Reply to: Deep brain stimulation in Parkinson's disease can mimic the 300 Hz subthalamic rhythm Subthalamic high-frequency stimulation drives subthalamic oscillatory activity at stimulation frequency while firing rate is reduced

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We have read with interest the letter by Foffani and Priori that will be published online alongside the same issue of Brain. Foffani and Priori hypothesize that high-frequency stimulation (HFS) of the subthalamic nucleus (STN) might induce oscillatory activity around 250 Hz in the basal ganglia network. To verify this assumption, we performed a new analysis of our entire data set, where we tried to be as close as possible to the analysis described in our recent publication (for details, seeMeissner et al., 2005). Accordingly, single-cell oscillations and synchronized oscillatory activity between pairs of neurons were assessed by calculating auto-correlograms (AC) and cross-correlograms (CC), respectively (1000 ms offset with a bin width of 1 ms instead of 5 ms to enable the analysis of frequencies up to 350 Hz). For each AC and CC the power spectrum was calculated between 3 and 350 Hz and the oscillatory activity was assessed for three distinct frequency bands: 3–30 Hz as in our recent publication, 31–200 Hz and 201–350 Hz. A peak in the power spectrum was considered to be significant if it was higher than the mean power of the entire spectrum [(3–350 Hz) + 5 SD] and if it had an oscillatory index >10%. The standard deviation was individually calculated for each frequency band using the two other frequency bands (i.e. for the 3–30 Hz band, the standard deviation was calculated in the 31–350 Hz range). Differences of AC and CC between the experimental states were assessed by using z-tests.