in the middle of the arena. Looking at Figure 10 it is nice to see that the theta band power of the frequency band 1 (6-10Hz) increases while the band power of band 2 (6-7Hz) decreases with increasing speed. These results confirm what is expected from literature.

The work was funded by the EU project synthetic forager. Coordinator: Paul Verschure, SPECS, UPF.