Indeed, the response to a 35 or 42 Hz, 10 ms stimulus looked remarkably similar regardless of stimulation intensities, with the primary differences manifesting in phase. Biphasic responses were also noted at higher intensities and lower frequencies, whereas unipolar depolarization was most common at 10 mW/mm2. At frequencies selleck greater than 35 Hz, the response waveform became largely sinusoidal. FIGURE 3 Peristimulus average hippocampal LFP responses to medial septal stimulation reveal the influence

of stimulation parameters on waveform shape. (A) Hippocampal LFP response to 50 mW/mm2, 7 Hz, 10 ms square-wave optical stimulation of the MS (magenta bar). … To further characterize the hippocampal LFP response to pulsatile stimulation, we examined the spectral properties of the mean signal from six trials of 50 mW/mm2, 10 ms stimulation pulses at 7, 23,

and 35 Hz (Figure ​Figure44). In all cases, multitaper spectrograms were generated using seven tapers (T = 4 W = 1) and a 4 s long moving window iterating at 0.5 s. This wide temporal window resulted in some temporal blurring of the stimulation onset and offset into the non-stimulation epochs, but allowed us to more precisely resolve the frequency domain. A clear increase in power in the spectrum corresponding to the stimulation frequency was apparent during the stimulation epoch as compared to the pre- and post-stimulus epochs in all cases (Figures 4A,D,G). A spectrogram of each case revealed the temporal precision of this response (Figures 4B,E,H), as well as some of the interactions with power at other frequencies. In all cases low-frequency (1–10 Hz) power was reduced as compared to the pre- and post-stimulus

epochs, presumably via stimulation-controlled hijacking of the LFP signal. Examining the mean autocorrelation lends further support to this idea: during stimulation in all cases, the signal became highly correlated at stimulation frequencies (Figures 4C,F,I). At higher frequencies the oscillatory nature of the LFP response dominated (Figure ​Figure3B3B), resulting in a highly correlated and almost sinusoidal signal that indicated the LFP rhythm was largely dominated and locked to the stimulus frequency Brefeldin_A and phase. FIGURE 4 Spectral and correlational response to medial septal pulse stimulation demonstrate time-locked and frequency specific responses. Stimulation at 50 mW/mm2, 10 ms pulse width, and 7 Hz (A–C), 17 Hz (D–F), and 35 Hz (G–I) each produced … Aside from increases in power at the stimulation frequency, there were concomitant increases of power at harmonics of that frequency. In the case of 7 Hz stimulation, power was also increased at 14 Hz, 21 Hz, and so forth (Figures 4A,B).